Development of a Fuel Cell System for Small Mobility Applications with Severe Load Fluctuations

In recent years, small electric mobility powered by fuel cells have been proposed as a way to achieve a carbon neutral society. One reason for the proposal is that fuel cells have an advantage over battery electric vehicle (BEV) in traveling range and refueling time. This study develops a hybrid system combining a fuel cell and a lithium-ion capacitor (LiC) for small electric mobility applications with severe load fluctuations. The proposed system achieves a 53% reduction in size, a 50% reduction in weight, and a 23% improvement in acceleration performance compared to a configuration using a lithium-ion battery (LiB) as the secondary battery, while also reducing load fluctuations in the fuel cell. Although LiCs tend to be compact, lightweight, and capable of high output, they have limited discharge capacity. To address this, a prototype hybrid system combining a fuel cell and an LiB was initially constructed to verify the system’s ability to suppress load fluctuations through current control of the fuel cell. When the power demand of the motor exceeded the fuel cell’s output, additional power was supplied by the LiB. When the demand was lower, the motor was driven while simultaneously charging the LiB to suppress load fluctuations. Subsequently, the LiB was replaced with an LiC, and system feasibility was evaluated through vehicle power balance simulations and test drives. By controlling the fuel cell output to maintain the LiC’s state of charge (SOC) between 60% and 70%, load fluctuations in the fuel cell were effectively suppressed, and drivability was improved. This paper presents the technological development and evaluation results of the proposed system.