Temperature as an influencing factor: Ensuring safe and efficient EV battery operation with proper control

Ensuring safe and efficient EV battery operation with proper control

Markus Winter

The mobility transition is essentially determined by the battery-powered, electric powertrain – the optimization of the high voltage (HV) battery is therefore an important adjusting screw. The focus is thus on two main aspects of testing: safety and performance. Ideally, both can be improved by deriving valuable findings from observing the thermal behavior. This is a good reason to perform detailed and close-meshed measurements of the temperatures inside a traction battery.

The use of an HV battery in a vehicle requires consideration of many aspects, including of whether safe operation is possible in every conceivable scenario. One emergency that should be avoided at all costs is a “thermal runaway”. In this case, a malfunction of the battery cells leads to a chemical chain reaction and an uncontrolled and unstoppable fire in the battery. If this cannot be predicted and prevented in time, it can lead to considerable damage to property and personal injury. But where should the few (possible) temperature sensors for monitoring be placed in the series production of a vehicle? How to reliably detect critical points – so-called “hot spots”?

Monitoring temperature management

At the same time, the HV battery needs a certain temperature range for ideal function, which is around 15 – 35°C for lithium-ion batteries, for example. To keep this ideal temperature constant, a powerful cooling and heating system must be installed in the battery housing to ensure that the battery neither overheats nor cools down too much. Here, too, there are temperatures to monitor: What is the temperature of the special battery coolant? Is the temperature management system effective and does it cool or heat the battery (evenly) to the desired temperature?

How can many measurement points be fitted into a small space?

Various types of batteries, including cylindrical, pouch or prismatic cells, can currently be found in the traction batteries of electric vehicle manufacturers. In turn, these form battery modules, which are arranged in groups and connected by busbars. The cooling system is routed throughout the system with the objective to optimize thermal conditions.  Flexible measurement technology that offers suitable sensors for a variety of measurement points (between cells, on the busbars, in the coolant, etc.) is required for the necessary measurements during the various development phases. When changing or comparing different systems, the same measurement technology should be used: a considerable advantage in terms of time and cost savings as well as the comparability of the measurement results.

Make as few interventions as possible

In addition to the measurement points on the battery cells, sensors must also be installed on the charging electronics, the busbars and in the coolant. Although this close-meshed monitoring of many temperatures on all components of the HV battery provides a very precise picture of the thermal processes, it also means that a large number of measurement points have to be installed in a very confined space. This presents the testing engineers and instrumentation technicians with new challenges – how can these specifications be implemented without interfering too much with the battery and the housing? After all, the more intact the test specimen – in the case of the HV battery, the housing – is, the more realistic results can be expected from the measurements, as the tightness of the battery housing is an important factor for safe operation. There is also another safety aspect to consider: The entire measurement technology must be HV-safe so that personnel and equipment are protected  according to necessary safety standards.

Measure at up to 512 points – with just one sensor cable

With the HV DTemp measurement system from CSM, comprehensive and precise temperature measurements can be performed reliably in HV batteries. The miniaturized and interference-free IC temperature sensors not only offer a measurement accuracy of ±0.1 °C to ±0.25 °C, but can also be easily applied where ever necessary. Depending on the application, there are individual options for how the sensors can be installed, for example as encapsulated individual sensors or mounted on an ultra-thin flexible circuit – ideal for measurements between different cell types. Four individual sensors can be combined to form a sensor chain and up to 64 sensors can be connected to eight controllers each. The HV DTemp controllers take over the addressing and power supply of the sensors. Like all components of the HV DTemp system, the focus was placed on a compact and robust design. The controllers transmit all signals bundled via a single, sealed pass-thru HV-safe cable to the central unit. This means that the system can be scaled up to 512 measurement points with just a single opening in the battery housing. The central unit controls the entire measurement system and supplies all components with the required supply voltage. All signals are transmitted digitally, which minimizes susceptibility to interference. The measurement data is transferred to the measurement computer via CAN. The HV DTemp measurement system can also be easily integrated into a larger measurement setup for the acquisition of additional values.

Analyze temperature curves precisely and comprehensively

HV-safe temperature measurement at many points in and around the battery is becoming increasingly important with the growing importance of electromobility. One of the difficulties here is the need for many measurement points with as little intervention in the battery as possible. With its flexible and individually applicable sensors, the HV DTemp measurement system makes it possible to measure almost anywhere within the HV battery system, regardless of the cell type and measurement point location. Other areas of application in the HV environment include temperature measurements on other components of the electric drivetrain, for example in the inverter.

 Markus Winter, Product Manager & Product Owner for thermal measurement technology, CSM GmbH