Research To Enhance The Operating Performance Of Low-frequency Low-cost PMSM

Permanent magnet synchronous motors are widely used in various fields due to their simple structure and relatively flexible design of permanent magnets.In order to reduce the cost of the PMSM controller and achieve reliable control,a Hall sensor switch is used as a position sensor.Since Hall sensors can only provide discrete position signals,accurate position information cannot be obtained at low frequencies.In order to prevent the PMSM driver inverter bridge from passing through the upper and lower arms,it is necessary to implant the dead zone on the upper and lower arms and also bring about the problem of torque ripple.Therefore,it is of great significance to study the high-precision control of the PMSM based on Hall sensors at low frequencies.The thesis first analyzes the reason why the switch Hall sensor can't accurately estimate the rotor position when the PMSM is at low speed.For the performance evaluation of the traditional vector observer based on the mechanical model of the motor,a vector observer based on the back-EMF model is constructed..By correcting the observation position error as a speed estimation compensation based on the Hall first-order algorithm,a better low-speed operation effect is achieved.The experimental results show that this method can effectively reduce the vibration of the motor during low-speed operation.This method achieves a smooth operation of 11r/min on the experimental platform.Then,in order to overcome the shortcomings of the traditional VF open-loop start-up control strategy,an IF control strategy is adopted,which is a speed loop open loop and a current loop closed loop.The sudden change of current and the cause of torque jitter in the process of switching from open-loop start to vector control are analyzed,and a state transition method that can smoothly transition is proposed.The experimental results show that this method makes the starting current have a better sine degree,and because it has the self-balancing characteristics of the torque power angle,it can pull the rotor into the synchronous operation faster.Finally,a voltage error observer is constructed by analyzing the voltage error and current harmonic caused by the dead-zone effect.The voltage distortion due to the dead zone effect is compensated by the observation of the voltage error observer and the decoupling term of the motor equation.Finally,the above method is verified by simulation.By using the proposed dead-zone compensation method,the phase current THD decreases from 3.29% to 2.61%.