Analysis on Thermal Management Technology of
Pure Electric Vehicle Power Battery
Power battery thermal management technology
1. Battery cooling
Generally, the power battery cooling methods of pure electric vehicles mainly include air cooling, liquid cooling and direct cooling.
1) Air cooling (air cooling) technology uses natural wind or cold air generated by the vehicle refrigeration system to remove heat through thermal convection or heat conduction to achieve battery cooling. Air cooling technology has the characteristics of simple system, low cost and easy maintenance, and is widely used.
2) Liquid cooling technology uses liquid as the heat transfer medium, and the liquid takes away heat when flowing through the pipes inside the power battery. The liquid used in liquid cooling is mostly coolant, which circulates in the vehicle cooling system. The heat carried away by the coolant is lost to the air through the radiator. Some vehicles are equipped with a heat exchanger called a Chiller in the cooling system to couple the vehicle cooling system and the refrigeration system to increase the system cooling effect. Compared with air cooling technology, liquid cooling technology has the characteristics of strong cooling capacity, good uniformity and fast speed.
3) Direct cooling technology uses the refrigerant in the refrigeration system to directly take away the heat from the power battery. A set of expansion valve and evaporator are installed inside the power battery. The refrigerant evaporates and absorbs heat in the evaporator. Since direct cooling technology does not have the heat exchanger found in liquid cooling technology, direct cooling is more efficient. However, when the power battery is cooling, part of the refrigerant in the refrigeration system needs to be removed, which will affect the cooling effect of the passenger compartment and reduce comfort.
2 Battery heating
There are two main types of power battery heating technologies: battery self-heating and the use of external heating elements. Battery self-heating, as the name suggests, uses the heat generated by the battery during charging and discharging to increase the battery temperature. However, this method has slow heating efficiency and has been basically abandoned.
The main use of external heating elements is heating film and PTC. The heating film is close to the surface of the battery module and generates heat to increase the battery temperature when power is supplied. Battery heating methods are similar to cooling methods, and there are three types: air heating, water heating and refrigerant direct heating.
3 Thermal management system
When the battery is cooled and heated, different methods can be selected independently. However, as the integration of vehicles becomes higher and higher, higher requirements are also put forward for the vehicle thermal management system. Therefore, thermal management systems have emerged that can both cool and heat the battery. Some vehicles have even developed highly integrated thermal management systems using heat pump air conditioners, which combine the vehicle cooling system, power battery cooling/heating, and passenger compartment cooling and heating. The three major systems are organically combined.
Vehicle thermal management system case
1. Thermal management system architecture
The thermal management system architecture of a certain pure electric vehicle is shown in Figure 1. This thermal management system uses a heat pump air conditioner to achieve the organic unity of direct cooling and heating of the battery, cooling of the electric drive system, and cooling and heating of the passenger compartment. In the electric drive circuit, a separate water cooling circuit is set up, which is connected to the heat pump system through a plate heat exchanger for heat transfer, which can realize waste heat recovery and stall heating functions; in cold winter, in order to solve the problem of poor heating effect of heat pump air conditioners, matching PTC to increase the heating effect of the passenger compartment. The thermal management system enables cooling and heating needs in multiple modes.
2. Principle of thermal management system
Because the system has multiple working modes, this article only introduces the working principle of cooling and heating modes where the battery or passenger compartment needs to be cooled.
1) Principle of power battery cooling. When the power battery temperature is high and needs to be cooled, the air conditioning and refrigeration solenoid valve, air heat exchange solenoid valve, battery electronic expansion valve and battery cooling solenoid valve in the system are opened (the battery heating solenoid valve is closed), and when the refrigerant flows through the battery electronic expansion valve , after throttling and expansion, it evaporates and absorbs heat in the battery pack plate heat exchanger, taking the heat away to achieve the purpose of battery cooling. If the passenger compartment also needs cooling at this time, you only need to open the refrigeration electronic expansion valve (the air conditioning and heating solenoid valve is closed), and part of the refrigerant will evaporate and absorb heat in the evaporator in the car to achieve cooling of the passenger compartment.
2) Principle of power battery heating. When the battery temperature is low and needs to be heated, the battery heating solenoid valve, battery electronic expansion valve, water source heat exchange solenoid valve, and air conditioning heating solenoid valve in the system open (heating electronic expansion valve, air conditioning and refrigeration solenoid valve, air heat exchange solenoid valve, The refrigeration electronic expansion valve is closed), and the high-temperature refrigerant compressed by the compressor flows through the battery pack plate heat exchanger to heat the low-temperature battery. After heating, the refrigerant temperature decreases, flows through the plate heat exchanger, absorbs the heat of the electric drive circuit, and realizes waste heat recovery. If the passenger compartment also needs heating at this time, you only need to open the heating electronic expansion valve, and part of the high-temperature refrigerant flows through the condenser in the car to release heat to the passenger compartment, and then merges with the battery heating refrigerant in front of the plate heat exchanger to continue participating in the cycle. . If the ambient temperature is very low, the system turns on the PTC auxiliary passenger compartment heating.
