On-line search based pulsating torque compensation of a fault modesingle-phase variable frequency induction motor drive

Improved reliability and fault tolerant operation of inverter-fed variable frequency AC motor drives are very important for critical industrial applications. The paper describes variable frequency, variable voltage operation of a three-phase induction motor drive in single-phase mode for inverter fault conditions, such as open base drive and device short circuit. The detailed mathematical analysis of the machine in single-phase mode indicates that odd harmonic voltages of appropriate magnitude and phase can be injected at the machine terminal to neutralize the large low-frequency pulsating torques so as to permit smooth drive operation. The magnitude and phase angle of the desired harmonic voltages have been derived theoretically. However, to eliminate the parameter variation effect and operating point dependencies, a general purpose search algorithm has been proposed in the paper which fabricates the desired harmonic voltages on a real time basis. The search algorithm was initially exercised manually on a simulated drive system to prove its validity, and than tested extensively on a volts/hertz controlled 3-hp drive system in the laboratory