Optimal on-off control of refrigerated transport systems

This paper presents a hysteretic on-off control scheme with optimization algorithms for temperature regulation in refrigerated transport systems. A nonlinear dynamic refrigerated transport system model, which consists of a refrigeration unit and a cargo space, is developed. The model serves as an analytical tool for control design. An optimal on-off control strategy is developed based on the time domain analysis of the temperature oscillations. A cost function involving temperature variations from the set-point, energy consumption and average compressor on-off cycling frequency is introduced for minimization. Choices of weighting values in the cost function give the flexibility of the control approach to meet different requirements. Simulation examples are presented that demonstrate the ability and robustness of the proposed method in achieving tighter temperature regulation and higher system efficiency control in transport refrigeration systems. The simulations are augmented by experimental validation via a novel hardware-in-the-loop load emulation approach.