Circulating currents in open-end winding PWM ac drives

Circulating currents have been experimentally observed in pulse-width modulated ac open-end winding drives. These currents have the effect of increasing conduction losses in the stator winding resistance of the ac machine. Two major causes for these currents have been identified as device voltage drops in power semi-conductor devices and dead-time used for over-current protection. Analysis of these effects and a mathematical description for predicting their severity is provided. Experimental results are presented that support the theory.