Improved reliability and fault tolerant operation of inverter-fedvariable frequency AC drives are very important for critical industrialapplications, The paper describes variable frequency variable voltageoperation of a three-phase induction motor drive in single phase modefor inverter fault conditions, such as open base drive and device shortcircuit. The detailed mathematical analysis of the machine in singlephase mode indicates that odd harmonic voltages of appropriate magnitudeand phase can be injected at the machine terminal to neutralize thelarge low frequency pulsating torques so it permits smooth driveoperation. The magnitude and phase angle of the desired harmonicvoltages have been derived theoretically. However, to eliminate theparameter variation effect and operating point dependencies, a generalpurpose search algorithm has been proposed in the paper which fabricatesthe desired harmonic voltages on real time basis. The search algorithmwas initially exercised manually on a simulated drive system to proveits validity, and then tested extensively on a volts/Hz controlled 3 hpdrive system in the laboratory. The on-line search algorithm along withestimation and control related to the project was implemented with Clanguage on a TMS320C30 digital signal processor board. The extensivelaboratory investigation shows that the proposed search algorithmperforms well and successfully eliminates low frequency pulsatingtorques not only in steady state condition but also during slowacceleration and deceleration of the drive
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