Analysis of thermal management system for electric drive of new energy vehicles

When driving new energy vehicles, the electric drive system converts the electrical energy of the battery pack into kinetic energy for the motor to rotate. During the energy conversion process, the lost energy is expressed in the form of heat energy. The operating temperature range of automotive motors and controllers is large, and the operating environment is harsh. Overheating of internal components will cause the electric drive system to violate the overall thermal safety goals and even reduce the life of the system. If the electric drive system is not properly protected, the controller may fail due to internal component burnout, and the motor may also suffer irreversible demagnetization. Appropriate thermal protection means that under harsh conditions, once the controller detects that the temperature of a certain position exceeds the limit, it will take power/torque derating measures. Therefore, the thermal protection problem is transformed into real-time acquisition of the temperature of key positions at least in an environment with thermal risks.

1

There are generally two ways to obtain temperature:

The advantage of this method is that the software logic is simple and no modeling and calibration are required. The disadvantage is that the deployment of multiple sensors increases the risk of hardware failure, increases costs, and makes the process more complicated. Sensors cannot be deployed in some locations, such as motor rotors. In addition, the temperature directly measured by the sensor does not represent the temperature of the hottest spot of the component and cannot play a good protective role. The advantage of this method is that the risk of hardware failure is small, but the disadvantage is that the software logic is complex and the calibration is difficult. United Electronics' latest generation motor controller platform Gen3evo has integrated a thermal model, and the controller's internal power module temperature, cooling water temperature and motor rotor temperature are obtained through model calculation. (As shown in the figure below)

Figure 1 Schematic diagram of thermal model

2

Thermal Model Calibration and Validation

The temperature monitored by the controller in real time is the model-calculated temperature rather than the actual temperature. In order to make the model-calculated temperature consistent with the actual temperature, the model needs to be configured with appropriate parameters. Therefore, calibration and verification must be performed to ensure that the calculated temperature is real and valid.

Figure 2 Flow chart of thermal model bench calibration of United Electronics' electric drive system. United Electronics' thermal model calibration adopts automated testing and verification solutions. It uses a high-power bench with a peak power of more than 300kW and a maximum speed of 20,000rpm for calibration. After the test data is acquired, a mature algorithm is used to calculate the temperatures of the motor controller and key positions of the motor. The deviation between the model-calculated temperature and the actual temperature is small, meeting higher precision requirements.

3

Specific applications and customer benefits of thermal models

At present, the controller and motor thermal models of United Electronics have been successfully applied to customer projects with various vehicle topologies including e-bridge, P2, and eDCT. The thermal models have good adaptability and robustness in various environments. Combined with the thermal models of electric drive system products, it can bring the following benefits to vehicle manufacturers:

01 Reduce costs and reduce the risk of hardware failure

Compared with the solution of directly measuring temperature with sensors, using models to calculate temperature and removing redundant temperature sensors can not only reduce the additional hardware costs of vehicle manufacturers, but also enable them to use more functions in combination with related functional software. While reducing hardware sensors, it also reduces the risk of hardware failure of the controller and increases the reliability of the controller and motor products.

02 Ensure performance

Under the protection of the thermal model, vehicle manufacturers can conduct tests under various extreme and endurance conditions, allowing the controller and motor to perform at their maximum performance in the current state without having to worry about over-temperature burnout.

03 Add temperature diagnosis function

When the cooling water flow or temperature is abnormal, the vehicle manufacturer can promptly detect the cooling problem through the temperature indication signal sent by the controller. In case of unexpected emergencies, it can provide timely warning to ensure safety.

04 Ensure vehicle driving safety

When the product is overheated, the controller can send a signal in time to reduce the power of the vehicle. If the temperature continues to rise, the vehicle is not allowed to continue driving until the temperature drops to a reasonable range, fully protecting the personal safety and property safety of the driver.

05 Optimizing torque control

Vehicle manufacturers can achieve more accurate torque control and energy management, and provide drivers with a better driving experience, making users feel more at ease.