Sensitivity analysis on frequency characteristics of a fuel cell-electrical double layer capacitor hybrid power source system

Polymer electrolyte membrane fuel cells (PEMFCs) attract much attention as next generation energy sources. To prolong durability of PEMFCs, which is one of the present challenges, we have developed a fuel cell-electrical double layer capacitor hybrid power source system to maintain the fuel cell current to a constant value, and investigated dynamic response with investigating relationship between load current changing and fuel cell current disturbance in our previous studies. In the present study sensitivity of circuit parameters on the frequency characteristics, which indicate dynamic response of the proposed FC-EDLC hybrid power system with developed multi-port bidirectional DC-DC converter has been analyzed by using numerical simulation. The model circuit parameters are set based on actual circuit's parameters. We chose electric capacitance and ESR of EDLCs and inductance of the EDLC port of the converter as parameters for analysis. The range of the electric capacitance of the EDLCs is from 1.12 mF to 56.0 F, the ESR of the EDLCs is from 70 mΩ to 1750 mΩ, and the inductance of the EDLC port is from 12.5 μH to 1250 μH. The simulation result yield the following conclusion: excessive electric capacitance of the EDLCs give no influence on the frequency characteristic, whereas decreasing electrical capacitance of the EDLCs leads to lower response speed of the power source system; reducing the ESR makes the response of the power source system better at the lower frequency than near 100 Hz, but when the ESR is 70 mΩ the stability of the system could become worse; the inductance of the EDLC port mainly affect the characteristic in the frequency range from 100 Hz to 1 kHz.