ONLINE SEARCH BASED PULSATING TORQUE COMPENSATION OF A FAULT MODE SINGLE-PHASE VARIABLE FREQUENCY INDUCTION-MOTOR DRIVE

Improved reliability and fault tolerant operation of inverter-fed vari able frequency ac drives are very important for critical industrial ap plications, The paper describes variable frequency, variable voltage o peration of a three-phase induction motor drive in single-phase mode f or 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 magnitu de and phase can be injected at the machine terminal to neutralize the large low-frequency pulsating torques so as to permit smooth drive op eration, The magnitude and phase angle of the desired harmonic voltage s 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 d esired harmonic voltages on real time basis, The search algorithm was initially,exercised manually on a simulated drive system to prove its validity, and then tested extensively on a volts/hertz controlled 3-hp drive systemin the laboratory. The on-line search algorithm along wit h estimation and control related to the project was implemented with C language on a TMS320C30 digital signal processor board. The extensive laboratory investigation shows that the proposed seat ch algorithm pe rforms well and successfully eliminates low-frequency pulsating torque s not only in a steady-state condition but also during: slow accelerat ion and deceleration of the drive. The search algorithm is perfectly g eneral and can be easily extended to other induction motor drives.