Study on Boost Converters with High Power-Density for Hydrogen-Fuel-Cell Hybrid Railway System

Abstract

Step-up DC/DC converters are needed generally for the hydrogen-fuel-cell (HFC) hybrid railway system since the HFC has difficulty directly generating a high link voltage of over 1500 V for the high-power capacity inverter to drive the traction motor in the vehicle. These step-up DC/DC converters demand a high conversion efficiency with low weight and volume, due to the limited space in vehicle. In this paper, step-up DC/DC converters are presented and are evaluated for the HFC hybrid railway system. By choosing the interleaved boost converter and the 3-level boost converter as promising candidates, characteristics and features of both converters are presented through the analysis of the operational principles. In addition, the optimal design methods and results of boost inductor, output capacitor, and power semiconductor devices are presented based on theoretical analysis and a real design specification for the HFC hybrid railway system. Moreover, an optimal digital control design in terms of dynamic current response and reliability, such as current-balance or voltage-balance controls, is presented in this paper. In order to verify the analysis and design results, prototypes of both converters with the 600 V input and 1200 V/20 kW output specifications are constructed and the performance of the interleaved and 3-level boost converters are demonstrated through the experimental results. The experimental results show that the 3-level boost converter is more suitable for the HFC hybrid railway system in the sense of efficiency, power-density, and dynamic current response.