Control of a Hybrid Thermal Management System: A Heuristic Strategy for Charging and Discharging a Latent Thermal Energy Storage Device

The use of a real-time controller for managing the recharging and discharging strategy of the thermal energy storage (TES) device in a hybrid thermal management system (TMS) is critical to realizing the intended performance benefits of such systems. For systems involving rapid cooling of power electronics, such as increasingly electrified air vehicles, new control strategies are needed that can accommodate (1) faster timescales associated with the TES dynamics and (2) limited knowledge of upcoming heat loads. This paper considers a hybrid TMS consisting of a single-phase cooling loop and a phase change material-based TES device. Unlike the model predictive control (MPC) and other optimal methods commonly used to control such systems, this paper implements a heuristic logic-based controller leveraging a higher-order TES model to gain additional knowledge of the internal temperature distribution of the TES. The controller regulates the temperature of the surface of a cold plate attached to a heat source that produces a transient heat load disturbance signal. Additionally, with no knowledge of upcoming disturbances, the controller must manage and conserve the state of charge of the TES device, specifically determining when it is possible to recharge and discharging only when necessary. A simulated case study demonstrates that the controller successfully maintains the cold plate temperature below a critical upper limit of 45°C during a 250 second simulation, with the exception of a 2 second period during the largest heat pulse (6 kW) when the upper limit is exceeded. Furthermore, it is shown that in order for a conventional TMS without TES to maintain the cold plate temperature below the same upper limit, the conventional TMS needs both a heat exchanger and fluid tank volume four times the size of those included in the hybrid TMS. During the same 250 second simulation, the oversized conventional TMS also exceeds the upper limit temperature during the 6 kW heat pulse, albeit for 5 seconds instead of 2; this is due to the slower dynamics of the heat exchanger as compared to those of the TES.