Research On Model Predictive Control For Five-Phase Permanent Magnet Synchronous Motor Drives

Five-phase permanent magnet synchronous motor(PMSM)drives have been widely studied in electrified transportation field,such as rail transit,electric vehicles and marine electric propulsion,due to the advantages of strong fault tolerance,low torque pulsation and high-power output at low voltage.Model predictive control(MPC)algotithms have the superiorities of fast dynamic response,simple and intuitive principle,and have attracted extensive attention in power electronics converters and motor dirves.In order to improve the steady-state performance and dynamic response of five-phase PMSM drives,the MPC algorithms are detailedly studied in this paper.The main research contents are as follows:The mathematical model of five-phase PMSM is firstly established,and the cause of common-mode voltage(CMV)is analyzed,which lays the foundation for the study of the control algorithms in the following chapters.The continue control set model predictive control(CCS-MPC)adopts the pulse width modulation(PWM)to modulate the reference voltage vector,which has high control accuracy.However,the space vector PWM(SVPWM)is complicated when applied to multiphase PMSM drives.In order to simplify the implementation of CCS-MPC,a simplified SVPWM scheme is proposed for multiphase twolevel voltage source inverters(VSIs)with odd phases.Finite control set model predictive control(FCS-MPC)has intuitive principle and can easily handle nonlinear constraints,which has been widely studied in three-phase motor drives.However,due to the increase of voltage vectors,conventional FCS-MPC schemes face with heavy computational burden in multiphase PMSM drives.To address this issue,a lowcomplexity FCS-MPC algorithm based on adjacent vectors is proposed in this paper.Virtual voltage vectors are used as control set to suppress third harmonic currents.Then,the distributions of reference voltage vector in the steady and dynamic state are analyzed,and the reducdant virtual vectors are eliminated,which avoids evaluating all vectors and reduces computation burden.In the five-phase PMSM with sinusoidal stator winding distribution,the FCS-MPC based on virtual vectors can reduce computation burden and improve steady-state performance.And the idea of duty ratio optimization can be introduced to further improve control accuracy.However,the dc-link utilization of this kind of FCS-MPC schemes based on virtual vectors is reduced.To improve the dc-link utilization,an improved FCS-MPC with high dc-link utilization is proposed in this paper.The large vectors are selected to predict the current evolution and evaluate the cost function,and duty ratio of large vectros are estimated,which can fully utilize the dc-link voltage.Then,two duty ratio assignments are designed according to the duty ratio range,reducing the third harmonic currents with volt-second balance in the fundamental subspace.Conventional FCS-MPC scheme with CMV reduction suffers from heavy computation burden,difficult parameter tuning and poor steady-state performance.Therefore,two new definitions of virtual voltage vector are studied and a low-CMV FCS-MPC scheme is proposed based on virtual vectors in this paper.Then,the effect of deadtime on CMV is analyzed,and the cause of CMV spikes is revealed.Based on the analysis,a duty ratio based low-CMV FCSMPC is proposed,which can completely eliminate the CMV spikes caused by deadtime.In the five-phase PMSM drive system where long cables are used and the switching speed of power devices is fast,voltage reflection phenomenon occurs at the motor terminal due to the impedance mismatch between the cable and motor.Conventional FCS-MPC will lead to line-to-line voltage polarity reversal,resulting in overvoltage spikes up to 3Vdc at the motor terminal,which will damage the winding insulation.To suppress the overvoltage spikes,an improved FCS-MPC with low differential-mode voltage spikes is proposed in this paper.The line-to-line voltage polarity reversal is avoided by rebuilding the control set,thereby reducing the differential-mode voltage spikes at the motor terminal.Moreover,to mitigate voltage spikes using low-CMV FCS-MPC scheme,a new FCS-MPC that can reduce both differentialmode voltage spikes and CMV is proposed.The differential-mode voltage spikes at the motor terminal are reduced by 1/3,and common-mode voltage is reduced by 80%.Finally,a scaled-down platform is set up,and experiments are carried out to verify the correctness and effectiveness of these proposed schemes.