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An electric vehicle powered by fuel cells (FCs) gives far more promising performance. An FC is a clean energy source and has a high energy-storage capability. However, an FC has a slow dynamic response. A secondary power source is needed during start-up and transient conditions. An ultracapacitor can be used as a secondary power source to improve the performance and efficiency of the overall system. Several methods have been devised to connect an energy-storage device to an FC. This paper presents a converter system for connecting an ultracapacitor as secondary energy storage to an FC electric-vehicle system. A bidirectional dc-dc converter is used for interfacing ultracapacitor energy storage to an FC system. The controller of the converter system was designed and implemented based on dynamic evolution control. The performance of the proposed dynamic evolution control is tested through simulation and experiment. Simulation and experimental results show that the proposed techniques are suitable for controlling bidirectional dc-dc converters.