TWI729630B - Method for charging energy storage unit - Google Patents

Abstract

The invention discloses a method for charging energy storage unit, and the method comprises the following steps. First, a first energy storage unit and a second energy storage unit are provided, and the first energy storage unit and the second energy storage unit are electrically connected in series in a first current path. And, a power converter is provided, and configured to provide a first charging current to the first current path. Then, the voltage of the first energy storage unit and the second energy storage unit are detected to obtain a first voltage value and a second voltage value. Then, the first voltage value and the second voltage value are determined whether one of them reaches a preset voltage. When the first voltage value reached the preset voltage and the second voltage value failed to reach the preset voltage, the first current path bypasses the first energy storage unit.

Description

Charging method of energy storage unit

The invention relates to a charging method, in particular to a charging method for simultaneously charging a plurality of energy storage units.

Generally speaking, after the battery is made, it is necessary to put the battery into the battery forming equipment, and after a period of forming process, it can function normally. For example, the battery formation device performs a series of charging and discharging of the battery, so that the active material in the battery can be activated. In addition, the battery formation device has multiple power converters, and each power converter is only electrically connected to one battery, and the power converter charges and discharges the respective battery. Traditionally, the power converter and the battery are connected in a one-to-one manner in order to pursue system stability and avoid interference from other power converters during battery charging and discharging. However, a person with ordinary knowledge in the relevant technical field can understand that the huge number of power converters not only takes up space, but also costs relatively high.

On the other hand, if only one power converter is used to connect multiple batteries in series, it is difficult to accurately provide the charging voltage or charging current required by each battery, which may reduce the efficiency of battery formation. Accordingly, the industry needs a more efficient and low-cost battery charging method.

The invention provides a method for charging an energy storage unit, which can charge a plurality of energy storage units with one power converter, and can judge whether the energy storage unit has been charged to a preset voltage.

The present invention provides a method for charging an energy storage unit, which includes the following steps. First, a first energy storage unit and a second energy storage unit are provided, and the first energy storage unit and the second energy storage unit are connected in series in the first current path. In addition, a power converter is provided to provide a first charging current to the first current path. Then, the voltages of the first energy storage unit and the second energy storage unit are respectively detected, and the first voltage value and the second voltage value are obtained accordingly. Then, it is determined whether one of the first voltage value and the second voltage value reaches a preset voltage. When the first voltage value reaches the preset voltage and the second voltage value does not reach the preset voltage, the first current path is set to bypass the first energy storage unit.

In some embodiments, the first charging current is a constant current, and the first charging current is set to a first current value. In addition, the charging method of the energy storage unit may further include the following steps. First, after setting the first current path to bypass the first energy storage unit, it can be determined whether the second voltage value reaches the preset voltage. When the second voltage value reaches the preset voltage, the first current path can be set to pass through the first energy storage unit and the second energy storage unit. And, when the second voltage value reaches the preset voltage, the power converter can be set to provide the second charging current to the first current path. The second charging current may be a constant current, the second charging current is set with a second current value, and the second current value is smaller than the first current value.

The present invention also provides a method for charging an energy storage unit, which includes the following steps. First, a first energy storage unit and a second energy storage unit are provided, and the first energy storage unit and the second energy storage unit are connected in series in the first current path. In addition, a power converter is provided to provide a first charging current to the first current path. Then, the voltages of the first energy storage unit and the second energy storage unit are respectively detected, and the first voltage value and the second voltage value are obtained accordingly. Then, it is determined whether the first voltage value and the second voltage value both reach the preset voltage. When the first voltage value and the second voltage value both reach the preset voltage, the power converter is set to provide the second charging current to the first current path.

In some embodiments, the first charging current and the second charging current are constant currents, the first charging current is set with a first current value, the second charging current is set with a second current value, and the second current value may be smaller than the first charging current. Current value. In addition, the charging method of the energy storage unit may further include the following steps. First, it is judged whether one of the first voltage value and the second voltage value reaches the preset voltage first, and when the first voltage value reaches the preset voltage and the second voltage value does not reach the preset voltage, the side of the first current path can be set Road first energy storage unit.

In summary, the energy storage unit charging method provided by the present invention can not only use one power converter to charge multiple energy storage units, but also can determine whether each energy storage unit has been charged to a preset voltage. When part of the energy storage units have been charged to the preset voltage, bypass the energy storage units that have reached the preset voltage, and continue to charge the energy storage units that have not reached the preset voltage. When all the energy storage units have been charged to the preset voltage, all the energy storage units are turned on, and all the energy storage units are continuously charged with a lower charging current. In this way, the charging method of the energy storage unit provided by the present invention can have a lower hardware cost and can improve the formation efficiency.

The features, objectives and functions of the present invention will be further disclosed below. However, the following are only examples of the present invention, and should not be used to limit the scope of the present invention, that is, all equivalent changes and modifications made in accordance with the scope of the patent application of the present invention will still be the essence of the present invention. Without departing from the spirit and scope of the present invention, it should be regarded as a further implementation aspect of the present invention.

Please refer to FIG. 1. FIG. 1 is a schematic circuit diagram of a charging method using an energy storage unit according to an embodiment of the present invention. As shown in FIG. 1, the energy storage unit charging method of the present invention can be applied to a charging system, and the charging system can be, for example, a battery formation device or various battery charging devices, which is not limited in this embodiment. In addition, the charging system may include a power supply 10, a power converter 11, a voltage detection unit 12, a switch control unit 13, a switch 14, a voltage detection unit 15, a switch control unit 16, and a switch 17. Among them, the voltage detection unit 12, the switch control unit 13, and the switch 14 correspond to the energy storage unit 20 (first energy storage unit), and the voltage detection unit 15, the switch control unit 16, and the switch 17 correspond to the energy storage unit 22 (the first energy storage unit). Two energy storage unit). It is worth mentioning that although Figure 1 only shows two energy storage units, the present invention is not limited to this. For example, the energy storage unit charging method of the present invention can also be applied to three or more energy storage units. unit. Hereinafter, the charging method of the energy storage unit of the present invention is illustrated by using various components in the charging system.

The power supply 10 shown in FIG. 1 can provide AC or DC power, and can output the power to the power converter 11, and then the power converter 11 converts the power received from the power source 10 into DC power for the energy storage unit 20 and the energy storage unit 22 for charging. In practice, the power converter 11 may include an ac/dc converter and/or a dc/dc converter, which is not limited in this embodiment. In addition, when the power converter 11 charges the energy storage unit 20 and the energy storage unit 22, the power converter 11, the energy storage unit 20, and the energy storage unit 22 may be connected in series in the same current path (first current path), In addition, the power converter 11 outputs different charging currents to the current path at different time points.

Here, the power converter 11, the energy storage unit 20, and the energy storage unit 22 are not fixedly electrically connected in the first current path, and the first current path may also bypass the energy storage unit 20 and the energy storage unit 22. . In an example, the energy storage unit 20 may be electrically connected to the power converter 11 through the switch 14. As shown in FIG. 1, the switch 14 can be, for example, a three-terminal element, wherein the terminal A can be electrically connected to the power converter 11, the terminal B can be electrically connected to the energy storage unit 20, and the terminal C can be connected to End point D of switch 17. In practice, the switch 14 can be controlled by the switch control unit 13, and when the switch control unit 13 controls the switch 14 to turn on the terminal A to the terminal B, it can be regarded that the energy storage unit 20 is connected in series in the first current path. Conversely, when the switch control unit 13 controls the switch 14 to turn on the end point A to the end point C, it can be regarded that the energy storage unit 20 is bypassed and is no longer connected in series in the first current path.

Similarly, the energy storage unit 22 can also be electrically connected to the power converter 11 through the switch 17. As shown in Fig. 1, the switch 17 can also be a three-terminal element, wherein the terminal D can be electrically connected to the energy storage unit 20 and the terminal C of the switch 14, and the terminal E can be electrically connected to the energy storage unit 22. The terminal F can be connected back to the power converter 11. In addition, the switch 17 can be controlled by the switch control unit 16, and when the switch control unit 16 controls the switch 17 to turn on the terminal D to the terminal E, it can be regarded that the energy storage unit 22 is connected in series in the first current path. Conversely, when the switch control unit 16 controls the switch 17 to turn on the terminal D to the terminal F, it can be regarded that the energy storage unit 22 is bypassed and is no longer connected in series in the first current path.

In practice, the switch control unit 13 and the switch control unit 16 can be controlled by the voltage detection unit 12 and the voltage detection unit 15 respectively. In one example, the voltage detection unit 12 may be electrically connected to the positive and negative ends of the energy storage unit 20 to detect the voltage of the energy storage unit 20 to generate the first voltage value. Similarly, the voltage detection unit 15 can be electrically connected to the positive and negative ends of the energy storage unit 22 to detect the voltage of the energy storage unit 22 to generate the second voltage value. At this time, the voltage detecting unit 12 and the voltage detecting unit 15 can respectively determine whether the first voltage value and the second voltage value reach a predetermined voltage. When the voltage detection unit 12, the switch control unit 13, the switch 14, and the energy storage unit 20 are only discussed here, and other energy storage units in the first current path are not discussed, when the voltage detection unit 12 determines the first voltage When the value reaches the preset voltage, the voltage detection unit 12 can send a command to the switch control unit 13, and the switch control unit 13 controls the switch 14 to turn on the terminal A to the terminal C, so that the energy storage unit 20 can be bypassed without Continue charging. Similarly, for the voltage detection unit 15, the switch control unit 16, the switch 17, and the energy storage unit 22, without discussing other energy storage units in the first current path, when the voltage detection unit 15 determines the second When the voltage value reaches the preset voltage, the voltage detection unit 15 can send a command to the switch control unit 16, and the switch control unit 16 controls the switch 17 to turn on the terminal D to the terminal F, so that the energy storage unit 22 can be bypassed, and Do not continue to charge.

However, since there are multiple energy storage units in the first current path, when all the energy storage units reach the preset voltage, the operation mode of the charging system is different from that there is only a single energy storage unit in the first current path. For example, the voltage detection unit 12 and the voltage detection unit 15 can not only send commands to the switch control unit 13 and the switch control unit 16, but can also transmit the charging information of the energy storage unit 20 and the energy storage unit 22 to the power converter 11. In other words, the power converter 11 can know whether all the energy storage units (such as the energy storage unit 20 and the energy storage unit 22 in FIG. 1) in the first current path reach the preset voltage. Here, reaching the preset voltage may be greater than or equal to the preset voltage, which is not limited in this embodiment. In one example, the energy storage unit 20 and the energy storage unit 22 may reach the preset voltage successively. Here, it is assumed that the energy storage unit 22 reaches the preset voltage first, since the voltage detection unit 15 can be informed by the power converter 11 that the first If there are other energy storage units in the current path that have not reached the preset voltage, the voltage detection unit 15 may instruct the switch control unit 16 to bypass the energy storage unit 22 by the switch 17.

Then, when the energy storage unit 20 subsequently reaches the preset voltage, because the voltage detection unit 12 can learn from the power converter 11 that other energy storage units in the first current path (such as the energy storage unit 22 in FIG. 1) have been When the preset voltage is reached, the voltage detection unit 12 can instruct the switch control unit 13 to leave the energy storage unit 20 in the first current path (not bypassed by the switch 14). In practice, when all the energy storage units reach the preset voltage, the voltage detection unit 15 will instruct the switch control unit 16 to make the energy storage unit 22 be connected in series to the first current path. In addition, the power converter 11 will use the second charging current to charge the energy storage unit 20 and the energy storage unit 22 instead. In one example, the second charging current corresponds to the second current value, and the second current value is less than the first current value of the first charging current. In other words, the power converter 11 of this embodiment will perform multiple cycles of charging. In the first round of charging, when all the energy storage units reach the preset voltage, the energy storage units that were originally bypassed will be recharged again. The series connection returns to the first current path, and the power converter 11 uses a smaller charging current to charge all the energy storage units for the second round.

In order to explain in more detail how the charging method of the energy storage unit of the present invention is applied to the charging system, the following uses a corresponding example to illustrate. Please refer to Figure 1, Figure 2 and Figure 3 together. 2 is a schematic diagram showing the current and voltage of the first energy storage unit according to an embodiment of the present invention, and FIG. 3 is a schematic diagram showing the current and voltage of the second energy storage unit according to an embodiment of the present invention. FIG. 2 illustrates a possible charging state of the energy storage unit 20. The upper part of FIG. 2 shows a schematic diagram of the voltage V20 and the time at the positive and negative ends of the energy storage unit 20, and the lower part of FIG. 2 shows the charging current I20 of the energy storage unit 20. Schematic diagram with time. Similarly, FIG. 3 illustrates a possible state of charge of the energy storage unit 22, wherein the upper part of FIG. 3 shows a schematic diagram of the voltage V22 and time at the positive and negative ends of the energy storage unit 22, and the lower part of FIG. 3 shows the energy storage unit 22 Schematic diagram of charging current I22 and time.

It can be seen from FIGS. 2 and 3 that, before time T0, the voltages V20 and V22 at the positive and negative ends of the energy storage unit 20 and the energy storage unit 22 have not reached the preset voltage Vset, so the energy storage unit 20 and the energy storage unit 22 Both are also connected in series in the first current path, and both receive the charging current Iset1 (first charging current) given by the power converter 11. It can be noticed that the voltage V20 at the positive and negative ends of the energy storage unit 20 and the voltage V22 at the positive and negative ends of the energy storage unit 22 both show a slow upward trend due to the stable charging current Iset1. At time T0, the voltage V22 of the energy storage unit 22 reaches the preset voltage Vset. As mentioned above, the voltage detection unit 15 will instruct the switch control unit 16 at this time to make the energy storage unit 22 bypassed by the switch 17. In addition, the voltage detection unit 15 can report to the power converter 11 to inform that the voltage V22 of the energy storage unit 22 reaches the preset voltage Vset.

It can be seen from Figure 3 that after the energy storage unit 22 is bypassed by the switch 17, because the energy storage unit 22 is not in the first current path, the charging current I22 of the energy storage unit 22 should be zero at this time, and the positive and negative ends of the energy storage unit 22 The voltage V22 will drop slightly (less than the preset voltage Vset). In detail, since the voltage V22 is measured by the voltage detecting unit 15 outside the energy storage unit 22, it is not entirely the battery cell voltage of the energy storage unit 22. Therefore, assuming that the battery cell voltage of the energy storage unit 22 is Vcap2 and the internal resistance of the energy storage unit 22 is R22, the voltage V22 can be expressed as the following formula (1): V22=Vcap2+I22×R22 (1)

Those with ordinary knowledge in the technical field can understand that when the energy storage unit 22 is bypassed by the switch 17 to make the charging current I22 return to zero, the voltage V22 measured by the voltage detection unit 15 will be the battery cell voltage of the energy storage unit 22 For Vcap2, because the item "I22×R22" is missing, it can be seen that the voltage V22 will drop slightly. Of course, the battery cell voltage Vcap2 or the internal resistance R22 mentioned in this embodiment is only for example, and is not used to limit various parameters of the energy storage unit 22. Since the energy storage unit 22 is in an open circuit state, the voltage V22 at the positive and negative ends of the energy storage unit 22 should be substantially unchanged from time T0 to time T1.

In addition, between time T0 and time T1, because the energy storage unit 20 has not reached the preset voltage Vset, it is still in the first current path, and the charging current Iset1 (first Charging current) for charging. Until the time T1, the energy storage unit 20 just reaches the preset voltage Vset. At this time, the voltage detection unit 12 can also report to the power converter 11 to inform the energy storage unit 20 that the voltage V20 has reached the preset voltage Vset. Since the power converter 11 receives the reports from all the voltage detection units (the voltage detection unit 12 and the voltage detection unit 15) in the first current path, it can know all the energy storage units (the energy storage unit 20 and the energy storage unit). 22) The charging in the first round has been completed. In other words, the charging time of the first round is from the beginning to time T1. It is worth mentioning that, as can be seen from Figures 2 and 3, the charging current Iset1 provided by the power converter 11 between time T0 and time T1 is fixed. It can be said that the power converter 11 uses constant current mode (CC mode) The energy storage unit 20 and the energy storage unit 22 are being charged.

Then, starting from time T1, the power converter 11 will reduce the charging current and use the charging current Iset2 (second charging current) to perform the second round of charging. As shown in the figure, after the power converter 11 changes to provide the charging current Iset2, the voltage V20 at the positive and negative ends of the energy storage unit 20 will also drop slightly (less than the preset voltage Vset). As mentioned above, since the voltage V20 is also measured by the voltage detection unit 12 outside the energy storage unit 20, it is not entirely the battery cell voltage of the energy storage unit 20. Therefore, assuming that the battery cell voltage of the energy storage unit 20 is Vcap1 and the internal resistance of the energy storage unit 20 is R20, the voltage V20 can be expressed as the following formula (2): V20=Vcap1+I20×R20 (2)

Since the charging current I20 of the energy storage unit 20 is changed from a larger charging current Iset1 (first charging current) to a smaller charging current Iset2 (second charging current), the voltage V20 will be less "(Iset1-Iset2)×R20 Therefore, it can be seen that the voltage V20 will also drop slightly when the second round of charging starts.

Similarly, between time T1 and time T2, the voltage V22 of the energy storage unit 22 first returns to the preset voltage Vset, and the voltage detection unit 15 will instruct the switch control unit 16 to bypass the energy storage unit 22 by the switch 17. . In addition, the voltage detection unit 15 can report to the power converter 11 to inform that the voltage V22 of the energy storage unit 22 has reached the preset voltage Vset in the second round of charging. As mentioned above, when the energy storage unit 22 is bypassed by the switch 17 during the second round of charging to make the charging current I22 return to zero, the voltage V22 measured by the voltage detection unit 15 is also the battery cell of the energy storage unit 22. The voltage is Vcap2. It can be seen from FIG. 3 that after the second round of charging is completed, the battery cell voltage Vcap2 of the energy storage unit 22 will increase a little. Using the aforementioned formula (1) to illustrate, due to the second round of charging, the charging current I22 of the energy storage unit 22 has only a small charging current Iset2 (second charging current), and when the internal resistance R22 remains unchanged, when the voltage When V22 reaches the preset voltage Vset, it can be known that the battery cell voltage Vcap2 will inevitably be higher than during the first round of charging. Obviously, because the power converter 11 reduces the charging current, and the battery cell voltage of the energy storage unit 22 is Vcap2, it will get closer and closer to the preset voltage Vset, that is, the energy storage unit 22 can store more power.

At time T2, the energy storage unit 20 reaches the preset voltage Vset in the second round of charging. At this time, the voltage detection unit 12 can also report to the power converter 11 to inform the energy storage unit 20 that the voltage V20 reaches the preset voltage Vset. Since the power converter 11 receives the reports from all the voltage detection units (the voltage detection unit 12 and the voltage detection unit 15) in the first current path, it can know all the energy storage units (the energy storage unit 20 and the energy storage unit). 22) The charging in the second round has been completed. In other words, the charging time for the second round is from time T1 to time T2. In one example, the power converter 11 can also continue to reduce the charging current, and use the charging current Iset3 (the third charging current) to perform the third round of charging, because the third round of charging is actually similar to the aforementioned first round of charging and charging. The second round of charging will not be repeated in this embodiment. It can be seen from Figures 2 and 3 that although the charging current of the power converter 11 is different between multiple rounds of charging, the charging current of each round is fixed. It can be said that the power converter 11 is used for each round. The CC mode is charging the energy storage unit 20 and the energy storage unit 22.

Of course, the more rounds of charging performed by the charging system, in theory, the battery cell voltage of the energy storage unit 20 is Vcap1 and the battery cell voltage of the energy storage unit 22 is Vcap2, which is closer to the preset voltage Vset. In this embodiment, There is no limit to how many rounds of charging the charging system can perform, and those with ordinary knowledge in the technical field can freely design it.

In order to facilitate the description of the energy storage unit charging method of the present invention, please refer to FIGS. 1 to 4 together. FIG. 4 is a flowchart of the steps of the energy storage unit charging method according to an embodiment of the present invention. As shown in the figure, in step S400, the charging system will include an energy storage unit 20 (first energy storage unit) and an energy storage unit 22 (second energy storage unit), and the energy storage unit 20 and the energy storage unit 22 Will be connected in series in the first current path. In step S402, the charging system includes a power converter 11, and the power converter 11 charges the energy storage unit 20 and the energy storage unit 22 in the first current path with a charging current Iset1 (first charging current). In step S404, the voltage detecting unit 12 and the voltage detecting unit 15 may detect the voltages of the energy storage unit 20 and the energy storage unit 22, respectively, to obtain the first voltage value corresponding to the energy storage unit 20 and the corresponding energy storage unit 22 The second voltage value. In step S406, the power converter 11 can determine whether at least one of the first voltage value and the second voltage value reaches a predetermined voltage according to the detection results of the voltage detection unit 12 and the voltage detection unit 15. If the power converter 11 determines that at least one of the first voltage value and the second voltage value reaches the preset voltage, it is assumed that the first voltage value corresponding to the energy storage unit 20 reaches the preset voltage and corresponds to the second voltage value of the energy storage unit 22 If the preset voltage is not reached, in step S408, the first current path is set to bypass the energy storage unit 20 that reaches the preset voltage. On the other hand, if the power converter 11 determines that both the first voltage value and the second voltage value have not reached the preset voltage, the power converter 11 will respond to the energy storage unit 20 and the energy storage unit 22 in the first current path. Continue to charge with the charging current Iset1 (first charging current).

Of course, the energy storage unit charging method of the present invention can not only bypass the energy storage unit that reaches the preset voltage, but also can change the charging current after the energy storage unit reaches the preset voltage. Please refer to FIG. 1 to FIG. 5 together. FIG. 5 is a flowchart illustrating the steps of a charging method for an energy storage unit according to another embodiment of the present invention. Similar to the embodiment of FIG. 4, in step S500, the charging system also includes an energy storage unit 20 (first energy storage unit) and an energy storage unit 22 (second energy storage unit), and the energy storage unit 20 and the energy storage unit 22 are also connected in series in the first current path. In step S502, the charging system also includes a power converter 11, and the power converter 11 also uses a charging current Iset1 (first charging current) for the energy storage unit 20 and the energy storage unit 22 in the first current path. Recharge. In step S504, the voltage detection unit 12 and the voltage detection unit 15 can also detect the voltages of the energy storage unit 20 and the energy storage unit 22, respectively, to obtain the first voltage value corresponding to the energy storage unit 20 and the corresponding energy storage unit The second voltage value of 22.

The difference from the embodiment in FIG. 4 is that in step S506, the power converter 11 can determine whether the first voltage value and the second voltage value are both based on the detection results of the voltage detection unit 12 and the voltage detection unit 15 The preset voltage is reached. If the power converter 11 determines that the first voltage value and the second voltage value both reach the preset voltage, in step S508, the power converter 11 changes the energy storage unit 20 and the energy storage unit 22 in the first current path to The charging current Iset2 (second charging current) charges. On the other hand, if the power converter 11 determines that the first voltage value and the second voltage value have not both reached the preset voltage, the power converter 11 will continue to perform the operation on the energy storage unit 20 and the energy storage unit 22 in the first current path. The charging current Iset1 (first charging current) charges.

In summary, the energy storage unit charging method provided by the present invention can not only use one power converter to charge multiple energy storage units, but also can determine whether each energy storage unit has been charged to a preset voltage. When part of the energy storage units have been charged to the preset voltage, bypass the energy storage units that have reached the preset voltage, and continue to charge the energy storage units that have not reached the preset voltage. When all the energy storage units have been charged to the preset voltage, all the energy storage units are turned on, and all the energy storage units are continuously charged with a lower charging current. In this way, the charging method of the energy storage unit provided by the present invention can have a lower hardware cost and can improve the formation efficiency.

10: Power 11: power converter 12: Voltage detection unit 13: Switch control unit 14: switch 15: Voltage detection unit 16: switch control unit 17: switch 20: Energy storage unit (first energy storage unit) 22: Energy storage unit (second energy storage unit) A~F: End point S400~S410: Step flow S500~S510: Step flow

FIG. 1 is a schematic circuit diagram of a charging method using an energy storage unit according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing the current and voltage of the first energy storage unit according to an embodiment of the present invention.

FIG. 3 is a schematic diagram showing the current and voltage of the second energy storage unit according to an embodiment of the present invention.

FIG. 4 is a flowchart showing the steps of a method for charging an energy storage unit according to an embodiment of the present invention.

FIG. 5 is a flowchart showing the steps of a method for charging an energy storage unit according to another embodiment of the present invention.

no

S400~S410: Step flow

Claims (6)

A charging method for an energy storage unit includes: providing a first energy storage unit and a second energy storage unit, the first energy storage unit and the second energy storage unit are connected in series in a first current path; and a power conversion is provided A device for providing a first charging current to the first current path; respectively detecting the voltages of the first energy storage unit and the second energy storage unit to obtain a first voltage value and a second voltage value accordingly ; Determine whether one of the first voltage value and the second voltage value reaches a preset voltage; when the first voltage value reaches the preset voltage and the second voltage value does not reach the preset voltage, set the first A current path bypasses the first energy storage unit; when the first current path is set to bypass the first energy storage unit, it is determined whether the second voltage value reaches the preset voltage; when the second voltage value reaches the Preset voltage, set the first current path to pass through the first energy storage unit and the second energy storage unit; and when the second voltage value reaches the preset voltage, set the power converter to provide the first current path A second charging current. The method for charging an energy storage unit according to claim 1, wherein the first charging current is a constant current, and the first charging current is set to a first current value. The energy storage unit charging method according to claim 2, wherein the second charging current is a constant current, the second charging current is set to a second current value, and the second current value is less than the first current value. A charging method for an energy storage unit, including: A first energy storage unit and a second energy storage unit are provided, the first energy storage unit and the second energy storage unit are connected in series in a first current path; and a power converter is provided for the first current The path provides a first charging current; respectively detects the voltages of the first energy storage unit and the second energy storage unit to obtain a first voltage value and a second voltage value; and determine the first voltage value and the second voltage value Whether the second voltage value reaches a preset voltage; and when the first voltage value and the second voltage value both reach the preset voltage, the power converter is set to provide a second charging current to the first current path. The energy storage unit charging method of claim 4, wherein the first charging current and the second charging current are constant currents, the first charging current is set to a first current value, and the second charging current is set to a second Current value, and the second current value is less than the first current value. The method for charging an energy storage unit according to claim 4, further comprising: determining whether one of the first voltage value and the second voltage value reaches the preset voltage first; and when the first voltage value reaches the preset voltage Voltage and the second voltage value does not reach the preset voltage, setting the first current path to bypass the first energy storage unit.

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