Analysis of Current Flowing Through Disabled Converters in Parallel AC/DC Power Conversion System

Abstract

When not all the converters are enabled in a parallel ac/dc power conversion system, some current flows through the disabled converters. This current not only distorts the current waveform of the ac side but also causes extra loss and unintended power flow from the ac to the dc side. In this article, the reason for this current flow is identified, and the total current according to the number of paralleled converters and its operating conditions are analyzed. A new pulsewidth modulation (PWM) method is proposed to minimize the current. And, the zero-sequence voltage and the consequent current flowing through the disabled converters under the proposed PWM method are compared to those under the conventional PWM methods. As a result, it was identified that discontinuous space vector PWM (DPWM) is not a proper PWM method because it causes a large current at some operating conditions. According to both simulation and experimental results, the magnitude of the current flows through disabled converters under the proposed PWM was about 40% less than that under sine PWM and DPWM, and it was about 10% less than that under continuous space vector PWM.