Research On Common-mode Harmonic And Common-mode Conduction Path Of Permanent Magnet Synchronous Motor Drive System

With the rapid development of semiconductor power devices,Silicon Carbide MOSFET(SiC MOSFET)has stood out among most of the switching devices for its fast switching speed,low switching loss and high junction temperature.Consequently,SiC MOSFET has become a satisfying replacement for silicon IGBT(Si IGBT)as the core device of power inverters.Despite of all the merits mentioned above,the high dv/dt and di/dt brought by the fast switching speed has indeed brought about complex EMC problems to the permanent magnet synchronous motor(PMSM)drive system.In order to meet the relevant EMC standards and optimize the system design,this paper mainly emphasizes on analyzing the common-mode harmonics and illustrating the commonmode conduction path of the PMSM drive system.Firstly,since the motor plays a significant role of common-mode harmonics conduction in PMSM drive system,it would be kind of important to establish appropriate model of the motor for the common-mode harmonics analysis,the conduction path research and the overall simulation model of the system.According to the current research on the modeling method of induction motor,based on the physical structure of the PMSM,this paper will propose a modeling method suitable for PMSM,and then verify the validity and rationality of the model through experiment to ensure the accuracy the model.Secondly,as the high-power and high-frequency switching devices in the PMSM drive system,the fast switching transition of power devices will generate some undesirable common-mode harmonics,which may as well seriously interfere the reliability of the system.This paper mainly establishes a mathematical model based on SiC MOSFET to analyze the switching transition of the power devices,and expounds the mechanism of harmonic generation in the switching transitions.The research process can be roughly divided into four steps:(1)According to the ideal conditions of double-pulse circuit and SiC MOSFET switching conditions,obtain the mathematical model of the switching transitions of SiC MOSFET.(2)By observing the deviation between the mathematical model calculated and experimental measured waveforms,the key parameters,which may leads to the such distinctions,are quantified,and the specific values of these parameters are figure out via appropriate methods.(3)Considering the impacts of these parameters,optimize the double-pulse circuit to obtain the mathematical model,which is able to properly describe the switching transitions of the SiC MOSFET under non-ideal conditions.(4)Based on the mathematical model,the spectrum analysis of the SiC MOSFET switching waveform is analyzed in three cases to study the commonmode harmonics generated during the switching process of SiC MOSFET.Finally,according to the laboratory motor drive system,the wires and cables are modeled,and the simulation system of the motor drive system is built with Simulink and Simplorer joint platform.The voltage(current)of the key nodes in the simulation system and the experimental system are analyzed in time domain and frequency domain,based on the results of comparative analysis,the simulation system will be furtherly optimized;Analyzing the above spectrum,according to the frequency component contained in the voltage(current)of the key nodes and different ground circuits,the influence of different grounding paths on high-frequency harmonics in the PMSM drive system will be determined accordingly,the common-mode conduction path of the PMSM drive system is given in different situations,and the difference between common-mode harmonics of the PMSM drive system is analyzed for different power devices.