Lithium battery BMS development present situation analysis

Source: 2020 - 04 - 04 'hits: lithium-ion battery development status quo of BMS BMS is the main solution of the security, security needs: 1) Overcharge protection, that is, when the voltage exceeds standard, should be timely termination of charging. 2) Over discharge protection that when groups within any single threshold voltage is lower than before discharge, discharge termination. 3) Over current, short circuit protection, the main function is when the discharge current is too large, or short circuit caused by accident, the output can be automatically shut down, the state of self-lock. At present, the basic protection function can be done by professional lithium-ion battery protection chip, such as TI, lint and other professional lithium-ion battery protection IC, equilibrium is the core issue of battery management. Concrete realization method of the treatment, according to the energy equalization can be divided into the dissipation and the dissipation. Dissipation is balanced by consumption on both ends of the battery in parallel on the parallel resistance of excess energy. This method is simple, low cost, but the thermal management problems. The dissipative equilibrium refers to a battery pack of the energy transfer between each unit in equilibrium. The equilibrium method with a variety of circuit topology structure, but there are often complex circuit, low efficiency of equilibrium, equilibrium problem such as slow speed, limiting its in the application in the field of electric vehicles, energy storage, such as large capacity. Because of the complexity of the structure and model, lithium battery SOC features by charge and discharge ratio, temperature, cycle count, and many other uncertain factors. Therefore, how to according to the measurable parameters for accurate estimate of the SOC is an urgent need to solve the problem to solve this problem. The common method to SOC estimation are discharge method, ammeter integral method, the open circuit voltage method and the kalman filter method. Discharge test method is a constant current of battery discharge, statistical power, until its terminal voltage reach discharge cut-off voltage. The method is reliable, applicable to different types of batteries. However, the main disadvantage is that the test process is very long, can't online real-time estimation. Therefore, this method is usually used to determine the cell parameters of the model. Ampere hour integral method through calculating the battery charge and discharge in a period of time in and out of the capacity to calculate SOC. After calculating charged status value, according to the environmental temperature and charge and discharge ratio charged state to compensate. The integral accumulation error and initial prediction problems. The open circuit voltage method using the curve of the corresponding relationship between the open circuit voltage and SOC to estimate SOC. However, in order to measure the open circuit voltage, the battery should be eliminated from the recovery effect, it takes a long time. Open circuit voltage method, therefore, cannot estimate SOC in real time, but can provide other algorithms with the initial value of the SOC. Kalman filtering is to use recursive iteration method to solve a method of filtering problems of discrete equations. Therefore, we can use the battery at the end of the state parameter to estimate the working state of the current moment, including battery current and the work as the system input parameters such as temperature, SOC state parameter, the battery voltage as output, and by using kalman filter to estimate the lithium battery SOC. At present, the kalman filter is still in the stage of theoretical simulation, reported fewer of its practical application. At present, the BMS system mainly adopts analog/digital temperature sensor to monitor the temperature, in the case of a limited cost thermistor may be used.