30-01-2012, 03:27 PM
Wind Electric Generators and Control
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Power Electronic Control
In a system incorporating a power electronic interface between the generator and the load (or the grid), the electrical power delivered by the generator to the load can be dynamically controlled. The instantaneous difference between the mechanical power and the electrical power changes the rotor speed following the equation
where J is the polar moment of inertia of the rotor, is the angular speed of the rotor, Pm is the mechanical power produced by the turbine and Pe is the electrical power delivered to the load. Up on integration, this equation yields,
Control of machines in the dynamic state
Various modulation techniques are used to study the transient performance of the machine under dynamic conditions. A generally used one is a dynamic d-q model, space vector modulation and spiral vector modulation. Out of these, the dynamic d-q model is discussed here in detail.
The wound field synchronous machine
In wind electric power generation systems, two types of wind turbines are generally used. These are variable speed and constant speed turbines. The high power variable speed synchronous generator, with field windings on the rotor, is a serious competitor for the wound rotor induction motor. In particular, direct drive variable speed systems use synchronous machines. As the name indicates, unlike in a wound rotor induction machine, the rotor of a synchronous machine runs in synchronization with the field produced by the stator winding currents. The salient aspect of the machine windings is considered for analysis purpose.
