Hybrid fuel cell/battery power-unit configurations are gaining growing attention; in fact, they offer advantages in terms of fuel cell downsizing, higher efficiency and fast fueling. In these configurations, the power-sharing is actively controlled employing power electronics, mainly boost converters, that affect the costs and performance of the system. In this work, a novel hybrid power-unit based on a passive fuel cell/battery system is proposed for a lightweight electric vehicle (5 kW nominal power). This configuration eliminates the need for costly power converters, and increases the overall performance. The hybrid power-unit consists of 5 fuel cell stacks, 6 battery modules and two resistors that allow safe fuel cell start-up and shut-down. The power profile requested by the electric motor is derived from an ARTEMIS drive cycle and tested by means of two electronic loads. The analysis on the power-unit behavior and performance has been carried out by means of a numerical model and experimental activities. The power-unit response has been analyzed focusing on: i) start-up operation; ii) drive cycle operation; iii) shut-down operation. During the whole test, the fuel cell produced about 51% of the total requested energy while the battery pack about 49%. The average stack efficiency during operation resulted to be 47%, while it dropped to 41% considering also start-up and shut-down. Results proved the technical feasibility as well as the safety of the system and showed that the developed power-unit has promising features for practical applications.
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