Research On Common-mode Voltage Reduction Strategy Of Dual Three-Phase Motor Variable Frequency Drive System

Under the circumstance of the increasingly severe problems of resources and environment,the green and environmental vehicles such as electric ship propulsion,electric locomotive traction,pure electric or hybrid electric vehicles have received extensive attention and research.Compared with the traditional three phase motor,multiphase motor is more suitable for these applications with high power and high reliability because of its advantages like high power output with low voltage,small torque ripple and good fault tolerance ability.In multiphase motor drive,the PWM modulation technology is the mainly used method.However,a related negative impact with PWM technology is the common-mode problem which brings unfavorable influence on the motor and the power grid.It is an important reason for winding faults and bearing aging or failure.In this dissertation,the dual three-phase permanent magnet synchronous motor drive system is chosen as research object and its vector control strategy is researched and the common-mode problem is deeply studied.Firstly,the mathematical model of dual three-phase permanent magnet synchronous motor(PMSM)in the stationary coordinate system is introduced.Its expressions in the rotating coordinate system are also obtained by the coordinate transformation based on the dual d-q transform and the space vector decoupling.Based on the coordinate transformations,the corresponding vector control strategies are further studied.The simulation in MATLAB / Simulink shows that the dual three-phase PMSM with two vector control strategies has consistent output performance when they have the same control parameter value.The control strategy based on space vector decoupling is chosen as the basic strategy in this dissertation.Then,the mechanism and expression of common-mode voltage of two level voltage source inverter are summarized.The harmonic characteristics of common mode voltage are discussed in frequency domain by the means of Fourier analysis,and the influence of dead time which is needed in practical application is discussed in detail.In order to effectively suppress the common-mode voltage in the dual threephase motor drive system,a SVPWM control strategy based on six transition vectors considering the stator harmonic current suppression is studied.On the basis of it,the SVPWM control strategy based on twelve transition vectors which can increase the DC bus voltage utilization is further discussed.The method to reduce the effect of dead zone on the suppression of common-mode voltage by optimizing the sequence of fundamental vectors is also used.The effectiveness of the control strategy is verified by simulation.Finally,based on the theory and simulation experiments,TMS320F28379 based dual three-phase PMSM coaxial dragging platform is used to verify the vector control and common-mode voltage suppression strategies of the dual three-phase motor drive system.