High-order sliding mode control of DFIG under unbalanced grid voltage conditions

This paper proposes a novel high-order sliding mode (HOSM) based control methodology for direct power control (DPC) of doubly-fed induction generator (DFIG) wind turbine which is operating under unbalanced grid voltage conditions. Firstly, a set power quality enhancement strategies are presented, incorporating six power compensation schemes corresponding to six selective control targets in both steady and variable speed conditions. Meanwhile, the DFIG output powers are regulated with the proposed HOSM-DPC scheme, wherein a super-twisting algorithm is employed to cope with the chattering phenomenon and simplify the controller structure. The Lyapunov function method is utilized to decide the stability region of the controller parameters. Experiments and simulations are conducted to prove the validity and the performance of HOSM-DPC, where the DPC method with lookup table and the first order sliding mode based DPC are incorporated for comparison purpose. The experimental tests fully reveal the effectiveness of HOSM-DPC in power quality improvement subjected to unbalanced grid voltage conditions, and the superior performance of HOSM-DPC in dynamic response, chattering phenomenon elimination and variable wind speed operation are also validated.