Controlling Power Quality from Wind Turbines
Power controller Most people think of the controller as the unit which runs the wind turbine, e.g. yaws it against the wind, checks that the safety systems are OK, and starts the turbine.
The controller does indeed do all these things, but it also looks after the power quality of the current generated by the wind turbine.
Grid Connection and Power Quality
In the section about power quality you will learn how electricity companies require that wind turbines connect "softly" to the grid, and how they have certain requirements that the alternating current and voltage move in step with one another.
The image to the right shows the high voltage section of a controller for a megawatt machine. This part of the controller operates e.g. the thyristors which ensure soft coupling to the electrical grid.
     
Reactive Power Control
Capacitor bank Voltage and current are typically measured 128 times per alternating current cycle, (i.e. 50 x 128 times per second or 60 x 128 times per second, depending on the electrical grid frequency). On this basis, a so called DSP processor calculates the stability of the grid frequency and the active and reactive power of the turbine. (The reactive power component is basically a question of whether the voltage and the current are in phase or not).
In order to ensure the proper power quality, the controller may switch on or switch off a large number of electrical capacitors which adjust the reactive power, (i.e. the phase angle between the voltage and the current). As you can see in the image to the left, the switchable capacitor bank is quite a large control unit in itself in a megawatt sized machine.
     
Electromagnetic Compatibility (EMC)
Radiation free room There are very powerful electromagnetic fields around power cables and generators in a wind turbine. This means that the electronics in the controller system has to be insensitive to electromagnetic fields.
Conversely, the electronics should not emit electromagnetic radiation which can inhibit the functioning of other electronic equipment. The image to the left shows a radiation free room with metal walls in the laboratory of one of the largest wind turbine controller manufacturers. The equipment in the room is used to measure electromagnetic emissions from the components of the controllers.
© Copyright 1997-2003 Danish Wind Industry Association
Updated 19 September 2003
http://www.windpower.org/en/tour/wtrb/control2.htm
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