The Study Of Torque Ripple Suppression Principle Of PMSM-DTC

Permanent magnet synchronous motor is widely used in many fields,such as household appliances,electric vehicles,rail transit and industrial control,for its simple structure,small size,high power density and high efficiency.Direct Torque Control is a common control strategy with simple structure and fast dynamic response.Its control characteristics directly affect the operation performance of the motor.In this paper,the PMSM-DTC control system was taken as the research object.The direct torque control of PMSM drive system under the normal topology of two-level inverters and faulttolerant four-switch inverters was studied in order to suppress electromagnetic torque ripple and improve the stability and reliability of motor operation.Firstly,the mathematical models of permanent magnet synchronous motor in three-phase stationary coordinate system,two-phase stationary coordinate system and two-phase rotating coordinate system were established respectively.Based on the mathematical model in two-phase rotating coordinate system,the FOC scheme of PMSM double closed-loop was given.Based on the mathematical model in two-phase stationary coordinate system,the DTC scheme of the hysteresis loop of torque and flux of PMSM was analyzed.The realization mode,parameter sensitivity and dynamic and static performance of the two control schemes were analyzed and compared.Secondly,the cause of the large torque ripple of traditional PMSM was analyzed.By comparing the effect of zero vector in direct torque control of induction motor and permanent magnet synchronous motor,the function of zero vector in PMSM-DTC is clarified.Combining with the particularity of PMSM-DTC,a zero vector optimization scheme of PMSM-DTC was proposed.Based on the simulation model of MATLAB/Simulink,the torque ripple performance of the motor under the action of traditional PMSM-DTC and proposed PMSM-DTC was compared.Aiming at the problem that the power switching devices of inverters were liable to failures,the topology of a two-level three-phase six-switch inverters was reconstructed after some phase failures occur,the mathematical model of the three-phase four-switch inverters with fault-tolerant topology was established,and the PMSM-DTC scheme under the three-phase four-switch inverters was designed.Considering the problem that the number of voltage vector of three-phase fourswitch inverters was limited and there was no zero,the strategy of virtual voltage vector expanded the voltage vector table in fault-tolerant operation in order to reduce the amplitude of electromagnetic torque ripple and improve the fault-tolerant performance of PMSM.Finally,the experimental platform of PMSM drive system was built,and the design schemes of protection circuit,isolation drive circuit,signal acquisition circuit and DSP control system were given.The experimental results were basically consistent with the simulation results,which proved the feasibility and superiority of the proposed PMSM-DTC strategy.