Three-phase Four-switch Inverter-position Sensorless Permanent Magnet Synchronous Motor System With Speed Re-commissionin

Three-phase four-switch inverters have been widely studied because of their simple topology,low hardware cost,and ability to provide fault-tolerant control for three-phase six-switch inverters.In the three-phase four-switch inverter-fed sensorless permanent magnet synchronous motor(PMSM)drive system,when abnormal operating conditions such as overvoltage or overcurrent occur,the power switching devices automatically close to cut off the main power supply,and the motor is freerunning.If the motor is still rotating when the power supply is restored to the system,an accurate rotor position is required to output the correct pulse signal to avoid excessive strike current.Therefore,it is of great significance to accurately calculate the rotor position at the moment of the restart for the reliable operation of the system.In this paper,a capacitor voltage balance strategy is firstly proposed.Without adding other hardware circuits and filters,the formula is used to calculate the capacitor voltage offset and correct the reference voltage of the αβ axis,which improves the control performance of the three-phase four-switch inverter-fed PMSM.This is also the basis for subsequent control.The traditional zero-voltage vector injection method can accurately calculate the rotor position and speed at the moment of the motor restart,but the three-phase four-switch inverter itself only has an effective voltage vector,and direct injecting the vector cannot detect the rotor position and speed at the moment of the motor restart.To solve this problem,the double equivalent zero-voltage vector injection method is proposed in this paper.After the power supply of the system is restored,two voltage vectors with exactly opposite directions are used to synthesize the equivalent zero-voltage vector into the inverter according to the vector calculation rule.Since the motor is in a rotating state,the back electromotive force will be generated.During the time of injecting the equivalent zero voltage vector,the motor three-phase winding is in an equivalent short-circuit state.At this time,the three-phase current of the motor can be equivalent to a short-circuit current.The short-circuit current is detected by the current sensor,and the rotor position and speed can be calculated at the moment when the motor is restarted.Before the inverter outputs the signal,the calculation result is used as the initial value of the rotor position and speed of the motor estimated by the position sensorless control,which is used for the system closed-loop control to restart the motor.After that,the rotor position and speed converge fast and the motor resumes normal operation.Finally,a three-phase four-switch inverter-fed sensorless PMSM drive system is built in this paper to verify the effectiveness of the proposed method.The experimental results show that the proposed capacitor voltage balance strategy can effectively improve the control performance of the system;on this basis,the proposed double equivalent zero-voltage vector injection methods can be used to accurately calculate the rotor position at different speeds to restart the motor.