An Optimal DC-DC Converter for Fuel Cell-Supercap Series-Connected Powertrain in Fuel Cell Electric Vehicles

This article proposes a new optimized dc-dc converter based on a series-connected power source configuration for Fuel Cell Electric Vehicles (FCEVs), along with a flexible series-parallel transition control strategy. By utilizing the series-connected configuration, the volume of each power source can be reduced, enabling optimal design of power sources in the FCEV by considering their cost, size, and other characteristics. Additionally, increasing input voltage of the converter reduces conduction current, thereby improving system efficiency. This article provides a detailed analysis of the power flow in the proposed converter under various load conditions and control strategy designed to improve the response characteristics of the converter during transient periods of series-to-parallel or parallel-to-series operation. A 120 kW proposed converter is designed, and the power source volume is compared with that of a conventional configuration to verify the volume reduction achieved by the series-connected structure. In addition, an efficiency analysis of the proposed converter is conducted under different operating modes. To verify the feasibility of the proposed converter and control strategy, a 12 kW prototype is designed and implemented. The operation of each mode is verified, and the series mode operation of the proposed converter through series-parallel transitions is also validated. In series mode operation, the efficiency of the proposed converter is measured at up to 98.4%. Based on the experimental results, the effectiveness of the proposed converter and control strategy is verified.