EV BMS Development Based on Master and Slave Structure

• Main Authors: Tai, Ya Lin, 戴亞霖
• Other Authors: Lin, Jeng-Chyan Muti
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/35878471993594171590

碩士 === 國立勤益科技大學 === 電機工程系 === 101 === Currently, Li-ion batteries are the best power source for electric vehicles (EV) because of their outstanding electrochemical performances. Li-ion batteries improve the efficiency of the EVs and increase EV's mileage. The Li-ion batteries own high energy and power densities; however, misusing the batteries sometimes result in disastrous accidents. A battery system required by an EV is usually composed of multiple Li-ion cells connected in series and parallel configuration. Thus, in order to avoid over-charging or over-discharging of any single cell and improve inconsistencies among cells, battery management system is constructed to make sure the battery operating in the safe range. Battery is the core component of an electric vehicle and battery management system is the primary mechanism to balance EV's security and performance. This study develops a set of multi-module battery management system suitable for the 96V32S Li-ion battery packs of the self-developed 96V electric vehicle. The battery management system is composed of the module battery management system and the master control system. The battery management system is developed based on the master-slave structure. 96V32S LiFePO4 batteries are divided into two packs in serials 48V16S. Battery modules are managed by two module battery management systems respectively and the master-control-system receives the module battery data from the module battery management systems. In the master-slave structure of this study, the master-control-system is master, and the two module battery management systems are Slaves. The master-control-system sends corresponding commands to corresponding module battery management systems and module battery management systems answer the requests of master-control-system accordingly. Master-control-system conducts analysis, calculation and alert according to the received data, and then deliver the data to human-machine interface of the vehicle information system, providing for the drivers or researchers to learn the state of the electric vehicle and battery packs, so as to achieve the aims of monitoring and security. The electric vehicle used in the current study is manufactured based on the tricycle structure with two front wheels and one power rear wheel. The body of the used EV is processed and assembled by aluminum materials, and uses the 96V/2500W hub motor as the power source. In addition to the lightweight electric vehicle, the module battery management systems have cell voltage measurement system, current measurement circuit, active balanced system, abnormal warning for module battery and isolated communication function, thus it can manage the 48V16S battery packs separately without master-slave structure. The master-control-system is the coordinator of multi-module battery management systems. The master takes charge of receiving the parameters and states of the two module battery management systems, detects the total voltage, total current of the battery and the driving data by its own measuring system, and calculates and controls the residual electricity and 2-phase charging method according to the data. Vehicle information system conducts intelligent instrumentation, data analysis and storage. HMI system written in the vehicle information system includes the virtual meters, cell data, state of battery pack and data storage, thus the drivers or researchers can know the state of the electric vehicle in real time. The battery management system developed in this study can accurately measure the parameters and state of the battery packs, including single cell voltages with accuracy within 20mV, active balance mechanism with maximum balancing current of 6A, and the multi-module battery management system with the master-slave structure, thus it is suitable for applying in the high-serial and multi-module battery systems. In addition, the 2-phase charging method of this study can guarantee each cell in full charge under the condition of no over-charge, accurately estimate the residual electricity of the battery packs according to the residual electricity, and control error to be less than 5%. This study will be installed and tested on the self-developed 96V electric vehicle. The test items include hill climbing, crusing, starting, accelerating. Test drives show and record the real-time data by the installed vehicle information system. After actual test, the battery management system can normally and stably operate in various road conditions with reliability. The 2-phase charging method can increase the covered mileages of the battery systems. It will more accurately estimate the residual electricity of the battery packs by coordinating with the residual electricity estimation, therefore, the drivers can accurately estimate the remaining runtime to avoid error state of charge estimation.