Undervoltage Operation Strategy of PMSM Based on Improved Voltage Loop Bidirectional Quasi-Z Source Inverter

In low-voltage servo systems powered by batteries, as the battery continues to discharge and the system enters an under-voltage condition, the PMSM's torque becomes limited due to the saturation of back electromotive force during motor startup. Additionally, in steady-state operation, the output torque is constrained. To address these issues, a novel control strategy is proposed that combines the Quasi-Z-source network with the low-voltage servo drive. The rate of change of the phase current amplitude of the PMSM is introduced as a compensation factor into the voltage loop control of the Quasi-Z-source network. This approach enhances the DC bus voltage and its dynamic response performance, thereby improving the motor's output torque. Consequently, the proposed strategy effectively improves the system's response speed and output capability under battery under-voltage conditions.