Abstract：Unbalanced grid voltage will affect the normal grid connection operation of the wind energy

conversion system（WECS），resulting in fluctuations in system output power and distortion of output current. In

addition，in the actual permanent magnet synchronous wind power system，there may be uncertainties in the

network side circuit parameters due to changes in ambient temperature and detection errors. If the parameter

changes，the performance of traditional control methods will decline. Based on this，a model-free adaptive control

（MFAC）scheme based on grey prediction was proposed to alleviate the performance degradation problem caused

by parameter uncertainty and make the control system have better anti-interference ability. Furthermore，three

independent control methods were adopted to solve the problem of grid connected output power fluctuation and

current distortion under unbalanced grid voltage. The simulation results show that the proposed control strategy not

only has good static and dynamic performance under nominal parameters，but also improves the robustness of the

system when the grid side inductance changes，which verifies the superiority of the proposed scheme.

      Key words：unbalanced grid voltage；wind energy conversion system（WECS）control strategy；grey prediction；model-free adaptive contro（l MFAC）scheme；parameter uncertainties