Development of an on-board charge and discharge management system for electric-vehicle batteries

To improve the service quality of its electric-vehicle (EV) fleet (≈500 vehicles) and master the behaviour of the valve-regulated lead/acid (VRLA) batteries, which power the major part of it, Electricité de France (EDF) has developed an on-board battery-management system. Information on the operating battery behaviour is given to the driver. Overdischarges can then be avoided. Rapid charging of VRLA batteries is monitored. The main available functions of this device are: (i) battery life recording, short- and long-term information storage is available; (ii) charge monitoring, communication with a 23 kW charger is established through an ISO 9141 interface; a fast-charging algorithm for VRLA batteries has been developed and up to 50% of the range can be returned to the EV in 20 min; (iii) battery management during driving, ‘orange’ and ‘red’ alarms related to the depth-of-discharge help the driver to manage the driving; cell overdischarges can then be avoided; (iv) maintenance, the faulty groups of cells are identified; (v) gauge (state-of-charge indicator), this function requires mid-term R and D; for the moment, only charged and discharged Ah are indicated but when more accurate state-of-charge prediction algorithms are available, the software will be up-graded.