DFIG wind generation systems operating with limited converter rating considered under unbalanced network conditions – Analysis and control design

This paper presents an analysis and operation of doubly-fed induction generator (DFIG)-based wind power generation systems under unbalanced network voltage conditions. The limited voltage and current ratings, and control capabilities of both grid side and rotor-side converters (GSC&RSC) for unbalanced network voltage compensation are investigated. A current control scheme consisting of a proportional integral (PI) controller plus a resonant (R) compensator is designed. The control scheme is implemented in the positive synchronous rotating reference frame and provides precise current control for both the GSC and RSC without involving the decomposition process of positive and negative sequence currents. By taking into account both the converters’ current ratings, a coordinated control strategy between the GSC and RSC is proposed and adjusted. Finally, simulation studies on a 1.5 MW DFIG generation system and experimental tests on a 1.5 kW prototype are carried out. The correctness of the analytical results as well as the feasibility of the proposed coordinated control scheme are confirmed when the network voltage is unbalanced.