Research On Battery Management System With Diagnostic Functions

Development of electic vehicle (EV) is an effective method to resolve problems such as recource shortage and environment pollution. Battery plays such an important role that it influences performance and safety of EVs greatly. Application of battery management system will improve safety, effeciency and life of batteries effectively. The goal is to improve safety and reliability of battery system, and hardware/software of battery management system will be designed respectively. Meanwhile, diagnostic functions are introduced to enhance reliability of BMS itself. To help developing and designing BMS, a diagnostic simulator is achieved.A distributed structure is adopted according to safety requirement of BMS, and the control system consists of a main control unit and several secondary control units. Two kinds of CAN protocol are applied for communication between control systems. Cell voltage and temperature acquisition solutions are analyzed and compared in detail for the secondary control unit. Dual MCU structure is designed for redundancy which improves the fault diagnosis in the main control unit. Linear software for BMS is programmed in terms of the function levels and embedded in RTOS(Real-Time Operating System)to strengthen its stability and flexibility.FMEA method is applied to analyze failure mode and consequence of the battery system. Corresponding detection and disposal methods are proposed. Diagnostic management system is designed to realize OBD functions in BMS. Diagnostic protocol is proposed based on SAE J1939. OBD functions provide BMS with self-diagnosis ability.A general diagnostic simulator, which is configurable and expandable, is implemented basing on analysis of sensors and actuators in battery system. CAN protocol is designed so that user can operate a PC to generate specific kind of signal and also can observe output results of the BMS. A battery system is achieved and the BMS is tested with its basic functions and diagnostic functions by the simulator. Results show that functions of BMS are realized and reliability of the battery system gets improved.