Comparative Studies on High-Power Density and Light-Weight Step-Up DC-DC Power Converter for Hydrogen-Fuel-Cell Hybrid System

Recently, the railway and electric vehicle (EV) propulsion system, based on the energy-efficient hydrogen-fuel-cell (HFC) and battery, has attracted attention. Due to the high price of the HFC, it is difficult to directly supply the high DC voltage of the inverter for driving the traction motor, a step-up DC-DC converter is required between the HFC and the inverter. However, HFC hybrid railway system has more limited space and weight compared with the general railway system, due to the additional space of hydrogen-fuel-cell and battery. As a result, a step-up DC/DC converter with high-power-density and light-weight is required. This paper describes a propulsion system for the HFC railway system and reviews step-up DC-DC converters suitable for high-power density and light-weight through various analyses. By selecting interleaving control and combination resonant LLC and 3-level buck converters with ‘parallel-input, series-output, and modular structure’ as step-up DC/DC converters, a new DC/DC converter suitable for high-power density and light-weight is proposed through their ripple analysis of input current/output voltage, design, efficiency, and volume. Finally, their operation and parameter design are verified by the PSIM simulation.