DE102008045938A1 - Method for controlling supply of electric power of wind turbine to electric alternating current network, involves adjusting current to zero until phase angle of current is adjusted to preset value based on changed supply voltage - Google Patents

Abstract

The method involves adjusting a phase angle of current (Iwea) supplied by a wind turbine to a preset value based on a phase angle of a supply voltage (Uwea), where the wind turbine supplies active power into an electric alternating current (AC) network. The current is adjusted to zero, during network-caused change of the phase angle of the supply voltage, until the phase angle of the current is adjusted to the preset value based on the changed supply voltage, where a period of zero setting of the current amounts to a period of a network frequency.

Description

The The invention relates to a method for controlling the feed electrical power of a wind turbine in an associated electrical AC network, in which the phase angle of the wind turbine fed current in relation to the phase angle of the mains voltage is set to a predetermined value at which the wind turbine Active power fed into the network.

at The wind energy plant also remains in this way during such processes network-related changes despite an associated change Breakdown of the mains voltage and / or a change in its phase angle on the net. This ensures that the wind turbine feed active power into the grid as uninterrupted as possible can. Will, however, according to older practice when occurring such changes the wind turbine temporarily galvanically isolated from the mains, is a longer period of time required to start the wind turbine again, so that they can provide active power to the network. The instant Willingness to reintroduce real power in changing Network operating conditions are the more important the larger the share of wind energy in the overall performance of the network is.

Especially In weak networks, the phase angle of the mains voltage can become change abruptly. Power disturbances due to Short-circuit-related network errors lead, for example to dips in the mains voltage.

In a known method of the aforementioned type ( Wuitel, M. Bartsch, WWEC 2007 (Mar del Plata / Argentina), 6th Conference and Fair of the World Wind Energy Association (WWEA), 02.10.-04.10. 2007 ), the phase angle of the current supplied by the wind energy plant is set such that the latter leads the then present network voltage by almost 90 ° in the event of a power failure. 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 the rectification of the power failure can increase the impedance of the Change network. This impedance change can be, for example based on the fact that for the correction of the network disturbance Lines or entire network areas switched off or switched become. Such an impedance change will make a corresponding change the phase angle between the returned mains voltage and the unchanged input of electricity. hereby It can lead to surges on the net or even to it come that the wind turbine from the grid real power refers. The danger of overvoltages is particular at one beyond the duration of the power failure sustained high reactive current feed. 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, the power supply is reduced in the occurrence of a power failure compared to the power supply present before the power failure and briefly increased after removal of the power failure, the power supply against the power supply present before the power failure significantly.

Also 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.

Of the Invention is based on the object, a method of the initially called type to create the surges on the grid or irregular power transfers between avoids the grid and the connected wind turbine.

According to the invention This object is achieved in that in a network-related change of Phase angle of the mains voltage of the current at least as long Is zeroed until its phase angle with respect to the changed Mains voltage adjusted to the specified value.

While the temporary invention Zeroing the injected current can its phase angle in Reference to the changed phase angle of the mains voltage on the for the undisturbed operation of the network adjusted according to suitable phase angle. If then the current with the thus set phase angle again can not be 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 fed Current of the broken down by the grid interference mains voltage leads by almost 90 °. Then could already with a slight impedance deviation of the suppressed Netzes the case occur that the phase angle between the power and the returned mains voltage is greater than 90 ° and the network feeds active power into the wind turbine.

In The following description describes the invention with reference to FIG the drawing exemplified. Show it:

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

2 one 1 corresponding phasor diagram when a line fault occurs,

3 one 2 corresponding phasor diagram when switching to voltage support,

4 one 3 Corresponding vector diagram when correcting the power failure, and

5 one 4 Corresponding phasor diagram of the undisturbed mains operation after rectification of the network fault.

1 shows the case that a wind turbine feeds an electrical AC network, which is in its undisturbed state. In the illustrated example, the phase angle between the mains voltage U _WEA present at the feed point and the current I _WEA 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 _WEA is in a predetermined range for the undisturbed operation of the network.

2 shows the case that a short circuit occurs on a remote from the feed point of the network. Because of the impedance conditions thereby changed breaks at the feed 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 3 the inverter of the wind turbine has detected the break in of the mains voltage and thus the line fault. In response, he sets the phase of the injected current I _WEA such that he leads the mains voltage U _WEA 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 4 the grid fault has been rectified and the mains voltage U _{WEA has} thus returned to its nominal range. As a result of the changed impedance of the suppressed network, the phase angle of the returned mains voltage U _WEA deviates slightly from the phase angle of the mains voltage existing before the occurrence of the system disturbance ( 1 ). A maintenance of the during the power failure according to 3 set phase angle of the current I _WEA would then mean that the current leads the voltage by more than 90 °. In this case, the grid would feed real power into the wind turbine.

Therefore, the power supply is reset to zero once the mains voltage has returned. This zero position is maintained at least until the power converter of the wind turbine has the phase angle of the current to be fed with respect to the returned mains voltage to the predetermined value for undisturbed operation, in the example shown, the value zero, has returned. 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 in 5 shown stable final state brought about.

The The duration of the ramp can be, for example, between 200 ms and 10 s. The duration of the zero setting of the current to be injected after detection the return of the mains voltage in its predetermined nominal range is not shorter than expediently a period of the AC mains, i. H. 20 ms for one Mains frequency of 50 Hz.

Out the above description, the inventive Method explained by way of example, it can be seen that it in particular for driving through network-related short circuits (Fault ride-through) is suitable. The required for this Control of the feed-in current can be achieved by a controlled full converter and chopper the wind turbine done.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• WO 2005/031941 A1 [0006]
• WO 99/33165 [0007]

Cited non-patent literature

• Wuitel, M. Bartsch, WWEC 2007 (Mar del Plata / Argentina), 6th Conference and Fair of the World Wind Energy Association (WWEA), 02.10.-04.10 .2007 [0004]

Claims (8)

A method for controlling the feeding of electrical power of a wind turbine into an electrical AC network connected thereto in which the phase angle of the current supplied by the wind turbine with respect to the phase angle of the grid voltage is set to a predetermined value at which the wind turbine feeds active power into the grid, characterized in that in a network-related change in the phase angle of the mains voltage, the current is set to zero at least until its phase angle is adjusted in relation to the changed mains voltage to the predetermined value. Method according to claim 1, characterized in that that the duration of the zeroing of the stream at least one Period of the grid frequency is. Method according to claim 1 or 2, characterized that the supply of the current after the zero position ramped is raised. Method according to one of claims 1 to 3, characterized in that the adjustment of the phase angle the current is carried out by a power converter of the wind turbine. Method according to one of claims 1 to 4, in which the mains voltage in the undisturbed operation of AC network within a predetermined target range that they are experiencing when a network malfunction occurs leaves and in which they after the removal of the network disturbance returns, characterized in that the zero position of the current when the mains voltage returns to its nominal range he follows. Method according to claim 5, characterized in that that at the occurrence of line disturbance of the phase angle is set to a value at which the wind turbine reactive power fed into the network. Method according to Claim 6, characterized that the set when the power failure Phase angle is at or slightly below + 90 °. Method according to one of claims 5 to 7, characterized in that the network failure detected by monitoring the mains voltage becomes.