Decoupled PWM Plus Phase-Shift Control for a Dual-Half-Bridge Bidirectional DC-DC Converter

This paper presents the analysis of low leakage inductance current regions, small-signal model, and decoupled control for a dual-half-bridge isolated bidirectional dc-dc converter with pulse width modulation plus phase-shift strategy. Traditionally, the duty cycle of the transistors is fixed at 0.5 and only the phase-shift is varied to regulate the output voltage. With PPS control, two control freedoms - the duty cycle is used to regulate the voltage gain and phase-shift is used to control the power flow - can be obtained to expand input-voltage variation range. In addition, since the amplitude of leakage inductance current is limited, the current stresses of transistors can be reduced. According to the analysis, there exists a region in which higher leakage inductance current leads to lower output power and thus, causes more conduction loss. Attention should be paid to avoid this operation region. Then, a small-signal model is derived in the low conduction loss region with the state space averaging method to facilitate the closed-loop design. In addition, a decoupled control strategy is proposed to eliminate the interactions between phase-shift ratio and duty cycle, so as to simplify the proportional-integral controller design significantly. A prototype was built to verify the theoretical analysis.