The present invention relates generally to energy management and more particularly to the implementation of a unique sequence to achieve optimization of variable selection.
Recent world-wide primary fuel shortages are forcing the industrial and commercial sectors of industrial nations to reduce and control power consumption. Energy management systems have been developed to permit individuals or plants to control their power demand and consumption, thereby lowering costs and making more effective utilization of power consumed. The general approaches toward regulating power demand are generally known as instantaneous demand, ideal rate, converging rate, predicted demand, and continuous integral. The first four methods concentrate on limiting the load in the demand charged interval measured by the utility companies.
The instantaneous demand controllers compare the rate of energy consumption, or slope of the energy curve relative to time, with a preset rate. When the instantaneous rate exceeds the preset rate, loads are shed to reduce consumption and when the instantaneous rate is less than the preset rate, loads are restored to increase the rate of consumption. This method generally does not take full advantage of the available power and has a tendency to short cycle loads turning them on and off frequently.
Another group of instantaneous demand controllers draws a straight line from zero to the power level required for the demand interval. This requires a synchronization pulse and the loads are instantaneously shed to stay below the line. A second line offset by a small margin from the first line having the same slope is the restoration line. As with the previous instantaneous demand controller, this system also does not take full advantage of the available power and tends to short cycle loads. An additional difficulty with this system is obtaining the demand interval synchronization pulse.
The ideal rate controllers operate as the instantaneous demand controllers except that the line representing the rate of power consumption for the demand interval is offset from time zero along the power axis as are the shed and restoration lines which lie below the ideal rate line. By offsetting these lines from zero, the system will not prematurely act to control the loads too early in the demand period. As with the previous system, a synchronization pulse is required and maximum use of the available power is not achieved.
A modification of the ideal rate controller is the coverging rate controller wherein the restoration line, shed line, and ideal rate line converge to a point at the end of the demand period. As with the previous system, it requires a synchronization pulse, and even though it comes closer to reaching the final target, it requires more load cycling than the ideal rate system.
The fourth system, requiring a considerable amount of calculation, is the predicted demand system. A curve of predicted usage for the remainder of the demand interval using the average usage in the interval and the instantaneous usage of the particular moment is estimated. If the curve of the projected usage exceeds the target point at the end of the interval, action is taken so as to modify the power usage and the predicted curve is modified accordingly. This method requires fairly sophisticated electronics and generally includes a computer, thus pricing itself out of the reach of all but major industrial users.
The fifth method of power control is the continuous integral method. In this method, power usage is monitored continuously over a very small time interval and loads are shed or restored to continuously maintain the power below a fixed level. This method is not related to the demand period and consequently does not need the synchronization pulse. By eliminating excessive cycling of loads produced by the other methods, this method achieves a higher overall power factor.
The following U.S. Patents show the state of the art of continuous integral controllers or hybrids thereof wherein the loads are added or shed to maintain the total power consumption below or within preset limits: U.S. Pat. Nos. 3,652,838; 3,714,453; 3,769,520; 3,862,430; 3,872,286; 3,987,308.
These prior art systems, though being of the continuous integral type and thus being an improvement over the prior art generally, unless they are computer controlled, do not provide optimization of the number of loads on and of the power consumption. The inability to achieve this optimization results from the priority scheme used for shedding and/or restoring loads. Thus there exists a need for a priority scheme or sequence for restoring and shedding loads which optimizes the number of loads on and the amount of power being consumed below a target value.