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　　Parameters and characteristics analysis and balance management of automobile power battery packs

　　Power batteries are considered to be the future of electric vehicles. Electric vehicles are a combination of three major technologies: electric source, motor and vehicle. The electric source is the core component of electric vehicles. There has been an upsurge in the development of power lithium-ion batteries and their special materials. Do As a new type of power technology, lithium batteries must be connected in series to meet the required voltage. The uneven performance of individual cells is not entirely due to battery production technology problems. There are many processes from coating to finished product. Even if each process goes through strict testing procedures to make the voltage, internal resistance, and capacity of each battery consistent, differences will occur after a period of use, making the technical problems of the use of lithium power batteries urgent, and must be done as soon as possible solve.

　　The service life of the power battery pack is affected by many factors. If the life of the battery pack is less than half of the average life of the battery pack, it can be inferred that it is due to improper use of technology. The primary reason is overcharging and over-discharging of the single battery. Premature failure. This article combines the characteristics of lithium power batteries, electronic power supplies, and computer control technology to study the use technology of power battery packs and explores the balance control and management of power battery packs.

　　Main performance parameters of power battery

　　1 voltage

　　Open circuit voltage = electromotive force + electrode overpotential, operating voltage = open circuit voltage + voltage drop caused by current on the internal impedance of the battery. Electromotive force is determined by the material characteristics of the electrode and electrolyte, and the overpotential of the electrode is related to material activity, state of charge and working conditions. .Metal lithium standard electrode potential -3.05V, 3V lithium battery 3.3~2.3V, 4V lithium 4.2~3.7V, 5V lithium 4.9V~3.0V

　　2 internal resistance

　　The steady-state model of the battery in a short period of time can be regarded as a voltage source, and its internal impedance is equivalent to the internal resistance of the voltage source. The size of the internal resistance determines the efficiency of the battery. The internal resistance of the battery includes two parts: ohmic resistance and polarization resistance. The resistance does not change with the frequency of the excitation signal, also known as AC resistance. During the same charge and discharge cycle, the ohmic resistance changes very little except for the influence of temperature rise. The polarization resistance is generated by the resistance reaction of the battery's electrochemical characteristics to external charge and discharge, and is related to Battery charge, charging and discharging intensity, and material activity are all related. For the same batch of batteries, if the internal resistance is too large or too small, it is abnormal. If the internal resistance is too small, it may mean material dendrite growth and micro short circuit. If the internal resistance is too large, it may be Plate aging, active material loss, capacity attenuation, and internal resistance changes can be used as one of the adequacy references for battery cracking.

　　3 temperature rise

　　The battery temperature rise is defined as the difference between the internal temperature of the battery and the ambient temperature. Most lithium batteries have an endothermic reaction when charging and an exothermic reaction when discharging. Both include internal resistance heat consumption. In the early stage of charging, the polarization resistance is the smallest and the absorption resistance is the smallest. Thermal reaction is dominant, and the battery temperature rise may be negative. In the later stage of charging, the impedance increases, releasing more heat than absorbing heat, and the temperature rise increases. During overcharging, with the emergence of irreversible reactions, gas escapes, internal pressure, and temperature Rise and rise until it deforms and bursts.

　　4Internal pressure

　　The internal pressure of the battery increases due to the gas escaping from the internal reaction of the battery. Excessive pressure will burst the shell and cause explosion. Based on safety considerations, on the one hand, lithium batteries are designed with one-way explosion-proof valves. On the other hand, they are made of plastic shells. .The gas evolution reaction is often accompanied by an irreversible reaction, which means the loss of active materials and the decrease in battery capacity. No gas evolution and small temperature rise charge and discharge are the most ideal.

　　5 power

　　In electricity, electricity is expressed in Wh, which is a unit of energy. One kilowatt hour is equal to 1kWh. Batteries often use Ah to calculate electricity. For power batteries, the focus is on power and energy. Wh is more direct, because the voltage of the battery changes, and it changes throughout the process. The amount can reach about half of the maximum value. Calculating the amount of electricity using Ah cannot accurately describe the power driving capability of the battery. However, Ah as the unit of electricity for the battery has its own history and reason. Both units of electricity can be used where there is no ambiguity.

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