| Permanent magnet synchronous motor(PMSM)has been widely concerned because of its high power density,high transmission efficiency,high torque density,speed regulation performance and control accuracy.Compared with the traditional transmission system of asynchronous motor and reducer,the low speed and high torque PMSM direct drive system has the characteristics of high transmission efficiency and good control effect.Compared with the traditional two-level inverter,neutral point clamped(NPC)three-level inverter has the advantages of small voltage stress,small output harmonic and small du/dt.Therefore,this paper takes the low-speed high torque permanent magnet synchronous motor based on NPC three-level inverter as the research object,and studies its torque ripple suppression strategy and speed sensorless control strategy.Aiming at the problem of large torque ripple in low speed and high torque PMSM control process,the mathematical model of PMSM+NPC inverter system is established,the cause of torque ripple is analyzed from the whole system,and the periodic torque ripple equation is established.A torque ripple suppression method based on proportional integral resonant controller is designed,and the design process of controller parameters is analyzed.The simulation results show that this method can effectively suppress the periodic torque ripple caused by inverter dead time,tube voltage drop and detection system error.Aiming at the problems of low reliability and high cost of hardware speed sensor in PMSM control system,a speed sensorless control strategy based on high frequency square wave injection is studied.The principle is analyzed from four aspects:high frequency signal injection,high frequency response signal separation,error signal decoupling and position observer design.Aiming at the problem that the filter will introduce phase delay and limit the bandwidth of controller and observer in the traditional method of high frequency signal extraction,a simplified high frequency signal separation method is adopted to improve the speed estimation effect.The simulation results show that this method can effectively estimate the motor speed and rotor position information,and improve the speed estimation accuracy.According to the specific requirements of the system control,a 7.5kW PMSM+NPC inverter hardware experimental platform is designed and built to verify the proposed method. |
