Control of multi-temperature transport systems

Abstract

Multi-temperature transport systems hold substantial promise for improving supply chain efficiency in the distribution of temperature-sensitive goods such as food and pharmaceuticals. By enabling simultaneous transport of products with different temperature requirements in separate, temperature-controlled compartments, these systems can reduce mileage and the number of delivery stops, and enhance the overall efficiency and flexibility of logistics operations. However, conventional systems face major challenges, including high refrigerant emissions, high energy consumption, and product spoilage due to inadequate temperature regulation. This raises significant economic and environmental concerns.This work addresses these challenges by developing a novel, more sustainable system architecture for cooling and heating, along with an advanced control strategy for accurate temperature regulation of the compartments. The proposed solution incorporates an indirect heat pump system with secondary loops, which significantly reduces refrigerant charge and leakage potential. The use of the natural refrigerant propane further minimizes emissions. Additionally, the secondary loops can be utilized as thermal storage, enhancing system flexibility and enabling optimized control under dynamic operation. The sizing of the secondary loops' thermal capacity was investigated through closed-loop simulations, allowing for optimal sizing tailored to the control concept, thereby significantly reducing energy consumption and improving temperature compliance. The cascaded system architecture with two heat pumps enables temperature regulation of three compartments: one cooled, one heated, and one capable of both, thereby improving operational flexibility across various ambient conditions. Serving as the foundation of the developed control concept, a scalable, control-oriented model is developed and experimentally validated using a laboratory test bed. The nonlinear model is exactly linearized and decoupled via feedback linearization, enabling the application of linear control techniques for independent temperature regulation of each compartment. A two-degree-of-freedom (2DOF) controller is implemented, comprising trajectory planning for prescribing desired closed-loop dynamics, a feedback controller for disturbance rejection, and an input transformation that maps virtual control inputs of the feedback-linearized system to the physical inputs. The controller also integrates actuator constraints and enables prioritizing critical compartments when full temperature compliance in all compartments is infeasible. Robustness analysis using Lyapunov methods and simulations confirms resilience to parameter uncertainties and unknown disturbances. Experimental analysis demonstrates that the system operates with only 287 g of propane refrigerant and achieves a 40–77% reduction in compartment temperature deviations compared to industry-standard control methods. Hence, the proposed approach could substantially enhance the sustainability and economic performance of multi-temperature transport by reducing refrigerant emissions, lowering energy consumption, and mitigating product losses due to temperature violations during transport.