A new control strategy to improve the performance of a PWM AC to DC converter under unbalanced operating conditions
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abstract
Abnormal harmonics of significant magnitude are generated at the output and input terminals of a PWM ac to dc converter under unbalanced operating conditions. A new control strategy is presented here to selectively cancel the generated lower order abnormal harmonics at the output and input terminals and thereby to preserve the high performance features of a PWM ac to dc converter. The proposed technique essentially involves computing the sequence components of the unbalanced input supply and suitably counter-unbalances the PWM gating signals of the converter switches to cancel the generated abnormal harmonics. The technique is essentially a feed forward approach and is suitable for higher power G.T.O. type PWM ac to dc converters. A procedure for implementing this technique in real time is discussed. Finally selected results are verified experimentally on a prototype PWM ac to dc converter. 1993 IEEE