Research On The Control Strategies Of Open-Winding Permanent Magnet Motor System Based On Four-leg Converter

Due to the high power density,high efficiency and good reliabiliy,Permanent Magnet Synchronous Motor?PMSM?has been widely applied in electric vehicles,high-speed machines,wind power generation and other fields.The open winding PMSM?OW-PMSM?driving system based on the dual inverter can achieve the wide speed operation and obtain the multilevel effect to improve the output performance of traditional PMSM driving system.In order to solve the problems of high cost and complexity of the OW-PMSM driving system based on the dual inverter,this paper proposes a novel low-cost four-leg converter for OW-PMSM and its modulation strategy and operational characteristics have been studied.Firstly,this paper introduces the topology and operational principle of four-leg converter for the OW-PMSM driving system in detail.On this basis,aiming at the asymmetric characteristics of the four-leg converter,the side effects of 3^rd back EMF,the asymmetric dead-time voltage produced by the multiplexed bridges and the voltage drop of IGBT on the phase winding current are analyzed.Then,the compensation method of the average dead-time voltage for the proposed system with the separated zero-sequence control scheme is given to suppress the current harmonics.Secondly,the simulation model of OW-PMSM driving system based on four leg converter is built in MATLAB,and the effects of 3^rd back EMF,dead-time effect and voltage drop of IGBT on zero sequence current are simulated.The harmonic characteristics of three phase current with and without the zero sequence current suppression strategy are compared,then the effectiveness of the zero sequence current suppression strategy is verified by the simulation results.Thirdly,the hardware platform based on the DSP28335 and CPLD has been built.By the comparison of experimental results of using the quasi PR controller and the proposed zero sequence current suppression strategy,the effectiveness of the zero sequence current suppression strategy is verified.The experiments speed regulation and load changing for the proposed four-leg converter OW-PMSM driving system have been done to verify the excellent output performance.Finally,in order to improve the bandwidth of current loop composed of PI controller,based on the analysis of the bandwidth constraints of current loop,a predictive control strategy is proposed.The simulation results preliminary verify the effectiveness of the predictive control strategy.