WO2011110193A1 - Method for controlling the feeding of electrical power of a wind turbine into an alternating-current network - Google Patents

Abstract

In order to avoid overvoltages and/or irregular power flows after a network disturbance has been rectified in a method for controlling the feeding of electrical power of a wind turbine into an electrical alternating-current network connected to the wind turbine, the current is set to zero when the network voltage returns to the target range of the network voltage at least until the phase angle of the current with regard to the returned network voltage is set to a value intended for normal operation.

Description

 Method for controlling the supply of electrical power

 Wind turbine in an AC network

The invention relates to a method for controlling the supply of electrical power of a wind turbine into an electric alternating current network connected thereto, in which the phase angle of the current fed in by the wind energy plant with respect to the phase angle of the mains voltage is set to a predetermined value, in which the wind turbine feeds active power into the grid.

In such methods, the wind turbine remains during Netzbetriebsbedingter changes despite an associated break in the grid voltage and / or a change in their phase angle on the grid. This ensures that the wind turbine can feed active power as possible interruption in the network. If, on the other hand, according to older practice, when such changes occur, the wind turbine is temporarily galvanically isolated from the grid, a longer period of time is required to re-start the wind turbine so that it can provide active power to the grid. Immediate readiness to re-energize as network operating conditions change is all the more important the greater the share of wind energy in the overall network performance. In particular, the phase angle of the mains voltage can change abruptly in weak networks. Mains faults due to short-circuit-induced network faults lead, for example, to mains voltage dips.

In a known method of the kind mentioned at the beginning ("Wind farms with power plant properties", E. Quitmann, S. Wachtel, M. Bartsch, WWEC 2007 (Mar del Plata / Argentina), 6th Conference and Fair of the World Wind Energy Association (WWEA), 02.10.- 04.1Ö.20Ö7) is set in the event of a power failure of the phase angle / of the current supplied by the wind turbine so that the latter then leads the then present mains voltage by almost 90 °. As a result, almost no active power is fed into the faulty network, but essentially only reactive power. The latter causes a support of the mains voltage at the feed point.

By rectifying the power failure, the impedance of the network may change. This change in impedance can be based, for example, on disconnecting or switching lines or entire network areas for rectifying the network fault. Such an impedance change draws a corresponding change in the phase angle between the returned mains voltage and the unchanged injected current by itself. This can lead to overvoltages on the grid or even cause the wind turbine to draw real power from the grid. The danger of overvoltages is given especially in the case of a persistent hchsn reactive current feed in excess of the duration of the mains disturbance. In particular, this is the case in weak or very distributed networks.

These problems also exist in another known method (WO 2005/031941 A1). There, when a network fault occurs, the power supply is reduced compared with the power supply present before the power failure and, after the power failure has been eliminated, the power supply is briefly increased significantly compared to the power supply present before the power failure.

Another known method (WO 99/33165) does not take these problems into account. It only provides to operate the wind turbine without power output when the grid voltage leaves a predetermined target range.

The invention has for its object to provide a method of the type mentioned that avoids overvoltages on the grid or irregular power transfers between the network and the connected wind turbine.

According to the invention, this object is achieved in that in a network-induced change in the phase angle of the mains voltage, the current is at least as long reduced, in particular set to zero until its phase angle is adjusted in relation to the changed mains voltage to the predetermined value.

During the temporary reduction or zeroing of the current fed in according to the invention, its phase angle can be readjusted with respect to the changed phase angle of the mains voltage to the phase angle suitable for undisturbed operation of the network. Then, when the current is fed back with the thus set phase angle, it can not come to overvoltages or irregular power flows.

This is particularly advantageous if the phase angle is set at the entry point to a value at the occurrence of a grid fault for the purpose of voltage support at the feed point at which the wind turbine feeds reactive power into the network, in particular to a value close below + 90 °, in which the fed Stream of through the mains failure leads the mains voltage by almost 90 °. Then could occur even with a slight impedance deviation of the suppressed network of the case that the phase angle between the current and the returned mains voltage is greater than 90 ° and the network feeds active power into the wind turbine.

In the following description, the invention will be described by way of example with reference to the drawings. Show it:

1 is a phasor diagram of mains voltage and current fed in undisturbed operation,

FIG. 2 shows a vector diagram corresponding to FIG. 1 in the event of a network fault, FIG.

3 is a Fig. 2 corresponding phasor diagram when switching to voltage support,

4 is a Fig. 3 corresponding phasor diagram when correcting the power failure,

FIG. 5 shows a phasor diagram of undisturbed network operation corresponding to FIG. 4 after rectification of the network fault, FIG.

Fig. 6 shows an embodiment of a wind turbine according to the invention, which has a full converter, and

Fig. 7 shows an embodiment of an inventive controlled wind turbine, which has a double-fed asynchronous generator.

Fig. 1 shows the case that a wind turbine feeds an AC electrical network, which is in its undisturbed state. In the example shown, the phase angle between the mains voltage U _W EA present at the feed point and the current IW _EA 3uf fed by the wind energy plant is set to zero. This adjustment of the phase angle, for example, by a controlled converter of the wind turbine. As a result of the phase angle set to zero, the wind turbine feeds pure active power into the grid. The mains voltage U _W EA is in a predetermined range for the undisturbed operation of the network.

Fig. 2 shows the case that a short circuit occurs on a remote from the feed point of the network. Because of the changed impedance conditions breaks the supply point, the mains voltage U _WEA , for example, to 50% of the undisturbed mains voltage. In addition, the phase of the mains voltage changes, for example by 30 °. However, the power converter of the wind turbine initially maintains the phase of the injected current unchanged. However, the current increases due to the impedance change up to its maximum value.

In Fig. 3, the power converter of the wind turbine has recognized the collapse of the mains voltage and thus the power failure. In response, he sets the phase of the injected current IWEA such that it leads the mains voltage UWEA by almost 90 °. As a result, essentially only reactive power is fed into the grid. This reactive power supply causes a support of the mains voltage at the feed point. The latter is required by grid connection rules of different network operators.

In Fig. 4, the power failure is corrected and the mains voltage U _WEA thereby returned to its desired range. As a result of the changed impedance of the suppressed network, the phase angle of the returned mains voltage U _W EA deviates slightly from the phase angle of the mains voltage present before the occurrence of the system disturbance (FIG. 1). Maintaining the phase angle of the current iwEA set during the power failure according to FIG. 3 would then mean that the current of the voltage will hurry by more than 90 °. In this case, the grid would feed real power into the wind turbine.

Therefore, the power supply is reduced, in particular set to zero as soon as the mains voltage has returned. This reduction or zero position is maintained at least until the power converter of the wind energy plant has returned the phase angle of the current to be fed in relation to the returned mains voltage to the value specified for undisturbed operation, in the example shown the value zero. Then, the power converter ramps up the power supply according to a ramp up to the value corresponding to the undisturbed operation. As a result, after the rectification of the power failure of the illustrated in Fig. 5 stable final state is brought about.

The duration of the ramp can be, for example, between 200 ms and 10 s. The duration of the reduction or zeroing of the current to be injected after detection of the return of the mains voltage to its predetermined nominal range is expediently not shorter than one period of the alternating current network, ie 20 ms for a mains frequency of 50 Hz. An exemplary embodiment of a wind power plant schematically illustrated in FIG. 6, which is controlled according to the method explained above, has an alternator G, which may be a synchronous generator or an asynchronous generator. To the three-phase output of the generator G, a generator-side converter GSC of a Voliumrichiers (Fu-scaie Converter) is connected. The gensrator-side converter GSC converts the three-phase AC voltage AC of the generator G supplied to it on the input side into an output-side DC voltage DC. The latter acts on the input side of a DC intermediate circuit connected to the generator-side converter GSC, to the output side of which a line-side converter LSC is connected. By the latter, the DC voltage DC of the DC intermediate circuit is converted into a three-phase AC voltage whose frequency coincides with the frequency of a to be fed from the wind turbine three-phase supply system. The three-phase output of the line-side converter LSC carrying this alternating voltage is connected to the supply network via a circuit-breaker PCB.

The generator-side converter GSC and the line-side converter LSC are controlled by a converter control unit (converter control). This causes on the one hand in a known manner a torque control, through which a maximum power output is achieved in dependence on the speed of the wind turbine. For this purpose, the inverter control unit, the actual value of the generator voltage U _g as the speed corresponding signal and the actual value Q of the generator power is supplied. From this, the inverter control unit determines a setpoint signal M for the generator torque. By means of this setpoint signal M, the generator-side converter GSC is controlled in the sense of a power output corresponding to the desired torque.

On the other hand, the converter control unit receives a signal indicative of the actual value U _{dc of} the DC voltage in the DC intermediate circuit and a signal u measured at the output of the mains side converter LSC, which reproduces the voltage of the supply network present there, both in terms of its amplitude and phase. In response to this signal u, the converter control unit outputs a setpoint signal i to the line-side converter LSC. By means of this setpoint signal i, the line-side converter LSC is controlled in such a way that adjusts the above-explained dependence between the mains voltage and the current fed into the network. In addition, the converter control unit monitors the DC voltage U _dc in the DC intermediate circuit. If this DC voltage due to the reduction of power loss due to the temporary interruption of the power supply to a should increase undesirably high value, it temporarily switches a consumer (DC link chopper, brake resistor) to the Gleichspannuhgszwischenkreis and thereby performs the excess power by means of this consumer until the DC voltage in the DC voltage intermediate circuit has fallen back to an acceptable range of values. The Lasttrennschaiter PCB is closed during these Regeivorgänge so that the wind turbine remains galvanically connected to the supply network.

In the exemplary embodiment explained above with reference to FIG. 6, the stator windings of the generator G are connected to the supply network via the full converter formed by the generator-side converter GSC, the DC intermediate circuit and the line-side converter LSC. As a result, this full converter controls the entire energy flow between the generator G and the supply network. Therefore, it is possible by its inverter control device in the simple manner described above, either dissipate the energy generated by the generator G in the supply network and / or temporarily connectable consumer, without thereby affecting the generator and to change the generator torque very briefly. Of this, the embodiment shown in Fig. 7 differs substantially in that the generator is a double-fed asynchronous generator DFIG, in which the inverter (partial load converter) is connected in the rotor circuit. In this embodiment, the generator-side converter GSC of the exemplary embodiment shown in FIG. 6 corresponds to the rotor-side converter RSC in FIG. 7. In the manner described with reference to the embodiment of FIG. 6, this is determined by its converter control unit (converter control) in the sense of an optimum generator torque M controlled. The network-side converter LSC connected by a DC voltage intermediate circuit to the rotor-side converter RSC is, as in the exemplary embodiment explained with reference to FIG. 6, connected on the output side via a load-disconnect switch PCB to the supply network to be fed. Further, as shown in Fig. 6, the power voltage is detected at the output of the power-side converter LSC, and the detection signal, which represents both the amplitude and the phase of the power voltage, is supplied to the inverter control unit. The latter outputs a setpoint signal ic for the amplitude and phase of the converter current to the line-side converter LSC in dependence thereon. The stator-side output of the double-fed asynchronous generator DFIG is connected via a high-speed thyristor switch TS to the load-disconnector PCB which establishes the connection to the supply network.

The above-explained reduction or zero position of the power supply takes place with a closed circuit breaker PCB in that the stator output of double-fed asynchronous generator DFIG is disconnected from the supply network and the rotor circuit by opening the thyristor switch TS. Instead, the inverter control unit couples the stator output to an electronic commutation unit CU, which immediately builds up a reverse voltage. In addition, the Inverter Tax Section Ii ICH uci il uiui aemyci i / nuayciny ues VJCI ICI caiui oi_ / nvj ii uueia einci

 CB-R short and thereby causes a sudden final magnetization of the generator. In this control process, the wind turbine remains connected by the inverter to the supply network to be fed. The startup of the power supply after its zero position is then carried out by disconnecting the commutation unit CU and closing the thyristor switch TS, whereby the inverter is started and the magnetization of the rotor is rebuilt.

From the above description, which illustrates the method according to the invention by way of example, it can be seen that it is suitable in particular for driving through network-related short-circuits (fault-ride-through). The required control of the feed-in current can be effected, for example, by a controlled full converter and chopper of the wind energy plant or a control of the partial converter of a doubly fed asynchronous generator connected to demagnetization.

Claims

claims A method of controlling the supply of electrical power to a wind turbine into an associated electrical AC grid, wherein the phase angle of the current injected by the wind turbine is in relation to the phase angle! the mains voltage is set to a predetermined value at which the wind energy system feeds active power into the network, characterized in that at a network-related change in the phase angle of the mains voltage, the current is at least as long reduced, in particular set to zero until its phase angle with respect to the changed mains voltage has been readjusted to the specified value. 2. The method according to claim 1, characterized in that the duration of the reduction or zero position of the current is at least one period of the mains frequency. 3. The method according to claim 1 or 2, characterized in that the feed of the current is ramped up after the reduction or zero position. 4. The method according to any one of claims 1 to 3, characterized in that the adjustment of the phase angle and / or the amplitude of the current is effected by a power converter of the wind turbine. 5. The method according to any one of claims 1 to 4, wherein the mains voltage is maintained in the undisturbed operation of the AC network within a predetermined target range, which it leaves in the event of a network failure and in which it returns after the rectification of the system failure, characterized in that the Reduction or zeroing of the current at the return of the mains voltage is carried out in its desired range. 6. The method according to claim 5, characterized in that when the line fault occurs, the phase angle is set to a value at which the wind turbine feeds reactive power into the grid. 7. The method according to claim 6, characterized in that the set during the occurrence of the power failure phase angle is at or slightly below + 90 °. 8. The method according to any one of claims 5 to 7, characterized in that the Grid fault is detected by monitoring the mains voltage. 9. The method according to any one of claims 1 to 8, characterized in that the wind turbine has a full converter with a generator-side converter, a grid-side converter and a generator-side converter with the grid-side converter connecting direct voltage intermediate circuit to the at a predetermined threshold exceeding increase its Voltage a temporary load is switched on. 10. The method according to any one of claims 1 to 8, characterized in that the wind turbine has a partial converter with a connected to the rotor of its generator inverter, a mains side converter and the rotor side connected to the mains side DC link voltage whose voltage is monitored and in response to a rise of its voltage exceeding a predetermined threshold, the generator is temporarily switched on the stator side to a commutation unit and short-circuited on the rotor side.