The state of charge is also called the remaining charge, and SOC is a parameter that reflects the current power in the lithium-ion battery pack as a percentage of the total usable capacity. SOC is the remaining charge of the battery, also known as the state of charge. Indicates the ratio of the remaining capacity of a battery to its total usable capacity after it has been used or shelved for a long time, often expressed as a percentage.
The accurate estimation of battery SOC is not only the most basic requirement for the estimated cruising range of electric vehicles, but also the basic guarantee for improving battery utilization efficiency and safety performance.
There are several methos below to get estimated SOC.
Open Circuit Voltage Method: First measure the open circuit voltage value under different temperatures and SOCs offline to form a table. After the battery system is installed, whenever the power supply state is stopped, the table data can be called to determine the battery state of charge according to the measured open-circuit voltage.
Ampere-hour Integration Method: Real-time measurement of the main circuit current of the lithium-ion battery pack, and integrate it against time, charging as negative discharge as positive. The discharge process uses the initial electricity subtracted from the integration result to obtain the current electric charge; The charging process uses the initial power and the integration result to obtain the current charge.
Internal Resistance Method: The trend of internal resistance following SOC change is very flat, and a small change in internal resistance or measurement error can cause a large error of SOC value. Measure the interference of excessive contact resistance, large battery current, and large polarization internal resistance; The inconsistency of the temperature rise of the lithium-ion battery makes the temperature of the temperature monitoring point and the temperature of the battery body inconsistent, resulting in deviations in temperature compensation.
Kaman Filter Algorithm: The core idea is to calculate the current "optimal value" based on the "measured value" of the current instrument, the "predicted quantity" of the previous moment, and the "error". The highlight is that the error is incorporated into the calculation, and the error exists independently of the measurement data.
Neural Network Algorithm: A new algorithm that simulates the human brain and neurons to deal with nonlinear systems, without delving into the internal structure of lithium-ion batteries, just extract input and output samples that meet the working characteristics from lithium-ion batteries in advance, and input them into the establishment system to obtain SOC values in operation.