FAULT MODE SINGLE-PHASE OPERATION OF A VARIABLE FREQUENCY INDUCTION-MOTOR DRIVE AND IMPROVEMENT OF PULSATING TORQUE CHARACTERISTICS

Improved reliability and fault tolerant operation of converter systems are extremely important for industrial ac drives. The paper considers variable frequency variable voltage operation of a three-phase induct ion motor in single-phase mode for two common faults of a three-phase inverter, i.e., open base drive and device short-circuit. The motor pe rformance has been extensively analyzed in single-phase mode and remed ial strategies have been developed to neutralize large second and othe r lower order harmonic pulsating torques. In a single-phase open loop volts/Hz control mode of a faulty three-phase inverter, it has been de monstrated that odd harmonic voltages at appropriate phase angles can be injected to neutralize the low frequency pulsating torques so as to permit smooth drive operation. It has been shown that the pulsating t orque can be further reduced by load dependent flux programming rather than operating with constant rated flux.