Control and Dynamic Modeling of Vapor-Compression Systems

Vapor compression cycles are predominantly used in air-conditioning, heat pump and refrigeration equipment. A good understanding of transient behaviors of vapor compression systems is critical to appropriately design the controllers in order to have reliable system operations. This is particularly important with the growing employment of variable-speed drives in vapor compression systems, since the strong nonlinear couplings between the various components may cause instability issues during transient operations. One example issue that is commonly encountered is EXV hunting and superheat oscillation. The instability issue gets even worse when the equipment is used to provide grid services.

We are actively researching on development of efficient dynamic models for vapor-compression systems. These models will be leveraged to facilitate development of new control algorithms. Current applications include superheat/EXV stabilizing control and fast load balancing control.

References:

• Liu, H. and Cai, J., Improved Superheat Control of Variable-Speed Vapor Compression Systems in Provision of Fast Load Balancing Services, International Journal of Refrigeration, 2021, preprint. DOI: 10.1016/j.ijrefrig.2021.08.028.
• Liu, H. and Cai, J., A Robust Gray-Box Modeling Methodology for Variable-Speed Direct-Expansion Systems with Limited Training Data, International Journal of Refrigeration, 2021, preprint. DOI: 10.1016/j.ijrefrig.2021.05.007.
• Liu, H., Cai, J. and Kim, D., A Hierarchical Gray-Box Dynamic Modeling Methodology for Direct-Expansion Cooling Systems to Support Control Stability Analysis, International Journal of Refrigeration, 2022, preprint. DOI: 10.1016/j.ijrefrig.2021.10.013.
• Liu, H. and Cai, J., Development of an accumulator liquid-level estimator to enable zero-superheat control and active charge management in vapor-compression systems, International Journal of Refrigeration, 2022.