Optimizing Control Algorithm for Indirect Liquid ThermalManagement of Batteries : A Study Executed at Northvolt

Abstract: The vast expansion of intermittent sustainable energy generation has favoured a gradual adoption of lithium-ion batteries in various industrial and automotive applications. Despite its many inherent merits, this storage technology is very vulnerable to temperature variations: the performance and lifespan of LIBs are substantially influenced by their load cycles, thermal behaviours, and operating temperature range. Hence, a good battery thermal managementsystem (BTMS) is essential to ensure the safety, longevity, and excellent performance of these batteries. This master thesis aims to explore and experimentally identify optimal control algorithms for indirect liquid battery thermal management. To enable experiments, the complexity of equipment is first constructed and prepared, including a hydraulic test rig with sensors, the National Instruments hardware for data processing, a reversible heat pump with a variable drive compressor, dummy-cell battery modules, and others. 3 types of battery module configurations are selected for the analysis and comparison: prismatic dummy-cell module with a cold plate (bottom-cooled), cylindrical dummy-cell module with a cooling channel (side-cooled), and cylindrical dummy-cell module with a cold plate (bottom-cooled). So, the comparison is made between two cell types (prismatic vs cylindrical), and two battery coolingmethods (side-cooled vs bottom-cooled). The battery load cycles are emulated by heat generation with cartridge heaters inside the cells. The control of the cooling service is executed by three mechanisms: coolant flow rate, coolant inlet temperature, and battery temperature window. The selected control strategies are compared for the following aspects: total systemefficiency, cooling response time, thermal resistance, impact on aging, adaptability, etc. Based on the results, optimal control algorithms are proposed and justified for certain applications or particular operating conditions. Moreover, as a secondary focus of this project, a chiller with avariable speed compressor is thoroughly examined experimentally to verify the optimizationstrategies for vapor-compression-cycle-based indirect liquid refrigeration. The suggestions for future work of this project could involve investigation of live batteries varying their charge/discharge cycles, operating the batteries and the chiller in a climate chamber at diverse ambient temperatures, and designing advanced controllers and automation instruments to implement these findings for battery thermal control strategies.