Study On Control Technology Of Dual Y Shift 30 Degrees Six-phase Permanent Magnet Synchronous Motor

Because multi-phase motors have many outstanding merits,such as small torque ripple, high efficiency and good fault-tolerance, they have been widely used in occasions of higher reliability, such as electric ship propulsion and more-electric aircraft drive system. In this paper, surface mounted dual Y shift 30 degrees six-phase permanent magnet synchronous motor(PMSM) is chosen as the study object, control technologies are studied when the motor is in normally operated or fault conditions.Firstly, through coordinate transformation, decoupled mathematical model of six-phase PMSM in d-q plane is built. Because Z-phase-opened motor can not been equivalent to symmetric machine in two-phase static coordinate system, after traditional rotating coordinate transformation, there are torque ripple whose frequency is twice of power frequency. To solve the problem of Z-phase-opened motor’s torque ripple, a modified rotating coordinate transformation is proposed. Vector control strategy based on id=0 is used to realize motor’s decoupling control.Secondly, pulse width modulation algorithm of multiphase motor is studied deeply. When applying three-phase motor normally used SVPWM algorithm to multiphase motor directly, the stator current harmonic is bigger. Taking advantage of more degrees of freedom in six-phase motor, SVPWM based on minimum loss is proposed to achieve the goal of minimizing both the motor’s stator copper loss and switching loss. For the case of chaotic distribution of open-phase motor’s voltage vectors, SVPWM based on effective time, with less calculation, is applied to motor control,this algorithm can improve response speed of system greatly and obtain better dynamic characteristics. Appling proposed algorithm in both motor normally operated and Z-phase-opened conditions, the algorithm’s correctness and effectiveness are verified.Finally, direct torque control(DTC) strategy is applied to multiphase motor variable speed system. When speed regulating scheme with DTC based on switching table(ST-DTC) is used, switching frequency is inconstant, using SVPWM algorithm in DTC strategy can avoid this problem effectively. When the motor occurs open-circuit fault, the selection of SVM-DTC based on effective time can make motor continue running, simulation results show that the variable speed system has fast response speed and good robustness.