Flexible PCC Voltage Unbalance Compensation Strategy for Autonomous Operation of Parallel DFIGs

This paper proposes a flexible compensation strategy for parallel-connected doubly fed induction generators (DFIGs) when connected to an unbalanced weak grid. The proposed strategy has two main advantages, the voltage unbalance factor at the point of common coupling (PCC) can be continuously controlled, thus, the flexible tradeoff between the balanced DFIG output current and the balanced PCC voltage can be achieved, and the negative sequence current required by the compensation can be properly shared among the parallel DFIGs and their grid side converters according to their respective operation conditions without the need of real-time communication. The operation performance and stability of the proposed strategy are analyzed. Simulation and experimental results are carried out to verify the proposed compensation strategy.