Design and analysis of electric vehicle thermal management system based on refrigerant-direct cooling and heating batteries

A thermal management system (TMS) based on R134a refrigerant is proposed, which not only meet the thermal requirements of cabin, but also refrigerant-directly cool and heat battery. Compared with the traditional electric vehicle (EV) TMSs, an electronic expansion valve (EXV) is equipped after the battery cooling/heating plate in the refrigerant branch circuit. The mainly working modes of the TMS and their control methods are described in detail. The paper applies mathematical one-dimension simulation method to analyze the feasibility of mainly working modes, including battery preheating mode, mixed heating mode, low-temperature mixed heating mode. The results show that the TMS is completely feasible to balance the heat distribution between cabin and battery by controlling the EXVs opening. In the battery pre-heating mode, the relationship between refrigerant state of cooling/heating plate outlet and the battery temperature uniformity is analyzed, and a control strategy to improve the battery temperature uniformity is proposed. In low temperature environment, when the TMS switches from cabin heating mode to mixed heating mode, the cabin air temperature will drop sharply. This is because the battery temperature is too low, that pressure of TMS is too low to maintain the heating demand of the cabin.