Research On Common-mode Voltage Suppression Method Of Dual Three-phase Permanent Magnet Synchronous Motor

Multiphase permanent magnet synchronous motor is widely used in aerospace,ship power and other fields.It has many advantages of both Multiphase motor and permanent magnet synchronous motor,such as high efficiency,high power density,high starting torque,suitable for low voltage and high power occasions,excellent electromagnetic performance and good faulttolerant control performance.In this thesis,national nature fund projects “Fault diagnosis and fault tolerant control of multiphase motor drive control system for electric vehicle(61603263)” is relied on,and the suppression method is researched for common-mode voltage which widely exists in the system composed of multiphase permanent magnet synchronous motor and inverter.The research object is dual three-phase permanent magnet synchronous motor which has two sets of phase-shifted 30° three-phase windings with independent neutral point.In this thesis,theory and simulation researches of common-mode voltage suppression method for space vector control strategy and model predictive control strategy are carried out respectively.Firstly,based on the mathematical model of dual Y-shifted 30° dual three-phase permanent magnet synchronous motor,the mathematical model in synchronous rotating reference frame is established by using vector space decomposition theory,and the model is simulated by using MATLAB/Simulink to verify the reliability of the mathematical model.The research on the causes of common-mode voltage shows that the use of zero vector is the primary reason for the high peak voltage and many changes of common-mode voltage.Therefore,based on the four-vector SVPWM control method,the synthetic vector is used instead of the zero vector to reduce the peak value of common-mode voltage and the number of changes.At the same time,the switching frequency of the inverter is reduced.Four-vector SVPWM control method has high computational complexity and high switching frequency of inverter.For this reason,this thesis studies the method of decoupling six-phase inverters into two independent three-phase inverters by three-phase decoupling algorithm and then controlling them separately.Based on this,nonzero vector SVPWM control method is used to reduce the peak value and changes of common-mode voltage,and the switching frequency of the inverters is further reduced.In this thesis,the model predictive control method which has good dynamic performance is studied.The method of synthetic vectors is used to reduce the complexity of prediction calculation.Traditional model predictive control method with single prediction makes the direction and amplitude of voltage vector fixed and has high current harmonics.Therefore,suppression common-mode voltage model predictive control method with twice prediction method is used in this thesis to reduce current harmonics and suppress common-mode voltage.