Optimum current command algorithm for wide speed range and four quadrant operation of PMSMS drive without regenerative unit

Low-power PMSMS (permanent magnet synchronous motor with sinusoidal excitation) drive systems are standard equipped with PWM inverter which employ a diode rectifier front-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 d- and q-axis reference currents for four quadrant operation of PMSMS drive system, for wide speed range, that is fed by PWM inverter equipped with diode rectifier front-end. The algorithm offers the optimum torque capability for the PMSMS despite significant changes in dc link voltage and machine parameters. This algorithm can be easy integrated in the field oriented control of PMSMS 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 generates the d-axis reference currents, 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. The experimental results show that the proposed algorithm provides good steady state and dynamic performance.