Control of DFIG wind turbines

The generation of electrical power using sustainable sources of energy is developing rapidly. The authors describe how the security and quality of electricity supply might be maintained. They discuss the control of variable speed using doubly fed induction generators (DFIG) in wind turbines. The DFIG is constructed from a wound rotor asynchronous machine. Variable speed operation is obtained by injecting a variable voltage into the rotor at slip frequency The injected rotor voltage is obtained using two AC/DC insulated gate bipolar transistor based voltage source converters (VSC), linked by a DC bus. The converter ratings determine the variable speed range. Speed control for optimum power, system frequency control, and machine inertia are also discussed.