A solid state relay battery management system for series connected batteries

In modern electric or hybrid electric vehicles, it is vital to monitor and equalize the battery cell voltages to maximize battery efficiency, prolong battery life, and prevent hazards. Current battery management systems usually consist of two separate units, an Equalization Unit (EQU) and an Electric Control Unit (ECU). The use of two separate units makes the battery management system expensive and produces a relatively large size. In this project, a new solid-state relay battery management system was designed, implemented and tested. The system utilizes a solid-state relay matrix to combine the EQU and the ECU into a single unit. This results in a smaller size, lighter weight, less noise and a more reliable system overall. Also, this system provides an intelligent equalization scheme that includes an adjustable digital current charger and a larger constant current charger. The system also has a high-speed measurement rate and provides very accurate voltage sampling. Furthermore, the system can be adapted to different kinds of batteries. A graphical interface program was written to monitor the battery management system with a personal computer via RS232. The CAN 2.0B communication protocol was used to communicate between the micro-controllers in the different modules.