Uninterruptible power supply device

Abstract

The uninterruptible power supply device (100) includes a converter (4) that converts AC power supplied from an AC power source (12) into DC power, an inverter (8) that converts DC power into AC power and supplies it to a load (14), a DC link (5) connected between the converter (4) and the inverter (8), and a bidirectional chopper (7) that performs DC voltage conversion between the DC link (5) and a power storage device (13). The bidirectional chopper (7) executes a charging operation of storing the DC power of the DC link (5) in the power storage device (13) when the AC power source (12) is healthy. When the charging termination voltage of the power storage device (13) is higher than the DC link voltage of the DC link (5) and the discharge termination voltage of the power storage device (13) is lower than the DC link voltage, when executing the charging operation, the bidirectional chopper (7) switches between a first step-down operation of stepping down the DC link voltage and a first step-up operation of stepping up the DC link voltage according to the voltage of the power storage device (13) and executes them.

Description

Technical Field

[0001] The present disclosure relates to an uninterruptible power supply device.

Background Art

[0002] For example, International Publication No. 2021 / 130981 (Patent Document 1) discloses an uninterruptible power supply device including a power converter connected between an AC power supply and a load. The power converter includes a converter that converts AC power supplied from the AC power supply into DC power and outputs it to a DC link, an inverter that converts the DC power received from the DC link into AC power and supplies it to the load, and a bidirectional chopper that exchanges DC power between the DC link and a power storage device.

[0003] In this uninterruptible power supply device, the power storage device is used as a power storage device that stores DC power to be used when the AC power supply fails. When the AC power supply is normal, the bidirectional chopper is controlled to charge the power storage device, and when the AC power supply fails, the bidirectional chopper is controlled to discharge the power storage device.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Many conventional uninterruptible power supply devices use lead-acid batteries as energy storage devices. In a conventional uninterruptible power supply device, in order to make the output voltage of the inverter directly become the AC output voltage of the uninterruptible power supply device, the DC link voltage input to the inverter is increased. On the other hand, in order to reduce the number of lead-acid batteries used as much as possible and miniaturize the energy storage device, an energy storage device with a use voltage range lower than the DC link voltage is adopted. Therefore, the bidirectional chopper is configured to step down the DC link voltage and output it to the energy storage device when charging the energy storage device, and step up the voltage of the energy storage device and output it to the DC link when discharging the energy storage device.

[0006] In recent years, the use of lithium-ion batteries has been progressing in various products such as mobile devices, electric vehicles, and industrial robots. Lithium-ion batteries have many advantages compared to lead-acid batteries, including: i) high energy density, enabling miniaturization and weight reduction; ii) high voltage and large current can be obtained, so the number of batteries used can be reduced; iii) long life; iv) fast charging possible; v) wide usable environmental temperature range.

[0007] By using this lithium-ion battery as the energy storage device of the uninterruptible power supply device, it is possible to expand the use voltage range of the energy storage device while suppressing the enlargement of the energy storage device. In addition, by using a lithium-ion battery as the energy storage device, advantages such as long life, fast charging possible, and wide usable environmental temperature range can be enjoyed. On the other hand, in an uninterruptible power supply device, the upper limit value of the use voltage range of the energy storage device may become higher than the DC link voltage. In order to cope with such a case, improvement of the bidirectional chopper is required.

[0008] The present disclosure has been made to solve such problems, and an object of the present disclosure is to provide an uninterruptible power supply device that can also cope with an energy storage device having a wide use voltage range.

Means for Solving the Problems

[0009] An uninterruptible power supply device according to an aspect of the present disclosure is connected between an AC power supply and a load. The uninterruptible power supply device includes a converter that converts AC power supplied from the AC power supply into DC power, an inverter that converts the DC power into AC power and supplies it to the load, a DC link connected between the converter and the inverter for inputting the DC power to the inverter, and a bidirectional chopper that performs DC voltage conversion between the DC link and the power storage device. The bidirectional chopper is configured to execute a charging operation of storing the DC power of the DC link in the power storage device when the AC power supply is healthy. When the charging end voltage of the power storage device is higher than the DC link voltage of the DC link and the discharge end voltage of the power storage device is lower than the DC link voltage, when executing the charging operation, the bidirectional chopper switches and executes a first step-down operation of stepping down the DC link voltage and a first boost operation of boosting the DC link voltage according to the voltage of the power storage device.

Advantages of the Invention

[0010] According to the present disclosure, it is possible to provide an uninterruptible power supply device that can also cope with a power storage device having a wide operating voltage range.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4A

Figure 4B

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Figure 6A

Figure 6B

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

[0012] Embodiments of the present disclosure will be described in detail with reference to the drawings. For the same or corresponding parts in the drawings, the same reference numerals are given and their descriptions are not repeated.

[0013] [Embodiment 1] [Configuration of Uninterruptible Power Supply Device] FIG. 1 is a circuit block diagram showing the configuration of an uninterruptible power supply device according to Embodiment 1. As shown in FIG. 1, the uninterruptible power supply device 100 is connected between the AC power supply 12 and the load 14. Note that the uninterruptible power supply device 100 receives a three-phase AC voltage from the AC power supply 12 and supplies a three-phase AC voltage to the load 14. However, for the sake of simplicity of the drawings and description, only a single-phase circuit is shown in FIG. 1.

[0014] The uninterruptible power supply device 100 includes an input terminal T1, a DC terminal T2, an output terminal T3, switches S1 to S3, a converter 4, current detectors CD1 to CD3, a DC link 5, a capacitor 6, an inverter 8, an operation unit 9, and a control device 10.

[0015] The input terminal T1 receives AC power of a predetermined frequency (for example, commercial frequency) from the AC power supply 12. The AC power supply 12 may be a commercial AC power supply or a generator. The instantaneous value of the AC input voltage VI is detected by the control device 10. Based on the instantaneous value of the AC input voltage VI, the presence or absence of a power outage is discriminated. The current detector CD1 detects the AC input current Ii flowing through the input terminal T1 and gives a signal Iif indicating the detected value to the control device 10.

[0016] The output terminal T3 is connected to the load 14. The load 14 is driven by AC power of a predetermined frequency (for example, commercial frequency) supplied from the uninterruptible power supply device 100.

[0017] The DC terminal T2 is connected to the battery 13. The battery 13 constitutes a "power storage device" that stores DC power. However, a capacitor may be connected instead of the battery 13. The instantaneous value of the voltage VB between the terminals of the battery 13 is detected by the control device 10. In the following description, the voltage VB between the terminals of the battery 13 is also referred to as the "battery voltage VB".

[0018] The switch S1 is connected between the input terminal T1 and the AC node of the converter 4 and is controlled by the control device 10. When AC power is being normally supplied from the AC power supply 12 (when the AC power supply 12 is healthy), the switch S1 is turned on, and AC power is supplied from the AC power supply 12 to the converter 4 via the switch S1. When AC power is not being normally supplied from the AC power supply 12 (during a power outage of the AC power supply 12), the switch S1 is turned off, and the connection between the AC power supply 12 and the converter 4 is interrupted.

[0019] Converter 4 is controlled by control device 10 and converts AC power from AC power supply 12 into DC power and outputs it to DC link 5 when AC power supply 12 is normal. Converter 4 is a well-known one including a plurality of sets of semiconductor switching elements and diodes.

[0020] Capacitor 6 is connected to DC link 5 to smooth and stabilize DC link voltage VD. The instantaneous value of DC link voltage VD of DC link 5 is detected by control device 10. In the following description, DC link voltage VD of DC link 5 is also referred to as "DC link voltage VD".

[0021] When AC power supply 12 is normal, control device 10 controls converter 4 so that DC link voltage VD becomes reference DC voltage VDR. When there is a power outage in AC power supply 12, control device 10 stops the operation of converter 4.

[0022] DC link 5 is connected to DC terminal T2 via bidirectional chopper 7 and switch S2. Switch S2 is controlled by control device 10. When uninterruptible power supply device 100 is used, switch S2 is turned on. When maintaining battery 13 and bidirectional chopper 7, switch S2 is turned off.

[0023] Bidirectional chopper 7 is controlled by control device 10 and performs DC voltage conversion between DC link 5 and battery 13 to transfer DC power between DC link 5 and battery 13. Bidirectional chopper 7 is configured to selectively execute a charging operation of storing the DC power of DC link 5 in battery 13 and a discharging operation of supplying the DC power stored in battery 13 to DC link 5. Current detector CD2 detects DC current IB flowing between battery 13 and bidirectional chopper 7 and gives a signal IBf indicating the detected value to control device 10.

[0024] When the AC power supply 12 is normal, the control device 10 controls the bidirectional chopper 7 so that the battery voltage VB becomes the reference DC voltage VBR. When a power failure occurs in the AC power supply 12, the control device 10 controls the bidirectional chopper 7 so that the DC link voltage VD becomes the reference DC voltage VDR. The bidirectional chopper 7 will be described in detail later.

[0025] Also, the DC link 5 is connected to the DC node of the inverter 8, and the AC node of the inverter 8 is connected to the output terminal T3 via the switch S3. The switch S3 is controlled by the control device 10. When the uninterruptible power supply device 100 is used, the switch S3 is turned on. During maintenance of the inverter 8, the switch S3 is turned off.

[0026] The current detector CD3 detects the AC output current IO of the inverter 8 and gives a signal IOf indicating the detected value to the control device 10. The instantaneous value of the AC output voltage VO applied to the load 14 is detected by the control device 10.

[0027] The inverter 8 is controlled by the control device 10, and converts the DC power supplied from the converter 4 and the bidirectional chopper 7 via the DC link 5 into AC power of a predetermined frequency (for example, commercial frequency) and supplies it to the load 14. The inverter 8 is a well-known device including a plurality of sets of semiconductor switching elements and diodes.

[0028] The operation unit 9 includes a plurality of buttons, a plurality of switches, and an image display unit. The user of the uninterruptible power supply device 100 can turn on and off the power of the uninterruptible power supply device 100, or operate the uninterruptible power supply device 100 in automatic operation or manual operation by operating the operation unit 9. The operation unit 9 outputs signals and information indicating the content operated by the user to the control device 10.

[0029] The control device 10 controls the switches S1 to S3, the converter 4, the bidirectional chopper 7, and the inverter 8 based on the signal from the operation unit 9, the AC input voltage VI, the AC output voltage VO, the DC link voltage VD, the battery voltage VB, the AC input current Ii, the DC current IB, and the AC output current IO.

[0030] FIG. 2 is a block diagram showing an example of the hardware configuration of the control device 10. Typically, the control device 10 can be configured by a microcomputer in which a predetermined program is stored in advance.

[0031] In the example of FIG. 2, the control device 10 includes a CPU (Central Processing Unit) 102, a memory 104, and an input / output (I / O) circuit 106. The CPU 102, the memory 104, and the I / O circuit 106 can exchange data with each other via a bus 108. A program is stored in a partial area of the memory 104, and by the CPU 102 executing the program, various functions described later can be realized. The I / O circuit 106 inputs and outputs signals and data to and from the outside of the control device 10.

[0032] Alternatively, different from the example of FIG. 2, at least a part of the control device 10 can be configured using a circuit such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). Also, at least a part of the control device 10 can be configured by an analog circuit.

[0033] In the uninterruptible power supply device 100 shown in FIG. 1, for example, a lithium-ion battery is used as the battery 13. Compared with a lead-acid battery, a lithium-ion battery has the following advantages: i) it can be made smaller and lighter because of its high energy density; ii) the number of batteries used can be reduced because a high voltage and a large current can be obtained; iii) it has a long service life; iv) it can be charged at high speed; and v) it has a wide usable environmental temperature range. Therefore, in recent years, it has been increasingly used in various products such as mobile devices, electric vehicles, and industrial robots.

[0034] A usable voltage range is set for the battery 13. In this specification, the lower limit value of the usable voltage range is referred to as the "discharge cut-off voltage V1", and the upper limit value of the usable voltage range is referred to as the "charge cut-off voltage V2". The discharge cut-off voltage V1 is the lower limit value of the discharge voltage at which discharge can be performed safely. The charge cut-off voltage V2 is the upper limit value of the charge voltage at which charge can be performed safely. A state in which discharge is performed to a voltage lower than the discharge cut-off voltage V1 is called "over-discharge", and a state in which charge is performed to a voltage higher than the charge cut-off voltage V2 is called "over-charge", both of which cause deterioration of the performance of the battery 13.

[0035] In this embodiment, it is assumed that the relationship V1 < VD < V2 holds among the discharge cut-off voltage V1, the charge cut-off voltage V2, and the DC link voltage VD. That is, the charge cut-off voltage V2 is higher than the DC link voltage VD, and the discharge cut-off voltage V1 is lower than the DC link voltage VD.

[0036] In a conventional uninterruptible power supply device using a lead-acid battery, in order to make the output voltage of the inverter 8 directly become the AC output voltage of the uninterruptible power supply device, while increasing the DC link voltage VD input to the inverter 8, and in order to reduce the number of lead-acid batteries used as much as possible to miniaturize the battery 13, a buck-boost chopper is inserted between the DC link 5 and the battery 13. When the battery 13 discharges, the battery voltage VB is boosted, and when the battery 13 is charged, the DC link voltage VD is bucked. This configuration is adopted. In this configuration, the relationship of V1 < V2 < VD holds between the battery voltage VB and the DC link voltage VD. That is, the discharge cut-off voltage V1 and the charge cut-off voltage V2 are lower than the DC link voltage VD.

[0037] By using a lithium-ion battery for the battery 13 of the uninterruptible power supply device 100, while satisfying the requirement for miniaturization of the battery 13, the usable voltage range of the battery 13 can be expanded compared to the conventional uninterruptible power supply device. Therefore, as in this embodiment, it is also possible to use a battery for which the charge cut-off voltage V2 is higher than the DC link voltage VD for the battery 13. In addition, by using a lithium-ion battery for the battery 13, advantages such as long life, fast chargeability, and a wide usable environmental temperature range can be enjoyed.

[0038] <Operation of the Uninterruptible Power Supply Device> Next, the operation of the uninterruptible power supply device 100 according to Embodiment 1 will be described.

[0039] FIG. 3 is a diagram for explaining the operation of the uninterruptible power supply device 100 when the AC power supply 12 is healthy. The arrows in the figure indicate the flow of power exchanged between the AC power supply 12, the load 14, and the battery 13.

[0040] As shown in FIG. 3, the converter 4 converts the AC power supplied from the AC power supply 12 into DC power and outputs it to the DC link 5. The inverter 8 converts the DC power input from the DC link 5 into AC power and supplies it to the load 14.

[0041] The bidirectional chopper 7 stores the DC power supplied from the converter 4 via the DC link 5 in the battery 13. The control device 10 controls the bidirectional chopper 7 so that the battery voltage VB becomes the reference DC voltage VBR. The reference DC voltage VBR is set to the charging termination voltage V2 of the battery 13. When the battery voltage VB rises and reaches the charging termination voltage V2, the control device 10 stops the charging of the battery 13 by stopping the bidirectional chopper 7.

[0042] Figures 4A and 4B are diagrams for explaining the charging operation of the battery 13 by the bidirectional chopper 7. In Figure 4A, the state where DC power is transmitted from the DC link 5 to the battery 13 by the bidirectional chopper 7 is shown. In this case, the input voltage of the bidirectional chopper 7 is the DC link voltage VD, and the output voltage of the bidirectional chopper 7 is the battery voltage VB.

[0043] Figure 4B shows an example of the time change of the battery voltage VB during the charging operation. In the example of Figure 4B, the battery voltage VB is equal to the discharge termination voltage V1 at the time t1 when the charging of the battery 13 starts. As the charging progresses, the battery voltage VB gradually rises from V1. Then, in response to the battery voltage VB reaching the charging termination voltage V2 at the time t3, the charging of the battery 13 is stopped.

[0044] Here, there is a relationship of V1 < VD < V2 among the discharge termination voltage V1, the charging termination voltage V2, and the DC link voltage VD. Therefore, during the charging of the battery 13, the bidirectional chopper 7 switches between a step-down operation of stepping down the DC link voltage VD, which is the input voltage, and a step-up operation of stepping up the DC link voltage VD according to the battery voltage VB and executes them.

[0045] Specifically, during the period when the battery voltage VB is lower than the DC link voltage VD (the period from time t1 to t2), the bidirectional chopper 7 executes a step-down operation. During the period when the battery voltage VB is higher than the DC link voltage VD (the period from time t2 to t3), the bidirectional chopper 7 executes a step-up operation.

[0046] FIG. 5 is a diagram for explaining the operation of the uninterruptible power supply device 100 during a power outage of the AC power supply 12. The arrows in the figure indicate the flow of power exchanged between the AC power supply 12, the load 14, and the battery 13. When a power outage occurs in the AC power supply 12, the switch S1 provided between the input terminal T1 and the AC terminal of the converter 4 is turned off, thereby disconnecting the AC power supply 12 from the uninterruptible power supply device 100. The operation of the converter 4 is stopped.

[0047] The bidirectional chopper 7 supplies the DC power of the battery 13 to the DC link 5. The inverter 8 converts the DC power input from the DC link 5 into AC power and supplies it to the load 14. The control device 10 controls the bidirectional chopper 7 so that the DC link voltage VD becomes the reference DC voltage VDR. When the battery voltage VB drops due to the discharge of the battery 13 and reaches the discharge termination voltage V1, the control device 10 stops the bidirectional chopper 7 to stop the discharge of the battery 13.

[0048] FIGS. 6A and 6B are diagrams for explaining the discharge operation of the battery 13 by the bidirectional chopper 7. FIG. 6A shows a state in which DC power is transmitted from the battery 13 to the DC link 5 by the bidirectional chopper 7. In this case, the input voltage of the bidirectional chopper 7 is the battery voltage VB, and the output voltage of the bidirectional chopper 7 is the DC link voltage VD.

[0049] FIG. 6B shows an example of the time change of the battery voltage VB during the discharge operation. In the example of FIG. 6B, the battery voltage VB is equal to the charge termination voltage V2 at the time t4 when the discharge of the battery 13 starts. As the discharge progresses, the battery voltage VB gradually decreases from V2. Then, in response to the battery voltage VB reaching the discharge termination voltage V1 at the time t6, the discharge of the battery 13 is stopped.

[0050] During the discharge operation, the bidirectional chopper 7 switches between a step-down operation of stepping down the battery voltage VB, which is the input voltage, according to the battery voltage VB, and a step-up operation of stepping up the battery voltage VB and executes them. Specifically, during a period when the battery voltage VB is higher than the DC link voltage VD (the period from time t4 to t5), the bidirectional chopper 7 executes a step-down operation. During a period when the battery voltage VB is lower than the DC link voltage VD (the period from time t5 to t6), the bidirectional chopper 7 executes a step-up operation.

[0051] Figure 7 is a flowchart for explaining the control of the bidirectional chopper 7 by the control device 10. The flowchart in Figure 7 is repeatedly executed by the control device 10 when the uninterruptible power supply device 100 is operating.

[0052] As shown in Figure 7, the control device 10 determines, in step (hereinafter simply referred to as "S") 01, based on the detected value of the AC input voltage VI, whether a power outage of the AC power supply 12 has occurred. If the AC input voltage VI is within the normal range, S01 determines NO, and if the AC input voltage VI is lower than the normal range, S01 determines YES.

[0053] When the AC power supply 12 is healthy (when S01 determines NO), the control device 10 proceeds to S02 and controls the bidirectional chopper 7 so as to store the DC power of the DC link 5 in the battery 13 (see Figure 3).

[0054] During the charging of the battery 13, the control device 10 compares the battery voltage VB and the DC link voltage VD in S03. When VB < VD (when S03 determines YES), the control device 10 controls the bidirectional chopper 7 in S04 so as to step down the DC link voltage VD and output it to the battery 13. When VB > VD (when S03 determines NO), the control device 10 controls the bidirectional chopper 7 in S05 so as to step up the DC link voltage VD and output it to the battery 13.

[0055] Returning to S01, when a power failure of the AC power supply 12 has occurred (when the determination at S01 is YES), the control device 10 proceeds to S06 and controls the bidirectional chopper 7 so as to supply the DC power of the battery 13 to the DC link 5 (see FIG. 5).

[0056] During the discharge of the battery 13, the control device 10 compares the battery voltage VB and the DC link voltage VD according to S07. When VB > VD (when the determination at S07 is YES), the control device 10 controls the bidirectional chopper 7 so as to step down the battery voltage VB and output it to the DC link 5 according to S08. When VB < VD (when the determination at S07 is NO), the control device 10 controls the bidirectional chopper 7 so as to step up the battery voltage VB and output it to the DC link 5 according to S09.

[0057] As described above, when charging the battery 13, the bidirectional chopper 7 switches between stepping down and stepping up the DC link voltage VD according to the battery voltage VB and executes it. Also, when discharging the battery 13, the bidirectional chopper 7 switches between stepping down and stepping up the battery voltage VB according to the battery voltage VB and executes it. Thereby, it is possible to charge and discharge the battery 13 whose charge termination voltage V2 is higher than the DC link voltage VD.

[0058] <Configuration Example of Bidirectional Chopper> Next, a configuration example of the bidirectional chopper 7 shown in FIG. 1 will be described.

[0059] (First Configuration Example) FIG. 8 is a circuit diagram showing a first configuration example of the bidirectional chopper 7. In FIG. 1, only the positive-side DC link 5 is shown, but in FIG. 8, the negative-side DC link 5n is also shown.

[0060] As shown in FIG. 8, the bidirectional chopper 7 according to the first configuration example includes a pair of DC terminals T11 and T12, a pair of DC terminals T13 and T14, semiconductor switching elements (hereinafter also simply referred to as "switching elements") Q1 and Q2, diodes D1 and D2, capacitors C1 to C3, and reactors L1 and L2. In FIG. 8, IGBTs (Insulated Gate Bipolar Transistors) are used as the switching elements Q1 and Q2, but any semiconductor element such as MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) can be used.

[0061] The pair of DC terminals T11 and T12 are connected to the battery 13. The positive-side DC terminal T11 is connected to the positive electrode of the battery 13, and the negative-side DC terminal T12 is connected to the negative electrode of the battery 13. The pair of DC terminals T13 and T14 are connected to the DC links 5 and 5n. The positive-side DC terminal T13 is connected to the positive-side DC link 5, and the negative-side DC terminal T14 is connected to the negative-side DC link 5n.

[0062] The collector of the switching element Q1 is connected to the positive-side DC terminal T11, and the emitter of the switching element Q1 is connected to the first terminal of the capacitor C2. The second terminal of the capacitor C2 is connected to the first terminal of the reactor L2. The second terminal of the reactor L2 is connected to the positive-side DC terminal T13. The switching element Q1 corresponds to an embodiment of the "first switching element".

[0063] The capacitor C1 is connected between the positive-side DC terminal T11 and the negative-side DC terminal T12. The first terminal of the reactor L1 is connected to the emitter of the switching element Q1 and the first terminal of the capacitor C1, and the second terminal of the reactor L1 is connected to the negative-side DC terminals T12 and T14.

[0064] The collector of the switching element Q2 is connected to the second terminal of the capacitor C2 and the first terminal of the reactor L2, and the emitter of the switching element Q2 is connected to the negative DC terminals T12 and T14. The capacitor C3 is connected between the positive DC terminal T13 and the negative DC terminal T14. The switching element Q2 corresponds to an embodiment of the "second switching element".

[0065] The diodes D1 and D2 are connected in anti-parallel to the switching elements Q1 and Q2, respectively. The diodes D1 and D2 are provided to allow a reflux current (freewheel current) to flow when the corresponding switching element Q is off. When the switching element Q is a MOSFET, the diodes D1 and D2 may be constituted by parasitic diodes (body diodes).

[0066] When charging the battery 13, the bidirectional chopper 7 according to the first configuration example switches between step-down and step-up of the DC link voltage VD applied between the pair of DC terminals T13 and T14 according to the battery voltage VB. At this time, the bidirectional chopper 7 operates the switching element Q2 in a switching manner and fixes the switching element Q1 in an off state. When the conduction ratio of the switching element Q2 is α2, the following equation (1) holds between the DC link voltage VD, which is the input voltage of the bidirectional chopper 7, and the battery voltage VB, which is the output voltage of the bidirectional chopper 7. The conduction ratio is the ratio of the time during which the switching element is on to the switching period of the switching element. As shown in equation (1), when α2 < 0.5, the DC link voltage VD is stepped down, and when α2 > 0.5, the DC link voltage VD is stepped up. VB = VD × α2 / (1 - α2) ··· (1) When discharging the battery 13, the bidirectional chopper 7 according to the first configuration example switches between step-down and step-up of the battery voltage VB applied between a pair of DC terminals T11 and T12 according to the battery voltage VB. At this time, the bidirectional chopper 7 switches the switching element Q1 in a switching operation and fixes the switching element Q2 in an off state. When the current conduction ratio of the switching element Q1 is α1, the following relationship of Equation (2) holds between the battery voltage VB which is the input voltage of the bidirectional chopper 7 and the DC link voltage VD which is the output voltage of the bidirectional chopper 7. As shown in Equation (2), when α1 < 0.5, the battery voltage VB is stepped down, and when α1 > 0.5, the battery voltage VB is stepped up. VD = VB × α1 / (1 - α1) ··· (2) FIG. 9 is a diagram for explaining the operation of the bidirectional chopper 7 according to the first configuration example. As shown in FIG. 9, step-down and step-up of the DC link voltage VD can be switched by the current conduction ratio α2 of the switching element Q2. Step-down and step-up of the DC link voltage VD can be switched by the current conduction ratio α1 of the switching element Q1.

[0067] When the AC power supply 12 is normal, when VB < VD, the control device 10 controls the bidirectional chopper 7 so as to step down the DC link voltage VD and output it to the battery 13 by setting the current conduction ratio α2 of the switching element Q2 < 0.5 (first step-down operation). When VB > VD, the control device 10 controls the bidirectional chopper 7 so as to step up the DC link voltage VD and output it to the battery 13 by setting α2 > 0.5 (first step-up operation).

[0068] When the AC power supply 12 fails, when VB > VD, the control device 10 controls the bidirectional chopper 7 so as to step down the battery voltage VB and output it to the DC link 5 by setting the current conduction ratio α1 of the switching element Q1 < 0.5 (second step-down operation). When VB < VD, the control device 10 controls the bidirectional chopper 7 so as to step up the battery voltage VB and output it to the DC link 5 by setting α1 > 0.5 (second step-up operation).

[0069] (Second Configuration Example) FIG. 10 is a circuit diagram showing a second configuration example of the bidirectional chopper 7. As shown in FIG. 10, the bidirectional chopper 7 according to the second configuration example includes a pair of DC terminals T11, T12, a pair of DC terminals T13, T14, switching elements Q1, Q2, diodes D1, D2, capacitors C1, C2, and a reactor L1. In FIG. 10, IGBTs are used as the switching elements Q1, Q2, but any semiconductor element such as a MOSFET can be used.

[0070] The pair of DC terminals T11, T12 is connected to the battery 13. The positive DC terminal T11 is connected to the positive electrode of the battery 13, and the negative DC terminal T12 is connected to the negative electrode of the battery 13. The pair of DC terminals T13, T14 is connected to the DC links 5, 5n. The negative DC terminal T14 is connected to the negative DC link 5n, and the positive DC terminal T13 is connected to the positive DC link 5. In the second configuration example, the polarities of the input voltage and the output voltage are reversed.

[0071] The collector of the switching element Q1 is connected to the positive DC terminal T11, and the emitter of the switching element Q1 is connected to the collector of the switching element Q2. The emitter of the switching element Q2 is connected to the negative DC terminal T14. The diodes D1, D2 are connected in anti-parallel to the switching elements Q1, Q2, respectively.

[0072] The capacitor C1 is connected between the positive DC terminal T11 and the negative DC terminal T12. The first terminal of the reactor L1 is connected to the emitter of the switching element Q1 and the collector of the switching element Q2, and the second terminal of the reactor L1 is connected to the negative DC terminal T12 and the positive DC terminal T13. The capacitor C2 is connected between the positive DC terminal T13 and the negative DC terminal T14.

[0073] When charging the battery 13, the bidirectional chopper 7 according to the second configuration example switches between step - down and step - up of the DC link voltage VD applied between the pair of DC terminals T13 and T14 according to the battery voltage VB. In this case, the bidirectional chopper 7 switches the switching element Q2 and fixes the switching element Q1 in the off state. When the current - flowing rate of the switching element Q2 is α2, the relationship of the above formula (1) holds between the DC link voltage VD which is the input voltage of the bidirectional chopper 7 and the battery voltage VB which is the output voltage of the bidirectional chopper 7. As shown in formula (1), when α2 < 0.5, the DC link voltage VD is stepped down, and when α2 > 0.5, the DC link voltage VD is stepped up.

[0074] When discharging the battery 13, the bidirectional chopper 7 according to the second configuration example switches between step - down and step - up of the battery voltage VB applied between the pair of DC terminals T11 and T12 according to the battery voltage VB. In this case, the bidirectional chopper 7 switches the switching element Q1 and fixes the switching element Q2 in the off state. When the current - flowing rate of the switching element Q1 is α1, the relationship of the above formula (2) holds between the battery voltage VB which is the input voltage of the bidirectional chopper 7 and the DC link voltage VD which is the output voltage of the bidirectional chopper 7. As shown in formula (2), when α1 < 0.5, the battery voltage VB is stepped down, and when α1 > 0.5, the battery voltage VB is stepped up.

[0075] FIG. 11 is a diagram for explaining the operation of the bidirectional chopper 7 according to the second configuration example. As shown in FIG. 11, step - down and step - up of the DC link voltage VD can be switched by the current - flowing rate α2 of the switching element Q2. Step - down and step - up of the DC link voltage VD can be switched by the current - flowing rate α1 of the switching element Q1.

[0076] When the AC power supply 12 is normal, when VB < VD, the control device 10 controls the bidirectional chopper 7 so as to step down the DC link voltage VD and output it to the battery 13 by making the current conduction ratio α2 of the switching element Q2 < 0.5 (the first step-down operation). When VB > VD, the control device 10 controls the bidirectional chopper 7 so as to step up the DC link voltage VD and output it to the battery 13 by making α2 > 0.5 (the first step-up operation).

[0077] When the AC power supply 12 fails, when VB > VD, the control device 10 controls the bidirectional chopper 7 so as to step down the battery voltage VB and output it to the DC link 5 by making the current conduction ratio α1 of the switching element Q1 < 0.5 (the second step-down operation). When VB < VD, the control device 10 controls the bidirectional chopper 7 so as to step up the battery voltage VB and output it to the DC link 5 by making α1 > 0.5 (the second step-up operation).

[0078] (The third configuration example) FIG. 12 is a circuit diagram showing a third configuration example of the bidirectional chopper 7. As shown in FIG. 12, the bidirectional chopper 7 according to the third configuration example includes a pair of DC terminals T11, T12, a pair of DC terminals T13, T14, switching elements Q1 to Q6, diodes D1 to D6, capacitors C1 to C4, and reactors L1, L2. In FIG. 12, IGBTs are used as the switching elements Q1 to Q6, but any semiconductor element such as a MOSFET can be used.

[0079] The pair of DC terminals T11, T12 are connected to the battery 13. The positive DC terminal T11 is connected to the positive electrode of the battery 13, and the negative DC terminal T12 is connected to the negative electrode of the battery 13. The pair of DC terminals T13, T14 are connected to the DC links 5, 5n. The positive DC terminal T13 is connected to the positive DC link 5, and the negative DC terminal T14 is connected to the negative DC link 5n.

[0080] The collector of the switching element Q1 is connected to the collector of the switching element Q5, and the emitter of the switching element Q1 is connected to the first terminal of the reactor L1. The second terminal of the reactor L1 is connected to the positive DC terminal T13. The emitter of the switching element Q5 is connected to the positive DC terminal T11. The collector of the switching element Q2 is connected to the emitter of the switching element Q1 and the first terminal of the reactor L1, and the emitter of the switching element Q2 is connected to the negative DC terminals T12 and T14. The diodes D1, D2, and D5 are connected in anti-parallel to the switching elements Q1, Q2, and Q5, respectively. The capacitor C1 is connected between the positive DC terminal T11 and the negative DC terminal T12. The capacitor C2 is connected between the positive DC terminal T13 and the negative DC terminal T14.

[0081] The first terminal of the reactor L2 is connected to the positive DC terminal T11, and the second terminal of the reactor L2 is connected to the emitter of the switching element Q4. The collector of the switching element Q4 is connected to the collector of the switching element Q6. The emitter of the switching element Q6 is connected to the positive DC terminal T13. The collector of the switching element Q3 is connected to the emitter of the switching element Q4 and the second terminal of the reactor L2, and the emitter of the switching element Q3 is connected to the negative DC terminals T12 and T14. The diodes D3, D4, and D6 are connected in anti-parallel to the switching elements Q3, Q4, and Q6, respectively. The capacitor C3 is connected between the positive DC terminal T11 and the negative DC terminal T12. The capacitor C4 is connected between the positive DC terminal T13 and the negative DC terminal T14.

[0082] In the third configuration example, the switching elements Q1, Q2, Q5, the diodes D1, D2, D5, the reactor L1, and the capacitors C1 and C2 constitute a "first bidirectional chopper". The first bidirectional chopper is configured to be able to transfer power bidirectionally when VB > VD.

[0083] Specifically, when the battery voltage VB is the input voltage and the DC link voltage VD is the output voltage, the first bidirectional chopper operates as a buck chopper that steps down the battery voltage VB. At this time, power flows from the battery 13 to the DC link 5, 5n, and the battery 13 discharges. The following relationship of Equation (3) holds between the battery voltage VB and the DC link voltage VD. α1 is the current conduction rate of the switching element Q1, and 0 < α1 < 1. VD = VB × α1 ··· (3) On the other hand, when the DC link voltage VD is the input voltage and the battery voltage VB is the output voltage, the first bidirectional chopper operates as a boost chopper that steps up the DC link voltage VD. At this time, power flows from the DC link 5, 5n to the battery 13, and the battery 13 is charged. The following relationship of Equation (4) holds between the battery voltage VB and the DC link voltage VD. α2 is the current conduction rate of the switching element Q2, and 0 < α2 < 1. VB = VD × 1 / (1 - α2) ··· (4) In the third configuration example, the switching elements Q3, Q4, Q6, the diodes D3, D4, D6, the reactor L2, and the capacitors C3, C4 constitute the "second bidirectional chopper". The second bidirectional chopper is configured to be able to transfer power bidirectionally when VB < VD.

[0084] Specifically, when the battery voltage VB is the input voltage and the DC link voltage VD is the output voltage, the second bidirectional chopper operates as a boost chopper that steps up the battery voltage VB. At this time, power flows from the battery 13 to the DC link 5, 5n, and the battery 13 is discharged. The following relationship of Equation (5) holds between the battery voltage VB and the DC link voltage VD. α3 is the current conduction rate of the switching element Q3, and 0 < α3 < 1. VD = VB × 1 / (1 - α3) ··· (5) On the one hand, when the DC link voltage VD is the input voltage and the battery voltage VB is the output voltage, the second bidirectional chopper operates as a buck chopper that steps down the DC link voltage VD. At this time, power flows from the DC link 5,5n to the battery 13, and the battery 13 is charged. The following relationship of Equation (6) holds between the battery voltage VB and the DC link voltage VD. α4 is the conduction rate of the switching element Q4, and 0 < α4 < 1. VB = VD × α4 ···(6) FIG. 13 is a diagram for explaining the operation of the bidirectional chopper 7 according to the third configuration example. As shown in FIG. 13, during charging of the battery 13, the step-down and step-up of the DC link voltage VD can be switched by the conduction rate α2 of the switching element Q2 and the conduction rate α4 of the switching element Q4. Specifically, the DC link voltage VD is stepped down according to the conduction rate α4 of the switching element Q4, and the DC link voltage VD is stepped up according to the conduction rate α2 of the switching element Q2. Note that when stepping down the DC link voltage VD, by turning off the switching element Q5, it is possible to prevent current from flowing from the DC link 5,5n to the battery 13 via the reactor L1. When stepping up the DC link voltage VD, the switching element Q5 is turned on so as not to interfere with the step-up operation of the first bidirectional chopper.

[0085] Also, during discharging of the battery 13, the step-down and step-up of the battery voltage VB can be switched by the conduction rate α1 of the switching element Q1 and the conduction rate α3 of the switching element Q3. Specifically, the battery voltage VB is stepped down according to the conduction rate α1 of the switching element Q1, and the battery voltage VB is stepped up according to the conduction rate α3 of the switching element Q3. Note that when stepping down the battery voltage VB, by turning off the switching element Q6, it is possible to prevent current from flowing from the battery 13 to the DC link 5,5n via the reactor L2. When stepping up the battery voltage VB, the switching element Q6 is turned on so as not to interfere with the step-up operation of the second bidirectional chopper.

[0086] When the AC power supply 12 is normal, when VB < VD, the control device 10 fixes the switching elements Q1 to Q3, Q5, and Q6 in the off state, and controls the conduction rate α4 of the switching element Q4 to step down the DC link voltage VD and output it to the battery 13, thereby controlling the bidirectional chopper 7 (first step-down operation). When VB > VD, the control device 10 fixes the switching elements Q1, Q3, Q4, and Q6 in the off state, fixes the switching element Q5 in the on state, and controls the conduction rate α2 of the switching element Q2 to step up the DC link voltage VD and output it to the battery 13, thereby controlling the bidirectional chopper 7 (first step-up operation).

[0087] When the AC power supply 12 is out of power, when VB > VD, the control device 10 fixes the switching elements Q2 to Q6 in the off state, and controls the conduction rate α1 of the switching element Q1 to step down the battery voltage VB and output it to the DC link 5, thereby controlling the bidirectional chopper 7 (second step-down operation). When VB < VD, the control device 10 fixes the switching elements Q1, Q2, Q4, and Q5 in the off state, fixes the switching element Q6 in the on state, and controls the conduction rate α3 of the switching element Q3 to step up the battery voltage VB and output it to the DC link 5, thereby controlling the bidirectional chopper 7 (second step-up operation).

[0088] In the above-described embodiment, the operation of the bidirectional chopper 7 when the relationship V1 < VD < V2 holds among the charge termination voltage V2, discharge termination voltage V1 of the battery 13, and the DC link voltage VD has been described. However, when the relationship V1 < V2 < VD holds, during charging of the battery 13, VB < VD always holds. Therefore, the bidirectional chopper 7 according to the first to third configuration examples only performs a step-down operation to step down the DC link voltage VD. Also, during discharge of the battery 13, VB < VD always holds. Therefore, the bidirectional chopper 7 according to the first to third configuration examples only performs a step-up operation to step up the battery voltage VB.

[0089] As described above, the uninterruptible power supply device according to Embodiment 1 can be compatible with both a battery having a charge termination voltage V2 higher than the DC link voltage VD and a battery having a charge termination voltage V2 lower than the DC link voltage VD. According to this, compared with the conventional uninterruptible power supply device, the usable voltage range of the battery connectable to the uninterruptible power supply device is widened, so that the types of batteries that can be used increase. Therefore, it becomes possible to propose a combination of an uninterruptible power supply device and a battery that is optimal in terms of the scale and cost of the device to the user of the uninterruptible power supply device.

[0090] [Embodiment 2] In the above-described Embodiment 1, the uninterruptible power supply device 100 including the power converters (converter 4, inverter 8, and bidirectional chopper 7) connected between the AC power supply 12 and the load 14 has been described. However, the uninterruptible power supply device 100 according to the present disclosure only needs to include at least the bidirectional chopper 7 that exchanges power between the battery 13 and the DC link 5. For example, the uninterruptible power supply device 100 may have the configuration shown in FIG. 14.

[0091] FIG. 14 is a circuit block diagram showing the configuration of the uninterruptible power supply device according to Embodiment 2. The uninterruptible power supply device 100 according to Embodiment 2 receives a three-phase AC voltage from the AC power supply 12 and supplies a three-phase AC voltage to the load 14. However, for the sake of simplicity of the drawing and description, only a single-phase circuit is shown in FIG. 1.

[0092] As shown in FIG. 14, the uninterruptible power supply device 100 according to Embodiment 2 includes an input terminal T1, a DC terminal T2, an output terminal T3, VCBs (Vacuum Circuit Breakers) 15 to 17, high-speed switches (HSSs; High Speed Switches) 20, a bidirectional converter 11, a bidirectional chopper 7, a reactor 21, capacitors 6 and 22, current detectors CD1 to CD3, and a control device 10. The uninterruptible power supply device 100 according to Embodiment 2 is also called a multiple power compensator.

[0093] VCB15, HSS20, and VCB16 are connected in series between the input terminal T1 and the output terminal T3. VCB15 and VCB16 are turned on during the normal operation of the uninterruptible power supply device 100, and are turned off, for example, during the maintenance of HSS20 (during bypass power supply for maintenance).

[0094] HSS20 is constituted by, for example, a semiconductor switching element and is controlled by the control device 10. HSS20 is turned on when the AC power supply 12 is normal and is turned off when the AC power supply 12 fails.

[0095] VCB17 is connected between the input terminal T1 and the output terminal T3. VCB17 is turned off during the normal operation of the uninterruptible power supply device 100, and is turned on, for example, during bypass power supply for maintenance. When VCB17 is turned on, the AC input voltage VI is supplied from the AC power supply 12 to the load 14 via VCB17, and the load 14 is operated.

[0096] The AC terminals of the bidirectional converter 11 are connected to the node N1 between HSS20 and VCB16 via the reactor 21. The DC terminals of the bidirectional converter 11 are connected to the DC link 5. The bidirectional converter 11 is a well-known one including a plurality of switching elements and a plurality of diodes, and is controlled by the control device 10, for example, by PWM (Pulse Width Modulation). By turning on and off each switching element included in the bidirectional converter 11 at a predetermined switching frequency, it is possible to convert AC power into DC power or, conversely, convert DC power into AC power.

[0097] The reactor 21 and the capacitor 22 constitute an AC filter. The AC filter is a low-pass filter that passes the current of the commercial frequency and blocks the current of the switching frequency generated by the bidirectional converter 11. In other words, the AC filter converts the output voltage of the bidirectional converter 11 into a sinusoidal AC voltage.

[0098] The capacitor 6 is connected to the DC link 5 to smooth and stabilize the DC link voltage VD. The instantaneous value of the DC link voltage VD is detected by the control device 10.

[0099] The bidirectional chopper 7 is connected between the DC link 5 and the DC terminal T2. The bidirectional chopper 7 is controlled by the control device 10 to transfer DC power between the DC link 5 and the battery 13. The bidirectional chopper 7 is configured to selectively execute a charging operation of storing the DC power of the DC link 5 in the battery 13 and a discharging operation of supplying the DC power stored in the battery 13 to the DC link 5. Any of the bidirectional choppers according to the first to third configuration examples described above can be applied to the bidirectional chopper 7.

[0100] The current detector CD1 detects the AC input current Ii flowing through the HSS20 and gives a signal Iif indicating the detected value to the control device 10. The current detector CD2 detects the DC current IB flowing between the battery 13 and the bidirectional chopper 7 and gives a signal IBf indicating the detected value to the control device 10. The current detector CD3 detects the AC output current IL flowing through the reactor 21 and gives a signal ILf indicating the detected value to the control device 10.

[0101] The control device 10 controls the entire uninterruptible power supply device 100 based on the AC voltages VI, VO, the DC voltages VD, VB, and the output signals Iif, IBf, IOf of the current detectors CD1 to CD3, etc.

[0102] In the uninterruptible power supply device 100 shown in FIG. 14, when the AC power supply 12 is normal, the HSS20 is turned on, and AC power is supplied from the AC power supply 12 to the load 14 via the VCB15, HSS20, and VCB16, and the load 14 is driven.

[0103] AC power is supplied from the AC power source 12 to the bidirectional converter 11 via the VCB 15 and the HSS 20, and the AC power is converted into DC power by the bidirectional converter 11 and supplied to the DC link 5. This DC power is stored in the battery 13 by the bidirectional chopper 7. At this time, the control device 10 controls the bidirectional converter 11 so that the DC link voltage VD becomes the reference DC voltage VDR. Further, the control device 10 controls the bidirectional chopper 7 so that the battery voltage VB becomes the reference DC voltage VBR.

[0104] When there is a relationship of V1 < VD < V2 among the discharge cut-off voltage V1, the charge cut-off voltage V2 of the battery 13, and the DC link voltage VD, the bidirectional chopper 7 switches between a step-down operation of stepping down the DC link voltage VD, which is the input voltage, according to the battery voltage VB, and a step-up operation of stepping up the DC link voltage VD and executes them. As described in the first embodiment, the bidirectional chopper 7 executes the step-down operation during the period when the battery voltage VB is lower than the DC link voltage VD. The bidirectional chopper 7 executes the step-up operation during the period when the battery voltage VB is higher than the DC link voltage VD.

[0105] When a power failure occurs in the AC power source 12, the HSS 20 is instantaneously turned off, and the AC power source 12 and the load 14 are electrically disconnected. At the same time, the DC power of the battery 13 is supplied to the DC link 5 by the bidirectional chopper 7. Then, the DC power is converted into AC power by the bidirectional converter 11 and supplied to the load 14, and the operation of the load 14 is continued. The control device 10 controls the bidirectional chopper 7 so that the DC link voltage VD becomes the reference DC voltage VDR. When the battery voltage VB drops due to the discharge of the battery 13 and reaches the discharge cut-off voltage V1, the control device 10 stops the discharge of the battery 13 by stopping the bidirectional chopper 7.

[0106] When there is a relationship of V1 < VD < V2, the bidirectional chopper 7 switches between a step-down operation of stepping down the battery voltage VB, which is the input voltage, according to the battery voltage VB, and a step-up operation of stepping up the battery voltage VB and executes them. As described in the first embodiment, during a period when the battery voltage VB is higher than the DC link voltage VD, the bidirectional chopper 7 executes a step-down operation. During a period when the battery voltage VB is lower than the DC link voltage VD, the bidirectional chopper 7 executes a step-up operation.

[0107] According to this, even in the uninterruptible power supply device according to the second embodiment, the same effects as those of the uninterruptible power supply device according to the first embodiment can be obtained.

[0108] The embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present disclosure is indicated by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims be included.

Explanation of Reference Numerals

[0109] 4 Converter, 5,5n DC link, 6,22, C1~C4 Capacitors, 7 Bidirectional chopper, 8 Inverter, 9 Operation unit, 10 Control device, 11 Bidirectional converter, 12 AC power supply, 13 Battery, 14 Load, 15~17 VCB, 20 HSS, 21,L1,L2 Reactors, 100 Uninterruptible power supply device, 102 CPU, 104 Memory, 106 I / O circuit, 108 Bus, T1 Input terminal, T2,T11,T12,T13,T14 DC terminals, T3 Output terminal, S1~S3 Switches, VB Battery voltage, VD DC link voltage, CD1~CD3 Current detectors, Q1~Q6 Switching elements, D1~D6 Diodes, S1~S3 Switches.

Claims

1. An uninterruptible power supply device connected between an AC power supply and a load, a converter that converts AC power supplied from the AC power supply into DC power, an inverter that converts the DC power into AC power and supplies it to the load, a DC link connected between the converter and the inverter for inputting the DC power to the inverter, and a bidirectional chopper that performs DC voltage conversion between the DC link and a power storage device, wherein the bidirectional chopper is configured to execute a charging operation of storing the DC power of the DC link in the power storage device when the AC power supply is normal, and to execute a discharging operation of supplying the DC power stored in the power storage device to the DC link when the AC power supply fails, when the charging termination voltage of the power storage device is higher than the DC link voltage of the DC link and the discharging termination voltage of the power storage device is lower than the DC link voltage, when executing the charging operation, the bidirectional chopper switches between a first step-down operation of stepping down the DC link voltage and a first step-up operation of stepping up the DC link voltage according to the voltage of the power storage device and executes them, when the charging termination voltage of the power storage device is higher than the DC link voltage and the discharging termination voltage of the power storage device is lower than the DC link voltage, when executing the discharging operation, the bidirectional chopper switches between a second step-down operation of stepping down the voltage of the power storage device and a second step-up operation of stepping up the voltage of the power storage device according to the voltage of the power storage device and executes them, the bidirectional chopper includes a first switching element that is turned on and off when executing the discharging operation and is in an off state when executing the charging operation, a second switching element that is turned on and off when executing the charging operation and is in an off state when executing the discharging operation, a first diode connected in anti-parallel with the first switching element, and a second diode connected in anti-parallel with the second switching element, the bidirectional chopper switches between the first step-down operation and the first step-up operation by controlling a second current-carrying rate of the second switching element according to the voltage of the power storage device and executes them, and switches between the second step-down operation and the second step-up operation by controlling a first current-carrying rate of the first switching element according to the voltage of the power storage device and executes them, an uninterruptible power supply device.

2. The bidirectional chopper executes the first step-down operation when the voltage of the power storage device is lower than the DC link voltage, and executes the first step-up operation when the voltage of the power storage device is higher than the DC link voltage. The uninterruptible power supply device according to claim 1.

3. The bidirectional chopper executes the second step-down operation when the voltage of the power storage device is higher than the DC link voltage, and executes the second step-up operation when the voltage of the power storage device is lower than the DC link voltage. The uninterruptible power supply device according to claim 1.

4. When the charge termination voltage of the power storage device is lower than the DC link voltage, the bidirectional chopper executes the first step-down operation when performing the charging operation, and executes the second step-up operation when performing the discharging operation. The uninterruptible power supply device according to claim 1.

5. An uninterruptible power supply device connected between an AC power supply and a load, A converter that converts AC power supplied from the AC power supply into DC power, An inverter that converts the DC power into AC power and supplies it to the load, A DC link connected between the converter and the inverter for inputting the DC power to the inverter, And a bidirectional chopper that performs DC voltage conversion between the DC link and a power storage device, The bidirectional chopper is configured to execute a charging operation of storing the DC power of the DC link in the power storage device when the AC power supply is normal, and execute a discharging operation of supplying the DC power stored in the power storage device to the DC link when the AC power supply fails, When the charge termination voltage of the power storage device is higher than the DC link voltage of the DC link and the discharge termination voltage of the power storage device is lower than the DC link voltage, when performing the charging operation, the bidirectional chopper switches and executes a first step-down operation of stepping down the DC link voltage and a first step-up operation of stepping up the DC link voltage according to the voltage of the power storage device, When the charge termination voltage of the power storage device is higher than the DC link voltage and the discharge termination voltage of the power storage device is lower than the DC link voltage, when performing the discharging operation, the bidirectional chopper switches and executes a second step-down operation of stepping down the voltage of the power storage device and a second step-up operation of stepping up the voltage of the power storage device according to the voltage of the power storage device, The bidirectional chopper A first bidirectional chopper configured to execute by switching between the first boosting operation and the second bucking operation when the voltage of the energy storage device is higher than the DC link voltage; An uninterruptible power supply device including a second bidirectional chopper configured to execute by switching between the first bucking operation and the second boosting operation when the voltage of the energy storage device is lower than the DC link voltage.

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