Decoupled Dual-PWM Control for Naturally Commutated Current-Fed Dual-Active-Bridge DC/DC Converter

The naturally commutated current-fed dual-active-bridge (CF-DAB) dc/dc converter is a suitable solution for the distributed generation system with low input current ripple and convenient current control. However, the efficiency under light load conditions is still a challenging issue with existing modulation schemes. In this article, a decoupled dual-pulse width modulation (PWM) control strategy is proposed to enhance the efficiency within a wide load range. The proposed modulation adjusts turn-on moments of secondary-side switches flexibly and charges the leakage inductor properly based on the instantaneous input current. The peak leakage inductor current, primary-side rms current, and the corresponding losses are reduced effectively compared to existing methods. Meanwhile, the proposed modulation strategy avoids the interactions between the primary-side duty cycle and the secondary-side duty cycle so as to decouple the voltage conversion ratio with leakage inductance and load conditions and simplify the control-loop design. The design process, power loss analysis, and implementation of the proposed modulation strategy are presented in detail. The impacts of deviations in parameters of input inductor and leakage inductor are also analyzed. Based on parameter estimation, a specific compensation loop without an additional current sensor is proposed to further improve the stability of the closed-loop control for the converter. The experimental results are given to verify the theoretical analysis and validity of the proposed modulation.