Experimental Evaluation of a 2DOF Controller for a Novel Multi-Temperature Transport System

Multi-temperature transport systems offer a significant opportunity to improve supply chain efficiency by enabling the simultaneous transport of goods with diverse temperature requirements. However, these systems present critical environmental challenges due to high energy consumption, refrigerant leakage, and the significant amount of goods being damaged or lost due to inadequate temperature control. To address these issues, this study proposes a novel indirect cascade multi-temperature transport system with two temperature-controlled compartments. The design features a compact, well-sealed refrigeration system with reduced refrigerant charge and utilizes the natural refrigerant propane. A nonlinear control strategy based on feedback linearization is introduced to decouple system dynamics and precisely regulate compartment temperatures. Specifically, a two-degree-of-freedom (2DOF) controller, consisting of a feedforward trajectory planning algorithm and a feedback controller, is implemented. Additionally, an optimization-based input transformation allows prioritization of specific compartments when actuator limitations prevent accurate tracking of all compartment temperatures. The control approach was experimentally evaluated on a test bed and compared with a conventional proportional-integral (PI) controller. Across the conducted experiments, the proposed 2DOF control law reduced temperature deviations during normal operation by 40% to 77%, clearly highlighting its quantitative superiority over the conventional approach.