# Sliding Mode Integral Separation PID Control for Hydrogen Fuel Cell Systems
## 4 Analysis of PEMFC Experimental Results
### Analysis of Experimental Results of Sliding Mode Integral Separation PID  
This paper presents the combination of sliding mode control and IS\(-\)PID control to obtain the sliding mode integral separation PID control (SMC\(-\)IS\(-\)PID) of OER, as illustrated in Figure 11. It also controls the electric stack temperature, as illustrated in Figure 12, the cathode-anode differential pressure, as illustrated in Figure 13, in accordance with the cathode-anode pressure differential in Figure 7, and the corresponding different polar pressure of the electric stack, as illustrated in Figure 14.  
In Figure 11, it can be seen that the conventional PID, integral separation PID, sliding mode control (SMC), and sliding mode integral separation PID control OER to 2 quickly. In the startup phase of the system, SMC has the advantage of no overshooting compared to PID and IS\(-\)PID, but the adjustment time is longer, and the adjustment time of SMC is 12.573 s. The sliding mode integral separation PID has a shorter adjustment time  
Figure 11: Effect diagram of OER controlled by SMC\(-\)IS\(-\)PID.  
Figure 12: Effect diagram of the stack temperature controlled by SMC\(-\)IS\(-\)PID.  
compared to the sliding mode control; specifically, the sliding mode integral separation PID adjustment time is 5.019 s. When the load current step occurs in the normal operation phase of the system, for example, in 100 s, the benefits of SMC\(-\)IS\(-\)PID over PID and IS\(-\)PID include less overrun and quicker response times, and it has a leg up on quicker response times compared to SMC. The PID adjustment time is 3.117 s, the IS\(-\)PID adjustment time is 2.983 s, the adjustment time of SMC is 7.341 s, and the SMC\(-\)IS\(-\)PID adjustment time is 2.092 s. SMC\(-\)IS\(-\)PID can reduce the occurrence of \"oxygen deprivation\" better than the other three control methods, and the sliding mode integral separation PID control method provides a superior control impact.  
From Figure 12, the sliding mode integral separation PID has a smaller overshoot and less oscillatory ripple compared to PID, integral separation PID, and sliding mode control. SMC has a peak time of 4.0814 s, an overshoot of 0.808% (T\({}_{\text{fc}}\) = 345.772 K), and an adjustment time of 41.817 s. SMC\(-\)IS\(-\)PID control has a peak time of 6.912 s, an overshoot of 0.134% (T\({}_{\text{fc}}\) = 343.469 K), and an adjustment time of 40.521 s.  
As can be seen from Figure 13, for a rapidly changing variable such as pressure, the differential pressure oscillates under conventional PID control with IS\(-\)PID control. The maximum differential pressure under traditional PID control is up to 10.938 kPa, and the maximum differential pressure under IS\(-\)PID control is up to 10.53 kPa, both of which deviate from the set value of differential pressure by a large amount, but the overall oscillation amplitude of IS\(-\)PID is much smaller than that of traditional PID. The oscillation can be basically eliminated by using SMC\(-\)IS\(-\)PID. According to the change of differential  
Figure 14: SMC\(-\)IS\(-\)PID controlled pressure difference diagram of anode and cathode pressure.  
Figure 13: Effect diagram of ca–an polar pressure difference controlled by SMC\(-\)IS\(-\)PID.  
pressure\(-\)setting value in Figure 7, the fastness of SMC\(-\)IS\(-\)PID is poorer than that of conventional PID and IS\(-\)PID while there are step variations in the load current. The SMC\(-\)IS\(-\)PID adjustment time varies from 6.136 s to 7.29 s, the IS\(-\)PID adjustment time is about 2.94 s, and the conventional PID adjustment time is 3.135 s. Overall, SMC\(-\)IS\(-\)PID control performs better than the other control strategies used in this paper.  
As shown in Figure 14, the cathode and anode pressure under SMC\(-\)IS\(-\)PID control is more stable, essentially oscillation\(-\)free, and has less pressure fluctuation compared to IS\(-\)PID and PID. Table 2 displays a comparison of the various strategies' performances.