Modelling and cooling power control of a TES-backed-up vapour-compression refrigeration system

TL;DR

This work tackles modelling and control of a thermal-energy-storage system based on PCM, integrated with a vapour-compression refrigeration facility. It develops a joint, multi-time-scale model that captures fast refrigeration-cycle dynamics and slow TES heat-transfer processes, and proposes a decentralised cooling-power control using PI regulators with a decoupling strategy and a cascade for expansion valves. Key contributions include: (i) a combined fast-slow model of the TES-backed refrigeration system, (ii) characterization of eight operating modes and their nonlinear power limits, and (iii) a decoupled control framework with RGA-informed input–output pairing that achieves fast reference tracking for multiple cooling powers. The approach supports real-time scheduling and economic/efficiency-aware operation, with simulations indicating robust performance and guiding future experimental validation and deployment.

Abstract

This work addresses the modelling, power control, and optimization of a thermal energy storage (TES) system combined with a vapour-compression refrigeration facility based on phase change materials (PCM). Given a novel design of a PCM-based TES tank and its interconnection with an existing refrigeration system, the joint dynamic modelling is first studied, exploring the different time scales that coexist at the interconnected system. Diverse operating modes are defined, according to the intended use of the TES tank as a cold-energy buffer to decouple cooling demand and production, whereas the static characteristic and power limits are calculated and show the high coupling between the main cooling powers involved (TES charging/discharging power, and direct power production at the evaporator). In this light, a decoupling control strategy is proposed, where the low-level controllers are simply PI regulators and the refrigerant/secondary mass flows are considered as virtual manipulated variables, applying a feedforward-based cascade strategy. The control performance is evaluated through a thorough simulation that includes all operating modes, where the reference tracking is shown to be fast and reliable enough to address high-level scheduling strategies, where the references on the main cooling powers are intended to be imposed considering economic and efficiency criteria.

Figures (20)

• Figure 1: Schematic diagram of the configuration proposed including a TES tank in parallel with the evaporator of a vapour-compression cycle.
• Figure 2: Schematic diagram of the experimental refrigeration plant.
• Figure 3: Schematic picture of the proposed configuration of the TES tank and input-output conceptualisation.
• Figure 4: Plan schematic view and picture showing the actual distribution of pipes and PCM cylinders within the TES tank.
• Figure 5: Temperature-specific enthalpy diagram of the PCM.