Grid Connected Wind Energy Conversion System
A wind energy conversion system converts the wind energy into some form of electrical energy. Such a system is shown in Figure A.
The function of controller is to derive the reference voltage and frequency signals from the grid and to sense the wind speed and its direction. The controller will process the power output of the generator and accordingly sends the signal to various blocks for taking the suitable correction measures.
The choice of electrical generator depends on the following :
1. Constant speed drive :
(a) DC . Generator : A permanent magnet type dc generator is used for small and medium scale power generation upto 100 kW rating.
(b) Synchronous generators : are used for medium and large scale power generation having constant speed with ± 1% of speed fluctuations.
(c) Induction type generators : are used for variable shaft speed upto ± 10%. These generators are preferred over DC and synchronous generators since they have low cost, low maintenance and better transient performance.
However, induction generators require AC excitation current which is mainly reactive. It draws the excitation current from the grid. Therefore, the net work must be capable of supplying this reactive power. However, the static capacitors can be used to overcome this problem.
2. Variable speed drive scheme :
Variable drive speed schemes use the power electronic converters or power conditioning. The block diagram of such a system is shown in Figure B.
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| Figure B |
In this system, the variable voltage and variable frequency output of a synchronous or induction type generator is first rectified to DC and then converted to fixed voltage and frequency using an AC inverter and connected to grid.