Transient modeling of a vapor-compression portable cooler based on pull-down identification: assessment of ON-OFF and PI-PWM control strategies

This study presents a transient model of a vapor-compression refrigeration system to predict the cycling behavior of a portable cooler under cabinet temperature control. The system is represented using lumped thermal capacities for the evaporator, condenser, cabinet, and compressor, with transient integration performed using a generalized θ -method. The model was validated against experimental pull-down test data, demonstrating its ability to accurately predict the transient thermal response of a portable cooler. Two cabinet temperature control strategies were investigated: (i) a conventional hysteretic ON-OFF controller and (ii) a pulse-width modulation controller with a proportional integral duty-cycle scheduler (PI-PWM). The PI-PWM strategy incorporates a symmetric deadband, anti-windup compensation, duty slew rate limiting, and minimum ON/OFF times to satisfy the operating constraints of the compressor. The performance was evaluated in terms of temperature regulation (setpoint error and maximum deviation), power demand, and accumulated energy consumption at ambient temperatures of 25, 32, and 43 ∘ C. The ON-OFF controller provided a rapid pull-down but produced larger cabinet temperature oscillations and restart temperature peaks compared to the other controllers. In contrast, the PI-PWM strategy distributed cooling more uniformly, reducing cabinet temperature fluctuations while lowering the total energy consumption by approximately 35%, 32%, and 19% at ambient temperatures of 25, 32, and 43 ∘ C, respectively, compared with the ON-OFF controller. The proposed framework demonstrates that a transient model identified and validated using pull-down test data can be effectively applied to evaluate cycling behavior and temperature control strategies, providing a practical tool for the design and optimization of portable vapor-compression refrigeration systems.