Improved Artificial Protozoa Optimizer-Based PI Control for Temperature and Power Regulation of PCM Thermal Energy Storage

Phase-change material (PCM) thermal energy storage requires effective discharge regulation because the available stored energy and resulting thermal output vary continuously during operation. This study develops an Improved Artificial Protozoa Optimizer (IAPO) for proportional–integral (PI) controller tuning to regulate outlet temperature and released thermal power. IAPO retains the main structure of the original APO while introducing a best-guided Lévy-flight perturbation into the autotrophic and heterotrophic foraging modes. Controller tuning is performed on a nonlinear PCM model previously validated against experimental discharge data, using the integral of time-weighted absolute error as the objective function. For temperature regulation, 25 independent runs show that IAPO reduces the mean ITAE by 6.11% relative to APO and 19.02% relative to Differential Evolution, while exhibiting lower run-to-run variability than APO and DE. Closed-loop comparisons further show the shortest rise and settling times with IAPO for both regulation objectives; for power regulation, the settling time is 11.70% shorter than that obtained with APO. The controller also tracks successive changes in temperature and power references. These results show that the proposed modification improves APO-based PI tuning for the investigated PCM discharge-regulation problems while preserving the simple PI control structure.