Battery Management System

Basic Description

Generally speaking, battery management systems monitor key operational parameters, such as voltages, currents, and temperatures, during charging and discharging of a battery. Lithium-ion batteries, in particular, require careful monitoring to ensure that they become over-charged or under-charged and that they don't over heat. In electric or hybrid-electric vehicles, the battery management system is a component of a complex, fast-acting energy management system and must interface with other on-board systems such as engine management, climate control, communication and safety systems.

Functions of a battery management system suitable for a electric or hybrid electric vehicle include:

• Monitoring the condition of the individual cells which make up the battery
• Maintaining all the cells within their operating limits
• Protecting the cells from out-of-tolerance conditions
• Providing a "Fail Safe" mechanism in case of an accident or abuse
• Isolating the battery in cases of emergency
• Compensating for any imbalances in cell parameters within the battery chain
• Setting the battery operating point to allow regenerative braking charges to be absorbed without overcharging the battery.
• Providing information on the State of Charge (SOC) of the battery. This function is often referred to as the "Fuel Gauge".
• Providing information on the State of Health (SOH) of the battery. This measurement gives an indication of the condition of a used battery relative to a new battery.
• Providing information for driver displays and alarms
• Predicting the range possible with the remaining charge in the battery (Only EVs require this)
• Accepting and implementing control instructions from related vehicle systems
• Providing the optimum charging algorithm for charging the cells
• Providing pre-charging to allow load impedance testing before switch-on and two stage charging to limit inrush currents
• Providing means of access for charging individual cells
• Responding to changes in the vehicle operating mode
• Recording battery usage and abuse (i.e. the frequency, magnitude and duration of out of tolerance conditions).

In practical systems the BMS can thus incorporate more vehicle functions than simply managing the battery. It can determine the vehicle's desired operating mode, whether it is accelerating, braking, idling or stopped, and implement the associated electrical power management actions.

Sensors

Thermal Sensors, voltage sensors, current sensors

Actuators

AC/DC Motor, relays, alarm and instrument panel indicator

Data Communications

CAN Bus data communication between ESP and vehicle

Manufacturers

A123 Systems, Compact Power, Continental, Johnson Controls

For More Information

[1] Electropaedia: Battery and Energy Technologies

[2] LG Chem website (a large battery manufacturer).

[3] Tesla Roadster (BMS) Battery Management System, YouTube video, 2008