“In electric vehicles, the temperature of all system units needs to be continuously monitored. High current will cause loss and generate corresponding heat, especially at the contacts. TDK has now developed a special high-voltage NTC temperature sensor for measuring connectors.
In electric vehicles, the temperature of all system units needs to be continuously monitored. High current will cause loss and generate corresponding heat, especially at the contacts. TDK has now developed a special high-voltage NTC temperature sensor for measuring connectors.
Nowadays, high-voltage batteries used in electric vehicles (xEV) have a rated voltage of up to 1000 V, so all system components must have the corresponding high-voltage capability. When achieving high drive power (some even more than 100 kW) through inverters and motors, hundreds of A of current will be generated. Together with line resistance and contact resistance, these high currents will cause a large amount of power dissipation and related heat loss, because power consumption is the square of the current: PV = I2 x R. This clearly shows that even a small resistance in the milliohm range will produce relatively large losses, so the temperature may rise critically. For example, if the resistance of the contact point is 10 mΩ and a current of 100 A is applied, the result will be a power consumption of 100 W, which will quickly lead to overheating. This is why the key contact points in the xEV-such as the connector between the battery and the motor inverter-must be thermally monitored, and the current must be reduced in time when overheating is about to occur. NTC-based temperature sensors can be used to monitor the temperature of the critical point and initiate current derating technology. Figure 1 illustrates its control principle.
Figure 1: The control principle of a temperature monitoring unit with corresponding current derating.
xEV’s high requirements for NTC temperature sensors
Electric vehicles put forward completely different requirements for the development and design of NTC temperature sensors, especially their integration into high-voltage systems. These include:
Fast response time
High temperature stability
Can be directly integrated into the connector
Under high temperature and high pressure, the design challenge focused on finding a material with both high electrical insulation properties and excellent thermal conductivity, and developing an integrated NTC component design. In addition, it should provide high temperature stability. The special ceramic bushing integrated with the sensor chip can realize these characteristics at the same time. Figure 2 illustrates the temperature sensor developed by TDK.
Figure 2: New temperature sensor for integration in the connector.
The use of ceramic bushings integrated with NTC components can achieve the required high voltage resistance and fast response time.
Innovative TDK temperature sensor meets all requirements
Tests have proved that the newly developed TDK temperature sensor can cope with the stringent requirements of electric vehicles. Under the high voltage test, the sensor reached a 5 kV DC dielectric strength-significantly higher than the 1 kV DC system voltage. In addition, it also has fast response time characteristics, especially in the case of sudden overheating, it is particularly important to reduce the current in time. The recorded τ value (63%) under typical installation conditions is much lower than that of the sensor. The upper plastic buckle part of the sensor is designed to meet different customer installation requirements, such as screw-in, clamp-in or clamp-in.
All in all, TDK’s new sensors have better electrical, thermal and mechanical properties, which help make electric vehicles safer and more efficient.
Figure 3: Excellent thermal insulation and fast response time test results