Bidirectional charging: Audi A2 e-tron as a mobile energy storage system

With the A2 e-tron, Audi is offering an all-electric entry-level model in the compact class for the first time. Depending on the variant, different energy storage systems are used: an 84 kWh nickel-manganese-cobalt battery or a lithium iron phosphate battery, or LFP for short, with a capacity of 52 or 61 kWh. In the LFP storage systems, the cells are integrated directly into the battery pack in a cell-to-pack design. Due to the higher packing density made possible by this, the energy content and energy density of the HV system can be increased with a reduced space requirement.

The temperature and cooling strategy of the high-voltage battery was a central development area of the A2 e-tron. The thermal management system continuously coordinates the battery temperature, current flow and state of charge during charging and discharging. The control strategy is designed to operate the battery within defined temperature ranges and enable reproducible charging behavior. More precise temperature control during charging and discharging makes a significant contribution to more stable battery behavior. For customers, this means not only a short charging time in everyday life, but also stable, comprehensible and reproducible charging and discharging behavior.

A battery management controller takes over the monitoring and regulation of the battery. In LFP batteries in particular, a flatter Open Circuit Voltage (OCV) characteristic curve of the cells makes it more difficult to precisely determine the state of charge and aging. For this reason, Audi uses an adapted algorithm. The information obtained is incorporated into the calculation of range, charging behavior and operating strategy.

The battery in the A2 e-tron is not only used as an energy storage system for driving, but can also generate additional benefits outside the vehicle, depending on the application.

Vehicle-to-Load(V2L) makes it possible to supply suitable external consumers with electrical energy via the vehicle. This makes the A2 e-tron a mobile and flexible energy source. The Vehicle-to-Home (V2H) function uses the A2 e-tron as a large battery storage system and, in conjunction with a compatible, bidirectional DC wallbox, makes it possible to use the stored electricity for the household.

Depending on the market, vehicle equipment, compatible charging infrastructure, home installation, regulatory requirements and, if necessary, a suitable electricity tariff, the compact Audi will enable Vehicle-to-Grid (V2G) in the future. Energy from the vehicle battery is provided for the public power grid. This makes the battery part of a larger energy system.

With the A2 e-tron, Audi is pursuing the goal of making electric mobility in the compact segment suitable for everyday use, efficient and flexible. The interplay of coordinated thermal management, intelligent charging electronics and advanced battery management ensures stable and reproducible charging behavior. At the same time, bidirectional charging functions extend the battery's range of application beyond driving and thus make the vehicle an active part of the energy system. In this way, the A2 e-tron combines efficient charging, intelligent energy use and a high level of everyday usability in a future-oriented overall concept.