# Sliding Mode Integral Separation PID Control for Hydrogen Fuel Cell Systems
## 5 Conclusions  
Aiming at the three key variables affecting the output characteristics of PEMFC (oxygen excess ratio, electric stack temperature, and electric stack cathode-anode differential pressure), the authors of this paper propose a control method for PEMFC systems based on sliding mode integral separation PID (SMC\(-\)IS\(-\)PID) control, which retains the advantages of the robustness of traditional sliding mode control, simplifies the difficulty of controller design on the basis of satisfying the output performance of the fuel cell, and greatly reduces the overshoot of the controller. The correctness and effectiveness of the control strategy above are verified by the self\(-\)developed controller and the constructed 3 kW fuel cell system. The experiments verified the polarization curves of the electric stack of PEMFC, and the experimental results were consistent with the trend of the polarization curves of the electric stack in the simulation and were close to the simulated values, which indicated the correctness of building the experimental system. The effectiveness of the sliding mode integral separation PID control strategy is verified and compared with PID and integral separation PID with sliding mode control. The results show that for the OER variable, SMC\(-\)IS\(-\)PID can achieve no overshooting compared to PID, IS\(-\)PID, and SMC. The SMC\(-\)IS\(-\)PID overshoot is only 0.134% for the stack temperature variable, which greatly reduces the overshoot. For the cathode-anode differential pressure and cathode and anode pressure, SMC\(-\)IS\(-\)PID can realize the system basically without oscillation compared with PID and IS\(-\)PID. In summary, the sliding mode integral separation PID control strategy for controlling the OER, electric stack temperature, and cathode-anode differential pressure in the PEMFC system has a good control effect, and the performance quality is significantly improved. Most of the existing hydrogen fuel cell vehicle controls use traditional PID control; in future research of fuel cell control strategy, the control strategy proposed in this paper can effectively control the whole fuel cell system, helping to solve the existing fuel cell system control single and other problems. In the future, we will consider the practical application of this strategy to existing hydrogen fuel cell vehicles. For fuel cell system research and experimental development (R and D) and application, this strategy can effectively shorten the control R and D cycle, reduce the system R and D cost, improve the system power generation performance, and improve the system service life. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Control** & **Control** & **Peak Time** & **Overshoot** & **Adjustment** \\
**Variables** & **Strategies** & & & **Time** \\ \hline Oxygen & PID & 2.132 s & 13.15\% & 4.57 s \\ excess ratio & IS\(-\)PID & 1.726 s & 10.15\% & 4.356 s \\ (OER) & SMC & 0 & 0 & 12.57 s \\  & SMC\(-\)IS\(-\)PID & 0 & 0 & 5.019 s \\ \hline  & PID & 4.134 s & 0.911\% & 40.027 s \\ Stack & IS\(-\)PID & 5.234 s & 0.578\% & 42.027 s \\ temperature (Tfc) & SMC & 4.018 s & 0.808\% & 41.817 s \\  & SMC\(-\)IS\(-\)PID & 6.912 s & 0.134\% & 40.521 s \\ \hline Cathode–anode & PID & Oscillatory system, Pcamax = 10.94 kPa & 3.135 s \\ differential pressure & IS\(-\)PID & Oscillatory system, Pcamax = 10.53 kPa & 2.940 s \\ (APca) & SMC\(-\)IS\(-\)PID & Basically non\(-\)oscillatory systems & 6.136 s \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Strategies performance comparison. **Author Contributions:** Conceptualization, Q.Y. ; methodology, J.W. and W.H. ; software, X.L. and Z.L. ; validation, Q.Y., J.W. and X.L. ; formal analysis, W.H. ; investigation, Z.L. ; resources, Q.Y. and H.D. ; data curation, X.L. and Z.L. ; writing--original draft preparation, W.H., X.L. and Z.L. ; writing--review and editing, Q.Y., J.W. and W.H. ; visualization, Q.Y. ; supervision, J.W. and W.H. ; project administration, Q.Y. and H.D. ; funding acquisition, Q.Y., J.W. and W.H.