Doubly-fed full-controlled induction wind generator for optimal power utilisation

Doubly-fed induction generators are used mainly for wind energy conversion in MW power plants. They have a rotor inverter and a front-end converter while the stator is linked directly to the grid. If a DC bus bar is available, a 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. Some investigations with the operating characteristic in wind-driven and constant power modes are presented and discussed.