The Anatomy of a Battery Electric Vehicle

Battery electric vehicles (BEV) may look the same as a conventional vehicle on the outside but underneath they are quite different. Forget about alternators, fuel-pumps, and turbochargers these are the basic BEV components.

Battery Pack

The battery pack is the fuel tank of a BEV and is made up of several battery cells, each around 3V DC. These cells are connected in series (a daisy chain arrangement) to produce a larger voltage (e.g. 350V DC) that is more suitable for power delivery to the traction motor. This series arrangement is not inherently stable, and a battery management system (BMS) is required to ensure its correct operation.

Battery Management System

The BMS is an electronic system that primarily monitors and controls each individual cell to ensure they stay within particular voltage, state of charge and thermal parameters.

Top-down view of BEV

Battery Charger

The battery charger processes incoming AC electricity from the charge port (usually 240V AC from a household plug) and delivers it to the battery at the correct DC power depending on the charging requirements.

Traction Motor

The traction motor uses power from the battery pack to drive the wheels, either directly or through a transmission. There are a few competing motor varieties but the most popular by far is the Permanent Magnet Synchronous Motor (PMSM) due to its efficiency and power density. PMSM’s operate on three-phase AC but since this is not directly available from the battery an inverter is required.       

Inverter

The inverter transmits power between the battery pack and the traction motor by converting DC to three-phase AC and vice versa. Power travels in both directions depending if the vehicle is motoring or regeneratively braking.   

DC-DC Converter

A DC-DC converter converts the higher DC voltage of the battery pack into a smaller voltage for auxiliary loads such as lights and communications.