Optimum current control for wide speed range operation of PMSM drive without regenerative unit utilizing PWM-VSI overmodulation

PMSM (permanent magnet synchronous motor with sinusoidal excitation) drive systems for low power applications are standard equipped with PWM inverter which employ a diode rectifier frond-end (has not a regenerative unit) to supply the ac power from the mains to the dc link. This paper proposes an algorithm to generate the optimum reference current for four quadrant operation of PMSM drive system, for wide speed range, that is fed by PWM-VSI, which operates in overmodulation regions and is equipped with diode rectifier front-end. The dynamic and steady-state performance of the proposed algorithm can be improved by increasing the inverter output voltage through overmodulation. The algorithm offers the optimum dynamic and steady-state performance for the PMSM drive despite significant changes in dc link voltage and machine parameters. This algorithm can be easy integrated in the field oriented control with or without mechanical sensors, but also in the scalar control algorithm. The algorithm identifies when the machine enters in the flux weakening region and also adjust the d- and q-axis reference currents and the limits of the PI speed controller according to the dc link voltage and the operating mode. In the motor mode a PI voltage controller generate the d-axis reference current and the q-axis current limit, while in the generator mode the power is dissipated in the machine and a PI overvoltage controller increases the d-axis reference current and limits the q-axis current.