Suppression Analysis of Zero-sequence Current Under Magnet Fault in an Open-winding Permanent Magnet Synchronous Machine

The open-winding configuration with a common DC topology allows the zero-sequence current (ZSC) to flow through the stator windings. For permanent magnet synchronous machines (PMSM) the origins of this ZSC are mainly attributed to pulsewidth modulation (PWM) induced common mode voltage and rotor third harmonic back electromotive force (EMF). However, Permanent magnets of a PMSM can get demagnetized due to the operating temperature, high instant armature field, short-circuit, and material corrosion. This paper shows that the demagnetization fault leads to low frequency harmonics in ZSC along with the third harmonic component of healthy condition. The order of these subharmonics depends on slot/pole combinations. These additional harmonics will increase the system loss and torque ripple. A resonant controller in combination with proportional for zero sequence and proportional-integral controller for dq-axis current was used to suppress additional harmonics induced due to demagnetization. The proposed method improves the total harmonic distortion of phase current from 11.4% to 2.61%. The strategy was investigated experimentally using a 1 kW open-winding permanent magnet synchronous machine (OW-PMSM).