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Development Status of Lithium Battery BMS

Development Status of Lithium Battery BMS

The priorities for BMS is safety problem, need to have:
1) overcharge protection, that is, when the need to charge the battery in time to terminate.
2) over discharge protection, that is, any one of the unit voltage is lower than the overdischarge threshold to terminate the discharge.
3) over-current and short-circuit protection, the main function for the accident caused by excessive discharge current or even short circuit, the output can automatically shut down and enter the self-locking state.

At present, these basic protection functions can be realized by a professional lithium protection chip, such as TI, Ling Te and other special lithium protection IC. Equilibrium is the core of battery management, domestic and foreign research is very active. Equalization of the specific realization of the method according to the energy treatment can be divided into dissipative and non-dissipative, dissipative balanced by the two ends of the battery in parallel bypass shunt resistor to consume excess energy to achieve a balance, this method has a simple, cost Low cost advantage, but there are thermal management problems. Non-dissipative equilibrium means that energy is transferred between the monomers in the battery pack to achieve equilibrium. There are many kinds of circuit topology in this kind of equalization mode, but there are many problems such as complex circuit, low efficiency of equalization and slow equilibrium, Limiting its use in electric vehicles, energy storage and other large-capacity areas.

Lithium battery due to the complexity of the structure and model, the SOC characteristics of many uncertain factors, the general charge and discharge magnification, temperature and charge and discharge times, so how to measure the parameters based on the SOC to make an accurate estimate is the current Urgent solution
The problem. At present, the industry commonly used SOC estimation methods are discharge method, an hour integral method, open circuit voltage method and Kalman filter method. Discharge test method is the battery constant current discharge, the statistical release of electricity until its terminal voltage reaches the discharge cut-off voltage. The method is relatively reliable and suitable for different types of batteries; however, the disadvantage is mainly that the test process is long and can not be estimated in real time. Therefore, this method is generally used to determine the battery model parameters. The hourly integration method calculates the SOC by calculating the capacity of the inflow or outflow of the battery during a period of time when the battery is charged and discharged, and then the SOC value is compensated according to the ambient temperature and the charge and discharge magnification. This method has the problem of integral cumulative error and initial value prediction. The open-circuit voltage method uses the battery open-circuit voltage and SOC to determine the relationship between the corresponding relationship between the SOC. However, in order to measure the open circuit voltage need to eliminate the battery self-recovery effect, time-consuming, so the open-circuit voltage method can not estimate the SOC in real time, but other algorithms can provide initial SOC value. Kalman filter is a method of solving the filtering problem in discrete equations by recursive iteration. It can estimate the current state value by recursion according to the state of the former time. So we can use the battery on a state parameter to estimate the current working state, that is, the battery current, operating temperature and other parameters as the system input, SOC as the state parameters, the battery voltage as the output, the use of Kalman filter lithium battery SOC Estimate. At present, Kalman filter method still stays in the stage of theoretical simulation, and there are few reports on practical application. The temperature monitoring of the current BMS system is mainly used analog / digital temperature sensor to achieve, for the cost of limited occasions can use thermistor.

At present, the United States and Germany in the BMS research and product level are walking in the forefront of the world, the United States A123System company first developed a lithium iron storage system, and in 2011 built the world's largest 32MWh lithium storage power station. At present, the research on the field of BMS in energy storage power station has already begun. For example, BMS, which is a special energy storage power station, is used to realize battery monitoring and can be used in large and small energy storage power plants.

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