The main problem with polymer lithium-ion battery applications is the problem of battery group applications. In order to solve the "battery consistency problem", battery equalization technology is widely used in the industry. At present, the industry divides mainstream battery equalization technology into passive equalization method (energy diversion method), active equalization method (dynamic equilibrium method), and internal equalization method (natural balance method).
　　 The passive equalization method is to make the battery voltage in the battery pack converge by means of discharge equalization. In the traditional energy-consuming BMS system, passive equalization is mainly used, and the single-cell parallel shunt energy consumption resistance is adopted, and only the equalization work can be performed in the charging process, and the excess energy is consumed to the consumption resistor, and the efficiency is zero. At the same time, the equalization current is small, usually less than 100 mA, the effect on the large-capacity battery is negligible, and the SOC estimation accuracy is also low.
　　 The passive equalization method is characterized by simple principle and easy implementation. When the equalization current is small, the device cost is relatively low. However, there are two major problems: First, the resistor can consume the discharge, waste energy, and generate heat; secondly, the discharge resistor cannot be selected too small. At the end of charging, the voltage of the small-capacity battery is the highest according to the characteristics of the battery. It is precisely the power of the small-capacity battery that is released, but the mutual difference between the batteries is increased.
　　 The active equalization method is to actively balance the voltage individual generated by the battery during use and the voltage difference generated by the self-discharge rate. Its main function is to actively balance the difference between battery cells in the battery pack during charging, discharging or placing of the battery pack, so as to eliminate the various types of batteries generated by themselves and during use. Inconsistency.
　　 The main characteristics of the active equalization method are DC/CD bidirectional active equalization circuit, which has high equalization efficiency; equalization is performed in charging, discharging and static processes; the balancing current is large and the equalization speed is fast. But there are also two major problems: First, the technology is complex, the cost is high, and the implementation is difficult; the second is to frequently switch the equalization circuit, causing great damage to the battery and affecting the battery life.
　　 At present, neither passive equalization technology nor active equalization technology can solve the problem well. The reason is that the current charging and discharging control process is based on a fixed voltage as the termination condition of charge and discharge, and the effective voltage range of the battery during operation is constant with temperature, charge and discharge current and cycle time. Change, therefore, using a fixed voltage to control charge and discharge, it is easy to cause overcharge or over discharge of the battery. The change in temperature causes aging of the material inside the polymer lithium ion battery, which causes the battery to deteriorate prematurely. Although researchers have been exploring and proposing solutions and modeling and simulating batteries, the algorithms are too complex to be run on microcontrollers in battery management systems. Due to the lack of universality, complex identification and modeling of specific brands and models of batteries is required, and improvements are made to the battery pack's charging equipment to obtain a smoother charging power source, but the effect is still limited.
　　 The internal equalization method is a topology algorithm for adjusting the charging current and controlling the charging voltage in the process of charging the series battery by the BMS, so that the charge amount of each single battery in the battery pack is substantially the same.
　　 The internal equalization technique is characterized by simple algorithm; no energy loss; no additional charging and discharging process, no impact on battery life; no increase in hardware equipment. However, if the charge of the battery varies greatly, it takes a long time to equalize.
　　 In recent years, BMS has used internal equalization methods to conduct a large number of actual verifications in more than 80 power battery factories and electric vehicle manufacturers of different models at home and abroad, and has achieved good application results, which has been widely praised by the industry.
　　 Through the comparison of three equalization modes, and through a large number of practical cases, BMS “internal equalization technology” follows the “battery inflection point” theory, which not only eliminates the complicated hardware cost of violating the inherent law of the battery, but also reduces the lithium polymer. The operating costs of ion battery group applications are widely recognized in the industry.