Thermal sensors are used throughout electric vehicles (EVs), including in the battery pack, charger, charging handle, traction inverter, motor, dc/dc converter, passenger cabin, and under the hood. These sensors are among the most important components in EVs.
This FAQ reviews the many uses of thermal sensors and closes with a review of the importance of sensor accuracy.
Batteries and charging
Battery systems can be particularly problematic. EV battery systems are complex and include electrochemical, electronic, and mechanical components — all requiring temperature monitoring. There are several places to monitor temperature in the battery and charger system including (Figure 1):
- Battery modules and cells
- Battery pack thermal management system
- Electronics and busbars in the onboard charger (OBC) and external chargers
- Charger cable and connectors
- Control and monitoring systems in external chargers
Figure 1. EV thermal sensors are placed in several locations, including in the vehicle’s battery and charger system. (Image: TDK Electronics)
If not monitored properly, fast charging can result in overheating of batteries, charging cables, and connectors. Heat presents a major hazard to EV batteries, but cold can also be damaging.
Various lithium-ion chemistries are used in EV batteries, each with their own thermal management specifications. Generally, these batteries have an optimal operating temperature range of 10° to 40° C. But it’s not that simple. The monitoring system must adjust the battery’s charge and discharge based on certain key temperatures.
- Below 0° C, the battery will deliver significantly less power, so the vehicle’s acceleration and driving range could be damaged if overused.
- Between 0° and 10° C, the battery might not be damaged but its performance will be impaired.
- Operation above about 40° C can lead to damage.
- Between 70° and 100° C, thermal runaway can initiate fire and the battery’s destruction.
Motor monitoring
The traction motors in EVs are tough but not indestructible. They have a preferred operating temperature range. Depending on the design, the optimal temperature for those motors can be between 90° and 95° C. Above 95° C, the vehicle’s motor will become less efficient and can be damaged.
The temperature sensors in the motor are used to monitor:
- Winding temperature
- Oil temperature
- Coolant temperature
Traction motors also become inefficient or damaged if operated at low temperatures. In some cases, the motor should be about 15° C before moving the EV. Used at excessively low temperatures increases the motor’s drain on the battery, which may also be experiencing thermal performance limitations.
In-cabin
In-cabin temperature sensors support two functions. They enable the driver and passengers to regulate the heat, ventilation, and air-conditioning (HVAC) system for maximum comfort. They can also interact with the battery management system (BMS), which monitors the battery’s state of charge (SOC) and estimates the remaining driving range.
The energy consumption of the HVAC system can be combined with calculating the remaining driving range, alerting the driver if the HVAC system must be adjusted to extend the range. That can be particularly useful if the vehicle is driving using active navigation to a destination and knows the remaining time and distance. The vehicle’s control system can compare the remaining range with the distance to the destination and the HVAC energy consumption to determine if any adjustments are required.
Exterior and under the hood
Typically, external temperature sensors are positioned under the hood of a vehicle. In an EV, these sensors inform the central control system about the operating environment and help it manage and balance the cooling and heating of the various EV system elements to achieve maximum overall performance. They also inform passengers about the outside temperature when they leave the vehicle.
Sensor accuracy
Using temperature sensors with the necessary accuracy is an important consideration, especially in applications like battery charging and the powertrain. These systems are implemented with advanced power semiconductors like gallium nitride (GaN) and silicon carbide (SiC), enabling smaller, lighter-weight solutions with higher power densities. GaN and SiC power semiconductors can also operate at higher temperatures than silicon devices.
However, increasing the operating temperatures of power converters can be challenging since other components (such as passive devices) are usually damaged by too high temperatures. Temperature monitoring in these systems includes a safety margin to account for sensor accuracy limitations, handle possible thermal runaway, and protect system operation.
Replacing temperature sensors that have an accuracy of 3° C with 1° C accurate devices can enable chargers, inverters, and other power converters to operate safely closer to the thermal design limit (Figure 2). That smaller safety margin can support higher-density power converter designs while ensuring reliable operation. Applications like exterior and in-cabin temperature monitoring may not benefit from using higher-accuracy sensors.
Figure 2. Using higher accuracy temperature sensors can enable power converters to operate with less safety margin. (Image: Texas Instruments)
Summary
EV thermal sensors are indispensable to safe, efficient, and comfortable vehicle operation. They’re positioned in several places inside and outside of electric vehicles.
References
- 7 places for electric car temperature sensors in vehicle design, Amphenol
- How to Maximize Powertrain Efficiency and Reliability with High-accuracy Temperature Sensors, Texas Instruments
- Reliable temperature monitoring during the charging process for xEV batteries, TDK Electronics
- Temperature Sensors in E-Mobility Applications, Yageo
Images
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Filed Under: FAQs, Sensors