One focus of use of the activation circuit is in the field of adjustment mechanisms for rotor blades, as are used, for example, in wind or water power facilities. They are used for the purpose of changing the attack angle of one or more rotor blades in relation to the flowing drive medium air or water in such a way that on one hand optimal efficiency of the power generating facility may be achieved, and on the other hand, in case of malfunction, the drive face of the rotor blades may be pivoted in relation to the drive flow into a neutral position (feathering position), so that the power generating facility may be put into an idle position. The requirement exists in this case that the required activation circuit allows at least emergency running operation even in the event of diverse malfunctions and supports fixing the rotor blades. The field of use of the activation circuit is not restricted to this area, it may also be used in other fields of technology.
In the above-mentioned usage case, three-phase current and/or DC motors are typically used. The activation circuits employed for this purpose comprise inverters in the case of three-phase current motors, such as frequency converters or servo controls, which may control the motor speeds. For this purpose, these converters are typically constructed as three-phase for asynchronous or synchronous three-phase current motors, one half-bridge being used for each motor phase, which typically comprises two power transistors, e.g., insulated gate bipolar transistors (IGBTs) and possibly two freewheeling diodes. The three phases of the power network are converted via a bridge rectifier into DC voltage for the power supply of such rotor blade adjustment devices based on three-phase current, and this DC is led to the three half-bridges of the inverter. Therefore, three types of voltage may be differentiated in these known activation circuits: the network voltage, the intermediate circuit DC voltage, and the arbitrarily controllable output voltage of the inverter.
Multiple implementations and variants of such an activation circuit are known from the prior art. Thus, for example, it is typical that both DC and also three-phase current motors may be used for the adjustment of rotor blades. The suggestion exists for this purpose that multiple DC and/or three-phase current motors may be used for one adjustment device of a single rotor blade. If three-phase current motors are used, a braking and stopping effect of the motors on the rotor blade may be achieved with the aid of a DC applied to the three-phase current motors, so that additional stopping brakes may be saved.
In addition, it is also typical to use mechanical motor brakes for stopping an electric drive, which are electromagnetically actuated in many cases and are coupled to the shaft of the motor. Such electromagnetically actuated stopping brakes may be operated in the range from extra-low voltage up to network voltage using DC or also AC voltage. Additional components are necessary for this purpose in many possible implementations, such as power supply units or cooling devices. The stopping brakes typically block in the unpowered state and open in the powered state. Special switch contacts for extra-low voltage, which directly support the activation function of such a stopping brake, are provided for operating such a stopping brake in commercially available converters, for example, in frequency converters or servo controls. In many cases, however, an external power source is required to operate a stopping brake, in order to provide the required operating voltage to the stopping brake. In this regard, operating stopping brakes using pulse-width-modulated activation voltages is known from the prior art, to adapt the available network voltage, intermediate circuit voltage, or motor voltage for the employed stopping brake and thus operate the stopping brake. Such pulse-width-modulated activation reduces the number of required additional circuits for the braking system, because no additional power sources or power supply units are required.
A high degree of operational reliability is absolutely required precisely in drive devices for rotor blades of power generating machines. Suggestions exist that upon the occurrence of a malfunction, the rotor blades may be moved into a neutral state with the aid of an emergency operation supply unit, so that the rotor blade assumes a feathering position, in which it does not offer any resistance to the flowing medium. Technical implementations exist for this purpose, which use a DC motor for the rotor adjustment, which pivots the rotor into a feathering position via an emergency battery in case of malfunction. Proceeding from this variant, activation circuits have been developed in which the emergency operation supply unit may be coupled either directly or indirectly via an activation circuit/an inverter to the DC motor. Such activation circuits offer the advantage that on one hand, upon breakdown of the inverter the DC motor may be operated directly via the emergency operation supply unit, on the other hand, during operation via the inverter, targeted control of the motor is possible, for example, via pulse width modulation. An alteration of this concept known from the prior art is to use a three-phase current motor instead of a DC motor. However, only coupling the operating voltage of the emergency operation supply unit in via the intermediate circuit of the inverter comes into consideration, because the DC voltage of the emergency operation supply unit must first be converted into three-phase current. In an alternative concept, the use of an inverter is dispensed with, so that only the possibility of making the emergency operation supply unit connectable directly to a DC motor exists.
Finally, it is known from the prior art that a DC motor having series and shunt windings is used for an adjustment device of a rotor blade, which is activated via a three-phase bridge inverter, as is typically used for activating three-phase current motors.
The possible implementations for activation circuits described above, in particular for adjusting rotor blades of wind or water power facilities, achieve specific objects of such adjustment devices and require multiple specialized components and special circuit technologies for this purpose.
Thus, for example, the use of three-phase current motors for an adjustment device and implementing the stopping function by DC powering of the three-phase current motors requires a special circuit for providing the DC voltage and a special controller, which performs the changeover between three-phase current operation and holding current operation. DC powering of a three-phase current motor has the disadvantage of restricted and often too low stopping and braking action in holding current operation. Furthermore, such a brake implementation is not intrinsically reliable, i.e., in case of malfunction, for example in the event of a motor defect, the danger exists that the stopping and braking action will break down completely, so that the rotor blade moves uncontrolled and may cause further damage.
For this reason, using separate stopping brakes, which may exert sufficiently high braking and stopping forces and offer a higher intrinsic reliability, is known. However, controlling these separate stopping brakes, typically by pulse-width-modulated control voltages, requires additional components, which generate the pulse-width-modulated voltages, as well as a separate control device, which activates the stopping brakes.
The combination of drive device with the aid of three-phase current motors and emergency operation supply units, which typically only provide DC voltage, requires the use of an extremely reliable and failsafe DC/AC converter and thus increases the overall costs of the activation circuit.
For this purpose, operating a DC motor via an inverter in which an emergency operation supply unit may be applied both directly to the DC motor and also indirectly via the inverter to the DC motor, is known. However, such an activation circuit requires the development and implementation of a special inverter for DC operation, which comprises at least two half-bridges. Furthermore, the problem results that a stopping brake, which is required in many cases, is not provided integrated in this concept.
Alternatively thereto, a concept which couples the emergency operation supply unit solely directly to the DC motor in case of fault does not allow defined control of the DC motor, so that the emergency operation of the adjustment device may only be performed by turning the DC motor on and off in binary form.
Finally, the operation of a DC motor having series and shunt windings via a three-phase bridge inverter does allow the operation of a DC motor, but not the use of an additional stopping brake or further actuators, without a separate activation circuit having to be added for this purpose.