Charging Device and Charging Method

Abstract

A charging device 10 comprises: a plurality of converters 40a, 40b that output a direct-current charging voltage and charging current to charge an assembled battery 50, and that are connected in series to one another; and a management unit 30 communicatively connected to the converter 40a. The management unit 30: acquires a voltage value of the assembled battery 50 before charging is started; sets, on the basis of the acquired voltage value, the charging voltage to a first voltage value at which a large current does not flow to the assembled battery 50, and causes the plurality of converters to start charging of the assembled battery 50; increases, after the charging is started, the charging voltage to a second voltage value higher than the first voltage value, and causes the plurality of converters to charge the assembled battery 50; and increases, after the charging is started, the charging current from a first current value at the start of the charging.

Description

Technical Field

[0001] The present invention relates to a charging device and a charging method for converting electric power from an AC power supply into DC power to charge a battery pack such as a storage module.

Background Art

[0002] Patent Document 1 discloses a battery charging method and a charger suitable for charging a lead-acid battery (see Patent Document 1, paragraph 0001).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, lithium-ion batteries have been applied not only to automotive applications but also to industrial applications. Conventional chargers for lead-acid batteries are often not suitable for charging lithium-ion batteries.

[0005] A plurality of lithium-ion battery cells are combined to produce a storage module. A plurality of storage modules may be combined to produce a storage pack. The storage module and the storage pack (hereinafter, these are also referred to as "battery packs") are maintained at a low state of charge (SOC) during transportation and are charged by a charging device when installed in or after installation in a system (such as a power storage system, a mechanical drive system, a moving body, etc.).

[0006] In addition, in order to stably operate a power storage system, a mechanical drive system, or a moving body (for example, a large AGV), there is a need to store a replacement (spare) battery pack near these systems. There is a need for a charging device for charging such a replacement battery pack on-site.

[0007] One aspect of the present invention provides a charging device that converts power from an AC power source into DC power to charge a battery pack such as a storage battery module. **Means for Solving the Problems**

[0008] The charging device according to one aspect of the present invention includes a plurality of converters connected in series that output a DC charging voltage and a charging current to charge the battery pack, and a management unit communicably connected to the converter, wherein the management unit acquires the voltage value of the battery pack before the start of charging, sets the charging voltage to a first voltage value such that a large current does not flow through the battery pack based on the acquired voltage value, and starts charging the battery pack by the plurality of converters, after the start of charging, raises the charging voltage to a second voltage value higher than the first voltage value and causes the plurality of converters to charge the battery pack, and raises the charging current from a first current value at the start of charging after the start of charging. **Advantages of the Invention**

[0009] By operating the management unit of the charging device as described above, while using a plurality of converters connected in series to obtain the necessary charging voltage, the battery pack can be stably charged. **Brief Description of the Drawings**

[0010]

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Embodiments for Carrying Out the Invention

[0011] The charging device includes a plurality of converters connected in series that output a DC charging voltage and a charging current to charge the battery pack, and a management unit communicably connected to the converter. The management unit acquires the voltage value of the battery pack before charging starts, sets the charging voltage to a first voltage value such that a large current does not flow through the battery pack based on the acquired voltage value, and starts charging the battery pack by the plurality of converters. After charging starts, the charging voltage is raised to a second voltage value higher than the first voltage value to cause the plurality of converters to charge the battery pack, and the charging current is raised from a first current value at the start of charging after charging starts. The charging current may be gradually increased from the first current value at the start of charging, but is not limited to this form. After the charging current reaches a second current value higher than the first current value, the battery pack may be charged by the plurality of converters with the charging current of the second current value.

[0012] With the above configuration, while using a plurality of converters connected in series to obtain the necessary charging voltage, the battery pack can be stably charged. The management unit sets the charging voltage at the start of charging based on the voltage value of the battery pack before charging starts. The management unit raises the charging current from a low current value (first current value). Therefore, it is possible to prevent a large current such as an inrush current from flowing through the battery pack.

[0013] Each of the converters may have a protection function of reducing the output voltage when an output current exceeding the upper limit current value flows.

[0014] When series-connected converters each have a protection function of autonomously reducing the output voltage when an output current exceeding the upper limit current value flows, output hunting is likely to occur. By operating the management unit as described above (that is, by increasing the charging voltage from the first voltage value to the second voltage value and, in parallel, increasing the charging current from the first current value), it is possible to prevent a large current from flowing through the battery pack and prevent output hunting.

[0015] The converter may include a converter in which the output voltage is set to a constant value and a converter in which the output voltage and output current are adjusted.

[0016] By using some converters as converters with a constant output voltage (hereinafter referred to as "base converters"), the communication load for controlling the base converters can be reduced. The communication capacity of the charging device can be allocated to communication with other converters and communication with the battery pack, and the battery pack can be charged stably.

[0017] Until the charging current reaches a second current value higher than the first current value and then switches to a constant voltage charging mode (CV charging mode), that is, during a constant current charging mode (CC charging mode), the management unit may cause the plurality of converters to charge the battery pack with the charging current of the second current value. Furthermore, the management unit may change the second current value according to the voltage of the AC power supply input to the charging device.

[0018] With the above configuration, the battery pack can be charged quickly. Also, for example, the charging device can be used without problems whether the power supply is AC 200V or AC 100V, and the versatility of the charging device is improved. The power supply may be in a voltage range other than AC 20V and AC 100V.

[0019] The charging device may further include a display unit, and the voltage value of the battery pack or the state of charge (SOC) of the battery pack corresponding to the voltage value may be displayed on the display unit.

[0020] With the above configuration, the user can start charging after understanding the state of the battery pack to be charged.

[0021] The charging device may also accept input of a target voltage value, a target SOC value, or a charging time of the battery pack before ending charging.

[0022] Depending on the situation, the battery pack is not necessarily charged to full charge. With the above configuration, the battery pack can be charged to a state according to needs or a state (voltage value, SOC value) suitable for each system in which the battery pack is installed, improving the versatility of the charging device.

[0023] Hereinafter, embodiments of the charging device will be described with reference to the drawings.

[0024] As shown in FIG. 1(A), the charging device 10 has a housing 11. The housing 11 may be formed of a metal plate. The housing 11 has a front surface 11a, a rear surface 11b, and a pair of side surfaces 11c, and has a substantially rectangular parallelepiped shape. The housing 11 incorporates a management unit and a plurality of converters to be described later.

[0025] The front surface 11a has an inclined surface facing obliquely upward and a vertical surface connected to the lower end of the inclined surface and extending in the vertical direction with respect to the installation surface of the charging device 10. A touch panel 20, which is a display unit and a reception unit (user interface), is provided on the inclined surface of the front surface 11a. The touch panel 20 provided on the inclined surface is easy for the user to visually recognize and operate from obliquely above. The rear surface 11b has a connection terminal 18 to which an AC power supply is connected. The side surface 11c has an opening 11e for cooling the inside of the charging device 10.

[0026] The charging device 10 is of a portable type and has a pair of handles 12 on its upper surface. As shown by the broken line in FIG. 1(A), the handles 12 can be folded into a posture parallel to the upper surface. The charging device 10 has a plurality of (four in this embodiment) legs 11d on its bottom surface.

[0027] As shown in FIG. 1(B), on the inclined surface of the front surface 11a, a power switch 14 of the charging device 10, a first communication channel 15a and a second communication channel 15b, which are communication interfaces between the charging device 10 and a battery pack to be described later, are provided. In this embodiment, a third communication channel 15c for CAN communication is further provided on the inclined surface. On the vertical surface of the front surface 11a, charging terminals (charging and discharging terminals for charging and discharging in this embodiment) 16 of the charging device 10, which are connected to the plus terminal and the minus terminal of the battery pack, are provided.

[0028] As shown in FIG. 2, the charging device 10 includes a management unit 30 electrically connected to a touch panel 20, a first converter (hereinafter referred to as an "adjustment converter") 40a communicably connected to the management unit 30, and a second converter (base converter) 40b communicably connected to the adjustment converter 40a. The management unit 30 may be directly communicable with both the adjustment converter 40a and the base converter 40b. The management unit 30 may be a battery management unit (BMU). In FIG. 2, the broken lines indicate communication paths.

[0029] The AC power input to the connection terminal 18 on the rear surface of the charging device 10 is supplied to the adjustment converter 40a and the base converter 40b via a breaker 14a interlocked with the aforementioned power switch 14. The AC power is also input to a power supply 32 for supplying the stepped-down power to the management unit 30.

[0030] The base converter 40b and the adjustment converter 40a are connected in series. The negative output terminal of the base converter 40b is connected to the charging terminal 16 on the front surface of the charging device 10 via a cutoff switch (for example, a relay) 34 and a current sensor 36. The positive output terminal of the base converter 40b is connected to the negative output terminal of the adjustment converter 40a. The positive output terminal of the adjustment converter 40a is connected to the charging terminal 16. The charging terminal 16 is connected to the positive and negative terminals of a battery pack such as the power storage module 50 on-site via a charging cable.

[0031] Each of the converters 40a and 40b has a protection function of automatically reducing the output voltage when an output current exceeding the upper limit current value (output limit value) flows.

[0032] In this embodiment, a discharge circuit 60 for discharging a battery pack such as the power storage module 50 is provided in the housing, and it is configured not as a mere charging device but as a charge-discharge device. The discharge circuit 60 may have a hollow resistor with high heat resistance. Alternatively, it may be configured as a mere charging device without a discharge circuit.

[0033] The power storage module 50 in this embodiment includes a plurality of lithium-ion battery cells 55a connected in series and a monitoring unit 52. The power storage module 50 may be stored near a system such as a power storage system, a mechanical drive system, or a moving body.

[0034] The monitoring unit 52 uses a voltage sensor to detect the voltage value of each battery cell 55a and transmits it to the management unit 30 of the charging device 10 by communication. The monitoring unit 52 transmits the sum of the voltage values of each battery cell 55a to the management unit 30 as the voltage value of the power storage module 50. Alternatively, the management unit 30 may calculate the sum of the voltage values of each battery cell 55a and recognize it as the voltage value of the power storage module 50. The management unit 30 may acquire the voltage value of the power storage module 50 via a voltage sensor (not shown) that measures the voltages of the charging terminals 16, 16. This configuration is suitable when the power storage module does not have the monitoring unit 52.

[0035] The monitoring unit 52 further uses a temperature sensor to detect the temperature of the power storage module 50 and transmits it to the management unit 30 of the charging device 10 by communication. When the management unit 30 is communicably connected to the power storage module 50 as in this embodiment (for example, when communicably connected to the monitoring unit 52), the management unit 30 can grasp in detail the state (for example, voltage) of the power storage module 50. The management unit 30 may grasp the voltage of each battery cell 55a of the power storage module 50 and determine whether the power storage module 50 includes an abnormal cell 55a (for example, a cell in which an internal short circuit has occurred).

[0036] Referring to FIG. 3, the charging operation (initial charging control) of the power storage module 50 by the charging device 10 will be described. FIG. 3(A) shows the output limit values of the charging voltage and charging current output from the charging device 10 (output from the serially connected converters 40a, 40b). The solid line indicates the output limit value of the charging current, and the broken line indicates the output limit value of the charging voltage. FIG. 3(B) shows the instruction value (solid line) of the output current and the instruction value (broken line) of the output voltage from the management unit 30 to the adjustment converter 40a, and FIG. 3(C) shows the instruction value of the output current (solid line) and the instruction value of the output voltage (broken line) from the management unit 30 to the base converter 40b.

[0037] The charging voltage (the first voltage value. In this example, it is a voltage lower than 50V, such as 48.0 volts [V]) at the start of charging in the charging device 10 shown in FIG. 3(A) is determined by the management unit 30 acquiring the voltage value of the power storage module 50 as will be described later. After starting charging, the charging device 10 raises the charging voltage to a second voltage value (such as 68V) to cause the converters 40a, 40b to charge the power storage module 50.

[0038] As shown in Fig. 3(A), the charging current at the start of charging in the charging device 10 is set to a low value (first current value, for example, 1 A to 6 A) of 10 amperes [A] or less. After the start of charging, the charging device 10 gradually increases the charging current, and after reaching the second current value (such as 30 A), it charges the power storage module 50 by the converters 40a and 40b with the charging current of that current value.

[0039] As shown in Fig. 3(B), in the adjustment converter 40a, after the start of charging, as the output voltage increases, the output current gradually (stepwise) increases. As shown in Fig. 3(C), in the base converter 40b, the output voltage is constant, and the output current is constant at, for example, the upper limit current value of the converter (for example, 33 A).

[0040] The sum of the output voltages of the adjustment converter 40a and the base converter 40b becomes the charging voltage of the charging device 10 shown in Fig. 3(A). The second current value (30 A), which is the current value reached by the charging device 10 in Fig. 3(A), is set to a value lower than the upper limit current value (33 A) of each converter.

[0041] The charging initial control shown in Fig. 3 will be described using the flowchart of Fig. 4. First, the management unit 30 acquires the voltage value of the power storage module 50 before the start of charging through communication (S10).

[0042] Based on the acquired voltage value, the management unit 30 sets the charging voltage of the charging device 10 to a first voltage value such that a large current such as an inrush current does not flow through the power storage module 50 (S20). For example, when the voltage value of the power storage module 50 before the start of charging is 47.5 V, the charging voltage of the charging device 10 is set to 48.0 V, which is obtained by adding 0.5 V to it (S20). The predetermined value added to the voltage value of the power storage module 50 before the start of charging for setting the charging voltage is not limited to 0.5 V.

[0043] For example, the management unit 30 sets the output voltage of the base converter 40b to 34.0 V and the output voltage of the adjustment converter 40a to 14.0 V, so that the charging voltage at the start of charging of the charging device 10 is 48.0 V. Thereby, it is possible to prevent an inrush current from flowing into the power storage module 50, and damage to the cutoff switch 34 (see FIG. 2) can also be suppressed.

[0044] Next, the management unit 30 sets the charging current at the start of charging of the charging device 10 to a first current value (for example, 1 A), and starts charging the power storage module 50 by the converters 40a and 40b (S30). The first current value may be set in advance, or charging may be started without setting the charging current in S30.

[0045] FIG. 5 shows the transitions of the charging voltage (dashed line) and the charging current (solid line) in the comparative example. In this comparative example, the output limit value of the charging voltage is set constant at 67 V to 68 V, and the output limit value of the charging current is set constant at 30 A. When charging the power storage module 50 by the converters 40a and 40b connected in series with such settings, there is a possibility that output hunting may occur in the converters 40a and 40b.

[0046] To explain more specifically. When the charging voltage is 67 V to 68 V and the voltage value of the power storage module 50 before the start of charging is 47.5 V, since the voltage difference is large, there is a possibility that an inrush current flows from the converters 40a and 40b toward the power storage module 50. As described above, each of the converters 40a and 40b has a protection function of autonomously reducing the output voltage when an output current exceeding the upper limit current value (for example, 33 A) flows. When an inrush current flows, each of the converters 40a and 40b autonomously reduces the output voltage. The protection functions of these converters 40a and 40b operate independently and do not necessarily operate synchronously (at the same timing). Therefore, when one converter reduces the output voltage and the output current temporarily decreases, the other converter may attempt to increase the output voltage and increase the output current. If such events continue, it leads to output hunting.

[0047] Returning to FIG. 4, in the present embodiment, the management unit 30 sets the charging voltage of the charging device 10 to a first voltage value such that no inrush current flows into the power storage module 50 (S20), sets the charging current to a first current value (for example, 1 A), and starts charging by the converters 40a and 40b (S30). Thereby, it is possible to prevent an inrush current from flowing into the power storage module 50 and to prevent hunting of the converter output.

[0048] Next, the management unit 30 raises the charging voltage from the first voltage value to the second voltage value (S40).

[0049] In the present embodiment, as shown in FIG. 3(A), immediately after the start of charging (for example, 1 second later), the charging voltage is stepped up from the first voltage value (48.0 V) to the second voltage value (68.0 V). In each of the converters 40a and 40b, if the current control is given priority over the voltage control, even if the voltage is increased as described above, the current is limited to the first current value (1 A), so no large current flows. Thereafter, the charging voltage is maintained at the second voltage value (68.0 V), and the power storage module 50 is charged by the converters 40a and 40b.

[0050] Next, the management unit 30 gradually increases the charging current from the first current value (1 A) (for example, increasing by 1 A every second), and after the charging current reaches the second current value (30 A), it maintains the charging current at the second current value and causes the converters 40a and 40b to charge the power storage module 50 (S50). This prevents an inrush current from flowing into the power storage module 50 even after the start of charging, and can prevent hunting of the converter output.

[0051] FIG. 6(A) shows the waveforms of the charging voltage (broken line) and charging current (solid line) from the charging device 10 to the power storage module 50, and FIG. 6(B) shows the output limit values of the charging voltage (broken line) and charging current (solid line) of the charging device 10. As shown in FIG. 6(A), the power storage module 50 is charged to full charge by CCCV (constant current constant voltage) charging as a whole. The initial charging control shown in FIG. 4 is performed at the initial stage of charging of the power storage module 50 as shown in FIG. 6(A).

[0052] Hereinafter, a display example of the screen of the touch panel 20 will be described. The maximum value (second current value) of the charging current may be displayed on the touch panel 20 according to the voltage of the AC power supply input to the charging device 10. The charging device 10 autonomously determines whether the input AC power supply is 100 V or 200 V. In the example of FIG. 7, since the AC power supply input to the charging device 10 is 100 V, it is displayed that the second current value is limited to 15 A. Alternatively, the charging device 10 may autonomously limit the second current value to 15 A when the input AC power supply is 100 V without displaying it on the touch panel 20. When the input power supply is 200 V, the charging device 10 may perform some display on the touch panel 20, or may set the maximum value of the charging current to the default value (30 A) without displaying it on the touch panel 20.

[0053] As shown in FIG. 8, the charging device 10 may display on the touch panel 20 a screen for receiving an input as to whether to charge or discharge the assembled battery.

[0054] As shown in FIG. 8, the charging device 10 may display on the touch panel 20 a screen that accepts whether to perform charging or discharging and also accepts selection of a charging / discharging stop method. In the example of FIG. 8, as the charging / discharging stop method, a plurality of options such as by SOC setting, by voltage setting, and by timer setting are presented.

[0055] When the charging mode is selected on the screen of FIG. 8 and the SOC setting is selected as the stop method, the screen transitions to the screen shown in FIG. 9.

[0056] In the example of FIG. 9, the screen shows a display indicating that the charging mode is selected, and a display (AC200V) indicating that the AC power input to the charging device 10 is 200V. In the target SOC column, the user can input a numerical value. The user may increase or decrease the numerical value by operating the arrow buttons. Below the target SOC column, a column showing the state (voltage, SOC, current, temperature) of the battery pack before charging starts, which is connected to the charging device 10, is displayed. When the user inputs a numerical value in the target SOC column and presses the charge start button, charging of the battery pack by the charging device 10 starts.

[0057] After charging starts, it is preferable that the numerical values (voltage, SOC, current, temperature) in the column showing the state of the battery pack change in real time as charging progresses. Such a display becomes possible when the management unit 30 of the charging device 10 communicates with the monitoring unit 52 of the power storage module 50.

[0058] When the charging mode is selected on the screen of FIG. 8 and the voltage setting is selected as the stop method, "target SOC" on the screen of FIG. 9 is replaced with "target voltage". The user inputs the numerical value of the target voltage. When the charging mode is selected on the screen of FIG. 8 and the timer setting is selected as the stop method, "target SOC" on the screen of FIG. 9 is replaced with "charging voltage" and "charging time". The user inputs the numerical values of the charging voltage and the charging time.

[0059] The present invention is not limited to the above-described embodiments. In the embodiments, an example using two converters 40a and 40b connected in series has been described. Alternatively, the number of converters may be three or more.

[0060] An example has been described in which the management unit 30 stepwise increases the charging voltage of the charging device 10 from a first voltage value to a second voltage value after the start of charging. Alternatively, the management unit 30 may gradually increase the charging voltage of the charging device 10, or may increase it in a two-step manner including a pause period for the increase in the charging voltage.

[0061] An example has been described in which the management unit 30 increases the charging current of the charging device 10 by 1 A every second from a first current value (1 A) after the start of charging. Alternatively, the management unit 30 may increase the charging current of the charging device 10 by several amperes (for example, 5 A) every few seconds, or may increase it by 0.5 A every second.

[0062] The charging device may be configured as follows. A plurality of converters connected in series that output a DC charging voltage and a charging current for charging a battery pack, A management unit communicably connected to the converter, The plurality of converters include a converter whose output voltage is set to a constant value and a converter whose output voltage and output current are adjusted, The management unit, Obtains the voltage value of the battery pack before the start of charging, Based on the obtained voltage value, sets the charging voltage to a first voltage value such that a large current does not flow through the battery pack, and starts charging the battery pack by the plurality of converters, A charging device that, after the start of charging, increases the charging voltage to a second voltage value higher than the first voltage value and causes the plurality of converters to charge the battery pack.

[0063] According to the above configuration, a plurality of converters can be connected in series and used to stably charge the assembled battery. Also, the communication load can be reduced for the control of a converter (base converter) with a constant output voltage.

Explanation of Signs

[0064] 10 Charging device 20 Touch panel (display unit) 30 Management unit 40a, 40b Converter 50 Assembled battery

Claims

1. A charging device comprising: a plurality of converters connected in series that output a DC charging voltage and a charging current to charge a battery pack; a management unit communicably connected to the converter; wherein the management unit: acquires a voltage value of the battery pack before charging starts; sets the charging voltage to a first voltage value greater than the voltage value of the battery pack before charging starts, such that a large current does not flow through the battery pack based on the acquired voltage value, and starts charging the battery pack by the plurality of converters; after charging starts, raises the charging voltage to a second voltage value higher than the first voltage value and causes the plurality of converters to charge the battery pack; and raises the charging current from a first current value at the start of charging after charging starts.

2. A charging device comprising: a plurality of converters connected in series that output a DC charging voltage and a charging current to charge a battery pack; a management unit communicably connected to the converter; wherein the management unit: acquires a voltage value of the battery pack before charging starts; sets the charging voltage to a first voltage value such that a large current does not flow through the battery pack based on the acquired voltage value, and starts charging the battery pack by the plurality of converters; after charging starts, raises the charging voltage to a second voltage value higher than the first voltage value and causes the plurality of converters to charge the battery pack; raises the charging current from a first current value at the start of charging after charging starts; and each of the converters has a protection function of reducing the output voltage when an output current exceeding an upper limit current value flows.

3. The plurality of converters include a base converter whose output voltage is set to a constant value and an adjustment converter whose output voltage and output current are adjusted, and the charging voltage is the total voltage of the output voltage of the base converter and the output voltage of the adjustment converter. The charging device according to claim 1 or claim 2.

4. After the charging current reaches a second current value higher than the first current value, the management unit causes the plurality of converters to charge the battery pack with the charging current of the second current value until switching to a constant voltage charging mode. The charging device according to any one of claims 1 to 3.

5. The management unit according to claim 4, wherein the management unit changes the second current value according to the voltage of an AC power supply input to the charging device.

6. Further comprising a display unit The charging device according to any one of claims 1 to 5, wherein a voltage value of the battery pack or a state of charge (SOC) of the battery pack corresponding to the voltage value is displayed on the display unit.

7. The charging device according to any one of claims 1 to 6, which receives an input of a target voltage value or a target SOC value or a charging time of the battery pack before charging ends.

8. The charging device according to any one of claims 1 to 7, wherein the management unit acquires, by communication, a voltage value of the battery pack before charging starts.

9. A plurality of serially connected converters that output a DC charging voltage and a charging current to charge a battery pack, and a management unit communicably connected to the converter, wherein the plurality of converters include a base converter whose output voltage is set to a constant value and an adjustment converter whose output voltage and output current are adjusted, wherein the charging voltage is a total voltage of the output voltage of the base converter and the output voltage of the adjustment converter, and the management unit acquires a voltage value of the battery pack before charging starts, sets the charging voltage to a first voltage value such that a large current does not flow through the battery pack based on the acquired voltage value, and starts charging the battery pack by the plurality of converters, and after charging starts, adjusts the output voltage of the adjustment converter to increase the charging voltage to a second voltage value higher than the first voltage value, and causes the base converter and the adjustment converter to charge the battery pack.

10. A charging method for charging a battery pack using a charging device including a plurality of serially connected converters that output a DC charging voltage and a charging current to charge the battery pack, and a management unit communicably connected to the converter, wherein a voltage value of the battery pack before charging starts is acquired by the management unit, based on the acquired voltage value, the charging voltage is set to a first voltage value greater than the voltage value of the battery pack before charging starts such that a large current does not flow through the battery pack, and charging of the battery pack by the plurality of converters is started, after charging starts, the charging voltage is increased to a second voltage value higher than the first voltage value, and charging of the battery pack by the plurality of converters is performed, and the charging current is increased from a first current value at the start of charging after charging starts.

11. A charging method for charging a battery pack using a charging device including a series-connected base converter and adjustment converter that output a DC charging voltage and charging current for charging the battery pack, and a management unit communicably connected to the converter, comprising: The charging voltage is the total voltage of the output voltage of the base converter and the output voltage of the adjustment converter; acquiring, by the management unit, a voltage value of the battery pack before charging starts; setting the charging voltage to a first voltage value such that a large current does not flow through the battery pack based on the acquired voltage value, and starting charging of the battery pack by the plurality of converters; after charging starts, adjusting the output voltage of the adjustment converter to increase the charging voltage to a second voltage value higher than the first voltage value, and charging the battery pack by the base converter and the adjustment converter.

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