At present, the electric vehicle power battery is a lithium ion battery. The performance of the lithium ion power battery is sensitive to temperature changes. The loading space on the vehicle is limited, the number of batteries required by the vehicle is large, and the batteries are closely arranged.
In electric vehicles, the cooling system is mainly divided into two parts: one is cooling the components of the drive system of the power system, the vehicle controller and DC/DC, and the other is cooling the power battery and the car charger of the power supply system. This article explores the power battery cooling system.
At present, the electric vehicle power battery is a lithium ion battery. The performance of the lithium ion power battery is sensitive to temperature changes. The loading space on the vehicle is limited, the number of batteries required by the vehicle is large, and the batteries are closely arranged. When the vehicle is running under different driving conditions with high speed, low speed, acceleration, deceleration, etc., the battery will discharge at different rates, generate a large amount of heat at different heat generation rates, plus time accumulation and spatial influence will produce uneven heat accumulation. As a result, the operating environment temperature of the battery pack is complicated and variable.
The cooling performance of the power battery directly affects the efficiency of the battery, and also affects battery life and safety. Since the battery itself generates a certain amount of heat during charging and discharging, the temperature rises, and the temperature rise affects many characteristic parameters of the battery, such as internal resistance, voltage, SOC, available capacity, charge and discharge efficiency, and battery life.
In order to optimize the performance and life of the battery pack, it is necessary to optimize the structure of the battery pack, thermal management of it, increase the heat dissipation facilities, and control the temperature environment in which the battery operates.
Main cooling scheme
Different thermal management systems, different types of components, different weights, different system costs and different control methods make the system achieve different performance. When designing the battery pack thermal management system type, it is necessary to consider the cooling performance requirements of the battery. Combined with the performance and space of the vehicle, the stability and cost of the system are also factors to be considered.
Figure 1 Comparison of advantages and disadvantages of different battery cooling schemes
Different cooling system work
1, air-cooled
There are mainly the following cooling methods for electric vehicle battery packs at home and abroad: air cooling, liquid cooling, and heat pipe cooling. At present, the air cooling method is still the main method, and air cooling is relatively easy to achieve, but the cooling effect is not good.
Figure 2 Schematic diagram of typical air cooling system
2, liquid cooling
Liquid cooling has a good cooling effect, and can make the temperature distribution of the battery pack even, but liquid cooling has high requirements on the sealing of the battery pack. If a conductive liquid such as water is used, the liquid and the battery bill are required. Body separation, which not only increases the complexity of the system but also reduces the cooling effect.
Generally, the cooling system is installed near the battery module. The principle is similar to that of the air conditioner. The cooling system is connected to the single battery module through the pipeline. The cooling fluid (usually ethylene glycol) is circulated in the pipeline, and the single battery module is connected. The heat is taken away, the cooling system cools the glycol, and the excess heat is discharged to the outside through the fan, and the ethylene glycol is circulated again into the battery module to continue to absorb the heat emitted by the battery.
Figure 3 Schematic diagram of typical liquid cooling system
3, heat pipe technology
The heat pipe technology can meet the requirements of high temperature heat dissipation and low temperature preheating of the battery pack. The response is fast and the temperature uniformity is good. As a new cooling method of the battery pack is proposed, it has a certain development and is the key direction of industrial research. However, due to the limitations of layout and volume, there is currently no real car use.
Figure 4 Schematic diagram of heat pipe technology work
From the perspective of existing electric vehicle power battery cooling methods, air cooling has always occupied a major position, especially for Japanese electric vehicles, which basically adopt air cooling systems. With the increasing demand for batteries in the application environment, liquid cooling has become a priority for car companies, such as Tesla, BMW and other brands. China's mainstream electric passenger car companies have also begun to turn to liquid cooling systems, from the medium and long-term trend, liquid cooling will dominate the mainstream.
Battery pack cooling system main components
Different cooling systems have corresponding cooling components: the main components of the air cooling system are fans, and the main components of the liquid cooling system are cooling plates.
Air cooling system components: cooling air duct, fan, resistance wire
The selection of the fan directly affects the cooling effect of the battery pack air cooling system. The selection requirements for the fan are as follows: the air flow rate is determined according to the heat generation rate of the battery; the temperature rise requirement of each module is met; and the fan that meets the requirements is selected based on the air flow required by the system and the pressure drop curve of the system.
Liquid cooling system components: water cooled pipe, cooling pump, cooling valve, cooling plate
The cooling plate is one of the most critical components in the battery-packed liquid cooling system, and the selection of the cooling plate is crucial. The selection of the cooling plate must meet the following requirements: the pressure drop of the cooling plate must meet the customer requirements; the consistency requirements of the cooling water flow; the bursting pressure requirements; the mechanical requirements of the cooling plate; the cooling plate must pass the vibration and impact load test; Tolerance requirements and space size requirements must be met.
There are many manufacturers of battery cooling system components. Most of the main components are provided by traditional electrical companies. At present, battery management system companies and PACK assembly companies also have customized products.
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