Research On Open-winding PMSM Syestem Supplied By Z Source Inverter With One Common DC Bus

As for a permanent magnet synchronous motor(PMSM)system supplied by a limited DC bus voltage,the field weakening control strategy is generally applied to achieve high requirements for the motor speed range.However,it has several drawbacks,such as the risk of permanent magnet irreversible demagnetization,reduced system efficiency,and reduced output torque,which means the field weakening control strategy cannot fundamentally solve the problem of limited system capacity.Under this background,the open-winding permanent magnet synchronous motor(OW-PMSM)system where dual inverters can be used to increase system capacity,and the Z-source inverter(ZSI)where a Z-source impedance network is applied to boost the DC bus voltage are discussed in this paper.Furthermore,the OW-PMSM system with one common DC bus based on ZSI is studied.The research content includes:(1)For the OW-PMSM system with one common DC bus,firstly mathematical models of the OW-PMSM and the inverters are established.Meanwhile,the generation mechanism of the zero sequence current(ZSC)which is caused by the common DC bus structure is analyzed.Secondly,a system control strategy based on the vector control(VC)which can achieve ZSC suppression is proposed,with an innovative three-phase decoupling modulation method included.Finally,the effectiveness of the proposed control strategy,as well as the advantages of the proposed three-phase decoupling modulation method over the space voltage vector modulation(SVPWM)is proved by the experimental results.(2)For the OW-PMSM system supplied by dual quasi-ZSI(qZSI)with common DC bus,firstly the mathematical model of qZSI is established to analyze its boosting principle.Meanwhile,the advantages of qZSI compared with traditional ZSI are introduced.Secondly,two novel modulation methods are proposed to solve the problem that it is difficult to achieve ZSC suppression and DC bus boost conversion at the same time with the existing modulation methods,including coordinated modulation and unified modulation.Furtherly,the modulation ability of the system is theoretically analyzed—the expressions of maximum modulation index and maximum speed range are respectively derived.The expressions consist of variables including motor parameters,operating conditions,and the shoot-through duty cycle of qZSI.Finally,the correctness of the proposed modulation method,as well as the effect of qZSI on the modulation ability improvement is verified by experimental results.(3)In order to reduce the cost and the volume,a four-arm OW-PMSM system based on series ZSI(sZSI)is proposed.Firstly,a mathematical model of sZSI is established and a comparison between qZSI and sZSI is made.Secondly,a voltage modulation method is proposed to adapt the multiplex power supply structure,where the number of switching bridge arms is reduced from 6 to 4.Furtherly,the modulation ability of the system is analyzed,with the expressions of maximum modulation index and maximum speed range derived.Thirdly,an optimized distribution algorithm of shoot-through time is proposed,which can reduce the inductor current ripple in the Zsource impedance network.Finally,the correctness of the proposed modulation method and the effect of the shoot-through time optimized distribution algorithm are verified by simulation results,and the modulation ability of the four-arm OW-PMSM system is compared with that of the six-arm OW-PMSM system.