In winter, electric cars have to bring the interior and the battery system to the right temperature. This double task demands a lot of energy from them. Cold outside temperatures exacerbate the problem and impair the performance of high-voltage batteries. However, there is no reason to worry about Audi's electric models losing too much range: with intelligent thermal management, the brand ensures the outstanding performance and range of its cars; Special protective mechanisms guarantee a long battery life. In an interview, Pierre Woltmann, head of thermal management for high-voltage batteries at Audi, and Thomas Anzenberger from thermal management for virtual function development explain how the company with the four rings effectively masters the challenges of winter operation.
Do drivers of electric Audi models have to reckon with restrictions in winter?
Thomas Anzenberger:I can answer this question with a resounding no. The size of our high-voltage batteries leaves unfounded doubts about performance and autonomy in winter. Our intelligent thermal management always chooses the most efficient methods to properly heat the register and the interior in winter. As a result, high-voltage batteries have a long service life if our customers are prepared for all seasons via so-called AC charging stations or a home wall box. This feature is especially useful in winter. It does not damage the cells and at the same time minimizes the loss of range, since the battery is already in the optimum temperature range and therefore does not have to get that hot.
How does cold affect a high-voltage battery?
Pedro Woltmann:The performance of a high-voltage battery essentially depends on the state of charge and the temperature. The colder it is, the less power the battery can deliver. Electrochemical processes contribute to this. At low battery temperatures, the internal electrical resistance of the battery increases and the usable capacity decreases. We conserve the battery by releasing less power at lower temperatures. In addition, the battery can absorb waste heat from liquid-cooled high-voltage components such as power electronics, drive system and charger and be heated directly by a coolant heater.
What effects does cold have on the cargo?
Woltmann:If the battery temperature is low, the charging process may take longer. For this reason, the battery should get warm while charging, ideally even on the way to charging. By connecting to the charging point, the vehicle automatically communicates with the power source.
In this way, the charging point knows how much current the battery can currently absorb. This is how we ensure that the battery is not overcharged. When charging, the battery draws the electricity it needs to heat up from the charging station.
What is the task of thermal management?
Anzenberger:Basically, the thermal management is responsible for the distribution of heat flows between the drive, high-voltage battery and interior. Our heat pump system in particular has proven itself in this context. Converts energy from the powertrain or from the ambient air. This is the heat that is available to the battery or, in winter, to the interior. The use of ambient air as a source of energy is relatively new: we use it to compensate for the dwindling waste heat from the drive train, which is working more and more efficiently. This gives us access to two independent systems via the powertrain and the ambient air, which we use to heat the interior and the high-voltage battery.
How is the battery and interior temperature controlled while driving?
Anzenberger:In order to ensure a reliable heat supply even in very cold temperatures, our heat pump system, which is integrated in most of our electric models, integrates additional high-voltage heaters into the operating strategy. This ensures a comfortable interior even in extreme situations and quickly establishes the ideal battery temperature of around 25 to 30 degrees Celsius (77 to 86 degrees Fahrenheit) for maximum performance. For the particularly cold northern countries, a second electric heater is available in our winter package. An additional electric bicycle heater is also available as an option on some models.
Woltmann:If our customers want to drive with maximum efficiency in cold outside temperatures, the thermal management algorithm warms the battery at lower temperatures, thereby releasing less drive power but also increasing the vehicle's range.
What other technical solutions has Audi developed to make the high-voltage battery independent of temperature influences?
Woltmann:As an interface to thermal management, we offer so-called preconditioning, which has a positive effect on both the battery and the interior. The exact departure time can be set with the charging and departure timer directly in the vehicle or with the myAudi app. As a result, the automatic charging process charges the battery to the preset level and at a favorable temperature as close to the departure time as possible. In this way, the loss of autonomy due to battery heating is significantly reduced. In addition, the pre-air conditioning regulates the temperature in the vehicle interior to the desired level before departure.
Anzenberger:insidee-tronGT quattro2y RSe-tronGT3, the conditioning for the charging process even works automatically while driving in order to be able to use fast charging stations, i.e. when thee-tronRoute planner is used in these models. Depending on the outside air temperature, the intelligent thermal management brings the battery into an optimum temperature range for charging, in addition to preconditioning while driving and before charging begins.
This additional mobile preconditioning of the battery in thee-tronGT quattro2y RSe-tronGT3guarantees the best and fastest possible loading results.
How does Audi reduce the range loss caused by heating the interior?
Woltmann:Compared to a combustion engine, an electric car has much less waste heat and energy available for heating. The heat generated by the battery, the electric motor and the power electronics can be conducted into the house with a heat pump. Basically, the heat pump works like a refrigerator, only in reverse. The more waste heat is available, the more efficiently the pump works. At best, you can generate up to three kilowatts of heat from one kilowatt of electrical power. This technology is very useful, especially in winter, as it replaces a thermoelectric heating element. Depending on the outside temperature, the heat pump can achieve a greater range than conventional heating.
What can customers do who do not have a garage available?
Woltmann:If you need more range when you get in, you should prepare it in advance. Ideally this should be done by AC charging, which is generally more efficient than DC charging as there is less power loss due to lower currents. AC charging is also smoother as it doesn't put as much strain on the battery. With AC charging, less current flows. The battery can also absorb this at very low temperatures, which means that the battery does not have to get that hot. Regardless of AC or DC power, charging must be done immediately before starting a ride via the output timer to use the highest battery temperature for range gain, or immediately after the ride to use the highest battery temperature to charge faster and more. efficient.
What happens to a cold battery in a fast charging station?
Woltmann:Regardless of the model, the vehicle's algorithm recognizes when the car is charging at a DC fast charging station. Currents are released regardless of the state of charge and temperature. With the active heating we have implemented, we significantly reduce the charging time in cold temperatures.
When do high-voltage batteries reach their limits?
Woltmann:In order to protect the battery, we no longer emit electricity from a core temperature of 30 degrees below zero (-22 Fahrenheit). But for that to happen, the car would have to be exposed to such extreme temperatures over a long period of time. Of course it is also possible to drive onee-tronModel with sufficient charge level and preheated high-voltage battery at outside temperatures of minus 30 degrees.
What additional tips can you give for the winter from a technical point of view?
Anzenberger:Using the on-board computer and range monitor in the Audi MMI with range prediction while driving, customers can see directly how much range they will gain if, for example, the interior temperature drops. The range can be increased with the range mode. This slightly limits comfort functions, drive power and top speed.