Active Capacity Maximiser for lithium ion batteries

Improved battery technology can greatly improve reliability and capacity of battery packs that
are used in critical applications such as hybrid and electric vehicles (EVs), green energy
storage, defence, aerospace and other industrial applications and are key success factors for
the broader adoption of battery technology.
Lithium ion (Li-ion) battery systems offer higher power densities than the currently-used
Nickel Metal Hydride (NiMH) battery packs for hybrid vehicles. However lithium ion
batteries require balancing to ensure each cell remains within operating specifications and for
optimum performance. Traditionally, this balancing process is implemented by redirecting the
excess charge from one cell into a resistor where the energy is lost as heat.
The proposed system would be most effective in larger lithium ion battery packs that are used
in, eg high performance electric vehicles, buses, trucks and vans.
This project is proof of concept of an Active Capacity Maximiser which moves energy from
the battery cell with the most charge and distributes it to the other cells, rather than losing the
energy as heat.
The project proposes to achieve this using DC-DC converters which move energy onto, and
take energy away from, a universal balancing bus. This method enables the balancing to occur
while the cells are being both charged and discharged, and effectively increases the usable
capacity of the battery back. In an automotive application this results in a higher range for the
vehicle on each charge. The larger the cell size, the more important active balancing becomes;
and so this technology will be particularly applicable to the large cells used in standby power
and grid load levelling. In addition there is a large market for second life batteries, which the
project will address by offering a method of extending the useful life of the battery pack, by
adding the Active Capacity Maximiser during the recycling of batteries that have gone beyond
their expected life sp