Improving the Reactive Power Capability of Grid Connected Doubly Fed Induction Generator

Due to increasing wind power generation in the electric power system, the reactive power generation by the wind farms is a major concern during both steady state and faulty conditions. This work, first, presents the reactive power capability (RPC) curve of doubly-fed induction generator (DFIG) considering three limitations (rotor voltage, rotor current and stator current) for reactive power production/consumption, for the complete operating range which is obtained by optimal rotor speed employing maximum power point tracking (MPPT) algorithm. It is established that the total reactive power generation is limited by rotor voltage at low speeds and by rotor current at higher speed. However, the total reactive power consumption is limited by stator current, for entire operating region. Selection of partial rated converter rating is crucial in terms of cost, efficiency, operating speed range and reactive power capability. The effect of converters rating on the enhancement of RPC of doubly fed induction generation is analyzed. Complete capability curves of DFIG for different stator voltages are developed considering grid-side converter (GSC) contribution towards reactive power capability.