A Battery Equalisation System for Electric Vehicle
Thesis DisciplineElectrical Engineering
Degree GrantorUniversity of Canterbury
Degree NameMaster of Engineering
Abstract In 1999, the Electrical and Computer Engineering Department at the University of Canterbury started building their third electric vehicle (EV3) based on a TOYOTA MR2 with the goal of building a higher performance vehicle to match present combustion engined vehicles. The car is powered by 26 12volt sealed lead-acid batteries connected in series to achieve a nominal 312V DC source. A battery voltage equaliser is a device that draws energy from a higher charged battery, then discharges into a lower charged battery. The need for a voltage equaliser is principally due to the differences in cell chemistry, temperature gradients along the battery string and the ages of the batteries. During the charging or discharging process, some batteries reach their nominal voltage or reach deep discharge states before the others. Then if the charger keeps charging the batteries or the load keeps drawing energy from these batteries, it results in damage to the batteries. Therefore maintaining the charge level on each battery becomes important. In addition, it also improves the battery life and vehicle travelling range. This thesis details the analysis of three different types of battery equaliser, which are based on a 24W buck-boost converter, 192W buck-boost converter and 192W flyback converter. In this design, all converters are designed to work under current mode control with average of 2A. To make each converter install without significant effect on the performance and the cost, each converter is also built with the goals of being small, lightweight, cost effective, flexible for mounting, maintenance free and highly efficient. At the end, the prototype battery equalisation converters were designed, constructed and tested, and the efficiencies from each converter are measured around 90 ~ 92%. The experimental results show two banks of series connected batteries can be successfully equalised by the designed equaliser. This thesis covers the design, simulation and the construction procedures of this battery equaliser system, and also details on some considerations and possible future improvement that were found during the experimental test.