A constant 800 volts, no matter how full or how old the battery is. No separate on-board charger for converting AC to DC. And perhaps even different cell chemistries in a single pack. Mercedes-Benz has unveiled the Power Converter, a research project aimed at reinventing the traction battery in electric cars.
An 800-volt EV battery doesn’t always deliver its full voltage. In a conventional battery, cells are connected in series to build up the voltage, which rises and falls depending on how much charge is left.
Aging can also take its toll, reducing capacity and performance. And just as a chain is only as strong as its weakest shackle, a single deteriorating cell can hold back an entire battery pack.
A parallel arrangement
Mercedes has been investigating how the battery of tomorrow can overcome its typical weaknesses and has unveiled Power Converter, a concept that introduces next-level technology for traction batteries.
As a starter, the German engineers have turned the principle of serially connected cells on its head. They connect them in parallel. Meanwhile, a set of programmable micro-converters, mounted directly on cells or cell pairs, manages energy flow.
Together they deliver a stable output of up to 800 volts, regardless of the cells’ state of charge (SoC), state of health (SoH), or chemistry. The number of cells no longer dictates the voltage, only the power and capacity of the pack.
In the bin: separate on-board charger
Reportedly, Mercedes could even adjust that system voltage later through a software update, without touching the battery hardware. As such, the battery pack becomes less a fixed energy storage system and more a software-controlled system.
It offers a different view of what a battery is: no longer a fixed arrangement of cells, but a flexible pack that manages voltage, charging and energy flows to suit each situation.
But one of the most promising features of the pack concerns charging. The Power Converter can handle both alternating current (AC) and direct current (DC). That means the separate on-board charger, which in every EV today converts AC from the wallbox, disappears. This also offers the opportunity to downsize other high-voltage components or drop them altogether, which saves weight and space.
Production benefits
Another – though rather obvious – part of the design is bidirectional charging, allowing energy to flow back out of the battery to a device, the home, or the grid. On top of that, Mercedes points to faster charging, lower charging losses, and a longer service life because every cell is controlled individually. And as for the handicap of the weakest link: a faulty cell can be spared or bypassed instead of slowing down the whole pack.
There are production benefits too. Because each cell is addressed individually, wider tolerances between cells become acceptable, and fewer cells are rejected on the production line.
But probably the biggest advantage is that once voltage is decoupled from cell chemistry, chemistries can be mixed. Mercedes explicitly names that possibility.
A pack could combine cheap, robust LFP cells with energy-dense NMC cells, or later with solid-state cells, with software calling on the most suitable cells for each situation. Engineers previously showed working prototypes on a test bench. That opens doors for AMG models seeking to combine peak power with range.
Cheap enough?
The new battery approach, which so far remains a lab experiment, arrives just as Mercedes is largely moving to 800 volts for its electrics. But most of these cars, from the new CLA to the C-Class, need an optional 400-volt converter to fast-charge at older high-speed stations.
A battery that chooses its voltage in software would make such compromises unnecessary. Better still, according to Mercedes, the system can also be deployed at voltages above 800 volts. The question remains whether the Power Converter ends up cheaper than today’s solutions.
