A Closed-Loop High-Frequency Current Shaping Method to Achieve Trapezoidal Transformer Current in a Current-fed Dual Active Half-Bridge Converter for Minimum RMS Current and Wide-range ZVS

This paper proposes the use of primary and secondary side duty ratio control along with the phase shift control in a Current-fed Dual Active Half-Bridge (DAHB) Converter to achieve trapezoidal transformer current which results in Zero Voltage Switching (ZVS) of all the switches and minimum RMS current even at light loads, for a wide range of input voltage. The high-frequency transformer current is directly sensed at specific transition instants by a delay-adjusted sampling strategy to be used as control variables in a current control structure. This is better because the voltage control of capacitor voltages would have required more expensive sensors. A simple and accurate small-signal model of the converter is developed, and the relevant transfer functions are derived. The controller design details are provided. Finally, experimental results on a 1kW laboratory prototype demonstrate the effectiveness of the closed-loop duty ratio control in achieving trapezoidal transformer current resulting in improved efficiency and ZVS of the switches, compared to a simple phase-shift control.