Control method in a wind turbine driven by 3-parallel back-to-back converters using PQR power transformation

A power conversion system in a wind turbine using a Permanent Magnet Synchronous Generator (PMSG) is directly connected between a generator and a grid. The capacity of power semiconductor switches and filters should be selected regarding the overall system rating and the output power quality. The use of an LCL-filter and n-parallel power conversion devices can be the best solution for these problems in a high power system. However, the resonant pole introduced in the LC part produces resonance in the system leading to the stability problem. The voltage difference between the parallel back-to-back converters generates a zero-sequence circulating current. In this paper, a novel control method using a PQR transformation for simultaneously compensating of both the LCL-filter resonance and the zero-sequence circulating current in a wind power system driven by 3-parallel back-to-back converters is proposed. The effectiveness of the proposed control method is verified by simulations.