Unbalanced Control Strategy for DFIG Used in Wind Turbines

Abstract

Unbalanced input voltages would make doubly fed induction generator (DFIG)-based wind turbine operating performance deteriorate, such as shaft tremble, temperature increasing, and so on, even make it cut out of the power grid. Meanwhile, without proper control the power ripples generated from wind turbines may further aggravate power grid. Considering the unbalanced conditions, DFIG was modeled in dual synchronous reference frame (SRF), namely the positive one and the negative one, based on which the dual PI current controllers were designed. To implement the dual current control, the sensing variables were divided into positive and negative sequence components, which were controlled in positive and negative SRF respectively. At the same time, to synchronize with the positive and negative sequence voltage components, a phase latch loop (PLL) control was designed. Experimental results on 11kW DFIG wind turbine test bed validated the designed control system.