A German start-up has come up with a technology that does away with the need for converters in battery-powered systems. The “AC battery” system, developed by Munich-based Bavertis, uses electronics to reconfigure battery cells several thousand times per second, and allows the battery to generate AC directly.

Usually, battery packs provide fixed DC voltages which need to be converted either to AC, or to lower DC voltages, for most applications.

In electric vehicles, for example, the battery usually produces DC that must be converted by an inverter into AC to power the vehicle’s electric motors. The inverter also controls the motor speeds.

Bavertis’ technology generates an AC or DC voltage directly from the battery. Compared to conventional converters, it is claimed to deliver superior AC voltage and current signals (in terms of harmonic distortion) without needing extra filters. The modular design can be used to drive various types of motor, or other AC or DC devices.

The technology integrates conventional battery cells with modules containing power electronic switches. The switches allow the modules to be connected either in series or parallel as required, or to be bypassed.

Compared to conventional battery packs, in which the cells are connected in a fixed configuration, this flexibility creates redundancy and additional degrees of freedom. In combination with an intelligent operating strategy, the technology can create AC or DC outputs at almost any voltage. External power electronics are not needed, and the cells can be discharged according to their state of charge and age, thus optimising efficiency and service lives.

The technology generates constant or dynamic voltage levels by linking small voltages intelligently. This “multi-level” approach has previously been used only for high-voltage applications. But, according to Bavertis, the recent demand for high-power, low-voltage switches for consumer electronics has made semiconductor switches more powerful and affordable, making multi-level inverters practical even for low-voltage applications.

The company claims that combining multi-level inverters with state-of-the-art battery technology and AI (artificial intelligence) makes its technology superior to conventional energy storage systems.

A battery management system (BMS) monitors and protects the battery constantly. A major challenge with larger battery packs is to balance the various cell capacities, and there are potential problems involving heat dissipation and charging times. Bavertis argues that its ability to control the load on each cell individually overcomes these limitations. Using cell-specific load profiles, it can increase the efficiency and lifetimes of storage systems, as well as eliminating the need for an external BMS.

The German company says that the freedom offered by the multi-level technology, allows it to synchronise energy storage systems with any AC or DC grid in a plug-and-play manner, handling both charging and discharging with one system.

Bavertis states that its technology is allowing it to “rethink” battery-based energy storage. “Our goal is to make planes fly, vehicles drive and energy available,” it says.

Some of the first applications are likely to be in electric vehicles. Bavertis has linked up with ABT e-Line, a German specialist in alternative EV drives, to develop a battery module which can generate any AC or DC voltage from 3.6–300V directly from a battery. With additional modules, the voltage could be extended up to 1kV. ABT will act as the system integrator.

The modular design of the technology will make it possible to power a variety of motors, as well as other AC and DC devices, and to charge the battery from an AC power grid.

According to ABT, one advantage of the technology is its high efficiency as a result of producing constantly high DC voltage. Safety is also increased “significantly” by the ability to intervene actively in individual cells. In the event of a fault, cells can be switched off individually, thus increasing reliability.

Other potential attractions for EV applications include faster charging, longer ranges, extended service lives and the ability to re-use battery packs.

Bavertis was founded in 2021 by three engineers and a business economist with the aim of making battery systems smarter, more modular and longer-lasting. The company believes that modular, intelligent energy storage systems can help to supply energy sustainably and efficiently around the globe.

► To view a digital copy of the latest issue of Drives & Controls , click here.

► To visit the digital library of past issues, click here

► To subscribe to the magazine, click here

"Do you think that robots create or destroy jobs?"