Real-time detection of intermittent misfiring in a voltage-fed PWM inverter induction-motor drive

This paper develops a real-time condition-monitoring algorithm for pulsewidth modulation (PWM) inverter induction-motor drives. It is designed to detect the intermittent loss of firing pulses of an individual switching device within the inverter. The mathematical model of the induction machine is linearized in the field-torque coordinates, and the misfiring of the inverter is represented by pulse functions, which have effects in both the field and torque directions. Since the fault considered is of an intermittent nature, the time-domain response of the magnetizing and the torque-producing components of the motor stator current is used to form the condition-monitoring signal. The method is adaptive to changes in the operating point during variable-speed operation. Digital simulation and laboratory experiment are utilized to illustrate the method and to evaluate the computational effort required.