Online SOC estimation method for lithium battery

Abstract

The invention provides an online SOC estimation method for a lithium battery. The online SOC estimation method comprises the following steps: step (1) establishing an SOC model of a battery by using an improved ampere-hour integration method; step (2) establishing a second-order RC equivalent circuit model of the battery and establishing an equivalent discrete state space model of a battery system; step (3) obtaining a functional relation between an open-circuit voltage of the battery and the SOC of the battery through experiments to obtain an initial value of the SOC; step (4) finally, estimating the SOC of the battery by using an extended Kalman filter algorithm. The online SOC estimation method provided by the invention compensates the capacity of the battery by considering influences of temperature, discharge current and cycle number in the process of generating a SOC equation; the selected second-order RC equivalent circuit model has relatively high precision and is easier to implement in engineering; the initial value is periodically calibrated to reduce an error, thereby making the precision of the estimated value higher while increasing a convergence speed of the extended Kalman filter algorithm.

Description

technical field [0001] The invention belongs to the technical field of electric vehicle power batteries, and in particular relates to an online SOC estimation method of a lithium battery. Background technique [0002] With the development of electric vehicles, the battery management system (BMS) has been widely used. In order to give full play to the power performance of the battery system, prevent the battery from overcharging and overdischarging, prolong the service life, optimize driving and improve the battery life of electric vehicles Performance requires BMS to accurately estimate the state of charge (SOC) of the battery. The SOC of the battery refers to the energy currently stored in the battery. Its function is similar to that of the fuel gauge in the fuel vehicle system, but the detection method is different. , the SOC of the battery cannot be obtained directly through the sensor, but must be obtained by estimating other measurable physical quantities such as the te...

AI Technical Summary

Problems solved by technology

The open-circuit voltage method estimates the SOC of the battery through the mathematical proportional relationship between the open-circuit voltage and the SOC of the battery. It requires the battery to stand for a long time to achieve voltage stability. The resting time required for the end of the internal chemical reaction is generally more than one hour, so it is not suitable On-line estimation; the integration of the battery current over time by the ampere-hour integration method will also produce cumulative errors, as well as errors caused by the initial value. The ampere-hour integration method estimates the battery charge by integrating the current flowing through the battery with time. Power state, the principle is simple, and it is applicable to all batteries, but this method has high requirements for the accuracy of current measurement. If the current measurement is inaccurate, estimation errors will occur, and the errors are cumulative and will increase with time; The network method requires sufficient operating conditions and continuous training through a large amount of data to calculate more accurate results, and different training methods have different accuracy, this algorithm requires a lot of resources

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