  Electrolysis systems use proportional-integral-derivative (PID) temperature
controllers to maintain stack temperatures around set points. However, heat
transfer delays in electrolysis systems cause manual tuning of PID temperature
controllers to be time-consuming, and temperature oscillations often occur.
This paper focuses on the design of the PID temperature controller for an
alkaline electrolysis system to achieve fast and stable temperature control. A
thermal dynamic model of an electrolysis system is established in the
frequency-domain for controller designs. Based on this model, the temperature
stability is analysed by the root distribution, and the PID parameters are
optimized considering both the temperature overshoot and the settling time. The
performance of the optimal PID controllers is verified through experiments.
Furthermore, the simulation results show that the before-stack temperature
should be used as the feedback variable for small lab-scale systems to suppress
stack temperature fluctuations, and the after-stack temperature should be used
for larger systems to improve the economy. This study is helpful in ensuring
the temperature stability and control of electrolysis systems.
