An approach to connect ultracapacitor to fuel cell powered electric vehicle and emulating fuel cell electrical characteristics using switched mode converter

Future generation automobiles are being developed on fuel cell as the principal source of power generation in automobiles. Automobiles have fast changing load requirements like acceleration or sudden uphill, thus drastically increasing load torque. Fuel cell cannot respond to these fast changing load due to it's slow dynamic response. A solution is to provide the additional energy required by increased load with secondary source of energy like ultracapacitor till fuel cell responds to the increased load current. This paper proposes a new approach to interface ultracapacitor with fuel cell as secondary source of energy using bi-directional synchronous buck converter. A novel scheme to control fuel cell terminal voltage is presented. This control scheme prevents any substantial droop in fuel cell terminal voltage during sudden load change or disturbance. The whole system with fuel cell model was simulated in SIMULINK for step change in load current. Simulation results show gradual transformation of fuel cell terminal voltage from initial steady state to final steady state with ultracapacitor providing energy during transients, hence avoiding the characteristic fuel cell voltage droop. This paper also proposes a novel method to emulate steady and dynamic electrical characteristics of fuel cell using DSP controlled buck converter.