Bidirectional charging places new demands on power electronics and BMS
Bidirectional charging is becoming a key topic in the power and automotive industry worldwide. In the first countries, framework conditions are emerging that enable the step from pilot projects to commercial applications. This shifts the requirements for onboard chargers, power electronics, and battery management systems (BMS): They no longer just have to charge efficiently but also need to act as an integral part of a networked energy system.
How are international regulations and V2G/V2H projects driving the market maturity of bidirectional charging worldwide?
Global regulations and projects are driving bidirectional charging. At EU level, the “Smart Charging Alignment for Europe (SCALE)” project aims to help improve the charging infrastructure and promote the spread of e-cars. In Germany, the path to bidirectional charging was cleared by abolishing double grid fees for feeding electricity back into the grid.
In the US, the Department of Energy (DOE) supports vehicle-to-everything (V2X) initiatives and projects, including via the Vehicle-to-Everything Memorandum of Understanding. Utilities in California are testing compensation models that make feeding electricity from vehicle batteries for fleets back into the grid economically attractive. Numerous vehicle-to-grid (V2G) projects are underway across Europe, including in France, the United Kingdom and the Netherlands. Japan, on the other hand, has been focusing on bidirectional applications for years with vehicle-to-home (V2H) programs, and is driving forward V2G applications that are currently still in the test phase.
Despite different regulatory approaches, the trend is similar. Bidirectional charging is becoming an economic factor and a strategic element in grid integration strategies. The more flexible the electricity markets become, the more the value of bidirectional vehicle fleets increases. This variety of regulatory approaches and projects is accelerating market maturity but also running up against technical requirements: Power electronics, communication and battery management systems must be interoperable in different grid and market environments in order to be commercially available.
Which technical requirements and power electronics concepts determine the implementation of bidirectional onboard chargers in AC and DC systems?
As a bidirectional onboard charger acts as an active power supply unit in feedback mode, the electronics must not only deliver high levels of efficiency but also meet strict grid requirements. SiC-based converters are becoming increasingly popular internationally because they offer low switching losses at high switching frequencies and high thermal conductivity. With DC-based systems, grid conformity is fully ensured by the DC wallbox, as the conversion from AC (alternating current) to direct current (DC) takes place in the wallbox. Only a few OEMs rely on AC-based bidirectional systems in which the energy path in the vehicle runs via the onboard charger, which looks after the conversion to DC.
How do battery management systems and communication standards influence battery life and grid conformity in bidirectional charging?
With frequent charging and discharging cycles, as is the case with bidirectional charging, batteries age more quickly and lose usable capacity. An intelligent charging strategy in the form of battery management systems (BMS) can help reduce this aging. They control charging and discharging cycles in such a way that defined state-of-charge limits and temperature ranges are adhered to, as these parameters have a significant influence on the degradation and service life of the cells.
In AC V2G systems, the onboard charger integrated in the vehicle must comply with the country- and grid operator-specific grid connection conditions. This is challenging on the software side because the corresponding grid parameters have to be transferred correctly to the vehicle and implemented there. Either numerous grid connection profiles are stored in the vehicle and regularly updated, or advanced communication protocols such as ISO 15118-20 are used, which transmit the settings for the respective grid connection point to the electric vehicle in real time.
Which missing standards, digital infrastructures and user concerns are slowing down the scaling of bidirectional charging solutions (V2G/V2X)?
Missing international standards remain one of the biggest challenges according to the German Research Institute for Energy Economy (FfE). In Europe, there are no such standards, except for the implementation of ISO 15118 for communication between the battery electric vehicle (BEV) and the charging station. The US, in turn, relies on IEEE standards for communication. As a result, bidirectional charging solutions are currently mainly implemented as manufacturer-specific, coordinated overall systems.
The digital infrastructure is also not uniform in many markets. Without widespread smart meter systems and reliable price and grid signals, many V2G applications have only limited scalability in technical or economic terms, according to a study by Fraunhofer and Transport & Environment. Drivers are also concerned about battery aging and its impact on warranty conditions if the limits set by the manufacturer for charging and discharging cycles are exceeded.
How are bidirectional charging and power electronics becoming a key component of the global energy and mobility ecosystem?
2024 and 2025 heralded a phase from the test field to the first commercial implementations. Regulators are opening up markets, energy suppliers are developing new business models, and OEMs are recognizing bidirectional functions as a distinguishing feature. A growing market is emerging for the electronics industry. SiC- and GaN-based power electronics form the technical backbone, while software-defined BMS architectures become the control center for an internationally networked energy system.
If the harmonization of standards and the implementation of a comprehensive digital infrastructure are successful, bidirectional charging could no longer be regarded as an additional function in the next generation of vehicles but could develop into a core component of a global energy and mobility ecosystem.