1. Novel pulse width modulation and control strategies for open winding permanent magnet synchronous machines
- Author
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Xu, Lei and Zhu, Zi-Qiang
- Abstract
Open winding permanent magnet synchronous machines (OW-PMSMs) can combine the synergies of high efficiency, torque density, and power density in PMSMs and high voltage utilization, fault tolerant capability, and flexible control freedom in OW inverter topologies. Pulse width modulation (PWM) can affect the control performance of an OW-PMSM drive in many aspects including current harmonics, common mode voltage (CMV), modulation region, and switching frequency. In this thesis, new and novel PWM and control strategies are proposed and investigated for both isolated and common DC-bus OW-PMSM drives. Firstly, the isolated DC-bus OW-PMSM drives have larger voltage utilization, more output voltage levels, and lower control complexity compared with other OW topologies, i.e. common DC-bus and floating capacitor topologies. Sinusoidal PWMs (SPWMs) have the advantages of easy implementation and less computation burden compared with space vector PWMs (SVPWMs), and are preferable for the isolated DC-bus OW drives due to abundantly available switching states. SPWM strategies with zero sequence voltage (ZSV) injection and unbalanced voltage distribution are proposed to reduce current harmonics and switching frequency for the isolated DC-bus OW drives with symmetrical and arbitrary DC-bus voltage ratios. Moreover, balanced and unbalanced voltage distributions of SPWM can cause different inverter nonlinearity characteristics and are utilized for the inverter nonlinearity compensation. Secondly, the common DC-bus OW-PMSM drives have lower cost, high fault tolerant capability, and better controllability of zero sequence current (ZSC) compared with other OW inverter topologies. The ZSC control is necessary but limits the utilization of vectors in the common DC-bus OW topology, so that SVPWMs are preferable for the switching pattern optimization due to visible voltage vectors, vector durations, and vector action sequences compared with SPWMs. With switching pattern optimization for SVPWM, ZSC is controlled under different objectives, i.e. low current harmonics, CMV variation elimination, and maximum operation range. Specifically, current harmonics can be reduced by the vector action sequence optimization. The voltage vectors with the same CMV are selected for CMV elimination, and further selected with different ZSVs for ZSC control to achieve the control of CMV and ZSC simultaneously. The operation range of an OW-PMSM can be extended by the optimal selection of the voltage vectors with non-null ZSV and the largest magnitude for the ZSC control.
- Published
- 2022