## 4 Results and Discussion
Figure 8: Impact of common rail buffer volume on air supply subsystem: (**a**) Maximum pressure drop; (**b**) Maximum power; (**c**) Energy consumption. Figure 10: The pressure in the hydrogen inlet common rail under the CWTVC condition. Figure 9: The air pressure in the common rail buffer under the CWTVC condition. In Figure 11, the anode inlet pressures of 20, 70, and 120 kW stacks are compared between the integrated hydrogen circulation structure with an inlet common rail and the distributed hydrogen circulation structure under the CWTVC condition. As shown in Figure 11a-c, the pressure overshoot of the distributed hydrogen supply subsystems gradually increases with the increase in the stack power when the load changes, while the pressure of the integrated hydrogen supply subsystem can keep up with the variation of demand pressure. In addition, distributed hydrogen supply subsystems require three hydrogen recirculation pumps for exhaust gas circulation, whereas integrated hydrogen supply subsystems require only one hydrogen recirculation pump for this function. Under the CWTVC condition, distributed hydrogen subsystems consume 2030 kJ to complete gas circulation, whereas the integrated hydrogen subsystem consumes only 1715 kJ. In contrast to the air supply subsystem, the hydrogen supply subsystem needs to circulate the anode outlet gas, which requires attention to the hydrogen concentration in view of the transmembrane transport of nitrogen. The variation of nitrogen concentration in anode channels of the 20, 70, and 120 kW stacks is presented under the CWTVC condition in Figure 12. Under the same power allocation strategy, the nitrogen concentration of the distributed hydrogen supply subsystem quickly reaches the set value of 1%, after which the hydrogen discharge valve is frequently operated to discharge nitrogen, and the time for  
Figure 6:0 The anode inlet pressure under the CWTVC condition: (**a**) 20 kW; (**b**) 70 kW; (**c**) 120 kW. the nitrogen concentration to reach the set value is gradually delayed with the increase in the stack power level and different power allocations. However, the nitrogen concentration in the integrated hydrogen supply subsystem reaches the set value of 1% only in the 20 kW stack, mainly due to the circulation of hydrogen throughout the anode pipeline and the fresh inlet hydrogen from the hydrogen tanks, which dilutes the nitrogen concentration in the anode channels. This phenomenon leading to a lower concentration of nitrogen is not necessarily an advantage, as it contaminates the anode inlet pipeline, making the hydrogen utilization less efficient, which can be explained by the previously mentioned Equation (6). For the integrated thermal subsystem, the coolant circulation affects the three stacks differently. The stable temperature of stacks at a load current of 100 A is shown in Figure 6:1 Figure 13a shows the relationship between inlet coolant temperature and PEM fuel cell steady-state temperature. Figure 13b,c show the stabilization time and stabilization temperature for three stacks at coolant temperatures of 333 K and 338 K, respectively. Figure 13d  
Figure 6:2 The variation of nitrogen concentration in anode channels under the CWTVC condition: (a) 20 kW; (b) 70 kW; (c) 120 kW. shows the relationship between the mass flow rate of coolant and the stabilization temperature of the three stacks. The reason for the conditions is the different masses of the three stacks and the different heat productions at the same current. The integrated thermal subsystem could result in the heat production of stacks, affecting the temperature of the other stacks. In Figure 14, the variations in the temperature are compared for three stacks, where the load current is changed from 100 A to 150 A at 475 s for each of the three stacks under a radiator fan speed of 1500 rpm and a coolant circulation pump speed of 2000 rpm. As the stack power level increases, an abrupt change in the load of the stack results in a gradual increase in its temperature, as well as that of other stacks.