The principle of equalizing charging of lithium-ion battery pack protection board, and how many types of equalizing charging circuits are divided into lithium-ion battery packs

The principle of equalizing charging of lithium-ion battery pack protection board, and what are the types of equalizing charging circuits for lithium-ion battery packs? Commonly used equalization charging techniques include constant shunt resistance equalization charging, on-off shunt resistance equalization charging, uniform battery voltage equalization charging, switched capacitor equalization charging, step-down converter equalization charging, inductance equalization charging, etc. When charging a group of lithium-ion batteries in series, ensure that each battery is charged in a balanced manner, otherwise the performance and life of the entire group of lithium-ion batteries will be affected during use. Principle of balanced charging of lithium-ion battery pack protection board When the lithium-ion battery pack is charged, the positive and negative poles of the external power supply of the lithium-ion battery pack protection board are connected to the positive and negative ends of the battery pack bAT+ and bAT- respectively, and the charging current flows through the positive electrode bAT+ of the battery pack. , Single-cell lithium-ion battery 1～N in the battery pack, discharge control switch device, charge control switch device, lithium-ion battery pack protection plate negative bAT-. The charging over-voltage protection control signal of the single-cell lithium-ion battery protection chip in the control circuit part of the lithium-ion battery pack protection board system is isolated by the optocoupler and output in parallel to supply the gate voltage for the conduction of the charging switch device in the main circuit; One or several lithium-ion batteries enter the over-voltage protection state during the charging process, and the shunt discharge branch connected in parallel to the positive and negative ends of the single-cell lithium-ion battery is controlled by the over-voltage protection signal to discharge, and at the same time, it is connected in series to the charging The corresponding single lithium ion battery in the circuit is disconnected from the charging circuit. While charging and protecting the lithium-ion battery pack protection board system, the protection chip controls the on and off of the shunt discharge branch switch device to achieve balanced charging. This method is different from the traditional method of achieving balanced charging at the charger end, and reduces lithium The cost of the design and use of the ion battery pack charger. Lithium-ion battery protection board electric equalization function 1. When the battery voltage of each battery in the battery pack has a difference due to the matching of the battery or the influence of the external environment, if the battery voltage difference between the series connected groups exceeds the set value, the equalization circuit is allowed to work , Equalization starts during the charging process, the equalization resistor discharges the battery pack with the highest relative capacity, and the equalization current is the equalization absorption current value to reduce the voltage rise of the battery pack. 2. When the voltage difference of each group of batteries in series is less than the set value At all times, the equalization circuit is prohibited from working, and there is no equalization. What are the types of equalization charging circuits for lithium-ion battery packs? In view of the design of the battery pack balancing charging circuit topology, domestic and foreign researchers have proposed many different circuit topologies. According to the energy consumption of the circuit during the equalization process, the battery pack equalization charging circuit can be divided into two categories: energy dissipative and energy non-dissipative. 1. Energy dissipative balance is achieved by discharging in parallel with shunt resistors at both ends of each single battery in the battery pack, thereby achieving balance. The shunt resistance discharge equalization circuit is the most straightforward equalization technology, which discharges the high-capacity single cells through the shunt resistance until the capacity of all the single cells is at the same level. 2. Related to energy dissipative equalization, the energy non-dissipative equalization circuit consumes less energy but is more complicated than the circuit structure. ①Flying capacitor is to connect each battery with a capacitor in parallel. This capacitor can be connected to its own battery in parallel by switching, or it can be connected in parallel to adjacent batteries. When the voltage of a battery is too high, first connect the capacitor in parallel with the battery, and the capacitor voltage is consistent with the battery, and then switch the capacitor to the adjacent battery, and the capacitor discharges the battery to realize energy transfer. ② Switched capacitor method balancing Regarding the power lithium battery pack composed of n single cells in series, the switched capacitor method balancing circuit requires n-1 capacitive elements and 2n switching devices. Take the inconsistency between the b1 and b2 terminal voltages of the single cells as an example. During the control process, there are two states. The disadvantage of this circuit is that it can only be used for the terminal voltage balance between the single cells, and it can only be used between adjacent single cells. Therefore, when the number of batteries in series is large, the equalization time is relatively long. ③The double-layer capacitor method equalization circuit is also a derivation and transformation of the switched capacitor method circuit. The difference is that the circuit uses two layers of switched capacitors to realize energy transfer between batteries. Compared with the balanced circuit of switched capacitor method, the advantage of this circuit is to use the newly added outer switched capacitor, so that the single battery can not only balance the voltage with the adjacent single battery, but also with the non-adjacent single battery. Equalization, so the equalization speed can be improved. The above is the principle of equalization charging of lithium-ion battery pack protection board and the classification of lithium-ion battery pack equalization charging circuit. Existing single-cell lithium-ion battery protection chips do not have a balanced charge control function. The balanced charge control function of a multi-cell lithium-ion battery protection chip needs to be externally connected to the CPU; it is realized through serial communication with the protection chip, which increases the protection circuit The complexity and difficulty of design reduce the efficiency and reliability of the system, and increase power consumption.