Continuing from last week’s article, this week we are going to discuss other parameters.

On the basis of the above-mentioned single cell heat generation model, the battery pack model was established by using SOLIDWORKS software to simulate the heat production and the battery pack under different usage conditions.

The following figure shows the battery temperature change curve under the continuous acceleration state (0.6C discharge for 10min, 0.8C discharge for 5min, 1C discharge for 2min). From the test results, it can be seen that the maximum temperature rise of the battery pack at the end of the test is 3.99℃, The maximum temperature difference in the battery pack is 2.11°C, which is lower than the maximum temperature rise. In addition, it is found that although forced air cooling is used for heat dissipation, most of the air flow will flow through the upper part of the battery, and only a small amount of gas will pass through the interior of the battery pack, which affects the heat dissipation effect of the battery pack.

The following picture shows the temperature change of the battery pack during the continuous deceleration of the electric vehicle. During the deceleration process, the discharge current of the battery pack will drop from 2C to 0.5C in steps. As can be seen from the figure, although the current continues to decrease, the heat generation rate of the lithium-ion battery decreases significantly, but due to the poor cooling effect, the heat inside the battery cannot be taken away in time, and the temperature of the battery still shows a continuous upward trend. At the end of the deceleration, the maximum temperature rise of the battery pack When the temperature reaches 5.22°C, the maximum temperature difference in the battery pack is as large as 3.73°C, which indicates that although the discharge current continues to decrease during the deceleration process, the cooling system of the battery pack still has to continue to work until the temperature of the battery pack returns to normal temperature.

Pulse discharge is also a common situation in the use of electric vehicles. The temperature change of the battery pack under pulsed conditions is studied. From the test results, the maximum temperature rise of the battery pack reaches 5.27 ℃, and the maximum temperature difference within the battery pack is 2.88℃.

The test results show that the charge-discharge rate has the greatest influence on the heat generation power of the lithium-ion battery. The larger the rate, the greater the heat generation power, by the ambient temperature. The higher the ambient temperature, the smaller the heat generation rate. The least impact is the battery SoC . , in the range of 70%-90% SoC, the higher the SoC , the greater the heat generation power. In the temperature study of the battery pack, it was found that no matter in the continuous acceleration, continuous deceleration and pulse discharge modes, the battery pack will generate a significant temperature rise, and the highest temperature rise is concentrated in the central position of the battery pack, and the airflow generated by forced air cooling and heat dissipation Most of it flows over the top of the battery pack, resulting in poor heat dissipation.