Investigation of a fuel cell hybrid system with a new modular test bench approach for all electric hybrid power train systems

Switching Logic for a Direct Hybrid Electric Powertrain

“…The efficiency achieved by Hoenicke et al [14] was above 99% during cruise and take-off which is higher than the usual efficiencies of DC/DC, which usually has efficiencies somewhere between 85% and 98%. Graf et al examine the influence of the battery SOC [25] and the influence of the low ambient pressure [26] at high altitudes on the direct hybrid system and the resulting implications for dimensioning of a fuel cell and a battery [27] is investigated. A power unit combining a fuel cell and a battery in a direct hybrid can be used flexibly with the help of a power management system (PMS) as proposed by Hoenicke et al [14] and already used in the previously described test-airplane HY4 [28].…”

“…To verify the defined switching procedures, the mode transitions were performed in a previously described laboratory setup [25]. The setup emulates the behavior of the fuel cell and the battery using two electronic sources.…”

“…The sum of the fuel cell (blue) and the battery (yellow) current results in the inverter (red) current. The deviations seen between the inverter, fuel cell and battery voltage can be traced to losses in the experimental setup (wires, switches, diodes) [25]. In order to switch from Hybrid Mode to Fuel Cell Mode, the power is reduced to fulfill the above described switching criteria.…”

“…The necessary power reduction when changing from Hybrid Mode into Fuel Cell Mode for an exemplary hybrid system based on the voltage-power curves of a 10 kW PEM fuel cell stack (HD10; Power: 10 kW; Cummins Inc. USA; prior Hydrogenics) and a high-energy battery module (SLPB120255255; Kokam Co., Ltd., Republic of Korea) was examined with the help of a Matlab simulation. For the simulation, data from a previous study [25] were linearized and an example system consisting of one motor, one fuel cell stack and one battery module was considered. Figure 7a shows the resulting voltage-power curve of the fuel cell-battery hybrid system.…”

“…The defined switching procedures for operation mode changes were implemented in the control of a previously described experimental setup [25] of a power train consisting of two DC sources representing the fuel cell and the battery, the power management system and a load. The results of the test and validation of the mode transitions with the switching procedures in the experimental setup are shown.…”