text:
« 159 - Future vehicles - fuels
161 - Alternatives to Internal Combustion »
This topic is not going to suggest that we do away with the internal (infernal) combustion engine, [ICE]. We have invested far too much in that development to abandon that work. I look here at the alternative designs and therefore possible changes to the design of the ICE.
Just so you know what I've included here: the Wankel, the OPOC, the Sucederi, the Selzer, the free piston and its related electric motor.
The Otto cycle describes the spark ignition piston engine. Combustion engines include continuous combustion such as in gas turbines, jet engines and rocket engines. I look here at some of the variations that have been tried. I recommend a look at animated engines.
The Wankel Engine
Please see an animation here. The Otto cycle is preserved but the pistons are combined with clever geometry to provide circular motion. This is a powerful engine once the seal technology is good (where the piston meets the chamber wall gets very hot so ceramic rotor tips are likely). It is a small motor, it works at high speeds and it is very smooth. My RX-8 was 1.3 but rated at 2.6 litres, putting out 230 bhp and revving very freely to 7000, with the usual engine note much higher than one is accustomed to with four-stroke engines. The RX-8 was discontinued because of the new Euro 5 emission regulations. I averaged 29mpg across the years I owned the car, far better than advertised; even so, this is unacceptable fuel economy this decade. I continue to hope for a return.
Opposed piston opposed cylinder [OPOC] as seen by EcoMotors is another variation on the ICE, but here (they're not flat engines like the boxer and they're not Selzer engines, next) they can have 1-3 crankshafts. The diagram shows a single unit on such a shaft. Each cylinder has a piston at both ends; no cylinder head, no valves, so simpler and cheaper. As of 2013 EcoMotor have a deal with ZhongDing Power to build car engines, with the blocks made of compacted graphite-iron [CGI]; production may occur in 2015.
The Scuderi engine (not Ferrari, that's Scuderia) is an improvement on the usual ICE, with paired cylinders in a split cycle arrangement that aims to reduce or eliminate losses from re-compressing the gas. Where standard Otto cycle pistons fires every second stroke, Scuderi engines fire every revolution. If combined in an air hybrid, recovered braking energy would be stored as compressed air. March 2015 has lawsuits from Toyota slowing things down. See link at top of paragraph. I'm betting the Sucderi family are hoping to make money off the patents while richer people do the development. Nice moving diagram of this at Wikipedia.
The Stelzer engine has the pistons joined end-to-end. This simplifies manufacture and has fewer moving parts. Its long axis could be horizontal, offering weight low down in a flat cuboid, or vertical, giving a narrow vertical block.
Do not, as I did, misread Stelzer as Selzer, which leads you to Cox model engines. the Stelzer engine uses maybe 30% less gasoline and is cheaper to make, says the NewYorkTimes 1983. It would cycle about twice as fast as we are used to, at high rpm. I read that this engine would be excellent for a compressor because of the reciprocal motion. Quoting NYT and thence Opel: ''Its thermal efficiency is good, its mechanical efficiency is better than in conventional gasoline or diesel motors, and its durability is virtually unlimited.''
The biggest problem, he [the man from Opel] said, was to transform the engine's shuttle-like motion into the mechanical drive a car needs. Opel developed theoretical models, without using the engine, involving mechanical, electrical and hydraulic systems, he said. But none proved feasible because of excessive weight, cost or installation space.
The Stelzer may be a Free Piston engine by being crankless (yellow/blue picture from heatenginescienceblogspot.com). The pistons lie back-to back in opposing pairs (an opposed piston CE) using a two stroke cycle. The combustion chamber lies between the pistons and the two outer chambers act as if closed, providing rebound. So there is no crankshaft. These engines have been developed for compressors and gas generators - they work well if driving a turbine. The design is simple, so the engine is compact and has low maintenance.
Toyota has a prototype free piston engine (right), which leads directly into the next page. In the FPEG (the link gives you a video), the piston goes through windings and produces 3-phase electricity - "The FPEG operates like a two-stroke engine but adds direct gasoline injection and electrically operated valves. It can also be run like a diesel, using compression rather than a spark plug to ignite its fuel mixture." The comment included: a two-cylinder FPEG is inherently balanced and would measure roughly 8 inches around and 2 feet long. An engine of that size and type could generate 15 hp, enough to move a compact electric vehicle at highway speed after its main drive battery has been depleted. That's the future.
See also the FKLG, the Freikolben-lineargenerator. Animation; turn the sound off.
These developments of the internal combustion engine have the great advantages of developing what we already know a great deal about. The work done in developing the ICE to its current level works against the development cost of other designs - there is too much climbing to do. However, as fuels become more expensive (and more scarce), that work becomes worthwhile.
Did you miss a π moment? March 14th, '15, at 9:26:53.. That's 3.1415 92653 58979 to 10 of the 15 s.f.
shown. I found it worrying that this image to the left, which I was tyrying to identify on Google so as to get tthe reference correct, is referenced as being on this page, as were several others. So I didn't delete any of them, even when not really knowing what the pic is of.
If you come across some engine types I've missed, do share, please. Email button below somewhere.
3 In Mazda's RX-8 with the Renesis engine, fuel economy met California State requirements, including California's low emissions vehicle (LEV) standards. This was achieved by a number of innovations. The exhaust ports, which in earlier Mazda rotaries were located in the rotor housings, were moved to the sides of the combustion chamber. This solved the problem of the earlier ash buildup in the engine, and thermal distortion problems of side intake and exhaust ports. A scraper seal was added in the rotor sides, and by use of some ceramic-made parts in the engine. This approach allowed Mazda to eliminate overlap between intake and exhaust port openings, while simultaneously increasing the exhaust port area. The side port trapped the unburned fuel in the chamber, decreased the oil consumption, and improved the combustion stability in the low-speed and light load range. The HC emissions from the side exhaust port Wankel engine are 35–50% less than those from the peripheral exhaust port Wankel engine, because of near zero intake and exhaust port opening overlap. Although peripheral ported RCEs have a better mean effective pressure, especially at high rpm and with a rectangular shaped intake port (SAE paper 288A).[44][45] However, the RX-8 was not improved to meet EuroV emission regulations and was discontinued in 2012.[46] wikipedia/wankel
For 2018, Mazda will revive the Wankel, in the RX-Vision. Of course it may be realsied as a hybrid, not a rotary at all…RX-9 in 2019? £50,000? I'd love to go back to driving one, but perhaps life has moved on.
http://www.popularmechanics.com/cars/g195/5-alternative-engine-architectures/
https://www.masterresource.org/smil-vaclav/smil-density-definitions-i/
http://en.wikipedia.org/wiki/Power_density
http://en.wikipedia.org/wiki/Internal_combustion_engine
http://en.wikipedia.org/wiki/Thomas_Newcomen
http://www.animatedengines.com/ltdstirling.html
http://www.slashgear.com/precer-groups-bioracer-uses-wood-pellets-for-fuel-12107602/
http://en.wikipedia.org/wiki/Free-piston_engine
http://www.nytimes.com/1983/06/27/business/free-piston-engine-debated.html
http://www.extremetech.com/extreme/185789-toyota-develops-high-efficiency-free-piston-no-crankshaft-combustion-engine-to-power-an-ev
http://www.digitaltrends.com/features/road-rave-free-piston-engines-power-next-plug-hybrid/
163 - Exercise may be good
161 - Alternatives to ICEs
160 - Alternative IC Engines
...you are here...
159 - Future vehicles fuels
158 - Future vehicles cars
157 - Future vehicles bikes


granite factory machinery costgreencover Go for Hualong Machinery Company Product. Pacific Hualong Stone Machinery is a Supplier/distributor in .
Granite Machinery - Granite Machinery Manufacturers .
Marble and Granite Factory Equipment and Stock for Sale . . Used Stone Machines - Trading of used machinery for Marble . Specialized in trading of used machinery for Marble and Granite industry. Get More. Cultured Marble .
The Finest Custom Made Granite and Marble Expert, Reliable Craftmanship from Start to Finish A Decade of Great Customer Service Assisting .
Manufacturing Process & Factory and Equipment Planning Glob marble offers molds, formulas and complete factory training to get you started in the cultured marble manufacturing.The manufacturing process the relatively simple, capital investment is low and row material prices represent only a small percentage of the expected retail .
granite factory machinery - miningbmwAbout Granite and Price Caculator - Caraco Ltd Prices are shown for each granite we sell, based on a typical small, me. READ MORE.
cost of a granite tile processing plant or factory. cost of a granite tile processing machinery, manufacture and supply of crushing equipment used in mining granite processing equipment cost - hoteleldoradobenin Admissions Process for .
Auction Calendar - EX-FACTORY Woodworking Machinery .
granite factory for sale in khammam Grinding Mill China. granite machinery sale in indiaChat Online Get Pricegranite cutting image of granite factory in khammam . Online Inquiry khammam granite factory sale – Grinding Mill .
Xiamen Bestlink Factory Co., Ltd is committed to provide the best drilling and cutting machine, tools and accessories products in marble and granite stone quarrying, as well as in civil engineering application, especial demolition project. it is now a leading manufacturer of cutting and drilling equipment for the extraction of marble, granite and .
Machinery Stone Factory With 25 Years Experience. STONE MACHINE FACTORY ARF & RFM Series Reciprocating Feeders are primary and secondary feeders suitable for charge of primary crushers as Jaw crushers and big size Impact crushers and RFM type suitable for river mine and moisture stone with clay.
Stone Cutting Tool | Diamond Blade and Segments | .
Huada is China diamond cutting tool manufacturer, offer stone cutting tool, granite diamond blade, marble diamond blade, diamond wire saw, diamond segment, and diamond fickert. We also provide stone quarry machinery such as DTH drilling machine, core drilling machine, and rock drilling machine, which are used for cutting and processing marble, granite .
Machinery Required For Granite Factory. Machinery Required For Granite Factory machinery required for granite miningmachinery required for granite mining XSM is a leading global manufacturer of Read more. Machinery .
high quality china factory sand crusher select 2016 high quality cone crusher machinery factory china high quality granite crusher high quality and low stone . china professional factory sand making machine with high . laizhou yuanda chemical industry machinery factory, high quality liquid china crusher machine sand making plant and other .
Stone Machinery. Bridge Saw / Block Saw CNC Bridge Saw CNC Work Center . Splitter Template Device Tile / Slab Line Vertical Diamond Band Saw Water Filtration Wire Saw. Glass Machinery. Bending & Tempering System Beveler (Shape) Beveler (Straight Line) CNC Work Center . [email protected] Warehouse, .
China Bridge Cutting Machine manufacturer, Stone .
Stone Machines, Granite Polishing Machines, Bridge Saws. Welome to SIMCO USA, Inc. Established in 1992 as a one-stop distribution shop for fabricators and machine shop equipment, SIMCO USA is now one of the leading suppliers of stone and countertop fabrication machinery. We supply the stone and construction industries all types of stone .
granite factory machinery cost: .-0773-5262220. Granite Processing Machines Cost caesarmachineryGranite Processing Machines Cost . Price List 420 Marble / Granite Machinery cost of a granite tile processing plant or factory. cost of a granite tile granite factory machinery bundelkhanduniversitygranite factory machinery cost, stone prices all stone .


Paul Wesley & Torrey DeVitto: Movie Date!. Paul Wesley catches a movie with his girlfriend One درخت ہل, لندن actress Torrey DeVitto at the ArcLight Theaters on Sunday (December 26) in Hollywood, Calif.. HD Wallpaper and background images in the The Vampire Diaries TV دکھائیں club tagged: the vampire diaries cast stefan paul wesley.
This The Vampire Diaries TV دکھائیں photo contains کاروبار سوٹ and بزنس سوٹ. There might also be اچھے کپڑے پہنے شخص, سوٹ, پتلون سوٹ, pantsuit, اچھی طرح کپڑے پہنے ہوئے شخص, and پنٹساٹ.


We have counted the 30 days of this magnificent month with appreciation, thankfulness, and gratitude.
We shared a glorious Thanksgiving Day, and we wrote of our joy; Some may have started a journal.
We have reflected on our blessings and realized how incredibly wealthy we are when it comes to our gifts and those things we value most in our lives.
We even gave ourselves a break or two, and fit in some revelationary time.
A November to December image found on Flickr.
11/01 Mahalo; We give thanks. Our November Ho'ohana.
11/06 Be Proactive: Values by Choice as Your Habit.
11/04 How to write Proactive, Considerate Emails – Please!
Mahalo nui loa for a November to cherish.
Please click back in tomorrow for our December Ho'ohana.
"Look to your source, find your truth" is the short and quick English translation I most often use for a Hawaiian value called Nānā i ke kumu.
When I hear the words Nānā i ke kumu, look to your source, it means I need to consider my emotional sense of place as well as my intellectual sense of reason.
When a child is troubled but hesitates to tell her parents just what the problem is, the elders will often say "Nānā i ke kumu." They are saying to find a place where you can sit quietly, and look within yourself for the source of what troubles you, for there you will also find strength within your inner spirit with which to deal with the trouble.
There's more. The chapter on Nānā i ke kumu is about 10 pages long, and I talk about sense of place, truth and authenticity, change and growth, vision and one's personal philosophy of leadership. I ask you some questions about those things you consider your non-negotiables. And of course, we talk about values with Nānā i ke kumu, for today, managing with the values of Aloha is clearly my source and truth.
In the effort to truly understand ourselves, or to come to peace with the decisions we have made, we will often look to our personal values as our source, for it is our values which influence our choices and determine our behavior.
Which key values create our source, giving us the conviction of deeply rooted belief we will identify as our personal truth?
However I do know that for others, the values connection doesn't give them a complete enough answer because they are actively seeking to change their personal hierarchy of values as their lives change focus. During these times, it will come up in my coaching that people want some simpler answers to discovering their source of well being as they take their values assessment journey.
The analogy I use in the chapter on Nānā i ke kumu is the one I call the inner wellspring, and I find this helps many people, for we all have one. Imagine you have a fresh, pure artesian well ever bubbling within you; it nourishes you and refreshes you, and you take comfort knowing it will never, ever run dry. It keeps you feeling good. Feeling centered. It is your source. When you Mālama and take care of it, it takes care of you.
What does it look like? It's different for all of us. I think we feel its effects more than we see it for what it is. The love of our family. The good health we take for granted. The faith we hold but rarely talk about. The friendships that allow us to be silly. We just have to learn to recognize our wellspring by allowing ourselves to feel good when it kicks into gear.
Sometimes, we get way too cerebral about things. We have to learn to give in to those times when what we think simply feels right. I'd bet that those are the times you have somehow physically, mentally, spiritually or emotionally "gone to the well" and taken a drink of your internal bubbling spring.
-How do you think best?
-What are the circumstances that must be taken care of for you, your conditions for fertile ground?
-When is it that you get the most clarity of thought, where things are crystal clear for you?
-When can you have a conversation inside your head, and feel you are giving yourself good, sound answers, the kind of answers you will not hesitate to take action on?
-When have your actions sprung from thought decisions that are not up for negotiation? You are so sure of them; end of story.
My own example: The draft for nearly every single chapter of Managing with Aloha was written in my head on the early morning run I take each morning. The first draft of my entire manuscript was done in less than three months because it was early summer and we had perfect running weather.
However when you understand the answer to this for yourself, you can go to the well whenever you need to, even when you aren't as healthy in every realm of your life.
When I am feeling less than fit for some reason, walking as my daily morning exercise (as opposed to running) has magnificent benefits. I'm not "in the zone" blanking out everything else in concentration, but now I notice more; I'm more observant. I'm more willing to let creative and completely crazy non-logical thoughts into my consciousness. When I walk I make sure I have a pen and a small notebook with me, for inevitably, I'll sit on a curb somewhere and have to get things out of my head; thoughts start to bounce around in there like the silver balls in a pinball machine. It's a different kind of thought process than when I'm running; more whacky and creative, but I am just as sure about things.
The best advice I can give you on this is to give in. Give in to recognizing those times things feel right and good. They are not as random as you may think.
Had a friend ask me today how it feels knowing so many people read Talking Story whom I will never know, and may never hear from.
It feels just fine. In fact, it feels great to think that I may help them in some small way when they hear about managing with aloha and begin to understand just how much that means.
Come to think of it, my book is the same way: I haven't met everyone who has read it, and I never will. However unlike some authors, I've chosen to blog too because I want to be here for people if they decide they want to continue the conversation Managing with Aloha may have started for them. www.ManagingWithAloha.com is about marketing my book; Talking Story is for talking story about everything in it, and our continued managing and leading journey since I had written it.
Just knowing you are out there keeps me going, keeps me writing, keeps me dreaming of how much better we can make things. You make me better.
"Some of the smartest people I've ever met, I've never met.
— Hillary Johnson, Why I read business blogs.
You may have already read the article, for it was published in Inc. magazine back in August. However I'd bookmarked it once it became available online, and I've come back to reading it a few times, because it's real nice to read what Johnson says from a reader's perspective.
I particularly like what she had to say about being part of a virtual community. Like our Ho'ohana Community.
I like to imagine those of you "out there" who read silently may feel much the same way she does, and like I said, it keeps me trying to live up to the expectation that you do.
And you know what else is great? I don't do this alone anymore; I've got a lot of company now when it comes to trying to inspire those who do read these pages: Just check out the comments, the trackbacks, and the links to everyone else in our community.
So mahalo for reading, thank you. Very much.
Talking Story Readers are in the most unexpected places.
Post updated: Okay, at the risk of you completely losing your train of thought and clicking away (4 link choices follow…), another reason to read business blogs is the new Dilbert blog by Scott Adams. You wouldn't call me a wild fan of his cartoon strip, and I've never bought a Scott Adams book, but I may now. I'm loving his new blog way more than his cartoons; I don't think his strip is big enough to contain him.
So there, another reason to read business blogs; you discover way more about the people you thought you may have knew well enough, but you really didn't and don't. Business is more colorful and imaginative these days than it's ever been before. Business just rocks, and so do business blogs.
Reading this for the first time? The original title of this post was, Ho'ohana Community, why do you read business blogs?


text:
On Scripture using Accommodated Language
"All scripture is given by inspiration of God, and is profitable…"
2 Tim. 3:16
"And the sun stood still, and the moon stayed, until the people had avenged themselves upon their enemies."
Josh. 10:13
On Geocentrism & Heliocentrism
Quotes 3
Historical Theology 10+
van Mastricht, Peter – chs. 1 & 5 of Vindications of the Truth & Authority of Sacred Scripture in Philosophical Matters Against the Dissertations of Dr. Christopher Wittich (Utrecht, 1655) in ch. 4, pp. 67-77 & 84-104 of J.A. Schlebusch, Cartesianism & Reformed Scholastic Theology: A Comparative Study of the Controversy a Master's thesis (Univ. of the Free State, South Africa, 2013)
Ch. 1 discusses the unity and differences between philosophy and theology, a Christian philosophy, and legitimate and illegitimate principles of accommodation in the language of Scripture.
In ch. 5, van Mastricht examines and vindicates 15 Scriptures that Wittich brought to claim that Scripture uses approving language of people's false beliefs in, not just natural, but practical, moral and spiritual things.
Hodge, Charles – 'Charles Christian Tittmann on Historical Interpretation' in Biblical Repertory: a Collection of Tracts in Biblical Literature (Princeton Press, 1825)
Fairbairn, Patrick – Part 1st, Section 5th, 'Of False & True Accommodation, or the Influence that should be Allowed to Prevailing Modes of Thought in Fashioning the Views & Utterances of the Sacred Writers' in Hermeneutical Manual… (Edinburgh, 1858), pp. 85-102
Guenther, Dan – 'The Accommodation Doctrine' (2010) a paper for a systematic theology class under J.I. Packer
Not every opinion in this paper is recommended, especially with regard to the author's tolerance for a non-historical reading of Gen. 1 and his breadth of what accommodation may encompass, but the paper is generally substantive, insightful, thought-provoking and helpful in its discussion, especially with regard to evangelical authors in the contemporary discussion, and working through the issues.
Abstract: "In fact, many scriptural difficulties can be resolved in this way: ancient views of nature, ethical inconsistencies, anthropomorphisms, irregular histories, genealogies and numerical problems. However, some contemporary theologians take issue with the idea that God would speak in "errant" language—making his Word less than completely truthful. This paper will argue that the doctrine of accommodation is fully consonant with the doctrine of inerrancy, when (a) accommodation is understood as an essential guide for biblical interpretation, and (b) inerrancy is understood in light of its motivating principle."
Madueme, Hans – 'Inerrancy & Divine Accommodation' (2018) Table Talk Magazine
Dr. Madueme has been a reformed professor of theological studies at Covenant College in Lookout Mountain, GA.
Van Raalte, Theodore G. – ch. 11, 'Another Wax Nose?: Accommodation in Divine Revelation' in eds. te Velde & Visscher, Correctly Handling the Word of Truth: Reformed Hermeneutics Today Pre (Lucerna; Wipf & Stock, 2014), pp. 226-252
Van Raalte is a professor of ecclesiology in the Canadian Reformed Theological Seminary in Ontario, Canada.
Commentary on Gen. 1:15
"By this method (as I have before observed) the dishonesty of those men is sufficiently rebuked, who censure Moses for not speaking with greater exactness. For as it became a theologian, he had respect to us rather than to the stars. Nor, in truth, was he ignorant of the fact, that the moon had not sufficient brightness to enlighten the earth, unless it borrowed from the sun; but he deemed it enough to declare what we all may plainly perceive, that the moon is a dispenser of light to us.
That it is, as the astronomers assert, an opaque body, I allow to be true, while I deny it to be a dark body. For, first, since it is placed above the element of fire, it must of necessity be a fiery body.† Hence it follows, that it is also luminous; but seeing that it has not light sufficient to penetrate to us, it borrows what is wanting from the sun."
† "Cavlin understood that the moon's surface consisted of a reflective element and thus did not emit light itself." – Hoon J. Lee
"16. The greater light I have said, that Moses does not here subtilely descant, as a philosopher, on the secrets of nature, as may be seen in these words. First, he assigns a place in the expanse of heaven to the planets and stars; but astronomers make a distinction of spheres, and, at the same time, teach that the fixed stars have their proper place in the firmament. Moses makes two great luminaries; but astronomers prove, by conclusive reasons that the star of Saturn, which on account of its great distance, appears the least of all, is greater than the moon.
Here lies the difference: Moses wrote in a popular style things which without instruction, all ordinary persons, endued with common sense, are able to understand; but astronomers investigate with great labor whatever the sagacity of the human mind can comprehend. Nevertheless, this study is not to be reprobated, nor this science to be condemned, because some frantic persons are wont boldly to reject whatever is unknown to them. For astronomy is not only pleasant, but also very useful to be known: it cannot be denied that this art unfolds the admirable wisdom of God.
Wherefore, as ingenious men are to be honored who have expended useful labor on this subject, so they who have leisure and capacity ought not to neglect this kind of exercise. Nor did Moses truly wish to withdraw us from this pursuit in omitting such things as are peculiar to the art; but because he was ordained a teacher as well of the unlearned and rude as of the learned, he could not otherwise fulfill his office than by descending to this grosser method of instruction. Had he spoken of things generally unknown, the uneducated might have pleaded in excuse that such subjects were beyond their capacity.
Lastly since the Spirit of God here opens a common school for all, it is not surprising that he should chiefly choose those subjects which would be intelligible to all. If the astronomer inquires respecting the actual dimensions of the stars, he will find the moon to be less than Saturn; but this is something abstruse, for to the sight it appears differently. Moses, therefore, rather adapts his discourse to common usage. For since the Lord stretches forth, as it were, his hand to us in causing us to enjoy the brightness of the sun and moon, how great would be our ingratitude were we to close our eyes against our own experience? There is therefore no reason why janglers should deride the unskilfulness of Moses in making the moon the second luminary; for he does not call us up into heaven, he only proposes things which lie open before our eyes. Let the astronomers possess their more exalted knowledge; but, in the meantime, they who perceive by the moon the splendor of night, are convicted by its use of perverse ingratitude unless they acknowledge the beneficence of God."
Commentary on Gen. 1:5
"I do not doubt that the most ancient fathers, to whom the coming night was the end of one day and the beginning of another, followed this mode of reckoning. Although Moses did not intend here to prescribe a rule which it would be criminal to violate; yet (as we have now said) he accommodated his discourse to the received custom. Wherefore, as the Jews foolishly condemn all the reckonings of other people, as if God had sanctioned this alone; so again are they equally foolish who contend that this modest reckoning, which Moses approves, is preposterous.
The first day: Here the error of those is manifestly refuted, who maintain that the world was made in a moment. For it is too violent a cavil to contend that Moses distributes the work which God perfected at once into six days, for the mere purpose of conveying instruction. Let us rather conclude that God himself took the space of six days, for the purpose of accommodating his works to the capacity of men."
The Whole of Church History
Benin, Stephen – The Footprints of God: Divine Accommodation in Jewish & Christian Thought SUNY series in Judaica (State Univ. of New York Press, 1993) 350 pp. ToC
On the Post-Reformation
Quote on Reformed Theology
PRRD (2003) 1.262
"accommodation occurs specifically in the use of human words and concepts for the communication of the law and gospel, but it in no way implies the loss of truth or the lessening of Scriptural authority.
The accommodation or condescension refers to the manner or mode of revelation, the gift of the wisdom of infinite God in finite form, not to the quality of the revelation or to the matter revealed."
Lee, Hoon J. – "Men of Galilee, Why Stand Gazing Up Into Heaven': Revisiting Galileo, Astronomy & the Authority of the Bible' JETS 53/1 (March 2010), pp. 103–116
Lee earned a PhD from Trinity Evangelical Divinity School. The article first recounts the heliocentric controversy surrounding Galileo and the Romanist Church, then it analyzes Augustine's doctrine of accommodation, and lastly it surveys Galileo's appropriation of Augustine's doctrine.
Lee, Hoon J. – 'Accommodation—Orthodox, Socinian & Contemporary' Westminster Theological Journal 75, no. 2 (2013) Ref
Klauber, Martin & Glenn Sunshine – 'Jean-Alphonse Turrettini on Biblical Accommodation: Calvinist or Socinian?' CTJ, 25, no. 1 (1990) Ref
Graves, Neil, D. – '[John] Milton & the Theory of Accommodation' Studies in Philology, vol. 98, no. 2 (Spring, 2001), pp. 251-272
Beeke, Joel & Todd Rester – 'Rejection of Copernicanism' & 'Defense of the Reality of Demons & Magic' in Preface in Petrus van Mastricht, Theoretical-Practical Theology (RHB), vol. 3, pp. xxxiv-xliii
Goudriaan, Aza – 4. 'Theories of Accommodation' in ch. 2, 'Creation, Mosaic Physics, Copernicanism & Divine Accommodation' in Reformed Orthodoxy & Philosophy, 1625–1750: Gisbertus Voetius, Petrus Van Mastricht, And Anthonius Driessen Buy (Brill, 2006)
Lee, Hoon J. – The Biblical Accommodation Debate in Germany: Interpretation & the Enlightenment Pre (Palgrave) 245 pp. ToC
This work is excellent. Calvin significantly used the principle of accommodation in a variety of ways in his commentaries. The first person since the Reformation to have prominently taught that God accommodates the false beliefs of his hearers appears to have been Socinus. Descartes followed.
The second chapter surveys the rise of the issue in the 1600's, Netherlands. The focus of the book on the literature debate in Germany, from 1761-1835, is because that is when the doctrine of Accommodation, during the rise of the Enlightenment, came into the greatest focus and debate in Church history.
On Luther & Calvin
Wedgeworth, Steven – 'Theories of Accommodation in the Theology of John Calvin' (2015) The Calvinist International
Balserak, Jon – "Deus humanitus saepe cum suis agere solet": an Analysis of Divine Accommodation in the Thought of John Calvin PfD diss. (Univ. of Edinburgh, 2002)
Shin, Jung Woo – God Hidden & Revealed in Luther & Calvin PhD diss. (Univ. of Edinburgh, 2005)
Voet, Gisbert – 'How Far does the Authority of Scripture Extend Itself?' in Select Theological Disputations, vol. 1, p. 29 ff.

redpajama_set_name: RedPajamaCommonCrawl


text:
Santa Inc. Season 2 Release Date
It's been 1 year and 1 month since HBO Max released the last season of Santa Inc., and fans of the animation series are wondering when is Santa Inc. Season 2 coming out?
As of January 2023, HBO Max has not officially confirmed the premiere date of Santa Inc. season 2. The show has yet to be renewed for a second season.
As we continue to monitor the news, below, we've compiled all you need to know about the possible new season, including cast, rumors, and news.
Santa Inc. is a animation TV show created by Alexandra Rushfield and is produced by Point Grey Pictures, Lionsgate Television, Rushfield Productions, oh us. and Stoopid Buddy Stoodios. The show stars Sarah Silverman, Seth Rogen and Maria Bamford.
There's one season(s) of Santa Inc. available to watch on HBO Max. On December 2, 2021, HBO Max premiered the very first episode. The television series has around 8 episodes spread across one season(s). New episodes usually come out on Thursdays. The show received an 1.5 rating amongst the audience.
Santa Inc. is rated TV-MA
Santa Inc. has yet to be officially renewed for a second season by HBO Max, according to Shows Streaming.
→ Was Santa Inc. cancelled? No. This doesn't necessarily mean that the show has been canceled. The show may be on hiatus, and the premiere date for the next season has yet to be disclosed. HBO Max did not officially cancel the show.
→ Will there be a season 2 of Santa Inc.? There is no word on the next season yet. This page will be updated as soon as more information becomes available. Sign up for updates below if you want to be alerted when a new season is announced.
Santa Inc. Season 2 Cast
Here are the main characters and stars of Santa Inc.:
Sarah Silverman plays as Candy Smalls (voice)
Seth Rogen plays as Santa Claus (voice)
Maria Bamford plays as Mrs. Claus / Big Candy (voice)
The current status of Santa Inc. season 2 is listed below as we continue to watch the news to keep you informed. For additional information, go to the Santa Inc. website and IMDb page.
Show Name Santa Inc.
Network HBO Max
→ Watch Santa Inc. video trailers
→ Where to buy Santa Inc. on DVD?
→ View popularity of Santa Inc. in the US
Previous articleMolly Of Denali Season 3
Next articleSix Season 3


Swarovski 8mm and 6mm pink Rose faceted cubes with a light aurora borealis finish on 2 sides are accented by clear crystal 8mm and 6mm square spacers and 4mm Swarovski Rose AB bicones topped with 2mm sterling silver beads. They are made with ball tipped sterling silver wires and put on fine sterling silver earring wires. These are very dainty earrings being only 1.5 inches or 40mm long including the posts. The dangles are 1 inch. This is a very popular selling earring style as they are lightweight yet super sparkly.
See all earrings or all Cube jewelry for more choices.


text:
Heathrow faces summer disruption as workers vote to strike
By Adam McCulloch on 12 Jul 2019 in Employee relations, Collective bargaining, Dispute resolution, Industrial action / strikes, Executive pay, Latest News, Pay settlements, Shift pay
Photo: Steve Parsons/PA Archive/PA Images
Heathrow airport could be shut down for several days this summer because of strike action by more than 4,000 workers.
Security guards, engineers, passenger service operatives and drivers have voted to walk out on 26-27 July, 5-6 August and 23-24 August over a pay dispute.
Unite union members supported strike action in eight ballots following the rejection of an 18-month pay offer of 2.7%, which according to the union adds up to just £3.75 extra day for the lowest paid workers – largely security guards – involved in the dispute. Unite told Personnel Today that its members were looking for a pay increase of 4.5% and a pathway to fairer pay for people doing similar jobs.
Can an employer change the date on which it pays employees?
Letter to an employee proposing to change the method of paying him or her
Industrial action stories at Personnel Today
First ever English footballers' strike/
According to the union, members have been annoyed by growing pay disparities between workers doing the same job at the airport and the size of the pay packet awarded to its chief executive John Holland-Kaye. Last year, he received a 103.2% rise with his basic pay soaring from £2.097m in 2017 to £4.2m in 2018.
Alex Flynn, head of media and campaigns at Unite told Personnel Today: "Our members' are scratching their heads somewhat as it appears to be one rule for one and one for another. If the CEO is getting rewarded for the airport's success then why aren't they, with a decent pay rise."
Unite regional coordinating officer Wayne King added: "They are fed up of being expected to accept crumbs while the chief executive pockets an eye popping 103% rise in his pay package and shareholders are handed dividends of over £2bn in the last two years alone.
"To add insult to injury there are widening pay disparities leading to airport security guards employed after 2014 earning up to £6,000 less than colleagues hired before that date. Bosses at Heathrow Airport need to get their heads out of the sand and start negotiating meaningfully over pay."
Unite yesterday (11 July) said it was balloting 100 of its members at Gatwick airport who were employed to scan passengers' luggage. It said they were paid £8.50 an hour and would be seeking a rise to £9 an hour to match Real Living Wage levels. The workers are employed by security firm ICTS.
There may also be some disruption at Stansted airport with 17 days of strikes planned by 43 check-in staff employed by Stobart Aviation Services, which has the easyJet contract at the airport. Again, the background to the strike action, while involving low pay compared with comparable jobs at the airport, is set against a large payment to a senior executive, in this case a multimillion pound bonus being paid to Stobart chief executive Warwick Brady.
A Heathrow spokesperson said the airport's management was disappointed about the prospect of strike action and would be instigating contingency plans to ensure the airport remains open.
She added: "We have proposed a progressive pay package giving at least a 4.6% pay rise to over 70% of our frontline colleagues. The total package offered is above RPI and is specifically designed to boost the wages of lower paid colleagues. We have invited our union colleagues back to the table and urge them to continue working with us to reach an agreement."
Workforce planning opportunities on Personnel Today
Browse more workforce planning jobs
British Airways pilots accept new pay deal
British Airways pilots have accepted a new pay deal, ending the dispute over pay and conditions that led to a...
Junior doctors to vote on four-year pay deal
Junior doctors are to be balloted on whether to accept a four-year deal which will mean annual pay uplifts of...
Royal Mail wins High Court injunction to halt postal strikes
Royal Mail has won a High Court injunction to prevent postal workers from striking in the run-up to Christmas.


Awning ~ Teardropailer Awning Awesome Photo Inspirations 7h0iqeqo764v For Sale Illinois By Owner Manufacturers Texas State Free Awesome Teardrop Trailer Awning Photo Inspirations. Used Race Car Trailer. Teardrop Trailer Plans Free. Haulmark Race Car Trailer Awning.


Sometimes rudimentary revelations hit so hard they're able to knock the wind out of people. I believe the Annie Dillard quote, "How you spend your days is how you spend your life," is one of those times.
It's easier to "waste" a day when one doesn't think that it's connected to their life which is why it is imperative to make that connection daily. It is when the connection is lost that people find destructive habits such as procrastination.
It's also imperative that you recognize the root of your procrastination. This takes an incredible amount of self-awareness and humility. While it may be difficult, this consciousness is key. After all, if you don't know your enemy—you'll never know where or what to fight.
This truth differs from person to person, but it is more or less the same: fear, laziness, insecurity, etc. To figure this out for yourself, start asking the tough 'why' questions and it will be clear enough. Why do you stay in a job you hate? Why are your projects never completed? Why?
Next, it's time to create a plan of action. After all, implementing a plan is procrastination's kryptonite. When creating your plan of action, ask yourself, "What can I do today, that will get me to my ultimate goal?" And, a plan is only good when implemented. So, make sure to follow through.
You'll know if your plans are working if you can see your behavior transform from week to week. You should also see visible progress. However, don't be afraid to alter your plan from time to time to achieve your ultimate goal. Always keep your end goal in mind.
Make the daily connection that your life is a mere reflection of your days.
Conquer the factors holding you back.
Make a Change Where It's Needed the Most.
The average person will spend roughly 1/3 of their life working. After you factor in commute, sleeping, and other basic necessities — there's not a whole lot of day left for much else!
That's an incredible amount of wasted time, energy, and resources on something if you don't love your career path. Yet, even knowing all of that, work procrastination consistently happens.
It's never too late or too early to switch to your dream career. Take our career for instance. Hundreds of our agents now know what it's like to fulfill a career dream — without hesitation or procrastination, they will tell you they're building their own business, have unlimited earning potential, and actually make a difference in their job. Not to mention, each day they go to work in the field, they are building up a residual income that will leave a legacy for their families.
Now, is the time to know what it's like to live your dream job.


This was the first year that YAC initiated a scholarship for Big Event. In October the committee awarded out 3 full conference registrations so that three young insurance professionals could attend MAIA's premier conference and trade show.
Boosting involvement of young agents at the association is central to the mission of the Young Agents Committee, and the Big Event is a perfect opportunity to participate. With so much to gain from this industry conference, the YAC really wants to see more young agents take advantage of this event. With that in mind, we thought we could break down part of the financial barrier of attendance with this scholarship.
MAIA's Young Agents are proud to announce the Big Event Scholarship Recipients.
Latora had the dual honor of being awarded a registration and being a finalist for the CSR Star Contest. As a Customer Service Rep in the Western part of the state, she was really looking forward to experiencing all the Big Event had to offer.
Paul and Jessica went for Maximum Value and used their full registrations to take the entire CPIA designation with Bruce Thomas while in Boston. Both were spotted in the packed VP Suite for Young Agents Rocking Reception on Thursday night. And, you may have seen them both interviewed in The Standard this month. They provided some fantastic insights about what make their careers interesting and worthwhile.
Were you at the Big Event with us? Check out the photos and #BigEvent14 social media updates. Hopefully we'll see you there next year.


For more than 150 years, TD has been dedicated to providing financial solutions to individuals and businesses around the world.
Inspired by our history and vision, my group and I are part of the same traditions. We are focused on building prosperity for Canadian families and businesses working with TD specialists in banking, estate planning, and trust and developing integrated wealth management solutions to help build, preserve, and transition your wealth.
The Q-ssis Wealth Management Group and I are committed to a superior quality of service to our clients and to help you achieve your financial goals. We recognize and respect that everybody's situation is unique. We take the time to better understand your present and future needs and lifestyle aspirations. We customize your investment management program to suit your individual circumstances.
Personally, I have achieved several of the industry's distinguished designations and credentials – The Canadian Investment Manager (CIM®) and Fellow of Canadian Securities Institute (FCSI®). I have been advising private clients for over 25 years and take a disciplined approach to investment management. I am passionate about literacy and have designed and facilitated financial education seminars for women. As a media spokesperson for TD, I am frequently quoted in various print publications.
My group and I look forward to helping you realize your dreams.
The Q-ssis Wealth Management Group is a part of TD Wealth Private Investment Advice, a division of TD Waterhouse Canada Inc. which is a subsidiary of The Toronto-Dominion Bank.
Canada's Housing market has been hot, with rising prices & sales masking the underlying regional phenomena. But what happens when mortgage rates rise? Diana Petramala, Economist, TD Bank Group tells MaryAnn that could be sooner than you think.


Scrap Car Ashford will collect your car for free in Ashford (SP6), Dorset. A lot of car owners are unaware that if they have a scrap car it will still need to be taxed even if the vehicle is not in use. Don't give a company money to tow away your car. We will collect your old scrap car at no cost to you in Ashford!
As well as offering a completely free collection, we are also currently able to offer cash for scrap cars in Ashford depending upon the weight of the vehicle!
We like to give our customers a service that they can rely on after trading in the Dorset area for over a decade we are still going strong. After trading here for over a decade we have built a knowledge of the local area meaning we are fast and reliable. We are proud to be able to offer an unrivalled service and will arrive to collect your car at the agreed time slot. Our collection service is there for you so we will dedicate a specific time slot to work around any commitments you may have.
We ensure that your car is properly disposed of. There are a few companies out there that will sell your scrap car as a runner and not scrap it, quite often they will not even inform the DVLA that the vehicle has a new owner. This can result and usually does in you being fined. Scrap Car Ashford will always notify the DVLA that your vehicle has been scrapped, meaning you can rest assured that you are in the very safest of hands. Any car that we scrap we ensure that it is scrapped in the most environmentally friendly way possible, we like to do our bit.
It is so simple to scrap your car in Ashford. Just by picking up the phone you can be told the process by our members of staff. On the other hand just take a look at our very helpful guide to scrapping your car so you can see what the procedure is before you call or book.
The car scrappage scheme in Ashford might seem like a great idea at first. There are a few flaws in the governments plans, as there will only be certain cars that qualify. You can't just go out and purchase any vehicle you want This can prove to be very frustrating as you have to choose a car that is currently in the scrappage scheme.


text:
Inglês (pdf)
Revista EIA
Rev.EIA.Esc.Ing.Antioq no.18 Envigado jul./dez. 2012
A SYSTEMATIC REVIEW ON IDENTIFICATION OF EXCITATION SYSTEMS FOR SYNCHRONOUS GENERATORS
REVISIÓN SISTEMÁTICA EN IDENTIFICACIÓN DE SISTEMAS DE EXCITACIÓN PARA GENERADORES SINCRÓNICOS
REVISÃO SISTEMÁTICA EM IDENTIFICAÇÃO DE SISTEMAS DE EXCITAÇÃO PARA GERADORES SINCRÓNICOS
Andrés Julián Saavedra-Montes*, Carlos Andrés Ramos-Paja** y José Miguel Ramírez***
*Ingeniero Electricista, Magíster en Sistemas de Generación de Energía Eléctrica y Doctor en Ingeniería Eléctrica, Universidad del Valle. Profesor Asociado, Departamento de Energía Eléctrica y Automática, Facultad de Minas, Universidad Nacional de Colombia. Medellín, Colombia. ajsaaved@unal.edu.co.
**Ingeniero Electrónico y Magíster en Ingeniería, Universidad del Valle; Doctor en Ingeniería Electrónica, Automática y Comunicaciones, Universitat Rovira i Virgili. Profesor Asociado, Departamento de Energía Eléctrica y Automática, Facultad de Minas, Universidad Nacional de Colombia. Medellín, Colombia. caramosp@unal.edu.co.
***Ingeniero Electricista y Magíster en Sistemas de Generación de Energía, Universidad del Valle; Doctor en Automática, Université Joseph Fourier, Grenoble, Francia. Profesor Titular, Escuela de Ingeniería Eléctrica y Electrónica, Facultad de Ingeniería, Universidad del Valle. Cali, Colombia. jose.ramirez@correounivalle.edu.co.
Artículo recibido 16-VI-2011. Aprobado 24-VII-2012
Discusión abierta hasta junio de 2013
This paper presents the state of the art on system identification applied to excitation systems. First, general overviews about system identification and excitation systems for synchronous generators are presented, highlighting the unique characteristics imposed by the excitation systems in an identification process. Then, a bibliographic classification method based on the excitation system characteristics was designed, which provides a results matrix condensing the topics addressed by more than 40 reviewed publications. From the results analysis the state of the art in excitation system identification was established, and open research areas in the topic were recognized.
KEY WORDS: excitation system; synchronous generator; system identification; literature systematization.
Este artículo presenta el estado del tema en identificación de sistemas aplicada a sistemas de excitación. Primero se presenta una visión general de identificación de sistemas y de los sistemas de excitación de generadores sincrónicos, resaltando las características impuestas por los sistemas de excitación en un proceso de identificación. Luego se presenta el diseño de un método de clasificación basado en las características de los sistemas de excitación. El resultado del método es una matriz que condensa los asuntos discutidos en más de 40 publicaciones. El estado se establece desde el análisis de los resultados y adicionalmente se reconocen áreas abiertas de investigación en la identificación de sistemas de excitación.
PALABRAS CLAVE: Sistema de excitación; generador sincrónico; identificación de sistemas; revisión sistemática.
Este artigo apresenta o estado do tema em identificação de sistemas aplicada a sistemas de excitação. Primeiro apresenta-se uma visão geral de identificação de sistemas e dos sistemas de excitação de geradores sincrónicos, realçando as características impostas pelos sistemas de excitação em um processo de identificação. Depois se apresenta o desenho de um método de classificação baseado nas características dos sistemas de excitação. O resultado do método é uma matriz que condensa os assuntos discutidos em mais de 40 publicações. O estado estabelece-se desde a análise dos resultados e adicionalmente reconhecem-se áreas abertas de investigação na identificação de sistemas de excitação.
PALAVRAS-CÓDIGO: Sistema de excitação; gerador sincrónico; identificação de sistemas; revisão sistemática.
The stability analyses support the planning and operation of power systems. The accuracy of stability studies depends on the model structures and parameters of the power system elements such as synchronous generators, excitation systems, turbines, and speed governors. A large number of generation companies around the world do not have appropriate models for these studies, particularly because they have no precise parameter values.
Nowadays there is renewed interest on the identification of excitation systems. This renewed interest is because regulators have recommended testing and verifying models of the elements in power generating units, among these excitation system models, as reported by Karl and Schaefer (2004) and Veloza and Cespedes (2006). The excitation system identification is a research topic well explored, i.e. there are a large number of publications about this subject, creating a challenge for those who want to research in the topic because open research issues are not evident.
To investigate in fields in which there is no previous knowledge or experience, it is possible to collect articles on the topic and try to identify open research issues. The success of this task is often associated with the researcher's experience. However, for those who start as young researchers and for those who choose to work in unfamiliar areas, tools to detect open research issues will be useful.
This paper presents the state of the art on system identification applied to excitation systems. First, general overviews about system identification and excitation systems for synchronous generators are given. Then, a bibliographic classification method is presented, which is used to review the publications in excitation system identification, to establish the state of the art, and to detect open research issues in the topic. The paper is organized as follows: a general description of system identification is presented in section 2, where a flow chart showing the four basic identification stages and some important aspects about each identification stage are discussed. Section 3 deals with the excitation systems for synchronous generators. The elements and signals that shape the excitation system and the excitation system classification according to the power source used for excitation are presented in this section. The modeling of excitation systems published and standardized by IEEE, and the characteristics of excitation system models are also presented. The state of the art in system identification applied to excitation systems is provided in section 4. To establish the state of the art, a bibliographic classification method was designed. The method was also used to review the publications in excitation system identification and to detect open research issues in the topic. In addition, the steps to develop the classification method are presented in this section. Finally, the conclusions are given in section 5.
2. BACKGROUND ON SYSTEM IDENTIFICATION
This section gives a general background on system identification to contextualize the analysis and results given in this paper. The background is mainly based on traditional references for system identification such as Eykhoff (1974), Söderström and Stoica (1989), and Ljung (1999), providing the required knowledge to extract the particular requirements for excitation system identification.
Figure 1 presents a flow chart that describes a general identification process. To identify a system, an experiment to collect input/output data of the system should be designed and carried out. The intended application and the previous knowledge about the model are used to design the experiment. The experiment consists in applying some perturbation signal, e.g. a step signal, sinusoidal signals, rich in frequency binary signals, etc., and sampling the input/output signals with a data acquisition system. The input/output data are recorded and stored for their pre-processing.
The next step is to select a model structure taking into account the knowledge about the system behavior to increase the possibilities of a successful identification. Then, the method to estimate the parameters of the chosen model is selected. These steps take into account the prior knowledge and the future use of the model. Among the criteria to select the estimation method are the model structure and the system operating conditions. Once the structure and the estimation method have been selected, a simulation is done in which the estimation algorithm adjusts the structure parameters until the output signal meets a previously defined criterion.
The model can be validated comparing its output against the system output to the same input and/or comparing a parameter set of reference with the estimated parameters. Also, there are several indexes to validate the model, which are chosen depending on the intended application. If validation criteria are met, the identification process concludes; otherwise previous steps must be revised looking for possible sources of error until a proper representation of the system is obtained.
To provide a background on the identification process given in figure 1, important aspects at each stage such as the input or excitation signals, the structure of linear models, the methods to estimate parameters and to validate models are discussed.
2.1 Input or excitation signals
At the design of the experiment stage, the most important aspects are the perturbation signal or input signal and the sampling time. Some input signals are the step signal, the sum of sinusoids, the chirp signal, and the pseudo-random binary signals. Detailed information of previous signals is found in Söderström and Stoica (1989) and Ljung (1999). A list of available programs on the Internet to generate some excitation signals in addition to its classification is found in Godfrey et al. (2005).
2.2 The model structure
There are several ways to classify dynamic models and therefore their structures. Based on the number of inputs and outputs, the model can be: single input, single output; single input, multiple outputs; multiple inputs, single output; or multiple inputs, multiple outputs. Based on the input-output dependency, the models can be linear and nonlinear; they are linear when the output or outputs depend linearly on the input or inputs. Also there are parametric and non-parametric models, the former are described by a set of parameters and the latter can consist of a curve or graph.
There is another classification based on the domain model. There are time domain and frequency domain models. Differential and difference equations are examples of time domain models, which can be discrete or continuous. Particularly a continuous time model can be fitted to a discrete time data.
2.3 Methods to estimate parameters
The methods to estimate parameters are classified as parametric and non-parametric. The nonparametric method results are curves or functions from which parameters must be obtained; among these, the transient analysis of a step response and the frequency response analysis are found. The parametric method results are parameter vectors. The least square (LS) method is used to estimate static models of linear regression. An extension of this method allows estimating dynamic models. An LS generalization is the prediction error method (PEM), and another LS generalization is the instrumental variable (IV) method. There are instances in which PEM is known as the generalized minimum square (GLS) method. In other cases PEM could be interpreted as the maximum likelihood (ML) method. When the LS, IV, and PEM methods are applied to estimate parameters on line, they are known as recursive estimation methods or online estimation methods.
2.4 Methods to validate models
Validating a model can be compared with the larger amount of information on the real system as much as practical. There are several methods of validation that could clear the doubts about the model and could create confidence in its use. A natural validation method is to solve the problem that inspired the modeling exercise. If the model succeeds in solving the problem set forth, then this model can be considered valid, but this method can be expensive and not practical. There are other methods that help create confidence in using the model.
When the model structures are based in physical parameters, i.e., the excitation system models, an important method of validation is to compare the estimated values with their estimated variances. Some knowledge of possible values must exist. Another method of validation is to compare the response from the model and the real system to the same input. This method shows which characteristics of the real system the model reproduces and which it does not.
The residual analysis is based on the residues that are part of the data that the model can not reproduce. Applying basic statistics on the residues some information can be had in regard to the model, but nothing convincing. The covariance between the residues and past inputs gives convincing information. For example, if the covariance is small, there are some reasons to believe that the data is relevant. The correlation of the residues between themselves also gives convincing information; for example, if the residues correlation is small, this is a sign of a deficient model.
3. EXCITATION SYSTEMS FOR SYNCHRONOUS GENERATORS
The excitation system is a control system associated with synchronous machines. When it works associated with a synchronous generator connected to the grid, its functions are to supply direct current to the generator field windings, regulate the generator terminal voltage, control the reactive power flow between the generator and the power grid, improve the stability of the power system, and provide limiting and control functions to the generator.
3.1 Elements and signals of excitation systems
Commonly, excitation systems are composed of a terminal voltage transducer, an automatic voltage regulator, an exciter and compensators. Sometimes, it also includes limitation and protection circuits, and a power system stabilizer as reported in IEEE (2006); see figure 2.
Terminal voltage transducer conditions the terminal voltage to introduce it to the automatic voltage regulator (AVR). The AVR processes and amplifies the input signal to an appropriate level and form in order to control the exciter, which provides the power of direct current to the field winding of the generator. Protective and limiting systems include a wide number of control and protection circuits that guarantee the operation within the capability limits of the exciter and the generator. Power system stabilizer introduces damping to mitigate the oscillations of the power system. Additional compensators could be introduced to deal with load transients, line drops, and reactive current. Finally, the excitation control system is composed by the excitation system and the synchronous generator. The description of the excitation system signals depicted in figure 2 is given in table 1.
3.2 Excitation systems classification
Excitation systems are classified in three groups according to the power source used for excitation (IEEE, 2006). Direct current (DC) excitation systems use direct current generators to feed the field windings of the synchronous machine. Alternate current (AC) excitation systems use alternate current generators in sets with rotary or static rectifiers to feed the field winding of the generator. Static (ST) excitation systems can be composed by transformers and rectifiers that feed with direct current the generator field winding.
In each one of the previous categories there are systems with distinctive characteristics that differentiate them, producing new subcategories. For almost each subcategory there is a model that represents the system (IEEE, 2006).
3.3 Modeling of excitation systems
In 1968 IEEE Power Engineering Society released a report about most widely known excitation system models in the USA and Canada (IEEE, 1968). The purpose of that document was to normalize nomenclature and structure of models existing at that time. The scope of the models is limited to studies of power systems. The parameters of those models are presented in per-unit system. Some nonlinearities, such as the magnetic saturation of rotating exciters and limits of the regulator signals, are presented. The models in IEEE (1968) were not the first models of excitation systems, but they were the first normalized models.
In 1981 the IEEE Working Group on Computer Modeling of Excitation System extended the work presented in IEEE (1968) in a new publication, IEEE (1981). The proposed models, which have been widely used by the industry, were improved for the new excitation systems that were not properly represented by the older models. In 1992 the recommended practice of the excitation system models for power systems stability studies is consolidated by IEEE. In this standard, models for the load compensator and the voltage transducer are presented. Per unit system, and the representation of the magnetic saturation, the regulation of rectifiers and the limits of signals are described too.
In IEEE (1996) new models were introduced representing the new equipment that had controllers based on digital technology; the models were presented in the continuous time domain to be used jointly with the models already proposed and programmed with available software. These models consider the flexibility that controllers based on digital technology have, particularly taking into account the use of PI and PID controllers.
Review and update of the practice recommended in 1992 was published in IEEE (2006). An extension presented is a new model for the load compensator. The most relevant change is the fact that it includes systems based on digital technology. This change is evidenced in the fact that PID or PI controllers that could be easily programmed in digital processors are included. Underexcitation and overexcitation limiters models are presented too, on real time domain to be used jointly with those already proposed and to be easily programmed in packages of power systems analysis.
The main characteristics of the described excitation system models are:
Excitation systems are represented through mathematical models on the bases of physical laws that describe the equipment. Some models have one input and one output, and some others have two inputs and one output; generally the output variable is the generator field voltage EFD.
These models have a reduced order and do not represent all the dynamics of the control loop. The models are in the continuous time domain, although some represent excitation systems based on digital technology. In addition, the models are described by a set of concentrated parameters, which are invariants in time.
Some of the models include nonlinearities such as signal limits, magnetic saturation of rotating exciters, and the nonlinear effect of rectifier regulation. According to IEEE (2006), the models are valid for frequency deviations of ± 5 % from rated frequency and oscillation frequencies up to 3 Hz.
4. SYSTEM IDENTIFICATION APPLIED TO EXCITATION SYSTEMS
Generally, scientific publications about system identification applied to excitation systems cover all the stages of the identification process, additionally excitation systems exhibit unique characteristics when they are identified. Each publication on excitation system identification is focused on some of the identification stages and takes into account some of the unique characteristics of excitation systems.
To establish the state of the art of excitation system identification a bibliographic classification method has been designed to review the publications, and to detect open research issues in the topic. The method is developed in three steps. First, the characteristics in excitation system identification and consequent conditions that should be fulfilled in an identification process are defined. Then, an assessment system based on the conditions defined in the first step is designed. The third step consists of reading and assessing every article by using the assessment system to identify distinctive characteristics and condense the information obtained in a results matrix.
4.1 Characteristics of excitation system identification
Based on the prior knowledge, five characteristics of excitation system identification and four consequent conditions are defined to assess the selected articles. The criterion to select the papers to be reviewed considers paper titles or abstracts focused on system identification or parameter estimation of excitation systems. The characteristics adopted are:
Since the excitation system (EXS) must work in closed loop with feedback from the generator terminals, the identification experiments should be performed under this condition. When a system operates in closed loop, the dynamics of the system elements affect each other, making it difficult to estimate them, as reported in Landau and Zito (2006). The experiment to identify the EXS can be carried out in open loop with no connection to the generator, but this would mean that the system would not be identified in its most common operation state.
The EXSs are modeled in detail by standard models accepted by engineers to analyze the power system, and analysis software packages have most of those models, or at least those that can be implemented in their libraries. This means that detailed structures of the models to be used in the identification are available.
The EXS belongs to a costly process that operates continuously, so the generator availability should be maintained. This means that the experiment for identification purposes must be carried out in short periods of time and preferably with the generator connected to the power system.
There are several types of excitation systems and each one has specific requirements for identification. For example, brushless excitation systems do not have the generator field signals available for measurement. In this case, the terminal voltage signal is measured including the generator in the identified model. Static excitation systems generate noise due to the bridge rectifier. This noise affects directly the generator field signal, thereby increasing the difficulty in the estimation process. Filtering the noise may filter also the dynamics of the system.
Since the generator can operate offline or online, the identification experiments can be carried out in the two regimes. When the generator operates offline there is interaction among the dynamics of the components of the excitation control system, including the generator. However, in this regime the generator model is simple and well known. When the generator is connected to the power grid, the generator model has complex dynamics, and the excitation control system is exposed to more disturbances.
From such characteristics, the main four conditions that should be fulfilled in an identification experiment are:
Carrying out the experiment in closed loop, regardless the generator is online or offline. The estimation method should take into account the limitations of closed loop identification.
Using the detailed and standard structures of the EXS models.
Avoid the unavailability of the generator. Experiments in short periods of time and perturbation signals with magnitudes that do not affect the operation and security of the generator should be used.
Using signals sufficient to estimate all the required parameters.
4.2 Assessment system
The assessment system is shown in table 2. The system includes the four typical stages of an identification process: design and carry out the experiment, select the model structure, select the parameters estimation method, and validate the model. At each stage, there are some categories, and in each category there are the actions or elements that can be reported in an article about excitation system identification. For example in the first stage, the category was generated because the experiment can be carried out with the generator online, offline or during a disturbance, see table 2.
The actions and elements are assessed according to the conditions defined in section 4.1. Table 2 shows a number in parenthesis in front of each category, which is the maximum value that receives that category. In front of each action or element appears the value to be assigned if the paper fulfills it. Such values were defined in agreement with the categories, actions and elements contribution to the defined conditions. For example, category 1(operating conditions of the synchronous machine) has a maximum value of 2, while category 3 (signal processing) has a maximum value of 1. Such a difference is caused by the stronger influence of category 1 in the conditions defined in section 4.1 over the impact of category 3. Similarly, in the evaluation of category 1, the element increases the category value because such an operation condition is clearly required in the third condition (c) defined in section 4.1, therefore generator offline has a null value. In the same category, a null value has been assigned to the element since it is not possible to design the perturbation signal and to schedule the tests.
Table 3 shows the results of the bibliographic classification method condensed in a matrix, in which there are the references and the thirteen categories assessed for each paper. In the last column there is reported the total value assigned to the reference according to the four conditions previously defined. In the last row the percentage of papers with the highest value PHV [%] for each category, is presented.
There are several approaches to extract information from table 3. The table can be interpreted by categories; e.g. in category 1 only six papers, or 20,6 %, have carried out experiments with the generator operating online. In category 5, eighteen papers or 62 %, have collected data in power plants. Table 3 could also be interpreted combining categories, e.g. in categories 1 and 5 it is observed that only four papers report experiments carried out with the generator operating online into power plants. Another interpretation is to observe the total value in the last column and determine the papers that better match the conditions given in section 4.1.
Since the references are organized in a chronological form, some information can be interpreted also in this way, e.g. in category 3, authors discussed the noise and signal processing between 1971 and 2000, the broader discussion took place between 1993 and 2000, and from 2000 until now the noise issue did not discussed again.
4.3 Results of the bibliographic classification method
From the results given in table 3 several analyses can be performed, where the most important to reach the conditions defined in section 4.1 are:
In category 1, only 20,6 % of the publications have reported experiments with the generator online: Shen, Zhu and Han (1991), Liaw et al. (1992), Liu et al. (1993), To and David (1996), Rasouli and Karrari (2004), Glaninger-Katschnig (2010), and only four publications have reported experiments in power plants, and not in prototypes or models. The low percentage of publications that report experiments with the generator operating online, in contrast to the requirement to avoid the unavailability of the generation, shows that the identification experiments with the generator online must be further investigated.
In category 2, references Shen, Zhu and Han (1991), Liaw et al. (1992), Liu et al. (1993), To and David (1996), Ludwig et al. (1998), Vermeulen and Strauss (1999), Bhaskar et al. (2000), Rasouli and Karrari (2004), Botero and Ramírez (2005), Hernandez et al. (2006), Shen and He (2007), Puma and Colome (2008) and Glaninger-Katschnig (2010) report the use of signals with persistently excitation as the PRBS signal. Those signals are rich in frequencies and perturb the system dynamics in the interest frequency range. In Rasouli and Karrari (2004) the authors use square and triangular signals with maximum frequencies less than 3 Hz. The validation results support the use of those signals. In category 3, it must be highlighted the fact that among the reviewed papers it was not a noise consideration or especial processing of signals from 2001 to 2010.
In category 4, 41,3 % of the publications report the use of input/output data from the complete excitation system to estimate all the linear model parameters. Similarly, in category 7 only 65,5 % of publications report that more than four parameters were estimated using input/output data of the complete excitation system model. Therefore, taking into account that not all the elements input/output terminals are available in the excitation system, algorithms that estimate all the model parameters from input/ output data of the complete excitation system must be proposed.
In category 9, the nonlinearities estimation of excitation systems is a topic actively explored from 2002. The estimation of the nonlinearities directly from the estimation method is reported in Benchluch and Chow (1993), Feltes et al. (2002), Paszek et al. (2005), Hernandez et al. (2006), and Puma and Colome (2008), while Ramírez, Saavedra and Vásquez (2003) report the nonlinearities estimation from independent experiments, which leads to undesired offline time of the generator.
In category 10, most of the publications have reported the use of parametric estimation techniques. Only in references Warchol et al. (1971), Gibbard and Kaan (1975), Ramírez, Saavedra and Vásquez (2003), Saldaña, Calzolari and Cerecetto (2006), and Glaninger-Katschnig (2010) non-parametric techniques have been reported. Usually, non-parametric techniques require more experiment time affecting the availability of the generator, but the parameters are estimated individually increasing the accuracy of the estimated value.
Category 11 shows the percentage of publications that used more approaches to validate the excitation system models, publications that have higher scores in this topic are Zazo et al. (1994), Vermeulen and Strauss (1999), Botero and Ramírez (2005), and Shen and He (2007), therefore they are a good introduction of validation procedures. The identifiability of the parameters of the excitation system has only been discussed in Benchluch and Chow (1993), Ludwig et al. (1998), Bhaskar et al. (2000), Liao et al. (2006), and Puma and Colome (2008). No reviewed publication has presented a quantitative treatment about parameter identifiability, which is assessed in the category 12.
4.4 Review of selected publications on excitation system identification
To analyze the contributions in the characteristics defined in section 4.1, a review of the articles that closely match such conditions is presented below. In this way, the most representative papers are selected based on the total value obtained in table 3, choosing the ones with a total value higher than 70 % of the maximum value achieved, 16 by Puma and Colome (2008). Therefore, the papers discussed are: Benchluch and Chow (1993), Wang et al. (1995), Rasouli and Karrari (2004), Abd-Alla et al. (2006), Shen and He (2007), and Puma and Colome (2008).
Benchluch and Chow (1993) use a trajectory sensitivity technique to identify nonlinear excitation system models. The technique is used to identify two types of nonlinearities: limits of signals and parameters of a magnetic saturation function. An important aspect in this paper is that singular values are used to provide information about the parameters identifiability. Additionally, the effect of the noise in the parameters identifiability is also studied.
Wang et al. (1995) presents a procedure to identify excitation system models based on discrete measurements from a plant transient recorded system. The authors use data collected during a fault of the system, therefore they do not use external perturbation signals. The gradient averaging stochastic approximation method is used to estimate the nonlinearities of the excitation system model.
Rasouli and Karrari (2004) present a nonlinear identification of an excitation system operating in a power plant, where the experiments are carried out with the generator online. Grey box and black box modeling are used to estimate the excitation system parameters. In grey box approach, the parameters of a transfer function are obtained using a well known estimation algorithms like prediction error method. In black box modeling, the excitation system is identified using a discrete wavelet transform. Both approaches report good results, however, the authors highlight that transfer function model will be more useful for power engineers in power system analysis.
A nonlinear identification method for an excitation system of a power plant in China is presented by Abd-Alla et al. (2006). A genetic algorithm and prediction error method are used to estimate the model parameters. The comparison of time responses and estimated parameters shows good results from both methods, but better results were obtained from the genetic algorithm. The experiments to collect the data were carried out with the generator offline.
Shen and He (2007) present the identification of an excitation system in a simulation environment. The excitation system and a single machine models are implemented using MATLAB/Simulink. A pseudorandom binary sequence is used as perturbation signal and a genetic algorithm is adopted to estimate the model parameters. The influence of different sampling periods on parameter identification results is also analyzed. Finally, the authors provide some advices in parameter estimation of excitation systems.
A methodology to estimate linear and nonlinear parameters of excitation system models is presented by Puma and Colome (2008). Genetic algorithms are used to estimate linear and nonlinear parameters simultaneously. The identification methodology is applied in a simulation environment over two excitation system standard models DC1A and ST1A, and over an actual excitation system in a power plant. The results obtained are good enough and the model responses are close to the system responses, and the identification experiments are carried out with the generator offline. Finally, authors report that the noise in the measurements does not affect the identification results.
4.5 Open research areas in excitation system identification revealed by the bibliographic classification method
The research areas in excitation system identification that are insufficiently explored can be selected from the results in the last row of table 3, which indicates the percentage of papers that deals with a specific category. In this case, characteristics with percentage equal or smaller than 25 % are defined as insufficiently explored research areas in excitation system identification and therefore discussed below.
Only 20,6 % of the publications have reported experiments with the generator online: Shen, Zhu and Han (1991), Liaw et al. (1992), Liu et al. (1993), To and David (1996), Rasouli and Karrari (2004), and Glaninger-Katschnig (2010). Rasouli and Karrari (2004) has reported identification experiments with the synchronous machine generating different levels of active power, obtaining different parameter values of the excitation system model for each operating point. The difference in the parameter values is associated with the nonlinearities of the system. Among the reviewed papers, no one has investigated the effect of the operating conditions on the identification results, taking into account that the excitation control system operates in closed loop during the identification experiment.
The percentage of category 3 is below 25 %, however, the effect of the noise in parameter estimation was widely investigated between 1971 and 2000. Published papers from 2000 do not dedicated strong efforts to work in the noise issue. In addition, Puma and Colome (2008) show a computational algorithm to estimate the parameters without adverse effect of the noise present in the measurements.
The nonlinearity values in excitation system models usually are given by the manufacturer or are taken from databases of power system analysis handbooks. The estimation of nonlinearities on the excitation system has been addressed only by the 17,2 % of the reviewed papers. Ramírez, Saavedra and Vásquez (2003), and Saldaña, Calzolari and Cerecetto (2006) calculate analytically the nonlinearities. In contrast, in Wang et al. (1995) and Bhaskar et al. (2000) the nonlinearities are linearized and then estimated, while in references Benchluch and Chow (1993), Feltes et al. (2002), Paszek et al. (2005), Hernandez et al. (2006), and Puma and Colome (2008) the nonlinearities are estimated with the estimation method. From those developments, genetic algorithms have demonstrated to be an effective technique to estimate the linear parameters and the nonlinearities simultaneously.
Parameters identifiability is another aspect that has not been actively addressed in papers about excitation system identification. No reviewed article has focused on evaluating the identifiability of excitation system parameters, nor on the identifiability taking into account the operating conditions of the synchronous generator, which is an important aspect since the dynamics of the excitation control system changes with the generator operating condition. Benchluch and Chow (1993), Ludwig et al. (1998), Bhaskar et al. (2000), Liao et al. (2006), and Puma and Colome (2008) slightly discussed the parameters identifiability of excitation systems, but not deeper analyses based on the results have been provided.
Validation stage is the category with the lowest percentage, only 13,7 %, among the defined categories. In most cases, papers in excitation system identification report the validation of the model comparing the system output to the model output, and some of them present an error index to quantify the differences between the outputs. When papers are focused on parameters estimation, they compare the estimated parameters with a set of reference parameters. Residual analysis is another way used to validate excitation system models, where the identification experiment conditions should be taken into account; for example, data collected with or without feedback path. Zazo et al. (1994), Vermeulen and Strauss (1999), Botero and Ramírez (2005), and Shen and He (2007) use several ways to validate excitation system models, providing a good comparison scenario that helps the reader to select a validation procedure depending on its particular requirements. Finally, standard indexes or validation procedures designed for excitation system identification must be developed to allow a comparison between different identification approaches.
To establish the state of the art in excitation system identification, a bibliographic classification method was designed and implemented. The proposed method was used to review publications in excitation system identification and to detect open research issues in this topic. The bibliographic method was applied to papers published from 1971 until 2010.
Among the results obtained with the method, the next are highlighted: the topic most discussed by the authors in the reviewed publications was the estimation algorithm or method, i.e. several estimation methods were used to estimate the parameters of an excitation system model. But few authors have focused their efforts to estimate the nonlinearities of excitation system models or to investigate the effects of carrying out the identification experiments with the generator online. Similarly, few papers report identification methodologies that match completely the conditions defined in section 4.1, which are required to deal with the requirements of identify parameters of excitation systems nowadays.
This work was supported by GAUNAL group of the Universidad Nacional de Colombia under the project SMART-ALEN, GICI group of the Universidad del Valle, and the Departamento Administrativo de Ciencia, Tecnología e Innovación (Colciencias) under the scholarship 095-2005.
Abd-Alla, A. N.; Cheng, S. J.; Wen, J. Y. and Zhang, J. (2006). Model parameter identification of excitation system based on a genetic algorithm techniques. Proceedings of the International Conference on Power System Technology, Chongqing, China (22-26 October). [ Links ]
Benchluch, S. M. and Chow, J. H. (1993). "A trajectory sensitivity method for the identification of nonlinear excitation system models". IEEE Transactions on Energy Conversion, vol. 8, No. 2 (June), pp. 159-164. [ Links ]
Bhaskar, R.; Crow, M. L.; Ludwig, E.; Erickson, K. T. and Shah, K. S. (2000). "Nonlinear parameter estimation of excitation systems". IEEE Transactions on Power Systems, vol. 15, No. 4 (November), pp. 1225-1231. [ Links ]
Botero, H. A. and Ramírez, J. M. (2005). A methodology for excitation systems identification. Proceedings of the IEEE International Conference on Industrial Electronics and Control Applications. Quito, Ecuador (29 November - 2 December). [ Links ]
Chow, J. H.; Glinkowski, M. T.; Murphy, R. J.; Cease, T. W. and Kosaka, N. (1999). "Generator and exciter parameter estimation of Fort Patrick Henry Hydro Unit 1". IEEE Transactions on Energy Conversion, vol. 14, No. 4 (December), pp. 923-929. [ Links ]
Eykhoff, P. System identification: Parameter and state estimation. New York: Wiley-Interscience, 1974. [ Links ]
Feltes, J. W.; Orero, S.; Fardanesh, B.; Uzunovic, E.; Zelingher, S. and Abi-Samra, N. (2002). "Deriving model parameters from field test measurements". IEEE Computer Applications in Power, vol. 15, No. 4 (October), pp. 30-36. [ Links ]
Gibbard, M. J. and Kaan, Q. H. (1975). "Identification of excitation system parameters". IEEE Transactions on Power Apparatus and Systems, vol. 94, No. 4 (July), pp. 1201-1207. [ Links ]
Glaninger-Katschnig, A. (2010). "Identification of excitation system transfer functions in hydro power plants using a binarypseudo random signal". E and I Elektrotechnik und Informationstechnik, vol. 127, No. 1-2 (February), pp. 8-12. [ Links ]
Godfrey, K. R.; Tan, A. H.; Barker, H. A. and Chong, B. (2005). "A survey of readily accessible perturbation signals for system identification in the frequency domain". Control Engineering Practice, vol. 13, No. 11 (November), pp. 1391-1402. [ Links ]
Guo, T.-Y.; Liu, C.-S.; Chen, Y.-T.; Ko, C.-K. and Huang, C.-T. (1995). "Identification of model parameters of excitation system and power system stabilizer of Mingtan#6 via finalization field tests". IEEE Transactions on Power Systems, vol. 10, No. 2 (May), pp. 795-802. [ Links ]
Hernandez, J. A.; Botero, H. A.; Ospina, J. D. and Perez, J. C. (2006). Excitation system parameters estimation using evolutionary algorithms. IEEE Transmission and Distribution Conference and Exposition: Latin America. Caracas (15-18 August), pp. 1-6. [ Links ]
Hsu, Y.-Y.; Liu, C.-S.; Luor, T.-S.; Chang, C.-L.; Liu, A.-S.; Chen, Y.-T. and Huang, C.-T. (1996). "Experience with the identification and tuning of excitation system parameters at the second nuclear power plant of Taiwan Power Company". IEEE Transactions on Power Systems, vol. 11, No. 2 (May), pp. 747-753. [ Links ]
IEEE (1968). "Computer representation of excitation systems". IEEE Transactions on Power Apparatus and Systems, vol. PAS-87, No. 6 (June), pp. 1460-1464. [ Links ]
IEEE (1981). "Excitation system models for power system stability studies". IEEE Transactions on Power Apparatus and Systems, vol. PAS-100, No. 2 (February), pp. 494-509. [ Links ]
IEEE (1996). "Computer models for representation of digital-based excitation systems". IEEE Transactions on Energy Conversion, vol. 11, No. 3 (September), pp. 607-615. [ Links ]
IEEE. IEEE recommended practice for excitation system models for power system stability studies. IEEE Std 421.5-2005. New York: IEEE, 2006. [ Links ]
Karl, D. S. and Schaefer, R. C. (2004). "NERC power industry policies". IEEE Industry Applications Magazine, vol. 10, No. 2 (March), pp. 30-38. [ Links ]
Landau, Y. D. and Zito, G. Digital control systems: Design, identification and implementation. London: Springer, 2006. [ Links ]
Liao, Q. F.; Liu, D. C.; Ying, L. M.; Cui, X.; Li, Y. and He, W. T. (2006). Parameter identification of excitation systems based on Hopfield neural network. Proceedings of the International Conference on Power System Technology, Chongqing, China (22-26 October), pp. 1-6. [ Links ]
Liaw, C. M.; Liu, T. S.; Liu, A. H.; Chen, Y. T. and Lin, C. J. (1992). "Parameter estimation of excitation systems from sampled data". IEEE Transactions on Automatic Control, vol. 37, No. 5 (May), pp. 663-666. [ Links ]
Liu, C.-S.; Hsu, Y.-Y.; Jeng, L.-H.; Lin, C.-J.; Huang, C.-T.; Liu, A. H. and Li, T.-H. (1993). "Identification of exciter constants using a coherence function based weighted least squares approach". IEEE Transactions on Energy Conversion, vol. 8, No. 3 (September), pp. 460-467. [ Links ]
Ljung, L. System identification: Theory for the user. New Jersey: Prentice Hall, 1999. [ Links ]
Ludwig, E.; Crow, M. L.; Erickson, L. and Shah, K. (1998). "A feasibility study of on-line excitation system parameter estimation". IEEE Transactions on Power Systems, vol. 13, No. 3 (August), pp. 910-916. [ Links ]
Paszek, S.; Bobon, A.; Kudla, J.; Bialek, J. and Abi-Samra, N. (2005). "Parameter estimation of the mathematical model of a generator, excitation system and turbine". Przeglad Elektrotechniczny, vol. 81, No. 11 (November), pp. 7-12. [ Links ]
Puma, J. Q. and Colome, D. G. (2008). "Parameters identification of excitation system models using genetic algorithms". IET Generation, Transmission and Distribution, vol. 2, No. 3 (May), pp. 456-467. [ Links ]
Ramírez, J. M.; Saavedra, A. J. y Vásquez, H. Modelado de los sistemas de control de la central hidroeléctrica de Salvajina. Parte II: Control de excitación. V Congreso Nacional de la ACA. Medellín, Colombia, 2003. [ Links ]
Rasouli, M. and Karrari, M. (2004). "Nonlinear identification of a brushless excitation system via field tests". IEEE Transactions on Energy Conversion, vol. 19, No. 4 (December), pp. 733-740. [ Links ]
Saldaña, C.; Calzolari, G. and Cerecetto, G. (2006). "ATP modelling and field tests of the AC voltage regulator in the Palmar hydroelectric power plant". Electric Power Systems Research, vol. 76, No. 8 (May), pp. 681-687. [ Links ]
Sanchez-Gasca, J. J.; Bridenbaugh, C. J.; Bowler, C. E. J. and Edmonds, J. S. (1988). "Trajectory sensitivity based identification of synchronous generator and excitation system parameters". IEEE Transactions on Power Systems, vol. 3, No. 4 (November), pp. 1814-1822. [ Links ]
Shen, F. and He, R.-m. (2007). A feasibility study of excitation system parameters identification based on measured perturbation. Proceedings of the International Power Engineering Conference. Singapore (3-6 December), pp. 904-909. [ Links ]
Shen, S.; Zhu, S. and Han, B. (1991). Identification of parameters of synchronous machine and excitation system by online test. Proceedings of the International Conference on Advances in Power System Control, Operation and Management, Hong Kong, China (5-8 November), vol. 2, pp. 716-719. [ Links ]
Söderström, T. and Stoica, P. System identification. Hemel Hempstead, UK: Prentice Hall, 1989. [ Links ]
To, K. W. V. and David, A. K. (1996). "On-line identification and control of an AC/DC power system". International Journal of Electrical Power and Energy Systems, vol. 18, No. 4 (May), pp. 223-227. [ Links ]
Veloza, O. P. and Cespedes, R. H. (2006). Regulatory mechanisms to mitigate the vulnerability of power systems to blackouts. Proceedings of the IEEE Transmission and Distribution Conference and Exposition: Latin America. Caracas (15-18 August), pp. 1-6. [ Links ]
Vermeulen, H. J. and Strauss, J. M. (1999). Off-line identification of an open-loop automatic voltage regulator using pseudo-random binary sequence perturbations. AFRICON, 1999 IEEE. Cape Town. [ Links ]
Wang, J.-C.; Chiang, H.-D.; Huang, C.-T.; Chen, Y.-T.; Chang, C.-L. and Huang, C.-Y. (1995). "Identification of excitation system models based on on-line digital measurements". IEEE Transactions on Power Systems, vol. 10, No. 3 (August), pp. 1286-1293. [ Links ]
Warchol, E. J.; Schleif, F. R.; Gish, W. B. and Church, J. R. (1971). "Alinement and modeling of Hanford excitation control for system damping". IEEE Transactions on Power Apparatus and Systems, vol. PAS-90, No. 2 (March), pp. 714-724. [ Links ]
Yao, X.; Karady, G. G.; Farmer, R. G. and Agrawal, B. L. (2001). Estimation of generator excitation-system parameters by tabu search. Proceedings of the IEEE Power Engineering Society Winter Meeting. Columbus, OH (28 January - 1 February). [ Links ]
Zazo, A.; Zamora, J. L.; Rouco, L. and Pagola, F. L. (1994). "Identification of excitation systems from time response tests". Proceedings of the International of Conference on Control, Coventry, UK (21-24 March), vol. 1, pp. 839-844. [ Links ]
Escuela de ingenieria de Antioquia
calle 25 sur 42-53 Envigado , Colombia
teléfono: 57-43333208
revista@eia.edu.co