Simulation research of megawatt permanent-magnet direct-drive wind turbine converters with interphase inductors

The permanent magnet synchronous generator is connected to the grid through full power converter. Due to the limitation of power devices and switching frequency, the parallel operation of converters is usually used in megawatt-level wind turbine system. The circulating-current impedance of the parallel topology with separate dc buses is larger than one with common dc buses. Moreover, the interphase inductor has the advantages of supporting current sharing and small size. Therefore, the novel topology of permanent-magnet direct-drive wind turbine converter with interphase inductors and separate DC buses was proposed. Its decoupling equivalent circuits and circulating-current route with high impedance were derived. The circulating-current suppression mechanism of interphase inductors wes illustrated and the models of the generator-side converters and the grid-side converters were obtained respectively. Then the control strategy of the system is designed according to the models. The parallel operation of wind turbine converters is achieved. The circulating-currents are suppressed well and the problems of current discrepancy and distortion are overcome. Therefore, the reliability and efficiency of the system are improved. Finally, the 1.5 MW wind turbine converters with interphase inductors are simulated, which verifies the validity of the above analysis and control strategy.