Recently offshore wind power have developed rapidly. As the mainstream generator of offshore wind farm, permanent magnet synchronous generator (PMSG) has been increasingly applied in offshore wind farm. The operating performance of PMSG based wind energy conversion system (WECS) depends on the performance of control system, which relies on the accurate measurement of phase-locked loop (PLL). This paper propose a modified PLL scheme to improve system stability. A DC-link voltage relaxation control strategy is also applied to obtain a fast response and lower over-voltage level, which can lead to better control performance and reduced cost. Small signal stability analysis as well as simulation results verified that the optimized system have greater stability and better performance.

PLL,WECS,Voltage relaxation,Small signal stability analysis