TWI405996B - Cell pack balancing method - Google Patents

Abstract

A cell pack balancing method is disclosed, wherein the cell pack includes a plurality of cells. The method firstly starts to charge the cell pack, and categorize the multiple cells into a first group and a second group. Each cell in the first group has an OVP count that records the times of the cell reaching an OVP point. Detect a lowest voltage of the cells in the second group, and then decrease the voltage of each cell in the first group to a decreased voltage lower than the lowest voltage. If any cell in the first group reaches the OVP point again during the charging procedure, the OVP count of the cell reaching the OVP point will be increased, and the cell pack will stop charging then.

Description

Battery pack balancing method

The present invention relates to a voltage balancing method for a battery pack, and more particularly to a passive balancing method for a battery pack.

Rechargeable batteries have been widely used to provide power for various electronic products. Due to the limited terminal voltage and capacity of single cells, some electronic devices that use batteries as power sources, such as notebook computers, A battery pack with a plurality of rechargeable batteries connected in series is used to increase the voltage output of the battery pack and increase the battery pack capacity. However, even in the same battery pack, the charge and discharge capacity, the charge conversion efficiency, or the initial charge of each battery are also inconsistent. Therefore, after a long period of reverse charging and discharging, the gap between the batteries is gradually increased, so that the battery pack is Performance is increasingly limited by poorly characterized batteries.

In order to extend the life of the battery pack and delay the limitation of the battery with lower performance and lower the power storage capacity, battery balancing mechanisms, such as passive balancing, will be provided in many smart battery controllers or control circuits. Among all the batteries, the battery with the lowest voltage is used as a reference, so that other series connected batteries will be higher than the voltage, and the resistance is converted into thermal energy exclusion so that each battery in the battery can be from the same voltage value. Start charging to solve the problem that the poorly performing battery is always unable to supply enough power.

However, the general passive battery pack balancing mechanism does not consider the difference in maximum charge and discharge capacity between each battery every time the voltage balance is performed, and determines the charge and discharge conditions on the same basis. This practice often results in a battery with better performance in the battery pack being limited to less efficient batteries during the balancing process. Moreover, this practice does not take into account battery aging factors.

For the sake of this, we have designed an improved battery balancing method to address the lack of existing battery balancing methods.

The purpose of the present invention is to provide a battery pack balancing method, which classifies each battery in a battery pack according to different characteristics, and then adjusts the balance according to the classification, so as to more effectively average the charge and discharge of each battery, and improve the battery. The group's ability to store electricity and effectively extend the life of the battery pack.

In order to achieve the above object, according to one aspect of the present invention, a battery pack balancing method is provided, the battery pack includes a plurality of rechargeable batteries, and the method includes: classifying the plurality of batteries into a first group and The second group, wherein the number of overvoltages of one of the batteries belonging to the first group reaching the overvoltage protection point is greater than zero, and the number of overvoltages of the batteries belonging to the second group is zero. When charging the battery pack, first detecting a minimum voltage value of the battery of the second group, so that the batteries of the second group are voltage balanced according to the lowest voltage value, and causing the batteries of the first group to be respectively according to the overvoltage thereof The number of times and a voltage constant reduce the voltage to less than the minimum voltage for voltage balancing. When the battery in the battery pack reaches the overvoltage protection point during charging, the number of overvoltages of the battery reaching the overvoltage protection point is added and the charging of the battery pack is stopped; and when the battery of the battery pack does not reach the overvoltage protection point When you continue to charge the battery until all the batteries are fully charged, stop charging the battery pack.

In order to achieve the above object, a battery pack balancing method is further provided, wherein the battery pack includes a plurality of rechargeable batteries, and the method includes: classifying the plurality of batteries into the first group and starting charging the battery pack; The second group, the batteries of the first group respectively have the number of overvoltages reaching one of the overvoltage protection points; then detecting the lowest voltage value of the battery of the second group; and then the batteries of the first group The voltage is reduced to a reduced voltage value that is less than the lowest voltage value, respectively, for charging. When the battery in the first group reaches the overvoltage protection point again, the number of overvoltages of the battery reaching the overvoltage protection point is added, and charging is stopped.

For details of the above technical means, please refer to the following embodiments and the description of the drawings.

The battery pack balancing method of the present invention can be applied to a charge and discharge controller coupled to a battery pack, wherein the controller includes a monitoring circuit for monitoring the state of each battery in the battery pack, and controlling each battery for charging and discharging. Balanced microcontroller. The various embodiments provided below can be performed by a microcontroller.

The first and second figures provide a flow chart of a first embodiment of a battery pack balancing method of the present invention. Since the battery pack performs voltage balancing in the repeated charging and discharging procedures, the charging procedure of the present embodiment will be described using the first drawing, and the second drawing is for explaining the discharging procedure.

In the first figure, each battery in the battery pack is first classified into a first group and a second group according to a charging speed (S101); the specific classification threshold can be drawn according to the number of times of overvoltage of each battery. Minute. The number of overvoltages represents the number of times the battery has reached the Over Voltage Protection point (OVP point) during charging. When some of the batteries in the battery pack charge faster than other batteries, the other batteries have not been charged before reaching the pre-charge. When the operating voltage is set, the faster battery has been charged, and since the battery pack is still charging, the charged battery will continue to increase the voltage until it reaches an overvoltage protection point set to protect the battery components. until. In this embodiment, the number of overvoltages of the batteries classified into the first group is greater than zero, and the number of overvoltages of the batteries of the second group is zero. The overvoltage protection point is the safe critical point for receiving the maximum voltage when the battery is charged. When any battery in the battery pack reaches the overvoltage protection point, it means that the voltage already received by the battery is higher than other batteries, and the battery has reached the battery. Accepted safety critical point, even if the other batteries in the battery pack have not been fully charged, the entire battery pack must stop charging to prevent the battery that has reached the overvoltage protection point from continuing to charge and damage the battery. However, the implementation of such protection means relatively wastes the remaining storage capacity of other batteries that are not yet fully charged.

The batteries of the two groups after classification are charged according to different voltage values: wherein the second group is based on the lowest voltage value of the lowest voltage among the plurality of batteries of the group, so that Each battery of the two groups performs passive voltage balancing according to the lowest voltage value during charging to averagely charge.

The battery in the first group reaches the overvoltage protection point record due to the premature occurrence of the battery in the previous charging process, and represents the speed ratio of the voltage increase in the battery in the first group at the same charging time. The battery that has not reached the voltage protection point is fast, so in the present embodiment, the charging reference point of the battery is adjusted by lowering the reference point of charging of the battery belonging to the first group.

The method is based on a voltage constant used to reduce the charging reference value of the first group of batteries, and the number of overvoltages recorded by each battery in the first group is adjusted multiples, and the batteries in the first group are The voltage is first adjusted to a lower voltage value lower than the lowest voltage value of the second group, and then the passive voltage balance is performed during the charging process according to the voltage drop value of the first group of the battery after the voltage reduction. (S103). Since the battery in the first group is reduced in voltage according to the number of times of overvoltage, in the previous charging procedure, the battery that has reached the number of overvoltages is reduced in amplitude, and the frequency is lowered. The lower the voltage drop value is.

After the above-mentioned down-conversion, the battery of the first group that has reached the voltage protection point is first discharged to its associated voltage drop value, that is, the battery of the first group and the battery of the second group are charged to the predetermined time. The difference in operating voltage is increased such that the cells in the second group have a higher probability of boosting the voltage to a predetermined operating voltage before the first group of cells reaches the overvoltage protection point.

After the charging balance reference values of the batteries of the first group and the second group are respectively set according to the above step S103, in the process of charging the battery pack, it is further determined whether there is still a battery before the other batteries are charged to reach the working voltage. First, the overvoltage protection point (S105) is reached, and the battery reaching the overvoltage protection point may be any one of the first group or the second group; if the battery does reach the overvoltage protection point during the charging process When the situation occurs, the number of overvoltages of the battery that has reached the overvoltage protection point is counted (S107), and charging of the battery pack is stopped (S111), and the battery that has reached the overvoltage protection point is prevented from being damaged.

If it is determined according to step S105 whether the battery reaches the overvoltage protection point, and it is found that there is no battery reaching the overvoltage protection point before the other battery is charged to the working voltage during the charging process, that is, the speed of charging each battery in the battery pack, Under the control of passive balance, the power is received equally and the voltage value is increased. In this case, each battery is continuously charged until all the batteries in the battery pack are charged (S109), that is, the preset is reached. After the operating voltage is applied, the charging process is stopped (S111). In this way, the procedure of charging the battery pack can be smoothly performed, and each battery in the battery pack can be charged on average.

The discharge program in the second figure is then performed after the charging process. When the battery pack is fully charged, it will be placed in the electronic product for discharge (S301), that is, the power supply to the electronic product operates. During the discharge of the battery pack, it is determined whether there is a battery in the battery pack that reaches the Under Voltage Protection (UVP) before the other batteries have not been discharged (S303). The undervoltage protection point is a minimum voltage critical point that allows the battery to discharge. When any battery in the battery pack is discharged such that the voltage drops to the undervoltage protection point, the re-discharge must be stopped to avoid damage to the battery.

If there is indeed a battery reaching the undervoltage protection point during the discharge process, it is necessary to further determine whether the battery is the first group of batteries (S305), that is, the battery is adjusted when it has reached the overvoltage protection point during charging. A battery that lowers the voltage reference value during charging. If the battery that reaches the undervoltage protection point belongs to the first group, it may indicate that the voltage reference value of the battery is lowered too low during the charging process, so that when the battery is discharged, the discharge speed is faster than Other batteries, first reach the undervoltage protection point. In this case, the number of overvoltages of the battery that first reaches the undervoltage protection point is subtracted (S307), to reduce the amplitude of the voltage of the battery during the next charging, and then the discharge is stopped (S309); On the other hand, if the battery that reaches the undervoltage protection point belongs to the second group, the battery in the battery pack has reached the limit under the normal discharge procedure, that is, the program for discharging the respective batteries is stopped (S311).

If it is determined whether the battery discharge reaches the undervoltage protection point as described in the above step S303, if it is determined that no battery first reaches the undervoltage protection point during the discharge process, it means that each battery in the battery pack is discharging at a relatively average speed. Then, the battery pack is continuously discharged until the battery in the battery pack is discharged (S309), and the discharging process is stopped (S311).

As described above, if the battery belonging to the first group is in the discharging process, the other battery reaches the undervoltage protection point, which means that the voltage drop value of the voltage is adjusted too low in the previous charging procedure; therefore, In the discharge program, when it is determined that the battery reaching the undervoltage protection point belongs to the first group, in addition to reducing the number of overvoltages, and further marking the battery reaching the undervoltage protection point for the secondary return battery When the group is charging, the amplitude of the voltage drop of the battery is reduced.

In addition, when it is determined during the charging process that the battery of the first group reaches the overvoltage protection point again (step S105 in the first figure), if the battery has a mark that has reached the undervoltage protection point, that is, in the previous discharge program When the medium reaches the undervoltage protection point first, it indicates that the battery has been aging, that is, the battery may be discharged due to excessive charging and discharging times or the battery life is about to be exhausted. The voltage rise rate is also fast when charging. In this case, the step of adding the number of overvoltages is not performed, but only the charging is stopped directly to avoid excessive deprivation of the opportunity of sufficient voltage of the aged battery.

The third and fourth figures further provide a detailed flowchart of the second embodiment of the battery pack balancing method. The third figure illustrates the flow of voltage balancing when the battery pack is charged; and the fourth figure illustrates the flow of the battery pack during discharge. .

In the battery pack balancing process shown in the third figure, first, a plurality of batteries included in the battery pack are charged one by one by the charge and discharge controller (S501). Each battery in the battery pack has an over-voltage number for recording that each battery is charged and discharged during the entire battery pack cycle, and has been charged until the other battery has not been charged to the preset working voltage. The number of times the operating voltage reaches the overvoltage protection point. This number of overvoltages can be implemented by a monitoring circuit or a microcontroller in the battery balancing circuit. In order to allow each battery in the battery pack to have an opportunity to charge to reach the operating voltage, rather than having to wait for one of the batteries to reach the critical point of stopping charging, the other batteries must be stopped before charging, so in this embodiment Medium, that is, according to the number of overvoltages of each battery, the battery in the battery pack is divided into a first group whose overvoltage is greater than zero and a second group whose number of overvoltages is zero (S503), that is, The batteries in a group are the batteries that have reached the voltage protection point, and the batteries in the second group are the batteries that have not reached the voltage protection point during the charging process. For example, the battery pack includes six batteries connected in series, named A, B, C, D, E, and F, where A, B, and C belong to the first group, and D, E, and F belong to the second group. group.

After the classification, the lowest voltage value is found from the batteries of the second group (S505). For example, the voltages of the batteries D, E, and F at the start of charging are 2.7 volts, 2.5 volts, and 2.8 volts, respectively. The lowest voltage value is 2.5 volts of battery E. The lowest voltage value is the reference value of voltage balance of each battery of the second group when charging. After finding the lowest voltage value in the second group, the microcontroller in the battery balancing circuit determines whether each battery belongs to the second group (S507) if it controls the charging of each battery, and if it belongs to the second group The battery of the group is caused to charge the battery according to the lowest voltage value as a reference value for voltage balance (S509).

For example, when the microcontroller determines that the batteries D, E, and F belong to the second group, respectively, according to the minimum voltage value found above, 2.5 volts, the batteries D and F are passively balanced, respectively. That is, in the process of charging the batteries D, E, and F, the electric energy of the batteries D and F is successively converted into heat energy through a resistive element such as a resistor, thereby reducing the voltage between the battery E and the batteries D and F. The gap is such that when both batteries D and F have been charged to reach a preset operating voltage (eg, 3.3 volts), battery E has not yet reached the operating voltage.

On the other hand, if the microcontroller determines that the other batteries in the battery pack belong to the first group, such as the batteries A, B, and C described above, since the batteries have reached the overvoltage in the previous charging procedure. In the case of a protection point, it can be known that if the battery of the first group and the battery of the second group are charged by the same voltage balance mechanism, the batteries included in the second group are before the voltage returns to the working voltage. It may be that the overvoltage protection point has been reached because the charging speed of any battery in the first group is too fast, so that the entire battery pack must stop charging, so that the battery of the second group has no chance to charge to reach the working voltage. Therefore, in the embodiment, the method of lowering the reference voltage of the battery in the first group is adopted, and the voltage difference between the batteries of the first group and the second group at the start of charging is increased, so that the first group is in the first group. It takes a lot of time for the battery to reach the effect of charging to the operating voltage so that the battery of the second group can also be fully charged.

Therefore, when the microcontroller determines that the battery belongs to the first group, it is further determined whether the voltage of the battery belonging to the first group when preparing to start charging is higher than the lowest voltage found from the second group. a value (S511), that is, 2.5 volts as described above; if the battery in the first group has a voltage higher than the lowest voltage value, discharging the voltage of the battery to a voltage drop value lower than the lowest voltage value and then continuing to charge ( S513). For example, the voltages of the batteries A, B, and C at the time of starting to charge are 3 volts, 2.4 volts, and 2.8 volts, respectively, wherein the voltages of the batteries A and C are higher than the lowest voltage, so the voltages of the battery A and the battery C are separately required. Downgrade. The mode of down regulation is adjusted in the present embodiment by using the product of the number of overvoltages of the battery and a voltage constant set by the designer, the voltage constant being a unit voltage amount of the voltage drop, for example 10 millivolts. Assuming that the number of overvoltages of battery A and battery C are 3 and 2 times, respectively, the microcontroller reduces the voltages of batteries A and C to 30 millivolts and 20 millivolts lower than the minimum voltage of 2.5 volts respectively; The voltage drop values of battery A and battery C after the reduction are 2.47 volts and 2.48 volts, respectively.

When the battery in the first group whose voltage value is higher than the lowest voltage value of the second group has been adjusted to the voltage drop value, the batteries of the first group also start to be charged according to the reference values respectively, as can be seen from the above description. After the batteries of the first group are adjusted, the reference values of each battery are not necessarily the same. For example, the reference values of the batteries A to C are 2.47 volts, 2.4 volts, and 2.48 volts, respectively. This point is different from the battery belonging to the second group using the lowest voltage value as the common reference value.

Then, during the charging process, it is still necessary to continue to monitor whether the battery in the first group reaches the overvoltage protection point again (S515). If the battery in the first group lowers the voltage, but the other battery is not yet charged. When the working voltage is reached, the overvoltage protection point (such as 3.7 volts) has been reached, indicating that the battery's voltage drop is still too high. In this case, it is necessary to further determine whether the battery that reaches the overvoltage protection point is in the previous discharge process. Marked to reach the undervoltage protection point (S517), if it is, the battery has been aging, charging fast, power consumption is fast; or the battery voltage drop adjustment has been adjusted too much, making the battery not normal In this case, even if the battery reaches the overvoltage protection point again, the microcontroller does not count the number of overvoltages, but simply stops charging the battery pack (S523). However, if the battery in the first group is subjected to the voltage drop, the overvoltage protection point is reached again during the charging process (S515), and the recording of the undervoltage protection point is not reached during the discharging (S517), After the controller adds the number of overvoltages of the battery once (S519), the charging of each battery is stopped (S523). For example, after the battery A is stepped down to reach the overvoltage protection point, and there is no undervoltage recording, the overvoltage is The number of times has increased from 3 to 4. In this way, when the battery pack is recharged again, if the minimum voltage is still 2.5 volts, the voltage drop of battery A will be reduced to 2.46 volts.

In addition, after the battery of the second group performs the voltage balance of the batteries D, E, and F according to the lowest voltage value (S509), if one of the batteries is like the battery of the first group during the charging process, before the other batteries are charged. When the amount of charge increases so that the overvoltage protection point (for example, battery D) is reached, the number of overvoltages of the battery reaching the overvoltage protection point should also be increased, that is, from zero to one, and all stops in the battery pack. Battery charging procedure. In this way, when the secondary battery pack is ready to be charged, the battery D originally classified in the second group is classified into the first group, and is charged according to the process below step S511.

The discharge process described in the fourth figure can be continued after the charging process of the third figure, or after the discharge process of the fourth figure is completed, followed by the charging process of the third figure. At the beginning of the discharge process, the charge and discharge controller discharges the plurality of batteries of the battery pack one by one (S701); and continuously determines whether the battery first reaches the undervoltage protection point (S703), that is, the minimum safety threshold for allowing the battery to discharge, For example: 2 volts. If there is no battery in the battery pack to reach the undervoltage protection point, it is further determined whether the battery in the battery pack has been discharged (S705), and if the monitoring circuit has judged that each battery has been discharged, the discharge can be stopped (S713). Wait for the battery pack to perform the charging procedure shown in the third figure; otherwise, if the batteries in the battery pack have not been completely discharged, continue to be discharged by the charge and discharge controller one by one, and return to determine whether the battery reaches the undervoltage protection point. Step (S703).

If during the discharge process, it is detected that the battery reaches the undervoltage protection point before the other batteries are discharged, the battery is first marked (S707), and then it is determined whether the marked battery belongs to the first group. Group (S709), the purpose of this step is to respond to step S517 in the above third figure, to determine whether the battery belonging to the first group is in the charging process, and the voltage reference value at the start of charging is lowered too much. . Therefore, if the battery that has reached the undervoltage protection point does belong to the first group, the number of overvoltages is first reduced in the discharge program (S711), and then all of the batteries are stopped (S713).

Continuing the example used in the third figure, assuming that the battery C first reaches the undervoltage protection point, it means that in the previous charging procedure, the voltage drop value of the battery C is lowered too much, although the battery C is prevented from reaching again. Overvoltage protection point, but when it is discharged, due to the faster discharge speed, after the discharge starting point is reduced from the overvoltage protection point of 3.7 volts to the working voltage of 3.3 volts, within the same time, the discharge The remaining voltage may drop rapidly from 2.8 volts to 2 volts below the undervoltage protection point. Therefore, in order to balance the overvoltage and undervoltage conditions, the microcontroller will first reduce the number of overvoltages of the battery C from 2 times to 1 time. Thereby, when the battery pack is recharged, the charging reference value of the battery C is reduced in amplitude, and the number of voltages after charging can be controlled between the working voltage and the overvoltage protection point, and can be lowered after the next discharge. The risk of battery C voltage being too low.

Finally, if it is found according to the judgment of step S709 that the battery that has reached the undervoltage protection point and is marked does not belong to the first group, that is, the battery belonging to the second group, the battery pack is directly stopped (S713).

In view of the above description of the embodiments, the present invention has disclosed a battery pack balancing mechanism, which classifies each battery in the battery pack according to its characteristics, and applies different control voltages according to different classifications, thereby improving the original battery. The characteristics are all applicable to the problem that the battery generated by the same balancing means cannot be charged and discharged on average, and the storage capacity and overall service life of the battery pack are actually improved.

However, the process steps and the component names described in the above embodiments are only used to illustrate the spirit and the means of the present invention, and are not intended to limit the scope of protection of the present invention. Therefore, the basis for classifying the battery pack is not It is limited to whether the number of overvoltages is greater than zero. Those who are familiar with the technology can change the threshold of the classification after adjusting the parameters appropriately (for example, the minimum voltage value is less than three times of overvoltage; the voltage is reduced after three times. Value), or a classification standard other than the number of overvoltages, as long as the charging speed is fast and the overvoltage protection point is easily separated from other batteries. Therefore, all modifications and variations of the present invention are intended to be included within the scope of the invention.

S101-S111. . . Process step

S301-S311. . . Process step

S501-S523. . . Process step

S701-S713. . . Process step

First: a charging flowchart of a first embodiment of a battery pack balancing method provided by the present invention;

Second: a discharge flow chart of a first embodiment of a battery pack balancing method provided by the present invention;

FIG. 3 is a charging flowchart of a second embodiment of a battery pack balancing method provided by the present invention; and

Fourth: A discharge flow chart of a second embodiment of a battery pack balancing method provided by the present invention.

S501-S523. . . Process step

Claims (21)

A battery pack balancing method, the battery pack having a plurality of rechargeable batteries, the method comprising: starting to charge the battery pack; classifying the batteries into a first group and a second group, the first group The batteries included in the group respectively have an overvoltage frequency, the number of overvoltages being the number of times the battery has reached an overvoltage protection point; detecting a minimum voltage value of the batteries in the second group; The voltages of the batteries in the first group are reduced to a voltage drop value, the voltage drop value being less than the lowest voltage value; and the batteries in the second group are all voltage balanced according to the lowest voltage value, The batteries in the first group are respectively voltage balanced according to the voltage drop value; and the charging is stopped. The battery pack balancing method of claim 1, wherein the step of reducing the voltage of the batteries in the first group to the voltage drop value comprises: determining whether the batteries of the battery pack are respectively </ RTI> belonging to the first group, if yes, determining whether the voltages of the batteries belonging to the first group are higher than the lowest voltage value; when the voltages of the batteries belonging to the first group are higher than the minimum a voltage value, the battery is discharged to a voltage lower than the lowest voltage value according to the number of times of the overvoltage of each of the batteries and a voltage constant; and voltages of the batteries belonging to the first group After reaching the voltage drop value, continue charging. The battery pack balancing method of claim 2, wherein determining whether the battery of the battery pack belongs to the first group comprises: if the battery does not belong to the first group, continuing Charging. The battery pack balancing method of claim 2, wherein the step of determining whether the voltage of the batteries belonging to the first group is higher than the lowest voltage value comprises: when belonging to the first group When the voltage of the batteries does not exceed the minimum voltage value, the batteries are continuously charged. The battery pack balancing method of claim 2, wherein the voltage drop value of each of the batteries is the product of the lowest voltage value minus the number of times of the overvoltage and the voltage constant. The battery pack balancing method of claim 1, wherein the step of stopping charging further comprises: when the batteries of the first group reach the overvoltage protection point again, the overvoltage protection is added. The number of overvoltages of the battery. The battery pack balancing method of claim 6, wherein the first group of the batteries reaches the overvoltage protection point again, and the step of adding the number of overvoltages includes: separately detecting the Whether the batteries of a group reach the overvoltage protection point again; and when detecting that the battery reaches the overvoltage protection point again, respectively, determining whether the battery reaching the overvoltage protection point has reached an undervoltage A record of the protection point to determine whether to add the number of overvoltages. The battery pack balancing method of claim 7, wherein the step of the first group of the batteries reaching the overvoltage protection point and adding the number of overvoltages includes: when the overvoltage is reached again When the battery of the protection point has a record reaching the undervoltage protection point, the number of overvoltages is not counted; and when the battery that reaches the overvoltage protection point again does not have a record of reaching the undervoltage protection point, The number of voltages. The battery pack balancing method of claim 7, wherein the step of detecting whether the batteries of the first group reach the overvoltage protection point again comprises: when the battery is not detected When the overvoltage protection point is reached again, the battery is continuously charged. The battery pack balancing method of claim 9, wherein before the step of stopping charging, the method further comprises: determining whether the batteries of the battery pack are fully charged; when the batteries are fully charged, performing The step of stopping charging; and when the batteries are not fully charged, returning to the step of detecting whether the batteries of the first group reach the overvoltage protection point again. The battery pack balancing method of claim 10, wherein the batteries of the second group include the number of overvoltages, wherein the number of overvoltages of the batteries of the second group is zero . The battery pack balancing method of claim 11, wherein the step of classifying the batteries into the first group and the second group further comprises: detecting the second group separately Whether the batteries reach the overvoltage protection point; and when detecting that the battery of the second group reaches the overvoltage protection point, adding the number of overvoltages of the battery reaching the overvoltage protection point, and executing Stop charging. The battery pack balancing method of claim 12, wherein the step of determining whether the batteries of the second group reach the overvoltage protection point further comprises: when the battery of the second group When it is not detected that the overvoltage protection point is reached, the voltage of the batteries of the second group is lowered to the lowest voltage value and the charging is continued. The battery pack balancing method of claim 8, wherein the step of stopping charging further comprises: starting to discharge the battery pack; when the batteries of the battery pack reach the undervoltage protection point, marking Reaching the battery of the undervoltage protection point; when the marked battery belongs to the first group, subtracting the number of overvoltages of the battery; and stopping discharging. The battery pack balancing method of claim 14, wherein the step of discharging the battery pack further comprises: respectively detecting whether the batteries in the discharge reach the undervoltage protection point; When it is detected that the batteries have not reached the undervoltage protection point, the discharge continues until the battery pack completes the discharge. The battery pack balancing method according to claim 15, wherein After the step of marking the battery reaching the undervoltage protection point, the method further includes: determining that the marked battery belongs to the first group or the second group; and when the labeled battery belongs to the second group , perform the step of stopping the discharge. A battery pack balancing method, the battery pack having a plurality of rechargeable batteries, the method comprising: classifying the batteries into a first group and a second group, wherein the first group belongs to the first group The battery is charged faster than the batteries of the second group; when the battery pack is charged, a minimum voltage value of the batteries in the second group is detected, and the batteries of the second group are based on The lowest voltage value is voltage balanced, and the batteries of the first group respectively lower the voltage to be lower than the lowest voltage value to perform voltage balancing; when any one of the batteries reaches the battery during charging At the voltage protection point, the number of overvoltages of the battery reaching the overvoltage protection point is added and the charging of the battery pack is stopped; and when the batteries of the battery pack do not reach the overvoltage protection point, continue to After the battery is charged until the batteries are fully charged, the battery pack is stopped. The battery pack balancing method of claim 17, wherein the step of adding the number of overvoltages of the battery to the overvoltage protection point includes: when the battery reaches the overvoltage protection point, the battery belongs to the In a group, it is determined whether the battery has a record of reaching an undervoltage protection point, and if not, the number of overvoltages of the battery is added. The battery pack balancing method of claim 18, wherein the step of determining whether the battery has a record of reaching the undervoltage protection point comprises: if it belongs to the first group, reaching the overvoltage protection point When the battery has a record of reaching the undervoltage protection point, the number of overvoltages is not counted. The battery pack balancing method of claim 19, wherein, after the step of stopping charging the battery pack, the method further comprises: when discharging the battery pack, respectively detecting whether the battery of the battery pack reaches The undervoltage protection point; when the batteries fail to reach the undervoltage protection point, continue to discharge the batteries; and when any of the batteries reaches the undervoltage protection point, stop discharging the battery. The battery pack balancing method of claim 20, wherein the step of stopping the discharging of the battery pack when any of the batteries reaches the undervoltage protection point comprises: when the undervoltage protection point is reached When the battery belongs to the first group, the number of overvoltages of the battery is reduced.