Research Of The Modularized Li-ion Battery Equalizer System

These years, people concentrate more on the research of clean and safe electric vehicle (EV) because of the aggravating petroleum resources shortage and environmental contamination problem. As the energy storage device for EV, the safety and service life of Li-ion battery are both the key performance indicators for EV. Inconsistencies of Li-ion battery cells may influence battery pack's safety and shorten its service life. So the research of the Li-ion battery equalizer is so important for the development of EV.Through the evaluation of Li-ion battery's performances and experiments about Li-ion battery's basic characters, we choose the equalizer system which will charge the Li-ion battery at the end of its discharge stage. For better fitting battery packs with different numbers of cells, this thesis chooses a multi-transformer method which is easily for modularization design to realize the equalizer. This equalizer system is consisted of two parts: the only equalization management master and several equalization modules. Equalization management master is to management several modules and to communicate with the controller of the whole vehicle. The modules are to realize the main circuit for equalization which is based the flyback converter and to monitor battery cells'voltage.This thesis introduces hardware and sofeware of the Li-ion battery equalizer respectively. In the hardware part, through analysis and simulation of the flyback converter we know the circuit's important characters (CCM and DCM mode). Then introduce the communication system, PWM generate system, MOSFET driver, flyback transformer design and buffer for the flyback converter circuit. In the software part, this thesis introduces the equalization strategy used in this equalizer, I~2C communication system, CAN communication system and PWM generate part. At the last part of this thesis, a group of experiments are done in order to verify the good stability and equalization effect of the equalizer.