How to estimate the state of charge of lead-acid batteries?

How to estimate the state of charge of lead-acid batteries? At present, the testing methods for lead-acid battery SOC at home and abroad can be roughly divided into two categories: The first category starts from studying the internal use mechanism of lead-acid batteries, and estimates the battery SOC by testing the electrolyte density. At the same time, some internal information of the battery can be obtained through external characterization and related experience, such as the sulfation of the electrode plate, the falling off of the electrode plate, the lowering of the electrolyte level, and so on. The other is from the perspective of studying the external characteristics of the battery, decomposing its terminal voltage, current, internal resistance and other battery characteristics, and using certain testing devices and algorithms to get the battery's SOC. This type of method is currently the most studied and most widely used, including the ampere-hour method, open circuit voltage method, internal resistance method, Kalman filter algorithm, neural network, fuzzy algorithm, and so on. (1) Ampere-hour method This method uses the integral algorithm to obtain the charged and discharged power by testing the current from the initial time to the time. After comparing with the rated capacity Cn, and then subtracting it from the initial SOC0 time, the time t can be obtained. SOC value. Ampere Method is widely used in SOC testing because of its simple test method and easy implementation. However, the ampere-hour method also has two important defects: a) a more accurate SOC initial value; b) the ampere-hour method is an open-loop current integration, and the battery is affected by factors such as charge and discharge rate, temperature, and aging during operation. If these factors are not considered, as time increases, the accumulated error of the ampere-hour method will become larger and larger, and an accurate SOC value will eventually not be obtained. (2) Open-circuit voltage method The open-circuit voltage method uses a relatively fixed functional relationship between the open-circuit voltage of the battery and the SOC, and estimates the SOC by measuring the open-circuit battery of a lead-acid battery. The open circuit voltage method is relatively simple, but due to the polarization application, the battery needs several hours or even ten hours of standing time to reach a stable open circuit voltage, which makes the measurement difficult. (3) Internal resistance method The internal resistance of lead-acid batteries is divided into AC internal resistance and DC internal resistance. Regarding the lead-acid battery, its internal impedance is closely related to the capacity and integrity of the battery. Therefore, it has been proposed that the measured impedance can be used to evaluate and predict the performance of the battery. In fact, it is more difficult to accurately measure the internal resistance of the battery online. (4) Neural network method and fuzzy theory method. As far as the battery is concerned, the relationship between its internal parameters is highly non-linear, and some parameters are even unknown, which makes it necessary to establish a simple and effective mathematical method to estimate The state of the battery is difficult. Neural network and fuzzy theory are both powerful tools to solve nonlinear systems. In recent years, researches using neural network and fuzzy theory to estimate battery SOC have continuously emerged. (5) Kalman filter method Kalman filter method estimates SOC through a series of mathematical recursive formulas to achieve the minimum variance estimation of SOC. The Kalman filter algorithm can not only maintain good accuracy in the process of estimating the SOC, but also has a strong correction purpose for the error of the initial value, which is suitable for various types of batteries. The Kalman filter algorithm has different ways of estimating SOC. Generally, the deformation formula of the ampere-hour method is selected as the state equation, and the state equation is directly obtained by using the battery mathematical model or relevant empirical formula. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete.