Uninterruptible power supply device

Abstract

The uninterruptible power supply (UPS) includes a converter (12), a bidirectional chopper (18), and an inverter (20). The converter (12) and inverter (20) each include branch circuits with multiple cascaded converter units (26). The bidirectional chopper (18) includes multiple chopper units (30) connected in series between a DC positive bus (14p) and a DC negative bus (14n). The energy storage device includes multiple energy storage units, each corresponding to and connected in parallel with the multiple chopper units. Each chopper unit (30) includes a first input / output terminal and a second input / output terminal, a capacitor connected between the first input / output terminal and the second input / output terminal, and a charging / discharging circuit for imparting and receiving DC power between the capacitor and the corresponding energy storage unit.

Description

Technical Field

[0001] This disclosure relates to uninterruptible power supply devices. Background Technology

[0002] For example, International Patent Publication No. 2014 / 132452 (Patent Document 1) discloses an uninterruptible power supply (UPS) device for supplying power to multiple servers installed in a data center or similar location. This UPS device is connected to a low-voltage (400V) AC power source. The UPS device is configured to include: a converter that converts low-voltage AC power (AC400V) from the AC power source into DC power; and an inverter that converts the DC power from the converter or DC power stored in a battery into low-voltage AC power (AC400V).

[0003] Existing technical documents Patent documents Patent Document 1: International Publication No. 2014 / 132452 Summary of the Invention

[0004] The problem that the invention aims to solve To supply AC power to loads with capacities ranging from tens to hundreds of MVA, multiple uninterruptible power supplies (UPS) are connected in parallel with the load to construct a power system. This power system supplies low-voltage AC power (AC400V) to the load via transmission lines.

[0005] In the aforementioned power supply system, the large current flowing through the transmission lines raises concerns about increased power loss and voltage drop. Furthermore, the need for multiple transmission lines to handle such large currents leads to larger power supply systems and increased equipment costs.

[0006] Therefore, the main objective of this disclosure is to provide an uninterruptible power supply device that can achieve miniaturization and high efficiency.

[0007] Methods for solving problems The uninterruptible power supply (UPS) device disclosed herein is connected between an AC power source and an AC transmission line. The UPS device includes a converter, a bidirectional chopper, and an inverter. The converter converts AC power supplied from the AC power source into DC power and supplies it between a DC positive bus and a DC negative bus. The bidirectional chopper converts the DC voltage between the DC positive bus and the DC negative bus and the DC voltage of the energy storage device. The inverter converts the DC power received from the DC positive bus and the DC negative bus into AC power and supplies it to the AC transmission line. The converter and inverter each include branch circuits having multiple converter units cascaded together. The bidirectional chopper includes multiple chopper units connected in series between the DC positive bus and the DC negative bus. The energy storage device includes multiple energy storage units, each corresponding to and connected in parallel with the multiple chopper units. Each multiple chopper unit includes a first input / output terminal and a second input / output terminal, a capacitor connected between the first input / output terminal and the second input / output terminal, and a charging / discharging circuit for imparting and discharging DC power between the capacitor and the corresponding energy storage unit.

[0008] Invention Effects According to this disclosure, an uninterruptible power supply device capable of miniaturization and high efficiency can be provided. Attached Figure Description

[0009] Figure 1 This is a circuit block diagram illustrating the uninterruptible power supply device of this embodiment.

[0010] Figure 2 It is a circuit diagram showing the main circuit structure of the converter, inverter, and bidirectional chopper.

[0011] Figure 3 This is a circuit diagram representing the first structural example of a converter unit.

[0012] Figure 4 This is a circuit diagram representing a second structural example of a converter unit.

[0013] Figure 5 This is a circuit diagram representing the first structural example of a chopper unit.

[0014] Figure 6 This is a flowchart illustrating the control circuit's control over the chopper unit.

[0015] Figure 7 This is a circuit block diagram used to illustrate the initial charging of a capacitor.

[0016] Figure 8 This is a circuit diagram representing the second structural example of a chopper unit.

[0017] Figure 9 This is a circuit diagram representing the third structural example of a chopper unit.

[0018] Figure 10 This is a flowchart illustrating the control circuit's control over the chopper unit.

[0019] Figure 11 This is a diagram illustrating a structural example of a power supply system using the uninterruptible power supply device of this embodiment.

[0020] Figure 12 It means Figure 11 The diagram shows the main circuit structure of the converter, inverter, and bidirectional chopper. Detailed Implementation

[0021] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Furthermore, the same or equivalent parts in the drawings will be labeled with the same reference numerals, and their descriptions will generally not be repeated.

[0022] Figure 1 This is a circuit block diagram illustrating the uninterruptible power supply device of this embodiment. (e.g.) Figure 1 As shown, the uninterruptible power supply (UPS) 10 is connected between the AC power source 1 and the AC transmission line 4. The UPS 10 receives three-phase AC voltage from the AC power source 1 and supplies three-phase AC voltage to the AC transmission line 4. However, for the sake of simplicity in the drawings and description, [the following is omitted as the original text is incomplete and cannot be translated]. Figure 1 Only one phase of the circuit is shown in the diagram.

[0023] In this manual, in accordance with the IEC (International Electrotechnical Commission) standards, regarding AC voltage levels, voltage levels above 230kV are classified as Extra-high Voltage Alternating Current (EHVAC), voltage levels from 35kV to 230kV are classified as High Voltage Alternating Current (HVAC), voltage levels from 1kV to 35kV are classified as Medium Voltage Alternating Current (MVAC), and voltage levels below 1kV are classified as Low Voltage Alternating Current (LVAC).

[0024] In addition, regarding DC, voltage levels exceeding 100kV are classified as high voltage (HVDC: High Voltage Direct Current), voltage levels from 1.5kV to 100kV are classified as medium voltage (MVDC: Medium Voltage Direct Current), and voltage levels below 1.5kV are classified as low voltage (LVDC: Low Voltage Direct Current).

[0025] Furthermore, in Japan, currently, regarding AC voltage, voltage levels above 7kV are classified as Extra High Voltage (EHVAC), voltage levels between 600V and 7kV are classified as High Voltage (HVAC), and voltage levels below 600V are classified as Low Voltage (LVAC). Regarding DC voltage, voltage levels above 7kV are classified as Extra High Voltage (EHVDC), voltage levels between 750V and 7kV are classified as High Voltage (HVDC), and voltage levels below 1.5kV are classified as Low Voltage (LVDC).

[0026] AC power source 1 is a power system that supplies medium-voltage AC power or a generator that produces medium-voltage AC power. AC transmission line 4 transmits medium-voltage AC power.

[0027] The uninterruptible power supply device 10 includes an input terminal T1, a DC terminal T2, an output terminal T3, switches S1 and S2, a converter 12, current detectors CD1 and CD2, a DC bus 14, a bidirectional chopper 18, an inverter 20, and a control device 22.

[0028] Input terminal T1 receives AC power of a specified frequency from AC power source 1 via transformer 2. The AC input voltage VI is a medium-voltage AC voltage, and its instantaneous value is detected by control device 22. Based on the instantaneous value of AC input voltage VI, it is determined whether a power outage has occurred. Current detector CD1 detects the AC input current Ii flowing through input terminal T1 and provides a signal Iif representing its detected value to control device 22.

[0029] Output terminal T3 is connected to AC transmission line 4. AC transmission line 4 transmits medium-voltage AC power. Multiple loads 6 are electrically connected to AC transmission line 4. A switch S3 and a transformer 5 are connected in series between AC transmission line 4 and each load 6. By turning on or off the switch S3 connected to each load 6, the load capacity of the uninterruptible power supply 10 changes.

[0030] When switch S3 is in the ON state, transformer 5 steps down the medium-voltage AC power supplied from AC transmission line 4 to low-voltage AC power and supplies it to load 6. Load 6 is driven by the low-voltage AC power supplied from transformer 5.

[0031] DC terminal T2 is connected to battery 3. Battery 3 constitutes an "energy storage device" for storing DC power. However, a capacitor can also be connected instead of battery 3. The instantaneous value of the inter-terminal voltage VB of battery 3 is detected by control device 22. The inter-terminal voltage VB of battery 3 when fully charged is, for example, several kV.

[0032] The battery 3 includes a plurality of battery cells 3a connected in parallel with each other. As described later, the plurality of battery cells 3a are respectively arranged corresponding to the plurality of chopping units included in the bidirectional chopper 18. The battery cells 3a constitute an "energy storage unit".

[0033] Switch S1 is connected between input terminal T1 and the AC terminal of converter 12 and is controlled by control device 22. When AC power is normally supplied from AC power source 1 (when AC power source 1 is functioning properly), switch S1 is closed, supplying AC power from AC power source 1 to converter 12 via switch S1. When AC power is not normally supplied from AC power source 1 (when AC power source 1 is de-energized), switch S1 is open, disconnecting AC power source 1 from converter 12.

[0034] Converter 12, controlled by control device 22, converts the medium-voltage AC power from AC power source 1 into medium-voltage DC power and outputs it to DC bus 14 when AC power source 1 is functioning properly. Converter 12 will be described in detail later. The instantaneous value of the DC voltage VD on DC bus 14 is detected by control device 22.

[0035] When AC power supply 1 is working properly, control device 22 controls converter 12 so that DC voltage VD becomes the reference DC voltage VDR. When AC power supply 1 is de-energized, control device 22 stops the operation of converter 12.

[0036] DC bus 14 is connected to the high-voltage side node 18a of bidirectional chopper 18, and the low-voltage side node 18c of bidirectional chopper 18 is connected to DC terminal T2. DC bus 14 includes a positive DC bus 14p and a negative DC bus 14n (see reference). Figure 2 ).

[0037] The bidirectional chopper 18, controlled by the control device 22, converts DC voltage between the DC bus 14 and the battery 3, thus supplying and receiving DC power between them. When the AC power supply 1 is active, the control device 22 controls the bidirectional chopper 18 so that the terminal voltage VB of the battery 3 becomes the reference DC voltage VBR. When the AC power supply 1 is de-energized, the control device 22 controls the bidirectional chopper 18 so that the DC voltage VD becomes the reference DC voltage VDR. The bidirectional chopper 18 will be described in detail later.

[0038] DC bus 14 is connected to the DC terminal of inverter 20, and the AC terminal of inverter 20 is connected to output terminal T3 via switch S2. Switch S2 is controlled by control device 22. When using uninterruptible power supply device 10, switch S2 is closed. When inverter 20 is under maintenance, switch S2 is open.

[0039] Current detector CD2 detects the AC output current Io of inverter 20 and provides a signal Iof representing its detected value to control device 22. The instantaneous value of AC output voltage VO applied to AC transmission line 4 is detected by control device 22.

[0040] Inverter 20, controlled by control device 22, converts the DC power supplied from converter 12 or bidirectional chopper 18 via DC bus 14 into AC power of a specified frequency and supplies it to AC transmission line 4. Inverter 20 will be described in detail later.

[0041] The control device 22 controls switches S1~S3, converter 12, bidirectional chopper 18 and inverter 20 based on AC input voltage VI, AC output voltage VO, DC voltage VD, terminal voltage VB of battery 3, AC input current Ii, DC current IB and AC output current Io.

[0042] The control device 22 can typically be constructed from a microcomputer with a pre-stored program. For example, the control circuit 54 is configured to include a CPU (Central Processing Unit), memory, and input / output circuitry. A program is pre-stored in a portion of the memory, and the CPU executes the program to perform the various functions described later.

[0043] Figure 2 This is a circuit diagram showing the main circuit structure of converter 12, inverter 20, and bidirectional chopper 18. (Example) Figure 2 As shown, the converter 12 and the inverter 20 are each composed of a modular multilevel converter (MMC) with multiple converter units cascaded together.

[0044] The converter 12 includes multiple branch circuits 12r, 12s, and 12t. These branch circuits 12r, 12s, and 12t are connected in parallel between the DC positive bus 14p and the DC negative bus 14n. In the following description, the multiple branch circuits 12r, 12s, and 12t are also referred to as "branch circuit 12x".

[0045] Branch circuits 12x are respectively set in multiple phases constituting the AC circuit. Figure 2 The diagram shows a three-phase AC power supply 1, with three branch circuits 12r, 12s, and 12t corresponding to phases R, S, and T, respectively. The AC input terminals Nr, Ns, and Nt of the branch circuits 12r, 12s, and 12t are connected to the input terminal T1 via switch S1.

[0046] Branch circuit 12r includes an upper arm 24 extending from the DC positive bus 14p to the AC input terminal Nr and a lower arm 25 extending from the DC negative bus 14n to the AC input terminal Nr. Since branch circuits 12s and 12t also have the same structure, the structure of branch circuit 12r will be described representatively below.

[0047] The upper arm 24 includes multiple cascaded converter cells 26 and reactors L1. The multiple converter cells 26 and reactors L1 are connected in series. Similarly, the lower arm 25 includes multiple cascaded converter cells 26 and reactors L2. The multiple converter cells 26 and reactors L2 are connected in series.

[0048] Reactors L1 and L2 are buffer reactors used to suppress short-circuit currents. Reactor L1 can be inserted at any position on the upper arm 24, and reactor L2 can be inserted at any position on the lower arm 25. Multiple reactors L1 and L2 can also be provided. Alternatively, only reactor L1 on the upper arm 24 or only reactor L2 on the lower arm 25 can be provided.

[0049] Inverter 20 includes multiple branch circuits 20u, 20v, and 20w. These branch circuits 20u, 20v, and 20w are connected in parallel between the DC positive bus 14p and the DC negative bus 14n. In the following description, when collectively referred to as multiple branch circuits 20u, 20v, and 20w, they are also referred to as "branch circuit 20x".

[0050] Branch circuits 20x are respectively set in multiple phases constituting the AC circuit. Figure 2 The diagram shows a three-phase AC load, with three branch circuits 20u, 20v, and 20w corresponding to phases U, V, and W, respectively. The AC output terminals Nu, Nv, and Nw of branch circuits 20u, 20v, and 20w are connected to output terminal T3 via switch S3. Branch circuits 20u, 20v, and 20w have the same structure as branch circuit 12r, therefore their description is omitted.

[0051] Figure 3 It means Figure 2 The circuit diagram shows a first structural example of the converter unit 26. (See diagram below.) Figure 3 As shown, the converter unit 26 of the first structural example includes a series conductor formed by connecting two switching elements SW1 and SW2 in series, a capacitor 28, and input / output terminals 26a and 26b.

[0052] The converter unit 26 of branch circuit 12r will be described representatively. In the upper arm 24, the input / output terminals 26a of the top-level converter unit 26 are connected to the DC positive bus 14p. The input / output terminals 26b of each converter unit 26 other than the bottom-level unit are connected to the input / output terminals 26a of the adjacent converter unit 26. The input / output terminals 26b of the bottom-level converter unit 26 are connected to the AC input terminal Nr.

[0053] In the lower arm 25, the input / output terminals 26a of the uppermost converter unit 26 are connected to the AC input terminal Nr. The input / output terminals 26b of each converter unit 26 other than the lowest level are connected to the input / output terminals 26a of the adjacent converter unit 26. The input / output terminals 26b of the lowest level converter unit 26 are connected to the DC negative bus 14n.

[0054] The series connection of switching elements SW1 and SW2 is connected in parallel with capacitor 28. The series connection of switching elements SW1 and SW2 forms a half-bridge circuit. Capacitor 28 constitutes a "storage element" for storing DC power.

[0055] The two terminals of switching element SW2 are connected to input / output terminals 26a and 26b, respectively. Converter unit 26 outputs the inter-terminal voltage Vc of capacitor 28, or zero voltage, to the input / output terminals 26a and 26b through the switching actions of switching elements SW1 and SW2. When switching element SW1 is on and switching element SW2 is off, converter unit 26 outputs the inter-terminal voltage Vc of capacitor 28. When switching element SW1 is off and switching element SW2 is on, converter unit 26 outputs zero voltage.

[0056] Figure 4 It means Figure 2 The circuit diagram shows a second structural example of the converter unit 26. (See diagram below.) Figure 4 As shown, the converter unit 26 of the second structural example includes: a first series circuit formed by connecting two switching elements SW1 and SW2 in series; a second series circuit formed by connecting two switching elements SW3 and SW4 in series; a capacitor 28; and input / output terminals 26a and 26b. The first series circuit, the second series circuit, and the capacitor 38 are connected in parallel. The first series circuit and the second series circuit constitute a full-bridge circuit.

[0057] The connection points of switching elements SW1 and SW2 are connected to input / output terminal 26a. The connection points of switching elements SW3 and SW4 are connected to input / output terminal 26b. The converter unit 26 outputs the voltage Vc, -Vc, or zero voltage between the terminals of capacitor 28 to the input / output terminals 26a and 26b through the switching action of switching elements SW1 to SW4.

[0058] Switching elements SW1 to SW4 are constructed by connecting freewheeling diodes (FWD) in reverse parallel with self-extinguishing arc-type semiconductor switching elements such as IGBTs (Insulated Gate Bipolar Transistors) and MOSFETs (Metal Oxide Semiconductor Field Effect Transistors).

[0059] return Figure 2 The bidirectional chopper 18 includes multiple chopper units 30 connected in series between the DC positive bus 14p and the DC negative bus 14n. As described below, the multiple chopper units 30 are configured to control the charging and discharging of corresponding battery cells 3a, and are therefore also referred to as "battery circuit units".

[0060] Figure 5 It means Figure 2 The circuit diagram of the first structural example of the chopper unit 30 is shown. Figure 5 As shown, the chopper unit 30 of the first structural example includes input and output terminals 30a and 30b, DC terminals 30c and 30d, switching elements SW5 and SW6, capacitor 40, bypass switch S4, charging and discharging circuit 45, switches S5 and S6, resistive element 46, voltage detectors 42 and 48, current detector CD3, fuse 50, power supply 52, and control circuit 54.

[0061] In the bidirectional chopper 18, the input / output terminals 30a of the uppermost chopper unit 30 are connected to the DC positive bus 14p. The input / output terminals 30b of each chopper unit 30 other than the lowest level are connected to the input / output terminals 30a of the adjacent chopper unit 30. The input / output terminals 30b of the lowest level chopper unit 30 are connected to the DC negative bus 14n.

[0062] DC terminal 30c is connected to the positive terminal of the corresponding battery cell 3a, and DC terminal 30d is connected to the negative terminal of the corresponding battery cell 3a.

[0063] The positive terminal of capacitor 40 is connected to input / output terminal 30a via DC line PL, and the negative terminal of capacitor 40 is connected to input / output terminal 30b via DC line NL. That is, the same number of capacitors 40 as the number of chopper units 30 included in the bidirectional chopper 18 are connected in series between DC positive bus 14p and DC negative bus 14n.

[0064] The series connection of multiple capacitors 40 constitutes a capacitor used to stabilize and smooth the DC voltage VD between DC buses 14p and 14n. Ideally, the inter-terminal voltage VDc of each chopper unit 30 of the capacitor 40 is the value obtained by dividing the DC voltage VD by the number of chopper units 30 included in the bidirectional chopper 18. The voltage detector 42 detects the instantaneous value of the inter-terminal voltage VDc of the capacitor 40 and provides a signal representing the detected value to the control circuit 54.

[0065] A bypass switch S4 is connected between input / output terminals 30a and 30b. The bypass switch S4 is configured to be turned on according to a command from the control circuit 54, thereby short-circuiting input / output terminals 30a and 30b. In one aspect, the bypass switch S4 can be used to short-circuit the chopper unit 30 in the event of a failure in the corresponding battery cell 3a. In this case, even if a battery cell 3a fails in a portion of the multiple chopper units 30, the operation of the uninterruptible power supply 10 can continue using the other chopper units 30.

[0066] The charging / discharging circuit 45 is configured to transfer DC power between the capacitor 40 and the battery cell 3a by performing bidirectional DC voltage conversion between them. Specifically, the charging / discharging circuit 45 includes switching elements SW5 and SW6 and an inductor 44. The switching elements SW5 and SW6 are respectively configured by connecting a freewheeling diode in reverse parallel with an arc-extinguishing semiconductor switching element such as an IGBT or a MOSFET.

[0067] Switching elements SW5 and SW6 are connected in series between DC line PL and DC line NL. The connection point of switching elements SW5 and SW6 is connected to the first terminal of reactor 44. The second terminal of reactor 44 is connected to DC terminal 30c via switch S5.

[0068] In addition, Figure 5 The example described herein includes a bidirectional chopper in the charging / discharging circuit 45, but is not limited thereto. The charging / discharging circuit 45 may include a known non-isolated DC / DC converter.

[0069] The charging / discharging circuit 45 is controlled by the control circuit 54. When the AC power supply 1 is intact, the charging / discharging circuit 45 stores the DC power supplied from the capacitor 40 via the DC line PL into the battery cell 3a. When the AC power supply 1 is interrupted, the charging / discharging circuit 45 supplies the DC power from the battery cell 3a to the capacitor 40 via the DC line PL. The current detector CD3 detects the DC current flowing between the charging / discharging circuit 45 and the battery cell 3a, and provides a signal indicating the detected value to the control circuit 54.

[0070] Switch S5 is connected between the second terminal of reactor 44 and DC terminal 30c, and is controlled by control circuit 54. Switch S5 is on when chopper unit 30 is in use. Switch S5 is off when uninterruptible power supply device 10 is started and when battery unit 3a is being maintained.

[0071] A fuse 50 is installed between switch S5 and DC terminal 30c. The fuse 50 blows when a large current flows between charging / discharging circuit 45 and battery cell 3a.

[0072] Resistor 46 and switch S6 are connected in series between the first and second terminals of switch S5. Switch S6 is controlled by control circuit 54, turning on when uninterruptible power supply 10 is started and turning off under normal conditions and during maintenance of battery cell 3a. Resistor 46 limits the current flowing from battery cell 3a to capacitor 40 when the uninterruptible power supply 10 is not accumulating DC power in capacitor 40 during startup.

[0073] Voltage detector 48 detects the instantaneous value of the inter-terminal voltage of the corresponding battery cell 3a and provides a signal representing the detected value to control circuit 54.

[0074] The first input terminal of power supply 52 is connected to DC terminal 30c, and the second input terminal of power supply 52 is connected to DC terminal 30d. Power supply 52 steps down the DC voltage supplied from battery cell 3a via DC terminals 30c and 30d to generate the power supply voltage for control circuit 54. Therefore, control circuit 54 can operate even when uninterruptible power supply device 10 is stopped.

[0075] The control circuit 54 is driven by the power supply voltage supplied from the power supply 52 and transmits and receives signals with the control device 22. The control circuit 54 controls the chopper unit 30 based on signals from the control device 22, the output signals of voltage detectors 42 and 48, and the output signal of current detector CD3.

[0076] The control circuit 54 can typically be constructed from a microcomputer with a pre-stored program. For example, the control circuit 54 may be configured to include a CPU, a memory, and input / output circuitry. A program is pre-stored in a portion of the memory, and the CPU executes the program to perform the various functions described later.

[0077] Figure 6 This is a flowchart illustrating the control circuit 54's control over the chopper unit 30. For example... Figure 6 As shown, the control circuit 54 determines in step S01 whether the uninterruptible power supply (UPS) device 10 has been instructed to start. When the user of the UPS device 10 instructs the UPS device 10 to start, the control device 22 sends a signal instructing the UPS device 10 to start to the control circuit 54 of each chopper unit 30. In S01, the control circuit 54 determines that the UPS device 10 has been instructed to start upon receiving the signal from the control device 22.

[0078] When the uninterruptible power supply device 10 is activated (when S01 is determined to be "yes"), the control circuit 54 turns on the switch S6 in step S02, thereby starting the initial charging of the capacitor 40 (step S03).

[0079] Figure 7 This is a circuit block diagram illustrating the initial charging of capacitor 40. During initial charging, bypass switch S4 and switch S5 are open.

[0080] When the voltage between the terminals of capacitor 40 is lower than the voltage between the terminals of battery cell 3a, when... Figure 6 When switching on switch S5 in step S02, if Figure 7 As indicated by the arrows, current flows from battery cell 3a through switch S6, resistor 46, reactor 44, switch element SW5, and DC line PL to capacitor 40. This current charges capacitor 40, causing the voltage between the terminals of capacitor 40 to rise. In step S03, control circuit 54 controls charging / discharging circuit 45 to make the voltage between the terminals of capacitor 40 a predetermined target voltage.

[0081] return Figure 6 When the initial charging of capacitor 40 ends, control circuit 54 disconnects switch S6 and turns on switch S5 through step S04.

[0082] During the operation of the uninterruptible power supply device 10, the control circuit 54 determines whether a power outage of the AC power supply 1 has occurred via step S05. The control device 22 determines whether a power outage of the AC power supply 1 has occurred based on the AC input voltage VI supplied from the AC power supply 1, and sends a power outage detection signal indicating the determination result to the control circuit 54 of each chopper unit 30. In S05, the control circuit 54 determines whether a power outage of the AC power supply 1 has occurred based on the power outage detection signal from the control device 22.

[0083] If it is determined that AC power supply 1 has not experienced a power outage and is functioning properly (when S05 determines "No"), the control circuit 54 controls the charging / discharging circuit 45 in step S06 to supply the DC power stored in the capacitor 40 to the battery cell 3a. In S06, the control circuit 54 controls the charging / discharging circuit 45 so that the voltage between the terminals of the battery cell 3a detected by the voltage detector 48 becomes the reference DC voltage VBR.

[0084] On the other hand, if it is determined that the AC power supply 1 has failed (when S05 determines "yes"), the control circuit 54 controls the charging and discharging circuit 45 in step S11 to supply DC power from the battery cell 3a to the capacitor 40. In S11, the control circuit 54 controls the charging and discharging circuit 45 so that the inter-terminal voltage VDc of the capacitor 40 detected by the voltage detector 42 becomes the reference DC voltage VDcR.

[0085] Furthermore, the control circuit 54 obtains the number of normal chopper units 30 from the signals transmitted and received between it and the control device 22. Then, the control circuit 54 calculates the reference DC voltage VDc by dividing the reference DC voltage VDR by the number of normal chopper units 30 included in the bidirectional chopper 18.

[0086] In step S07, the control circuit 54 detects a fault in battery cell 3a based on the output signals of voltage detector 48 and current detector CD3. In S07, a fault in battery cell 3a is detected if at least one of the inter-terminal voltage of battery cell 3a detected by voltage detector 48 and the current of battery cell 3a detected by current detector CD3 deviates from the allowable range.

[0087] If no fault is detected in battery cell 3a (when S07 is determined to be "No"), the control circuit 54 executes steps S05-S06 and S11. On the other hand, if a fault is detected in battery cell 3a (when S07 is determined to be "Yes"), the control circuit 54 proceeds to step S08, disconnecting battery cell 3a from the chopper unit 30 by turning off switch S5. Additionally, the control circuit 54 short-circuits the chopper unit 30 by turning on bypass switch S4.

[0088] Control circuit 54 disconnects switching elements SW5 and SW6 in step S09, thereby stopping the operation of charging and discharging circuit 45. Control circuit 54 sends a fault detection signal indicating a fault in chopper unit 30 to control device 22 in step S10. Upon receiving a fault detection signal from the control circuit 54 of one of the multiple chopper units 30, control device 22 determines the position of the chopper unit 30 based on the received fault detection signal and notifies the user of the uninterruptible power supply device 10 and the control circuits 54 of the other chopper units 30 of the determined position.

[0089] Therefore, the user of the uninterruptible power supply 10 can maintain the battery cell 3a of the malfunctioning chopper unit 30 based on the acquired information. In addition, the control circuit 54 of each chopper unit 30 can determine the number of normal chopper units 30 based on the acquired information.

[0090] As explained above, the multiple chopper units 30 connected in series between DC buses 14p and 14n are each configured to include a smoothing capacitor 40 and a charging / discharging circuit 45 for imparting DC power between the capacitor 40 and the corresponding battery cell 3a. In this configuration, the voltage applied to each chopper unit 30 can be reduced depending on the number of chopper units 30 included in the bidirectional chopper 18. Therefore, electrical insulation between the capacitor 40 and the battery cell 3a is not required in the charging / discharging circuit 45. As a result, the bidirectional chopper 18 can be miniaturized, which in turn enables the uninterruptible power supply device 10 to be miniaturized.

[0091] Furthermore, since multiple battery units 3a are provided corresponding to multiple chopper units 30 respectively, even if one of the battery units 3a fails, by turning on the bypass switch S4 of the chopper unit 30 corresponding to the failed battery unit 3a to short-circuit the chopper unit 30, the operation of the uninterruptible power supply device 10 can continue while the maintenance of the failed battery unit 3a is carried out using other chopper units 30.

[0092] Next, other structural examples of the chopper unit 30 will be described.

[0093] Figure 8 This is a circuit diagram representing a second structural example of the chopper unit 30. For example... Figure 8 As shown, the chopper unit 30 of the second structural example and Figure 5 The difference in the chopper unit 30 of the first structural example shown is that it has a built-in battery unit 3a.

[0094] By incorporating battery units 3a into each chopper unit 30, it is unnecessary to place the battery pack containing multiple battery units 3a externally to the uninterruptible power supply device 10. Therefore, the size of the power supply system including the uninterruptible power supply device 10 can be miniaturized.

[0095] Figure 9 This is a circuit diagram representing a third structural example of the chopper unit 30. For example... Figure 9 As shown, the chopper unit 30 in the third structural example and Figure 5 The difference in the chopper unit 30 of the first structural example shown is that it has a built-in battery unit 3a and includes an equalization circuit 56.

[0096] The equalization circuit 56 is disposed between the input / output terminals 30a and 30b and the capacitor 40. The equalization circuit 56 is used to equalize the voltage VDc between the terminals of the capacitors 40 of the multiple chopper units 30.

[0097] When the inter-terminal voltage VDc of the capacitors 40 in multiple chopper units 30 deviates, the operation of the charging / discharging circuit 45 in each chopper unit 30 also deviates. For example, consider a case where the inter-terminal voltage VDc of the capacitors 40 in some chopper units 30 exceeds a reference DC voltage VDcR. In this case, in order to reduce the inter-terminal voltage VDc of the capacitors 40 in that chopper unit 30, the charging / discharging circuit 45 is controlled to supply DC power from the capacitors 40 to the battery unit 3a, i.e., to charge the battery unit 3a.

[0098] Conversely, in a portion of the chopper unit 30, if the inter-terminal voltage VDc of the capacitor 40 is lower than the reference DC voltage VDcR, in order to increase the inter-terminal voltage VDc of the capacitor 40, the charging and discharging circuit 45 is controlled to supply DC power from the battery cell 3a to the capacitor 40, that is, to discharge the battery cell 3a.

[0099] In this way, in each chopper unit 30, the charging and discharging of the battery cell 3a is individually controlled according to the inter-terminal voltage VDc of the capacitor 40. Therefore, if a deviation occurs in the inter-terminal voltage VDc of the capacitor 40 in multiple chopper units 30, the number of times the battery cell 3a is charged and discharged will differ among the multiple chopper units 30. Battery cells 3a typically degrade gradually with increasing charge and discharge cycles. Therefore, battery cells 3a with more charge and discharge cycles degrade more rapidly compared to battery cells 3a with fewer charge and discharge cycles. Due to this deviation in the number of charge and discharge cycles, the lifespan of the multiple battery cells 3a varies. The equalization circuit 56 reduces the deviation in the inter-terminal voltage VDc of the capacitor 40 in the multiple chopper units 30, thereby suppressing the deviation in the lifespan of the multiple battery cells 3a and achieving a longer lifespan.

[0100] The equalization circuit 56 includes switching elements SW7 and SW8. Switching elements SW7 and SW8 are respectively constructed, for example, by connecting freewheeling diodes in reverse parallel with self-extinguishing arc-type semiconductor switching elements such as IGBTs and MOSFETs. Switching elements SW7 and SW8 are connected in series between DC line PL and DC line NL. The connection point of switching elements SW7 and SW8 is connected to the input / output terminal 30a. As described later, the control circuit 54 controls the switching elements SW7 and SW8 to turn on and off based on signals from the control device 22 and the output signal from the voltage detector 42.

[0101] Figure 10 This is a flowchart showing the control circuit 54 controlling the chopper unit 30 of the third structure example. Figure 10 Flowcharts and Figure 6 The difference in the flowchart shown is that it includes step S04A and replaces step S09 with step S09A.

[0102] like Figure 10 As shown, during the operation of the uninterruptible power supply device 10, the control circuit 54 of each chopper unit 30 controls the equalization circuit 56 through step S04A to equalize the voltage VDc between the terminals of the capacitors 40 of the multiple chopper units 30.

[0103] In S04A, control circuit 54 obtains the output signal of voltage detector 42 from other chopper units 30 via control device 22. Based on the output signal of its own chopper unit 30's voltage detector 42 and the obtained output signals of the voltage detectors 42 of other chopper units 30, control circuit 54 calculates the average value VDcave of the inter-terminal voltage VDc of the capacitors 40 of the multiple chopper units 30. Control circuit 54 calculates the deviation ΔVDc (ΔVDc=VDcR-VDc_ave) between the calculated average value VDc_ave and the reference DC voltage VDcR. Control circuit 54 controls the switching elements SW7 and SW8 to be turned on and off in a manner that makes the deviation ΔVDc zero.

[0104] In Figure 6 If a fault is detected in battery cell 3a in the same step S07 (when S07 is determined to be "yes"), the control circuit 54 proceeds to step S08, disconnects battery cell 3a from chopper unit 30 by opening switch S5, and short-circuits chopper unit 30 by closing bypass switch S4. Then, in step S09A, the control circuit 54 stops the operation of charging / discharging circuit 45 by opening switching elements SW5 and SW6, and stops the operation of equalization circuit 56 by opening switching elements SW7 and SW8.

[0105] As explained above, in this embodiment, the converter 12 and the inverter 20 are each composed of a modular multilevel converter (MMC). By staggering the timing of the operation of each converter unit 26, the MMC can output a stepped multilevel voltage waveform, making the output AC voltage approximately sinusoidal, thus eliminating the need for an AC filter.

[0106] By applying MMCs suitable for high voltage and high capacity to the converter 12 and inverter 20 respectively, the uninterruptible power supply 10 can supply medium-voltage AC power to the AC transmission line 4. Therefore, compared with existing uninterruptible power supplies that supply low-voltage (e.g., 400V) AC power to the AC transmission line, the current flowing through the AC transmission line can be reduced. As a result, power loss and voltage drop in the AC transmission line can be reduced. In addition, since the number of AC transmission lines can be reduced, the power system can be miniaturized and equipment costs can be reduced.

[0107] Furthermore, in this embodiment, the bidirectional chopper 18 is composed of a plurality of chopper units 30 connected in series. Each of the plurality of chopper units 30 includes a smoothing capacitor 40 and a charging / discharging circuit 45 for imparting DC power between the capacitor 40 and the corresponding battery cell 3a. Depending on the number of chopper units 30 included in the bidirectional chopper 18, the voltage applied to each chopper unit 30 can be reduced, and therefore, electrical insulation between the capacitor 40 and the battery cell 3a is not required in the charging / discharging circuit 45. Therefore, the bidirectional chopper 18 can be miniaturized, resulting in the miniaturization of the uninterruptible power supply device 10.

[0108] Furthermore, since multiple battery units 3a are provided corresponding to multiple chopper units 30 respectively, even if one of the battery units 3a fails, by turning on the bypass switch S4 of the chopper unit 30 corresponding to the failed battery unit 3a to short-circuit the chopper unit 30, the operation of the uninterruptible power supply device 10 can continue while the maintenance of the failed battery unit 3a is carried out using other chopper units 30.

[0109] Furthermore, such as Figure 9 As explained, by providing an equalization circuit 56 in each chopper unit 30 to equalize the voltage VDc between the terminals of the capacitors 40 of the multiple chopper units 30, the deviation in the number of charge and discharge cycles of the multiple battery units 3a can be suppressed, thereby achieving a longer lifespan for the multiple battery units 3a.

[0110] Next, an application example of the uninterruptible power supply device 10 of this embodiment will be described.

[0111] Figure 11 This is a diagram illustrating a structural example of a power system using the uninterruptible power supply device 10 of this embodiment. The power system can, for example, be applied to large-scale data centers.

[0112] like Figure 11 As shown, the power supply system includes multiple uninterruptible power supply (UPS) units 10 connected in parallel between AC power source 1, 1A and AC transmission line 4. The basic structure of each UPS unit 10 is similar to... Figures 1 to 10 The structure of the uninterruptible power supply device 10 described herein is the same. Figure 11 The uninterruptible power supply device 10 shown differs in that it includes a switch S7 instead of a switch S1, and has a transformer 2.

[0113] Switch S7 is configured to be controlled by a control device (not shown) to connect either of the two AC power sources 1 and 1A to the primary side of transformer 2. AC power source 1 is, for example, a commercial AC power source, and AC power source 1A is, for example, a generator. That is, the uninterruptible power supply 10 is configured to switch between the commercial AC power source and the generator as the AC power source.

[0114] like Figure 11 As shown, converter 12 receives 13.8kV (medium voltage) AC power from AC power source 1 and 1A via switch S5 and transformer 2. The AC power is 50MVA.

[0115] exist Figure 12 The middle shows Figure 11 The main circuit structure of converter 12, inverter 20, and bidirectional chopper 18 is shown. Figures 2 to 4 As described, converter 12 is composed of a modular multilevel converter (MMC) that converts 13.8kV AC power (50MVA) into 22.5kV (medium voltage) DC power and outputs it to DC bus 14.

[0116] As in Figure 2 and Figures 5 to 10 As described in the text, the bidirectional chopper 18 is configured to include a plurality of chopper units 30 connected in series.

[0117] Inverter 20, composed of a modular multilevel circuit (MMC), converts 22.5kV (medium voltage) DC power supplied from converter 12 or bidirectional chopper 18 via DC bus 14 into 13.8kV (medium voltage) AC power and supplies it to AC transmission line 4. AC transmission line 4 is approximately 1,000 feet long. The 13.8kV (medium voltage) AC power transmitted in AC transmission line 4 is converted to 415V (low voltage) AC power by transformer 5 and supplied to the load.

[0118] The embodiments disclosed herein should be considered illustrative in all respects and not restrictive. The scope of this disclosure is not defined by the foregoing description, but by the scope claimed, and is intended to include equivalents of the scope claimed and all modifications within that scope.

[0119] Explanation of reference numerals in the attached figures 1. 1A AC power supply; 2. 5 transformer; 3. Battery; 3A battery cell; 4. AC transmission line; 6. Load; 10. Uninterruptible power supply (UPS); 12. Converter; 12R, 12S, 12T, 20U, 20V, 20W branch circuits; 14. DC bus; 14P DC positive bus; 14N DC negative bus; 18. Bidirectional chopper; 20. Inverter; 22. Control device; 24. Upper arm; 25. Lower arm; 26. Converter unit; 26A, 26B, 30A, 30B input / output terminals. 28, 38, 40 Capacitors, 30 Chopper Unit, 30c, 30d, T2 DC Terminal, 42, 48 Voltage Detectors, 44, L1, L2 Reactors, 45 Charging / Discharging Circuit, 46 Resistor Element, 50 Fuse, 52 Power Supply, 54 Control Circuit, 56 Equalization Circuit, CD1~CD3 Current Detectors, NL, PL DC Lines, S1~S3, S5~S7 Switches, S4 Bypass Switch, SW1~SW8 Switching Element, T1 Input Terminal, T3 Output Terminal.

Claims

1. An uninterruptible power supply device, connected between an AC power source and an AC transmission line, wherein, have: The converter converts the AC power supplied from the AC power source into DC power and supplies it between the DC positive bus and the DC negative bus; A bidirectional chopper converts the DC voltage between the DC positive bus and the DC negative bus and the DC voltage of the energy storage device. as well as The inverter converts the DC power received from the DC positive bus and the DC negative bus into AC power and supplies it to the AC transmission line. The converter and the inverter each include branch circuits with multiple cascaded converter units. The bidirectional chopper includes multiple chopper units connected in series between the DC positive bus and the DC negative bus. The energy storage device includes multiple energy storage units that are respectively arranged corresponding to the multiple chopper units and connected in parallel with each other. The plurality of chopper units respectively include: First input / output terminal and second input / output terminal; A capacitor is connected between the first input / output terminal and the second input / output terminal; and A charging and discharging circuit is used to transmit DC power between the capacitor and the corresponding energy storage unit.

2. The uninterruptible power supply device according to claim 1, wherein, It also includes a control device that controls the converter, the inverter, and the bidirectional chopper. The plurality of chopper units further include: A control circuit, communicatively connected to the control device, controls the charging and discharging circuit; and The power supply generates the power supply voltage of the control circuit based on the DC voltage of the corresponding energy storage unit.

3. The uninterruptible power supply device according to claim 2, wherein, In each of the plurality of chopper units, the control circuit is, When the AC power supply is intact, the charging and discharging circuit is controlled to supply DC power from the capacitor to the corresponding energy storage unit. When the AC power supply fails, the charging and discharging circuit is controlled to supply DC power from the corresponding energy storage unit to the capacitor.

4. The uninterruptible power supply device according to claim 2, wherein, Each of the plurality of chopper units further includes a resistive element and a switch connected in series between the charging / discharging circuit and the corresponding energy storage unit. When the uninterruptible power supply device is started, the control circuit turns on the switch, supplying the DC power of the corresponding energy storage unit to the capacitor through the resistive element and the charging and discharging circuit.

5. The uninterruptible power supply device according to claim 2, wherein, Each of the plurality of chopper units further includes a bypass switch that connects the first input / output terminal and the second input / output terminal. In the event of a malfunction in the corresponding energy storage unit, the control circuit stops the operation of the charging and discharging circuit and activates the bypass switch.

6. The uninterruptible power supply device according to claim 2, wherein: Each of the multiple chopper units also includes an equalization circuit comprising multiple semiconductor switching elements. The control circuit controls the switching on and off of the plurality of semiconductor switching elements to balance the voltage between the terminals of the capacitors of the plurality of chopper units.

7. The uninterruptible power supply device according to claim 1, wherein, Each of the multiple chopper units has a corresponding built-in energy storage unit.

8. The uninterruptible power supply device according to any one of claims 1 to 7, wherein, The AC power source is a power system or generator that supplies medium-voltage AC power. When the AC power supply is intact, the converter will convert the medium-voltage AC power supplied by the AC power supply into medium-voltage DC power and supply it between the DC positive bus and the DC negative bus. The inverter converts the medium-voltage DC power received from the DC positive bus and the DC negative bus into medium-voltage AC power and supplies it to the AC transmission line.

9. The uninterruptible power supply device according to claim 7, wherein, The energy storage device is configured to store medium-voltage DC power. When the AC power supply fails, the converter stops operating, and the bidirectional chopper supplies the medium-voltage DC power of the energy storage device to the DC positive bus and the DC negative bus.

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