TWI635691B - Battery pack active balancing system - Google Patents

Abstract

The invention provides a battery pack active balancing system, which includes: a battery pack including a plurality of battery cell units connected in series with each other; a step-down converter connected to the battery pack; a main switch unit connected to The battery pack and the buck converter; a battery cell voltage sensing unit connected to the battery pack; a plurality of battery cell switching units connected to the battery cell units and connected to the buck converter respectively; The control unit is connected to the main switch unit, the cell voltage sensing unit and the cell switch units. The present invention uses an external power source or a series battery pack itself as the power source. The core switching circuit performs active balancing of individual single cells.

Description

   Battery pack active balancing system   

The invention relates to a power balancing technology for a rechargeable battery, and particularly to an active balancing system for a battery pack.

Although lithium-ion batteries have good performance and high safety, they must still avoid overcharging, over-discharging, or over-temperature conditions. In order to extend the life of the battery and protect the safety of users, a battery management system (Battery Management System (BMS) to ensure that the battery operates within a safe range. Basically, the main function of a battery management system is to measure the voltage of a single cell and protect it. In series battery packs, due to different internal resistances or manufacturing processes, inconsistent battery voltages may occur. Such problems will cause series batteries to overcharge or discharge early because of a certain battery cell, which will greatly affect the battery. Group efficiency and life.

In fact, there is a slight difference in the internal resistance and capacity of each battery cell. This difference will gradually increase with the number of charge and discharge cycles. If there is no management, the difference between the battery cells will be expanded to the battery module and the module. So that the battery modules cannot be in a consistent state. The inconsistency between modules will still cause early overcharge and overdischarge of the battery pack. Therefore, the inconsistency between cells and modules must be corrected through an appropriate management system to fully utilize the lithium iron battery. In order to improve the effectiveness of this problem, a balance mechanism must be added, which shows the importance of BMS and the balance mechanism.

There is a certain degree of management system to choose from in low-voltage equipment. For example, battery management technology is already quite mature in all kinds of portable devices. Major IC companies such as Texas Instrument, Texas Instruments, Linear Technology companies and Maxism companies have commercial chip products of exclusive battery management ICs, and have been widely used in the application of hand-held products, but most of these exclusive battery management ICs are corresponding to the management of small capacity, small series and parallel number The battery pack has almost no cell balancing mechanism built into it.

If the size of the battery pack is increased and applied to large-scale power storage applications such as high-voltage energy storage systems or electric buses, the problems caused by the imbalance between cells or modules can no longer be ignored; taking electric vehicles as an example, the most People are criticized for battery price and service life, and the reason is that if the current battery management technology fails to perform the balance between cells or modules, the weakest battery will trigger the management system protection to stop running early. Reduce the use efficiency, or the system does not immediately protect the weakest battery cells from overcharging / overdischarging, and shorten the life of the overall energy storage device.

The current uniformly balanced battery technology is mainly divided into two balancing methods, active technology and passive technology. The cell balancing mechanism is an important technology for extending the battery life. Early battery management systems were mainly based on the passive balancing method. The passive balancing technology mainly achieves the balancing effect by consuming the battery energy for a long time. It does not actively pull the lowest voltage or power of the series battery pack. The battery capacity is called the passive balance method. Although this method has a simple circuit and low cost, it has the disadvantages of low efficiency and long equilibration time, and is not suitable for high-capacity battery packs.

The active balancing method charges the minimum voltage cells in the battery pack, raises its voltage to the same as the maximum voltage, and then continues to perform the same actions on the remaining cells until all the cell voltages reach a balanced state. It can be divided into the following balance modes due to different operating methods: inductive balance method and capacitive balance method. Inductive balance method or capacitive balance method is a series of battery packs in parallel with a balanced and balanced secondary circuit with an inductor or a capacitor and a switch. The cell that detects the highest voltage or capacity stores its energy in the inductor or capacitor, and then The switching circuit switches it to the cell with the lowest voltage or power, and repeats the same action until the voltage or power of all single cells is uniformly balanced, but the energy conversion of this method is limited by the capacity of the inductor or capacitor, and the balance time is long. It is not applicable where lithium-ion batteries can tolerate high current charging and discharging. Multi-winding transformer balance method: Use a transformer with multiple windings on the secondary side and a switching circuit outside each winding. In addition to charging the series battery pack at the same time, you can also control the switch to charge a single cell with a lower voltage or power. Due to the same number of turns of the multiple windings on the secondary side, it can be regarded as constant voltage charging. When all control switches are turned on to charge all single cells, the battery with a higher charge will get a lower charge, otherwise it will receive a higher charge. Quantity, so it can reach the effect of balance after charging for a period of time. However, in fact, the coupled windings have mutual inductance and leakage inductance. Even if the number of turns is the same, it is impossible to obtain the same voltage, and due to the multiple windings, the volume will be too large.

In high series applications, the battery packs are usually distributed and managed in a modularized manner. Even if the battery management system provided in the market can make the battery cells in the module reach a balanced state, it cannot ensure that the modules can reach a balance. The inconsistency between modules will still cause the problem of inconsistent working conditions of the battery pack, so the balance existing only in the module will eventually fail.

The large-capacity and high series-parallel number battery pack application environment is very different from the 3C hand-held application, but at present the market for high-series, high-voltage battery pack applications, especially for the balancing strategy between modules But there is no complete management system. This phenomenon will not cause much impact in low-voltage or consumer electronics products, but if the battery pack is enlarged and applied to large-scale power storage applications such as energy storage systems and electric buses, this phenomenon can no longer be ignored. Derived problems.

In order to solve the shortcomings of the prior art, the present invention provides a battery pack active balancing system. The present invention uses an external power source or a series battery pack itself as a power source, and uses a switch circuit corresponding to any single cell to perform individual Single cell active balancing. The above power supply can use an external power supply or a flyback power electronic converter to isolate and ground the same charging power source and convert the voltage into a single cell charging voltage. Energy balance charging. The active balancing method of the present invention can be executed when the battery pack is charged, discharged, or left to stand, and the goal of battery pack balance can be achieved in a short time.

The invention is a battery pack active balancing system, which includes: a battery pack including a plurality of battery cell units connected in series with each other; a step-down converter connected to the battery pack, which has a first side winding and a A second side winding sensed by the first side winding; a main switching unit connected to the battery pack and the buck converter; a cell voltage sensing unit connected to the battery pack for sensing the electricity Individual voltages of the core unit; multiple cell switching units are connected to the cell units and connected to the second side winding of the step-down converter respectively; a control unit is connected to the main switching unit and the cell The voltage sensing unit and the cell switching units.

According to an embodiment of the present invention, an external power source is further connected to the battery pack and the main switch unit.

In one embodiment of the present invention, the external power source is commercial power.

In one embodiment of the present invention, the external power source is a wind power generation system, a solar power generation system, or another type of renewable energy power generation system.

In one embodiment of the present invention, the cell switching unit is a photo relay.

In one embodiment of the present invention, a positive electrode and a negative electrode of each battery cell unit are connected to a battery cell switching unit.

In one embodiment of the battery pack active balancing system of the present invention, it has a two-stage charging mode; the first stage is a series charging (series charging) stage. When the battery pack lacks power, the external power source will perform a charging action on the battery pack. That is, the charging current I ₁ flows out from the external power source and enters the whole string of battery packs. The control unit uses the cell voltage sensing unit to measure the voltage of individual single cell units and detects the lowest voltage cell unit. At the same time, the external power source outputs power to the step-down converter. The step-down converter reduces the voltage of the power to 5V and treats it as externally balanced power I ₂ ; when the voltage of the lowest voltage cell unit and the highest voltage cell unit If the difference exceeds a balanced set value (for example, 30mV), the control unit will enable the two cell switching units corresponding to the lowest voltage cell unit. The step-down converter injects the current of the external balanced power I ₂ to the Among the lowest voltage cell units, the current on the lowest voltage cell unit is I ₁ + I ₂ , and the current of other cell units is I ₁ , so that the lowest voltage cell can be quickly pulled up. single The power, which is the same until the average voltage of the battery pack. The end condition of the first stage is that after any single cell in the battery pack exceeds a high voltage set value (such as 3.6V), the series charging is cut off. This cut-off condition setting can prevent any single cell in the battery pack from being overcharged. State, which causes adverse effects on the health, capacity, and internal resistance of the battery cell. In one embodiment of the present invention, the battery pack usually has a capacity of more than 80% after the first stage (string charging stage) is terminated and charged.

In one embodiment of the battery pack active balancing system of the present invention, when any battery cell reaches the high voltage set value (3.6V) during the first stage of series charging, it enters the second stage of the charging stage, which is a separate battery cell. Balanced charging; when entering the split charging stage, the control unit will sort according to the voltage of each battery cell unit, and perform the individual single battery cell balancing in order from low to high. When the battery cell that is balancedly charged reaches a high voltage Set value (such as 3.6V), then the next cell unit will be balanced according to the order from low to high, until all the cells of the entire battery pack After the units are fully balanced, charging ends. The control unit judges that the battery pack has completed the two-stage charging method according to the information through the battery cell units, that is, a complete two-stage charging is ended.

The above summary and the following detailed description and drawings are all for further explaining the methods, means and effects adopted by the present invention to achieve the intended purpose. Other objects and advantages of the present invention will be described in the following description and drawings.

A, B‧‧‧ battery pack

B0 ~ B15‧‧‧Battery

11, 23‧‧‧ Buck Converter

12‧‧‧ main switch unit

13‧‧‧cell voltage sensing unit

14, 22‧‧‧ cell switch unit

15‧‧‧Control unit

16, 21‧‧‧ external power supply

S11 ~ S17, S21 ~ S28‧‧‧Process

FIG. 1 is a schematic diagram of the battery pack active balancing system architecture of the present invention.

FIG. 2 is a schematic diagram of an embodiment of a battery pack active balancing system according to the present invention.

FIG. 3 is a flowchart of an active balancing mechanism of a battery pack under a charging state according to an embodiment of the present invention.

FIG. 4 is a flowchart of an active balancing mechanism of a battery pack in a discharged state according to an embodiment of the present invention.

The following is a description of specific embodiments of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

Please refer to FIG. 1, which is a schematic diagram of a battery pack active balancing system according to the present invention. As shown in the figure, the battery pack active balancing system includes: A battery pack A includes a plurality of battery cell units connected in series with each other; a buck converter 11 is connected to the battery pack A and has a first side winding and a second side winding inductive to the first side winding; A main switching unit 12 is connected to the battery pack A and the step-down converter 11; a battery cell voltage sensing unit 13 is connected to the battery pack A for sensing individual voltages of the battery cell units; plural The battery cell switching unit 14 is correspondingly connected to the battery cell units in the battery pack A and is connected to the second side winding of the buck converter 11; a control unit 15 is connected to the main switching unit 12, The cell voltage sensing unit 13 and the cell switching units 14; an external power source 16 is connected between the battery pack A and the main switching unit 12.

In one embodiment of the present invention, the step-down converter 11, the main switching unit 12, the cell voltage sensing unit 13, the cell switching units 14 and the control unit 15 are integrated into a BMS circuit board.

In one embodiment of the present invention, the main switch unit 12 is capable of switching on and off states. When the state is "on", it is connected to the positive and negative poles of the external power source and the positive pole of the first side winding of the step-down converter. When connected to the negative electrode, the state is "off", which connects the positive and negative electrodes of the battery pack and the positive and negative electrodes of the first side winding of the buck converter.

In an embodiment of the present invention, the positive and negative electrodes of each battery cell unit in the battery pack A are respectively connected to a battery cell switching unit 14, and the battery cell switching units 14 and the first The positive and negative sides of the two-side winding are connected.

In an embodiment of the present invention, the control unit 15 is The individual voltage of each cell unit measured by the cell voltage sensing unit 13 controls the switching operations of the main switch unit 12 and the cell switch units 14 to achieve the effect of balancing the voltage of each cell unit.

In one embodiment of the present invention, the external power source is a commercial power source, and may also be a wind power generation system, a solar power generation system, or other types of renewable energy power generation systems. The external power supply is used as the external balanced power (balanced power supply) of the battery pack active balance system to balance the uneven power (voltage, power) between the battery cells. In one embodiment of the present invention, The battery pack itself can be used as external balanced power.

The battery pack active balancing system of the present invention uses an independent external balanced power (external power supply) in conjunction with a switching circuit method (the buck converter, the main switching unit, the cell voltage sensing unit, and the cell switching units). And the control unit) to overcome the disadvantages of the existing balanced charging method. The external power supply can use an external power supply or a flyback power electronic converter to isolate and ground the same charging power source, and convert the voltage to a single cell charging voltage to directly lower the voltage (or power). The cell unit performs uniform and balanced charging with a large energy. At the same time, the battery pack active balancing system of the present invention continuously detects the minimum voltage of the battery cell unit, and pulls up its power to the same as the battery cell of the second lowest voltage, because the balance current is large, it can reach the balance in a short time The effect.

One embodiment of the battery pack active balancing system of the present invention is shown in FIG. 2. This embodiment is used to explain the operating principle of the active balancing circuit channel (ie, balanced charging) of the present invention. In practical applications, lithium iron phosphate is used. The battery is taken as an example. The maximum balancing current of the active balancing system of the battery pack of the present invention can reach 6A, and the pressure difference of the battery cells after balancing does not exceed 30mV. This embodiment uses an external power source 21 (solar, wind, or mains power) or a battery pack B as a balanced power source. The battery pack B consists of 16 groups of cells (B0, B1, ..., B14, B15). Composed in series, with 32 groups of photo relays as the cell switching unit 22, that is, the positive and negative electrodes of each cell are connected to a group of cell switching unit 22. When charging, switch the correct cell switching unit to balance individual single cells. The charging process can be divided into the following two stages: (1) Series charging: When the entire battery pack lacks power, the external power supply 21 will perform battery pack B. The charging action is that the external power source 21 flows out of I ₁ current into the entire battery pack B for charging. A microcontroller (not shown) performs individual single-cell voltage measurement at this stage and detects the lowest voltage. At the same time, the battery is reduced to 5V by an external power supply 21 through a step-down converter 23, which is regarded as external balanced power; when the voltage difference between the lowest voltage cell and the highest voltage cell exceeds the balance set value (for example, 30mV) , The microcontroller (control unit) will enable the two cell switching units corresponding to the lowest voltage cell, the buck converter 23 and inject I ₂ current into the lowest voltage cell, at this time the lowest voltage The current on the battery cell is I ₁ + I ₂ , and the current on the other cells is I ₁ , so that the lowest voltage cell can be quickly pulled up until its voltage is the same as the average voltage of the battery pack 21. (II) Split charging: When any cell reaches a high voltage set value (such as 3.6V) during the first stage of charging, the individual cells will enter the second stage for balanced charging. When entering the sub-charging stage, the microcontroller will Sort the voltage according to the voltage of each cell, and perform the individual single cell balancing charging in order from low to high. When the voltage of the balanced cell reaches the high voltage set value (3.6V), the next power is performed according to the order. The balancing of the cores is completed until all the cells of the entire battery pack are fully balanced, and the charging is terminated. In this embodiment, the system may have a main switching unit (not shown) connected to the buck converter. The invention can ensure that even if the lithium iron phosphate battery has a large difference in capacity or internal resistance, all the series cells can be fully charged without overcharging any one cell, and the discharge balance can effectively extend the battery. Using time, the charge and discharge balance strategy of the present invention can achieve the effect of extended range without adding any hardware.

FIG. 3 is a flowchart of an active balancing mechanism of a battery pack under a charging state according to an embodiment of the present invention. During the charging phase, the voltage S11 of each battery cell unit is continuously measured, and whether the voltage of any battery cell unit is greater than high Voltage set value S12. If the voltage of any cell unit is higher than the high voltage set value, the voltage of each cell unit is sorted according to the voltage level, and the cell units are sequentially balanced from the low voltage to the high voltage to the high voltage set value S13 (that is, The charging stage mentioned above); before the voltage of any cell unit is higher than the high voltage set value, if the voltage difference between any of the lowest voltage cell units and the highest voltage cell unit exceeds the balance set value S14, The system first confirms whether the lowest voltage cell unit is accepting the balance work S15. If not, the balanced charging function S16 is turned on (ie, the aforementioned series charging stage) until the voltage of the lowest voltage cell unit and the average of each cell unit If the voltage is the same, the balance charging S17 is turned off, and it continues to detect whether the voltage difference between any one of the lowest voltage cell unit and the highest voltage cell unit exceeds the balance setting value.

FIG. 4 is a flowchart of an active balancing mechanism of a battery pack under a discharging state according to an embodiment of the present invention. During the discharging phase, continuously measure Voltage S21, determine (find) the highest voltage battery cell unit and the lowest voltage battery cell unit S22; determine whether the voltage difference between the highest voltage battery cell unit and the lowest voltage battery cell unit is higher than the balance set value S23; if so, determine the lowest Whether the voltage of the voltage cell unit is lower than the equilibrium starting value S24 (that is, the system setting must give a balanced voltage starting value); if so, determine whether the voltage of the lowest voltage cell unit is lower than the low voltage setting value S25 If the value is lower than the low voltage setting value, the battery cell unit may be degraded, so it will no longer be balanced. If the voltage of the battery cell with the lowest voltage is between the initial balance value and the low voltage setting value, the balance is turned on. Function (balanced charging function) S26, balance charging of the lowest voltage cell unit until the battery cell in the balance and the battery cell with the lowest voltage in the battery pack (the lowest voltage other than the battery cell in the balance) After the pressure difference is greater than the balance cut-off value S27, the balance function S28 is turned off.

The battery pack active balancing system of the present invention can take into account full-time (charging, discharging, standing) and full-battery (can be actively balanced for any series battery cell unit). Regardless of the presence or absence of an external power source, the voltage of each battery cell unit is continuously monitored to determine whether to open the balance circuit channel. The battery pack active balancing system of the present invention has the following operation modes: when there is an external power source and when the battery pack is charged: when the battery pack is charged by an external power source, the integrated BMS circuit board (built-in buck converter, main switch) of the present invention is used. Unit, cell voltage sensing unit, multiple cell switching unit and control unit) convert high-voltage external power to low-voltage power, and balance the lowest discrete piezoelectric core (at this time, the state of the main switching unit is "on"); if any One cell reaches high voltage The set value stops serial charging, but the balance mechanism continues to operate, and the balance logic turns to each cell to be charged in sequence according to the voltage level, until the battery pack reaches the set protection voltage (high voltage set value).

When the external power source and battery pack are discharged: The present invention can perform a balance mechanism for delaying the overdischarge of the battery cells. When the voltage status of each battery cell is excessively discrete (the individual voltage difference is too large), and the battery cell voltage is lower than the set balance start When the value is reached, the active balancing mechanism of the battery pack of the present invention is started, and external power supply is required to delay the over-discharge of the battery cells that need assistance (at this time, the state of the main switch unit is "ON"), so that the series battery cells can reach the Discharge state, that is, the weakest cell is delayed and overdischarged earlier.

With external power source and battery pack at rest: When the battery pack is at rest and when the voltage state of each cell is excessively discrete (individual pressure difference is too large), the present invention can activate the active balancing mechanism of the battery pack (at this time, the state of the main switch unit is "On") to balance discrete low-voltage cells from an external power source to the average voltage of the battery pack.

When there is no external power supply and the battery pack is discharged: The present invention can perform a balance mechanism for delaying the overdischarge of the battery cells. When the voltage status of each battery cell is excessively discrete (the individual voltage difference is too large) and the voltage of a single battery cell is lower than the set balance, At the initial value, the active balancing mechanism of the battery pack of the present invention is activated (at this time, the state of the main switch unit is "off"), and the weakest battery is supplemented with the entire battery pack to delay the over-discharge of the battery cell to achieve a series battery cell At the same time, the over-discharge state is reached (that is, the weakest cell has the weakest complementary delay and the cell is over-discharged earlier).

When there is no external power source and the battery pack is at rest: When the battery pack is at rest and when the voltage state of each cell is excessively discrete, the battery pack of the present invention is activated Type balance mechanism (at this time, the state of the main switch unit is "off"), the weakest battery is balanced with the entire battery pack to equal voltage.

In summary, the present invention provides a battery pack active balancing system. The present invention uses an external power source or a series battery pack itself as a power source, and performs individual single power supply with a switch circuit corresponding to any single cell. Active balance of the core. The above power supply can use an external power supply or a flyback power electronic converter to isolate and ground the same charging power source and convert the voltage into a single cell charging voltage. Energy balance charging. The active balancing method of the present invention can be executed when the battery pack is charged, discharged, or left to stand, and the goal of battery pack balance can be achieved in a short time. The invention can ensure that even if the battery has a large difference in capacity or internal resistance, all series cells can be fully charged without overcharging any one cell, and the balance of discharge can effectively extend the battery use time. With the battery pack active balancing system and the charging and discharging balancing strategy of the present invention, the effect of increasing the battery life can be achieved without adding any additional hardware.

The above-mentioned embodiments are merely illustrative for describing the features and effects of the present invention, and are not intended to limit the scope of the essential technical content of the present invention. Anyone skilled in the art can modify and change the above embodiments without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the rights of the present invention should be listed in the scope of patent application described later.

Claims (8)

A battery pack active balancing system includes: a battery pack including a plurality of battery cell units connected in series with each other; a step-down converter connected to the battery pack, which has a first side winding and is connected to the first side Winding-sensed second-side winding; a main switch unit connected to the battery pack and the buck converter; a cell voltage sensing unit connected to the battery pack for sensing individual cells of the cell units Voltage; a plurality of cell switching units are respectively connected to the cell units and connected to the second side winding of the step-down converter; a control unit is connected to the main switching unit and the cell voltage sensing unit And the battery cell switching units; wherein the battery pack active balancing system in the discharging state of the battery pack active balancing mechanism flow is: during the discharge phase, continuously measure the voltage of each battery cell unit to determine the highest voltage battery cell Unit and lowest voltage cell unit; determine whether the voltage difference between the highest voltage cell unit and the lowest voltage cell unit is higher than the balance set value; if so, determine the lowest voltage cell unit Whether the voltage is lower than the initial value of the balance; if so, determine whether the voltage of the lowest voltage cell unit is lower than the low voltage set value; if the voltage of the lowest voltage cell unit is between the balanced initial value and the low voltage set value Time, the balanced charging function is turned on, and the lowest voltage battery cell is balancedly charged until the battery cell in the balance and the battery cell with the lowest voltage in the battery pack (the lowest voltage other than the battery cell in the balance). When the pressure difference is greater than the balance cut-off value, the balance charging function is turned off. The battery pack active balancing system according to claim 1, further comprising: an external power source connected between the battery pack and the main switch unit. The battery pack active balancing system according to claim 2, wherein the external power source is mains power. The battery pack active balancing system according to claim 2, wherein the external power source is a wind power generation system, a solar power generation system, or another type of renewable energy power generation system. The battery pack active balancing system according to claim 1, wherein the cell switching unit is a photorelay. The battery pack active balancing system according to claim 1, wherein the battery pack active balancing system in the state of charge of the battery pack active balancing system is as follows: during the charging phase, the voltage of each battery cell is continuously measured And monitor whether the voltage of any battery cell unit is higher than the high voltage set value. If the voltage of any battery cell unit is higher than the high voltage set value, the voltage of each battery cell unit is sorted from low to high voltage in order. Balance each cell unit to the high voltage set value; before the voltage of any cell unit is higher than the high voltage set value, if the voltage difference between any one of the lowest voltage cell unit and the highest voltage cell unit exceeds the balanced set value, The system first confirms whether the lowest voltage cell unit is accepting the balancing work. If not, the balanced charging function is turned on until the voltage of the lowest voltage cell unit is the same as the average voltage of each cell unit. Then the balanced charging is turned off and the detection is continued. Measure whether the voltage difference between the lowest voltage cell unit and the highest voltage cell unit exceeds the balance set value. According to the battery pack active balancing system described in claim 2, when the battery pack lacks power, the external power source performs a charging action on the battery pack, that is, the charging current I ₁ flows from the external power source and enters the entire battery pack. The control unit borrows The cell voltage sensing unit performs voltage measurement on individual single-cell units, and detects the lowest-voltage cell unit. At the same time, the external power source outputs power to the step-down converter. When the voltage of the power drops to 5V, it is regarded as the external balanced power I ₂ ; When the pressure difference between the lowest voltage cell unit and the highest voltage cell unit exceeds a balance setting value, the control unit will enable the lowest voltage cell unit The corresponding cell switching unit, the step-down converter injects the current of the external balanced power I ₂ into the cell unit with the lowest voltage, and the current on the cell unit with the lowest voltage is I ₁ + I _2, the current of the other unit cell was I _1, thereby quickly lift amount of the minimum unit cell voltage, until it is the same as the average voltage of the battery pack, the battery pack according to any one cell more than a single high After the pressure set value, the charging cutoff. According to the battery pack active balancing system described in claim 7, when any battery cell reaches the high voltage set value, the control unit will sort according to the voltage level of each battery cell unit, and perform individual single power sequencing from low to high. Balanced charging of cores. When the balanced and charged cell units reach the high voltage setting value, the next cell unit is balanced according to the order from low to high until all the cell units of the entire battery pack are completely balanced. This is the end of charging.