Research On Hybrid-inverter Open Winding Permanent Magnet Synchronous Motor Drive System

Open winding electric machine (OWEM) system is a new system topology in which each side of the opened windings is connected to a converter, realizing the formation of double-ended power supply. With high output power, flexible power supply mode selection, diverse voltage vector modulation, redundancy and fault tolerance and other characteristics, OWEM system shows broad application prospects in high power, high capacity and wide speed range occasions. And the hybrid-inverter topology with one inverter connecting power source and the other connecting capacitor has drawn wide attention of scholars because of its advantages such as no zero sequence current, low cost and flexible control. Meanwhile, considering the high efficiency, large power density, small volume, convenient maintenance and easy control of permanent magnet synchronous motor (PMSM), hybrid-inverter OWEM system is combined with PMSM and its control strategies are studied in this paper.Firstly, the research background as well as the research status of open winding electric machine system is analyzed and summarized. A variety of topologies and their multilevel features are introduced. Also, the key modulation and control technology are reviewed. And, the commonly used PMSM control strategies and the flux weakening (FW) control are summarized.Secondly, the power supply principle based on hybrid inverter OW-PMSM drive system, is analyzed and its mathematic models under different coordinate frames are given. The series compensation concept is introduced into the hybrid inverter topology and the variety power compensation ways from conditioning inverter (CI) are pointed out.The third part explores the control theory of hybrid inverter OW-PMSM drive system. The active and reactive power characteristics with speed variation are analyzed in details. On the basis, the power compensation principle of CI is illustrated aiming to enhance the system performance. The effect with different capacitor voltage amplitudes is discussed and verified on motors with a variety of flux weakening ratio and saliency. The vector control and direct torque control strategies are presented and has been confirmed by simulation and experiments.In part four, a hybrid modulation vector control strategy is developed. Voltage cutting method based on double-vector synthesis is proposed. By selecting the main inverter active voltage vector according to the current vector and adding zero voltage vector, the reference active voltage component can be synthesized accurately and the capacitor voltage can be controlled stably. Meanwhile, the conditioning inverter is controlled to compensate the harmonic and reactive power. Additionally, an optimum zero vector selection algorithm and a flux weakening method based on the acitve voltage vector duration feedback have been presented, realizing the high efficiency and high speed operation of PMSM. Simulation and experiment have been carried out to prove the effectiveness and feasibility.