Optimum torque control algorithm for wide speed range and four quadrant operation of stator flux oriented induction machine drive without regenerative unit

In general, low power induction motor drive systems are equipped with PWM inverter using a diode rectifier frond-end (has not a regenerative unit) to supply the ac power from the mains to the dc link. The main features of the proposed algorithm are the capability to generate the optimum torque, for four quadrant operation of drive system, over the wide speed range that is fed by PWM inverter equipped with diode rectifier front-end. The algorithm offers the optimum torque capability for the induction motor drive despite significant changes in dc link voltage and machine parameters. The algorithm identifies when the machine enters in the flux weakening region and also adjust the stator flux reference and q-axis current limit according to the dc link voltage and the operating mode. In the motor mode a PI voltage controller generates the stator flux reference 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 stator flux reference limit and limits the q-axis current.