Neutral point DCoffset voltage suppression in threephase fourswitch inverterfed PMSG drives based on secondorder notch filter
                                                     SHI Wen, ZHU Chong, YANG Huan, ZHAO Rongxiang
                                      (College of Electrical Engineering, Zhejiang University, Hangzhou 310027, China)

Abstract: Aiming at the neutral point DCvoltage offset existing in the threephase fourswitch(TPFS) lowspeed PMSG drives can easily lead to overmodulation of the converter, the principle of overmodulation and composition of neutral point voltage of TPFS converter were studied. The neutral point voltage is composed of DC offset and low frequency AC components.A DCvoltage offset suppression strategy based on secondorder adaptive notch filter was proposed. A neutralpoint DCvoltage offset suppression system based on stator current compensation with secondorder adaptive notch filter was designed. The lowspeed permanent magnet synchronous power generation system platform based on DSP2808 was used to verify the designed system.The experimental results show that the proposed secondorder adaptive notch filter can improve the response speed of the neutral voltage control loop, suppress the second harmonic component of the electromagnetic torque produced by PMSG and realize the stable operation of the threephase fourswitch PMSG drives system.

Key words: threephase fourswitch inverter; lowspeed; DCoffset voltage; secondorder notch filter