With the Government’s commitments to decarbonising transport in the UK, researchers at WMG, University of Warwick, have been advancing technologies to ensure peak performance and prolonged battery life for electric vehicles (EVs).

In EVs, it is common to connect lithium-ion cells in series and parallel to increase voltage and power. However, a battery module with cells connected in series can become imbalanced over time due to cell-to-cell inconsistencies and through the impact of interconnection resistance and temperature variations within the module. The cells with the lowest charge will restrict the ability of the battery to deliver power. Conversely the cell with the highest charge will restrict the ability of the battery to store energy. This degrades the performance of the battery. An active balancing system redistributes energy from the strong cells to the weak cells using power electronics and sophisticated control software. This maximises the available energy, increases the capacity of the battery module and can extend battery life.

Boosting Battery Performance Through Active Balancing

Research at WMG, supported by the High Value Manufacturing Catapult, further improved the energy efficiency of an active balancing system by addressing the trade-off between the energy loss on the active balancing hardware and the balancing speed. With the same active balancing system, the new optimal control algorithm is capable of reducing energy loss during the process of active balancing while meeting the basic cell balancing requirement. Validated on a test rig, the proposed active balancing strategy improved performance in reducing total energy loss during the whole balancing process compared to standard rule-based active balancing algorithms. Active balancing systems can benefit from this upgraded balancing algorithm without needing to install any additional hardware.

This latest discovery enhances WMG’s expertise in Battery Management Systems (BMS). Expertise is shared through academic publications and through projects with industry partners. The technologies developed are not only applicable in an automotive context but other situations where a battery is used as a propulsion system, for example, in the development of a battery for an electrified or more electric aircraft.

WMG and the High Value Manufacturing Catapult are exploring a range of applications that would benefit from this innovation. To support sustainability within the battery supply chain, active balancing within second-life or remanufactured batteries will enable higher levels of efficiency and energy storage to be realised. In addition, within the context of safety critical propulsion, the same hardware and software concepts can be scaled-up to realise a new opportunity in fault-tolerant battery systems in which the energy distribution within the battery is manged, in real-time, to “by-pass” damaged or degraded components.

To learn about active balancing, watch this WMG video on You Tube: https://youtu.be/k1N2LyXtK-k

The research outlined can be found in this journal paper: Shi, Kai, Bui, Truong Minh Ngoc and Marco, James (2021) Optimal control of bidirectional active clamp forward converter with synchronous rectifier based cell-to-external-storage active balancing system. Journal of Energy Storage, 41.