Optimal control of doubly-fed full-controlled induction wind generator with high efficiency

Conventional doubly-fed induction generators for wind energy conversion usually have two converters connected to the rotor while the stator is linked directly to the grid. In this case the stator voltage and flux cannot be manipulated for optimal system operation. If a DC bus bar is available, double feeding can occur about the inverter. This paper describes a doubly-fed full-controlled induction wind generator which offers high flexibility of stator side control to ensure minimal losses as well as optimal power utilisation. The equation of the optimal loss regime is derived while simulation results show improvements in the efficiency power extraction. The special wind converter system has been investigated at a glance of installed off-shore MW-generators, where a DC-transmission is advantageous because of the avoided reactive power. The precalculated improvements behave 6% at most in the wind-driven range. First experiences with the operating characteristic and some control features are presented and discussed.