Out-of-step Problems And Countermeasures Of Sensorless Control For Permanent Magnet Synchronous Motor

Permanent magnet synchronous motor has the advantages of simple structure,small size,large power density and high transmission efficiency,So it has been widely researched and applied in the fields of industry,transportation and aerospace.Using sensorless control can effectively reduce the system volume and reduce product cost.The application background of the subject is the propulsion motor of the underwater submersible vehicle.Under actual operating conditions,the secondary pump load has a large torque shock due to the influence of the water flow between the motors.The motor is in the I/F control stage and sliding mode Observers are prone to out-of-step phenomenon during the state switching phase.This article focuses on countermeasures for the motor out of step in the above phase.In the motor start-up phase,this paper uses the method of pre-positioning to drag the motor rotor to a predetermined position before the motor speeds up.For the positioning blind area problem of current pre-positioning,a secondary positioning method is studied to ensure a reliable rotor for the motor Pre-positioning.The stability of the I/F control is analyzed.The load curve is set offline,and it converges according to the mechanical characteristics,and it is easy to get out of step under irregular loads.In I/F control,a closed loop of current vector frequency adjustment based on the high frequency component of active power is used to compensate the damping torque of the motor when the load changes,increase the damping component of the system,and improve the convergence characteristics of the system.The closed-loop adjustment of the current vector amplitude based on the motor torque angle is used to make the motor torque angle converge to the reference value.When the reference value is set to 0°,the motor runs at the maximum torque/current ratio characteristic.This method increases the motor’s ability to adapt to the load To prevent the motor from being out of step due to a sudden increase in load exceeding the maximum electromagnetic torque,further improving the stability and convergence characteristics of the system.For realize the position sensorless control of the permanent magnet synchronous motor in the full speed range,it is necessary to switch the motor control strategy between I/F control and double closed-loop control based on sliding mode observer.This paper analyzes three state switching algorithms.The weighted function state switching can improve the torque impulse and speed oscillation during state switching,but it has poor adaptability to the load.The switching strategy to reduce the amplitude of the current vector has better adaptability to the load,but the speed is poor and it is easy to cause the motor to step out due to the load torque shock.Analysis of the shortcomings of the above method further adopts instantaneous switching based on the double DQ space coordinate system as the state switching strategy.Finally,the principle of the sliding mode observer is analyzed,and a normalized phase-locked loop is introduced to decouple the motor back-EMF.According to the relationship between the line voltage of the motor and the back-EMF,the real-time out-of-step detection of the motor is performed at low speed,and An experimental platform of permanent magnet synchronous motor drive system was built.