Flexible unbalance compensation strategy for doubly fed induction generator based on a novel indirect virtual impedance method

Abstract

This study presents a flexible unbalance compensation strategy for doubly fed induction generator (DFIG)-based wind power generation system connected to an unbalanced weak grid, which can achieve flexible trade-off between the two common control targets, i.e. the balanced output current of DFIG and the balanced voltage at the point of common coupling (PCC), thus the operation performance of DFIG and the power quality at PCC can be considered comprehensively. In order to achieve this target, a novel indirect virtual impedance (IVI) method is proposed, which can control the negative sequence output impedance (NSOI) of the DFIG from zero to infinity. The advantage of the proposed IVI method is to solve the drawback of the traditional virtual impedance method, i.e. the open-loop gains for the system disturbances are highly related with the required virtual impedance, which may introduce oscillation during dynamic periods or even risk the system stability when the required NSOI is large. Meanwhile, the sequential decomposition of the voltage or the current can be avoided in the proposed strategy. The compensation performance and the system stability are theoretically investigated. The availability and advantages of the proposed flexible unbalance compensation strategy are verified by experimental results.