State-of-charge estimation method for lead-acid batteries

??State of charge estimation is an important basis for lead-acid battery charge-discharge control and balanced management. As an important energy storage element, lead-acid #battery directly affects the stable operation of photovoltaic power generation systems. In order to prolong the service life of the battery and ensure the safe, reliable and economical operation of the photovoltaic energy storage system, it is necessary to accurately estimate the state of charge (#SOC ) of the #battery .

(1) Ampere hour method?

The method detects the current from the initial time to the time, and uses the integral algorithm to obtain the charged and discharged power. After comparing with the rated capacity Cn, and then subtracting it from the initial SOC0 time, the SOC value at time t can be obtained.

The ampere-hour method is widely used in SOC detection because of its simple detection method and easy implementation. However, the ampere-hour method also has two important defects: a) a more accurate initial #SOC value is required; 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, with the increase of time, the cumulative error of the ampere-hour method will become larger and larger, and the accurate #SOC value cannot be obtained in the end.

(2) Open-circuit voltage method

The open circuit voltage method uses the open circuit voltage of the battery to have a relatively fixed functional relationship with the SOC, and estimates the SOC by measuring the open circuit battery of the lead-acid battery. The open-circuit voltage method is relatively simple, but due to the polarization application, the battery needs several hours or even a dozen hours of standing time to reach a stable open-circuit voltage, which makes the measurement difficult.

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(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, so 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.