Abstract
The auxiliary converter (AXC) has been presented as a cost-effective solution to retrofit the conventional diode rectifier into a unity-power-factor and regeneration-enabled front-end. However, the pulse width modulation (PWM) switching of the AXC often causes circulating current between the AXC and diode rectifier. The zero vectors of each PWM cycle induce zero sequence current, which results in increased operational losses and electrical noise. This study analyzes the circulating current and investigates the use of multi-carrier PWM for its suppression. This multi-carrier PWM can synthesize the desired output voltage without using zero vectors for the active filtering and re-generation operations of the AXC, thus significantly suppress the circulating current. Test results are presented to validate the proposed multi-carrier PWM in the AXC system.