Current Sharing Strategy of Three-Phase Series Capacitor Buck Converter for Wide Output Voltage Range Application

Abstract

Series capacitor buck (SC Buck) converters are widely used in voltage regulator modules (VRMs), electric vehicle, photovoltaic (PV) systems, and so on, for the reason that these converters have the characteristics of high step-down ratio and large output current. However, these characteristics can be realized only when the converter operates in a limited duty-cycle range. In this article, a modified pulsewidth modulation (PWM) scheme based on the principle of ampere-second balance is proposed for the three-phase SC Buck converter to solve the problem. The ampere-second balance of series capacitors is used to balance the phase currents over the entire duty-cycle range. The operating modes, voltage gain and current sharing performance of the converter, control diagram of the proposed converter, and parameter variation analysis are given. Theoretical analysis shows that with the proposed PWM scheme, the converter will have a larger output voltage, unified linear voltage gain expression, and sensorless automatic current sharing over the full duty-cycle range. Moreover, the results show that the parameter variation has nearly influence on the current sharing effect and the excellent balanced current can be achieved under steady state and transient state using the proposed PWM scheme. Finally, a 100-W experimental prototype has been fabricated to verify the performance of the proposed PWM scheme.