Optimal Design of LCC Resonant Converter With Phase Shift Control for Wide Input/Output Voltage Ranges in Fuel Cell System

Abstract

This paper proposes an optimal design of an LCC resonant converter with a phase shift control for a fuel cell system which has wide input and output voltage ranges. The proposed optimal design focuses on the circulating energy minimization by adjusting the transformer turns ratio according to the maximum gain of resonant tank. This makes the root mean square (RMS) value of resonant current and turn-off current stationary even though the resonant tank change. Thus, designers can select resonant tank optimized for the converter specifications without considering the conduction and switching losses. By the proposed optimal design, the efficiency degradation at worst case, which is a significant issue of the fuel cell system with wide output voltage range, can be minimized. In addition, for the fuel cell converter with wide input voltage range, a phase shift control which operates the full-bridge inverter with a constant effective duty cycle according to the fuel cell voltage is proposed. This control scheme improves the light-load efficiency without deteriorating the rated-load efficiency by reducing the circulating current and switching frequency. The validity of the proposed works is confirmed by experimental results of the 30kW LCC resonant converter.