Torque Control Study Of Dual Three-Phase Permanent Magnet Synchronous Motor

Compared with the traditional three-phase permanent magnet synchronous motor,the multi-phase permanent magnet synchronous motor has the advantages of large output torque,high fault tolerance and low torque pulsation.Therefore,it has received extensive attention and research.In this thesis,the torque control of dual three-phase permanent magnet synchronous motor is studied.In this thesis,the mathematical model of the motor is firstly established and its coupling property is pointed out.Then the idea of vector space decoupling is used to realize the decoupling of the mathematical model through the Clark array of space vector decoupling,and the transformation matrix under the synchronous rotation coordinate system is given to facilitate the introduction of the three-phase motor control method and reduce the design difficulty of the multi-phase motor control system.Then the direct torque control is introduced in detail,the voltage vector space distribution of the six-phase voltage source inverter is given,and the effect of the voltage vector is analyzed,and the values of torque and magnetic chain are combined to analyze how to reasonably select the voltage vector under different operating conditions.For the problems of torque fluctuation and current harmonics during motor operation,two improvement methods are proposed.To reduce the current harmonics during motor operation,multiple voltage vectors are used in one cycle,and the harmonic component is kept zero by adjusting the action time of the voltage vectors.In order to achieve both torque pulsation and current harmonic reduction,the newly synthesized voltage vectors are applied to the hysteresis loop comparator and duty cycle control algorithms,respectively,in this thesis.The direct torque control hysteresis comparator is replaced by a multi-stage hysteresis comparator,and the multi-stage hysteresis comparator is used for the purpose of graded torque error regulation.To address the shortcomings of the direct torque control voltage vector adjustment range,the duty cycle technique is used to increase the adjustment range and reduce the torque fluctuation.To address the problems of large computation and difficult design of weight coefficients in model prediction control,an improved method is proposed for predictive torque control.In order to reduce the computational effort of model predictive control while reducing the difficulty of designing weight coefficients,a control algorithm without weight coefficients is proposed.Based on the effect of the voltage vector on the electromagnetic torque and the stator chain,the sector where the stator chain is located is predicted by the system state and the voltage vector at two adjacent moments.The number of control sets that need to be predicted by the control system is also simplified based on the prediction results to reduce the computational pressure on the system as much as possible.