The state of charge is the ratio of the remaining capacity of the battery after a period of use or long-term shelving to its fully charged capacity, usually expressed as a percentage. Its value range is 0~ 1, when SOC=0, the battery is completely discharged, and when SOC= 1, the battery is fully charged. Its English, SOC (state of charge).
When controlling the operation of the battery, the charging state of the battery must be considered.
State of charge (SOC) of supercapacitor: Based on the actual measured capacitance energy, expressed as a percentage of the square of the maximum nominal voltage of the capacitor.
State of charge (SOC) of electromechanical flywheel: Based on the actual measured energy state of electromechanical flywheel, it is expressed as a percentage of the square of the rated speed of flywheel per minute.
SOC algorithm has always been one of the key technologies in the development and application of lithium-ion battery management system. The higher the estimation accuracy of SOC, the higher the cruising range of electric vehicles can be. High-precision SOC estimation can maximize the performance of lithium-ion batteries.
At present, the most commonly used calculation methods are ampere-hour integration method and open circuit voltage calibration method. By establishing a lithium-ion battery model, collecting a large amount of data and comparing the actual data with the calculated data, this is also the technical secret of each company, which takes a long time to accumulate a large amount of data and is also the most technical part of Tesla. Tesla applied for hundreds of core patents in BMS-related fields such as lithium-ion battery cooling, safety and charging balance.
The estimation of state of charge (SOC) of lithium-ion battery is the basis of battery application research. The deep charge and discharge of lithium-ion battery will greatly reduce its service life, and accurate SOC estimation can prevent this from happening. The accurate display of the remaining power can also help the automobile control system to calculate the driving range, and the driver can also plan the driving route better.