Analysis and control of circulating current in parallel permanent-magnet-direct-drive wind power system

Parallel connection technique can improve the power capacity of the permanent-magnet-direct-drive wind power system effectively. But it causes some problems, such as circulating current, unbalanced current distribution, etc. To solve these problems, this paper proposed a new topology of permanent-magnet-direct-drive wind power system. Its average model and circulating current were analyzed. It can be seen that the generator-side and line-side circulating currents are independent with each other. Moreover, the circulating current is caused by the zero-axis component discrepancy of the three-phase bridge duty between the parallel modules. Based on the above analysis, the circulating current controller was proposed to suppress the circulating current. It not only has no influence on other controlled variables, but also does not increase the hardware cost. This method suppresses the generator-side and line-side circulating currents effectively and improves the reliability and efficiency of the system. The simulation and experimental results verify the validity of the proposed method.