What is the SOC of Li-ion battery? SOC is the calculation of the available range of power battery system, which is the percentage of available capacity and rated capacity of Li-ion battery, and is a more common method used at home and abroad. The SOC of the power battery system needs to be estimated online in real time, so the remaining capacity of the battery is mostly estimated by using parameters such as current, time, voltage and internal resistance, which are easier to measure in the vehicle state, and inputting them into the preset model and algorithm.
I. What is the SOC of Li-ion battery?
SOC of Li-ion battery is simply how much electricity is left in the battery; SOC is the most important parameter in the BMS, because everything else is based on SOC, so its accuracy and robustness is extremely important.SOC is the state of charge, mainly used to reflect the remaining capacity of the battery, which is numerically defined as the ratio of the remaining capacity to the battery capacity.
SOC definition is for the power lithium battery monomer, for the power battery system there is no more uniform definition, in practice, the simpler way is to equate the power battery pack as a battery monomer. In order to ensure the safety of lithium batteries, often use the SOC of the worst-performing battery cells to define the SOC of the battery pack.
SOC as an important threshold for charging and discharging the lithium battery to play a regulatory and protective role. From the definition of the direct decision SOC value is two parameters, the maximum available capacity of the lithium battery and the current power. From a variety of algorithms are used parameters, lithium battery terminal voltage and loop current is the most important measurement parameters.
Second, the power battery system SOC available range calculation
Power lithium battery is the core component of electric vehicles, without power battery electric vehicles can not be started. Power lithium battery is an important factor that directly affects the dynamics of electric vehicles.
SOC available range: The SOC range minus the remaining part of the buffer area of the SOC is the SOC available range. There are many ways to calculate the SOC of a power battery, but they are only calculated values and can only be used as a reference. the SOC test is conducted in two parts.
The first part: the charging process
According to the battery charging characteristics curve (charging current, voltage change curve and the relationship between battery capacity), the simulation calculates, the battery is fully charged state.
The second part: the discharge process
The remaining capacity of the battery can be simulated according to the battery discharging characteristic curve.
The power battery system must meet the peak discharge power requirements of the vehicle load within its application SOC to ensure that the battery system has a peak discharge capacity greater than the maximum power demand of the load; at the same time, in order to receive as much recovered energy as possible, it should meet the set peak charge power/recharge power requirements.
As the charging and discharging power capacity of the power battery system is mainly limited by the power capacity of the selected single battery, of which the discharge power of the single battery will be limited under low temperature and low SOC conditions; under low temperature and high SOC conditions, the charging/recharging power of the single battery will be limited. Therefore, it is necessary to define the available range of SOC in combination with the peak power demand of the vehicle power system.
The key to SOC available range is still determined by the accuracy of the lithium battery parameters, as well as the accuracy of the BMS algorithm. At the same time, under the premise of ensuring battery safety, in the face of various operating conditions BMS strategy and algorithm can not be a one-size-fits-all, more accurate multi-level implementation is required. Under the premise of Li-ion battery safety, the battery capacity is fully used to optimize and maximize the available range of SOC.
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