Research On Direct Torque Control For Harmonic Suppression Of PMSM

Permanent magnet synchronous motor is widely used in electric vehicle drive systems due to such advantages as simple structure,small size,high efficiency,and high power density.In this paper,the surface-mounted permanent magnet synchronous motor is taken as the research object,and the control strategies of suppressing the current harmonics and torque ripple of the motor are studied.Two direct torque control methods for harmonic suppression are proposed,and simulation and experiment are used as verification methods.The harmonic characteristics of the voltage,current,torque and speed signals of the motor under the direct torque control base on duty cycle modulation are studied.After the selection rule of the output voltage vector and the distribution of the duty cycle are analyzed through qualitative analysis,its harmonic characteristics are discussed.Besides,for the harmonic characteristics of current,torque and speed are analyzed based on their relationship and verified by simulation and experiment.The effects of the factors including the inverter nonlinearity,load angle,switching frequency,and space vector sequence are studied through simulation.An improved DDTC considered the angle of voltage space is proposed.In the proposed method,the sector division is designed based on the influence of the load angle on the duty ratio distribution while the duty ratio is formulated according to the relationship between the stator flux vector and the stator voltage vector to avoid complicated calculation of the torque slope.It is robust to reduce the dependence on the motor parameters.Both simulation and experimental results confirm that the low-frequency harmonic of current and the speed are suppressed under the control of the proposed method.Besides,the experimental results show that the low-frequency vibration of the motor is suppressed.An improved direct torque control method combined with duty cycle control is proposed based on the comparison of DDTC and SVM-DTC.In the proposed method,the amplitude of the output voltage vector is obtained through the duty ratio calculation while the direction is determined through the stator flux deviation.Simulation results show that the low-frequency harmonics of current,torque,speed and flux ripples are suppressed effectively under this method.In this paper,the harmonic suppression is studied from the perspective of control strategy,and two improved direct torque control methods are proposed which can suppress the lowfrequency current,torque and speed harmonics and is beneficial to suppress the low-frequency vibration of PMSM.