A Simulation Based Study of using GaN for Switching in Li ion Battery Cell Equalisation Circuits

Li-ion battery packs are vital for electric vehicles, smart homes and smart grid applications. Keeping those large battery packs healthy over long periods of time is beneficial to performance, economics and environmental aspects of using Li-ion cells. Series connected Li-ion cells can become imbalanced over charge discharge cycles due to different operating conditions and manufacturing variations. This imbalance primarily causes loss of usable capacity (driving range in EVs). Cell equalisation circuits can be used to re-balance these cells therefore improving battery health and extending battery life. This paper looks at wide band gap (WBG) semi-conducting switches and if they can be used to improve cell equalisation circuits. WBG switches can operate at much higher frequencies than Si MOSFETS. Simple MATLAB simulations suggest that high frequency switching allows for faster equalisation times, smaller passive components and therefore smaller circuit footprint. A more detailed simulation carried out using manufactures device models in LTSpice show that GaN switches only provide benefits at high frequency and because of the GaN cascade HEMT (High Electron Mobility Transistor) technology that switching losses are still a factor.