Glossary

Three phase motor controller

A three phase motor controller is an electronic device that drives an AC motor using a fixed DC battery voltage. Its performance and efficiency directly impacts the performance of the entire vehicle.

Battery Management System (BMS)

A BMS both monitors and adjusts the charge level of individual battery cells, referred to as State of Charge (SoC).

Electric vehicle battery packs are usually comprised of many cells in series to create the high voltage and high power required for electric vehicles. However, wiring the pack in series leaves it susceptible to mismatch between the cells' self discharge current, and capacity. Mismatch results from the cell manufacturing process and ageing.

With the cells wired in series, the capacity of the pack is dictated by the lowest capacity cell. To avoid overcharging or over-discharging the lowest capacity cell, the voltage of all cells must be monitored and kept within an acceptable range.

The self-discharge of each cell complicates the battery management further. Over time, the State of Charge (SoC) of each cell becomes offset relative to the others, leading to the effective pack capacity being reduced to that of the weakest cell.

Due to the different cell self-discharge currents, the offset between the SoC of each cell increases over time and the total battery pack capacity continues to diminish. To bring the SoC of all these cells into balance, a system must be implemented to match the average self discharge current between cells over a charge cycle. This is achieved through a balancing step at top of charge.