Abstract: A fuel cell hybrid powertrain system is composed of a fuel cell engine, a direct current to direct current converter (DCDC), a nickel metal hydride battery and a tractional motor. A fuel cell hybrid model is developed on the basis of bench test data. The model takes into consideration the fuel cell performance degradation, influence of bus voltage on motor torque and efficiency, DCDC efficiency and its dynamic process, and the internal resistance property of battery charge and discharge. Performance degradation of fuel cell leads to invalidation of energy management strategy. DCDC efficiency keeps a nearly constant value in city bus cycle. Its dynamic process can be simulated by using a first delay algorithm block. The internal resistance of battery charge and discharge influences the computation of equivalent hydrogen consumption. The influence of bus voltage on motor efficiency and torque can be considered by using a correction coefficient. The power demanded by motor is provided by fuel cell and battery according to an energy management strategy, including a battery state of charge (SOC) balanced strategy and a fuel cell dynamic power compensation algorithm. Simulating results show that, the hybrid model reflects the performance of actual system well, battery SOC is kept in a suitable range and the fuel cell dynamic power is limited. Further results show that, by adjusting the SOC balanced strategy, battery SOC level can be kept in the suitable range although the performance of fuel cell degrades. Therefore, vehicle economy and drivability can be guaranteed. But if the fuel cell performance degrades further, the vehicle economy and drivability cannot be adjusted by energy management strategy.

Key words: Dynamic compensation, Energy management, Fuel cell, Hybrid powertrain, Performance degradation