Control of Doubly‐fed Induction Generators for Wind Turbines

This chapter introduces the principles of doubly‐fed induction generators (DFIGs). It presents PQ control and direct torque control (DTC) of DFIGs. The chapter describes low‐voltage ride through (LVRT) of the DFIG. The DFIG consists of a wound rotor induction generator (WRIG) with the stator windings directly connected to the constant‐frequency three‐phase grid and with the rotor windings mounted to a bidirectional back‐to‐back voltage source power converter. The power converter consists of two parts: the rotor‐side converter and grid‐side converter. PQ control is widely used in the practice, giving decoupled active power and reactive power. DTC is considered to be a simple and robust control scheme that achieves quick and precise torque control response. A major drawback of DFIGs is their LVRT capability during grid faults. Faults in the power system can cause a voltage dip at the connection point of the wind turbine.