As the main energy storage device for loading battery packs on electric vehicles, the battery pack is a key component of hybrid/electric vehicles, and its performance directly affects the performance of hybrid/electric vehicles. At present, batteries generally have disadvantages such as lower energy and specific power, shorter cycle life, and greater use performance due to temperature. Due to the limited space of the vehicle, the heat generated during the operation of the battery may cause uneven temperature and affect the consistency of the battery cells. Thereby reducing the charge and discharge cycle efficiency of the battery, affecting the power and energy of the battery, and in severe cases, it will lead to thermal runaway, affecting system safety and reliability. In order to achieve the best performance and longevity of the battery pack, the battery needs to be thermally managed to control the temperature of the battery pack within a reasonable range.
The main functions of battery thermal management include: accurate measurement and monitoring of battery temperature; effective heat dissipation when battery pack temperature is too high; rapid heating under low temperature conditions; uniform distribution of temperature field of battery pack; battery heat dissipation system and other heat dissipation units match.
The cooling of the battery pack is air-cooled and liquid-cooled. Studies have shown that the air-cooling method is easy to implement, but the battery pack temperature gradient changes greatly, which is not conducive to stable battery operation. The liquid cooling method in which heat is exchanged between the coolant and the refrigerant of the air conditioning system has gradually become mainstream. For the scientific management of the heat problem of new energy vehicle batteries, it is necessary to consider the interaction of multiple systems. The relationship between the systems is shown in Figure 1. The battery pack cooling has different degrees of coupling with multiple systems such as automotive air conditioning systems, motor cooling systems, and engine cooling systems. In this way, when doing battery system temperature control strategy and thermal management, it is necessary to analyze the influence relationship with other systems at the same time.
solution
In order to solve the complex coupling system between the fluid systems in the thermal management of the battery, a one-dimensional simulation model can be built using the evaporation cycle library, liquid cooling library and battery library of Dymola software. To simulate the entire model system and analyze the coupling relationship between different systems, so as to realize the control of complex systems.
Figure 2 Dymola model library
Dymola software has a rich model library, which can be easily built with a base library and a commercial library. The Evaporation Cycle Library covers almost all major refrigerants on the market, with accurate two-phase flow models and heat exchanger models modeled by structure; resistors, diodes, thyristors, which take into account component heat and temperature effects on the electrical performance of the component. Basic component models such as motors; heat transfer element models with heat capacity, heat transfer, convection, radiation, temperature, heat flow boundary conditions, etc.; can be used in liquid cooling systems for battery flow line modeling, component selection, and system performance studies. Models such as pipelines, control valves, thermostatic valves, pumps, fans, heat exchangers, expansion tanks, etc.; Modelon battery banks that take into account differences in battery cells and temperature effects on battery capacity and external characteristics, can be used to analyze battery electricity and heat , life and other aspects of the characteristics.
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