1 Parameter differences between monomer batteries
The state differences between single batteries mainly include the differences between the initial differences between the single battery and the parameters generated during the use process. There are many uncontrollable factors during battery design, manufacturing, storage, and use, which will affect the consistency of the battery. Improve the consistency of monomer batteries is a prerequisite for improving the performance of battery packs. The influence of the monomer battery parameters, the current parameter state is affected by the initial state and time accumulation.
Battery capacity, voltage and self -mount rate
The inconsistency of the battery capacity will cause the depth of the battery battery battery to discharge the depth of discharge depth. The battery with a small capacity and poor performance will reach a full charging state in advance, causing a large -capacity and good -performance battery to reach full charging state. The inconsistency of the battery voltage will cause the single battery in the parallel battery pack to charge each other. The battery with a higher voltage will charge the battery with a lower voltage, which will speed up the attenuation of the battery performance and lose the energy of the entire battery pack. The battery capacity of a large -speed rate is large, and inconsistent battery self -discharge rates will cause the battery loading status and voltage to cause differences, affecting the performance of the battery pack.
Battery
In the series system, the internal resistance difference of the single battery will cause the charging voltage of each battery to be inconsistent. The battery with large internal resistance will reach the upper limit of the voltage in advance. At this time, other batteries may not be fully charged. The battery energy with large internal resistance is large, the heat generates high, and the temperature difference is further increased, resulting in a vicious cycle.
In the same way, the internal resistance differences will cause inconsistency of the current of each battery, and the battery voltage with a large current changes rapidly, making the depth of the charge and discharge of each single battery inconsistent, resulting in the design value of the actual capacity of the system. The battery working current will be different, and its performance will cause differences during use, and will eventually affect the life of the entire battery pack.
2 charge and discharge
The charging method affects the charging efficiency and charging status of the lithium battery pack. The battery will damage the battery when it is charged. At present, there are several types of lithium -ion battery charging methods, but common segmented constant current charging methods and constant current constant voltage charging methods. Hengliu charging is an ideal way, which can carry out safe and effective full charge; Hengli Convergence charging effectively combines the advantages of constant current charging and constant voltage charging, which solves the problem that the general constant current charging method is difficult to accurately charge. Avoid the effects of constant voltage charging method in the early stages of charging, which is simple and convenient to operate.
3 temperature
The performance of lithium batteries at high temperature and high electrical power will be obviously attenuated. This is because lithium -ion batteries can cause the decomposition of positive active substances and electrolytes when using lithium -ion batteries at high temperature conditions. This is the process of heat dissipation. In a short time, heat can cause the temperature of the battery to increase further, and the temperature increases. It has also accelerated the phenomenon of decomposition, forming a vicious circle, and accelerating the decomposition to further decrease the battery performance. Therefore, if the thermal management of the battery pack is improper, it will bring irreversible performance damage.
4 Circuit Circuit
Connection method
In the scale energy storage system, the battery will be combined in a series of combination, so there will be many connection circuits and control components between the battery and the module. Because the performance of each component or component is different from aging, and the energy consumed by each connection point is inconsistent, the effects of different devices have different effects on the battery, causing inconsistency of the battery pack system. The inconsistency of the battery attenuation and speed in the connected circuit will accelerate the deterioration of the system.
Connectary impedance will also have an impact on the incompleteness of the battery pack. The resistance values of the connection tablet are different. The resistance value of the chilo -to each single battery branch circuit is different. Large and the current is small. The connected chip will make the single battery connected to the extremely column first reached the cut -off voltage, causing the energy utilization rate to reduce the battery performance, and the aging of the single battery will lead to the connected battery overcharge with it over charge. Causes hidden safety hazards.
As the number of battery cycles increases, the ratio of Ohm's internal resistance will increase and the capacity attenuation, and the ratio of Ohm internal resistance to connecting chips will change. In order to ensure the safety of the system, the impact of connecting the resistance value must be considered.
BMS input circuit
The battery management system (BMS) is the guarantee of the normal operation of the battery pack, but the BMS input circuit will adversely affect the consistency of the battery. The monitoring methods of battery voltage include precision resistance voltage, integrated chip sampling, etc. These methods cannot avoid the exterior leakage current of the sampling line due to the existence of the resistance and circuit board channel. SOC) inconsistency affects the performance of the battery pack.
5 SOC estimation error
The reason for the inconsistency of the SOC is inconsistent with the initial nominal capacity of the monomer battery and the dextering of the single battery nominal capacity attenuation in the work. For parallel circuits, the internal resistance differences of monomer batteries will cause uneven current distribution, which will cause SOC inconsistency. The SOC algorithm includes the Ashishi Points, the opening voltage method, the Karman filtering method, the neural network method, the vague logic method, and the discharge test method.
The Ashishi Pointing Method has better accuracy when the starting of the State Electric Status SOC0, but the efficiency of Kulun is greatly affected by battery loading status, temperature, and current. It is difficult to accurately measure. Therefore The accuracy requirements for the estimation of the lotus state. After the opening voltage method is stated for a long time, the opening voltage of the battery has a certain functional relationship with the SOC, and the estimated value of the SOC is obtained by measuring the end voltage. The opening voltage method has the advantages of high accuracy, but the shortcomings of long static time also limited their scope of use.