Uninterruptible power supply device

Abstract

An uninterruptible power supply device (10) is connected between an AC power supply (1) and an AC transmission line (4). The uninterruptible power supply device (10) is provided with a converter (12), a bidirectional chopper (18), and an inverter (20). The converter (12) converts AC power supplied from the AC power supply (1) into DC power and supplies the DC power to a DC bus (14). The bidirectional chopper (18) exchanges DC power between the DC bus (14) and a power storage device (3). The inverter (20) converts DC power received from the DC bus (14) into AC power and supplies the AC power to the AC transmission line (4). Each of the converter (12) and the inverter (20) includes a plurality of arms for each phase of the AC power supply (1), and each of the plurality of arms has a plurality of converter cells cascade-connected to each other.

Description

Uninterruptible power supply device

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

[0002] For example, International Publication No. 2014 / 132452 (Patent Document 1) discloses an uninterruptible power supply device for supplying power to a plurality of servers installed in a data center or the like. This uninterruptible power supply device is connected to a low-voltage (400V system) AC power supply. The uninterruptible power supply device includes a converter that converts low-voltage AC power (AC400V) from the AC power supply into DC power and supplies it to a DC bus, and an inverter that converts DC power from the converter or DC power stored in a battery into low-voltage AC power (AC400V).

[0003] International Publication No. 2014 / 132452

[0004] In order to supply AC power to a large-capacity load ranging from several tens of MVA to several hundreds of MVA, a power supply system is constructed by connecting a plurality of uninterruptible power supply devices in parallel to the load. This power supply system supplies low-voltage AC power (AC400V) to the load via a transmission line.

[0005] In the above power supply system, since a large current flows through the transmission line, there are concerns about an increase in power loss and voltage drop. Also, since a large number of transmission lines are required to carry a large current, there is a problem that the power supply system becomes larger and the equipment cost increases.

[0006] Therefore, the main object of the present disclosure is to provide an uninterruptible power supply device that can be miniaturized and made more efficient.

[0007] The uninterruptible power supply device according to the present disclosure is connected between an AC power supply and an AC transmission line. The uninterruptible power supply device includes a converter, a bidirectional chopper, and an inverter. The converter converts AC power supplied from the AC power supply into DC power and supplies it to a DC bus. The bidirectional chopper exchanges DC power between the DC bus and a power storage device. The inverter converts DC power received from the DC bus into AC power and supplies it to the AC transmission line. Each of the converter and the inverter includes a plurality of arms for each phase of the AC power supply, and each of the plurality of arms has a plurality of converter cells connected in cascade with each other.

[0008] According to this disclosure, it is possible to provide an uninterruptible power supply that can be miniaturized and made more efficient.

[0009] This is a circuit block diagram showing an uninterruptible power supply according to this embodiment. This is a circuit diagram showing the main circuit configuration of the converter and inverter. This is a circuit diagram showing a first configuration example of the converter cell shown in Figure 2. This is a circuit diagram showing a second configuration example of the converter cell shown in Figure 2. This is a block diagram showing the configuration of a bidirectional chopper. This is a circuit diagram showing the main circuit configuration of the DC / DC converter shown in Figure 5. This is a diagram illustrating an application example of the uninterruptible power supply according to this embodiment. This is a diagram showing a first configuration example of a power supply system using the uninterruptible power supply according to this embodiment. This is a circuit diagram showing the main circuit configuration of the converter, inverter and bidirectional chopper shown in Figure 8. This is a diagram showing a second configuration example of a power supply system using the uninterruptible power supply according to this embodiment. This is a circuit diagram showing the main circuit configuration of the converter, inverter and bidirectional chopper shown in Figure 10.

[0010] Embodiments of this disclosure will be described in detail below with reference to the drawings. In the following, the same or corresponding parts in the drawings will be denoted by the same reference numerals, and their descriptions will not be repeated in principle.

[0011] Figure 1 is a circuit block diagram showing an uninterruptible power supply (UPS) according to this embodiment. As shown in Figure 1, the UPS 10 is connected between the AC power source 1 and the AC transmission line 4. The UPS 10 receives a three-phase AC voltage from the AC power source 1 and supplies a three-phase AC voltage to the AC transmission line 4, but for the sake of simplicity in the drawing and explanation, only a single-phase circuit is shown in Figure 1.

[0012] In this specification, in accordance with IEC (International Electrotechnical Commission) standards, AC voltages are classified as follows: voltages of 230 kV or higher are classified as extra-high voltage (EHVAC: Extra-high Voltage Alternating Current), voltages of 35 kV to 230 kV are classified as high voltage (HVAC: High Voltage Alternating Current), voltages of 1 kV to 35 kV are classified as medium voltage (MVAC: Medium Voltage Alternating Current), and voltages of less than 1 kV are classified as low voltage (LVAC: Low Voltage Alternating Current).

[0013] Furthermore, for direct current, voltage classes exceeding 100kV are classified as high voltage (HVDC: High Voltage Direct Current), voltage classes between 1.5kV and 100kV are classified as medium voltage (MVDC: Medium Voltage Direct Current), and voltage classes below 1.5kV are classified as low voltage (LVDC: Low Voltage Direct Current).

[0014] In Japan, AC voltages are currently classified as follows: 7kV and above are classified as extra-high voltage (EHVAC), 600V to 7kV as high voltage (HVAC), and below 600V as low voltage (LVAC). DC voltages are classified as follows: over 7kV as extra-high voltage (EHVDC), 750V to 7kV as high voltage (HVDC), and below 1.5kV as low voltage (LVDC).

[0015] AC power source 1 is a power system that supplies medium-voltage AC power, or a generator that generates medium-voltage AC power. AC transmission line 4 transmits medium-voltage AC power.

[0016] The uninterruptible power supply 10 includes an input terminal T1, a DC terminal T2, an output terminal T3, switches S1 to S3, a converter 12, current detectors CD1 to CD3, a DC bus 14, a capacitor 16, a bidirectional chopper 18, an inverter 20, and a control device 22.

[0017] Input terminal T1 receives AC power of a predetermined 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 the AC input voltage VI, it is determined whether or not a power outage has occurred. Current detector CD1 detects the AC input current Ii flowing through input terminal T1 and provides a signal Iif indicating the detected value to control device 22.

[0018] The output terminal T3 is connected to the AC transmission line 4. The AC transmission line 4 transmits medium-voltage AC power. Multiple loads 6 are electrically connected to the AC transmission line 4. A switch S4 and a transformer 5 are connected in series between the AC transmission line 4 and each load 6. The load capacity of the uninterruptible power supply 10 changes when the switch S4 connected to each load 6 is turned on or off.

[0019] When switch S4 is ON, 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.

[0020] The DC terminal T2 is connected to the battery 3. The battery 3 constitutes a "power storage device" that stores DC power. However, a capacitor may be connected instead of the battery 3. The instantaneous value of the terminal voltage VB of the battery 3 is detected by the control device 22. In the following description, the terminal voltage VB of the battery 3 will also be referred to as the "battery voltage VB". When the battery 3 is fully charged, the battery voltage VB is, for example, several kV.

[0021] Switch S1 is connected between the input terminal T1 and the AC node of the converter 12 and is controlled by the control device 22. When AC power is supplied normally from the AC power supply 1 (when the AC power supply 1 is healthy), switch S1 is turned on, and AC power is supplied from the AC power supply 1 to the converter 12 via switch S1. When AC power is not supplied normally from the AC power supply 1 (when the AC power supply 1 fails), switch S1 is turned off, and the connection between the AC power supply 1 and the converter 12 is interrupted.

[0022] The converter 12 is controlled by the control device 22 and, when the AC power supply 1 is functioning properly, converts the medium-voltage AC power from the AC power supply 1 into medium-voltage DC power and outputs it to the DC bus 14. The converter 12 will be explained in more detail later.

[0023] Capacitor 16 is connected to the DC bus 14 and smooths and stabilizes the DC voltage VD of the DC bus 14. The instantaneous value of the DC voltage VD of the DC bus 14 is detected by the control device 22.

[0024] When AC power supply 1 is functioning properly, the control device 22 controls the converter 12 so that the DC voltage VD becomes the reference DC voltage VDR. When AC power supply 1 fails, the control device 22 stops the operation of the converter 12.

[0025] The DC bus 14 is connected to the high-voltage side node 18a of the bidirectional chopper 18, and the low-voltage side node 18c of the bidirectional chopper 18 is connected to the DC terminal T2 via switch S2. Switch S2 is controlled by the control device 22. When the uninterruptible power supply 10 is in use, switch S2 is turned on. When the battery 3 or the bidirectional chopper 18 is being maintained, switch S2 is turned off.

[0026] The bidirectional chopper 18 is controlled by the control device 22 and performs DC voltage conversion between the DC bus 14 and the battery 3, thereby transferring DC power between the DC bus 14 and the battery 3. The current detector CD2 detects the DC current IB flowing between the battery 3 and the bidirectional chopper 18 and provides the control device 22 with a signal IBf indicating the detected value.

[0027] When AC power supply 1 is functioning properly, the control device 22 controls the bidirectional chopper 18 so that the battery voltage VB becomes the reference DC voltage VBR. When AC power supply 1 fails, 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 explained in more detail later.

[0028] The DC bus 14 is connected to the DC node of the inverter 20, and the AC node of the inverter 20 is connected to the output terminal T3 via switch S3. Switch S3 is controlled by the control device 22. When the uninterruptible power supply 10 is in use, switch S3 is turned on. When the inverter 20 is being maintained, switch S3 is turned off.

[0029] The current detector CD3 detects the AC output current Io of the inverter 20 and provides the control device 22 with a signal Iof indicating the detected value. The instantaneous value of the AC output voltage VO applied to the AC transmission line 4 is detected by the control device 22.

[0030] The inverter 20 is controlled by the control device 22 and converts the DC power supplied from the converter 12 or bidirectional chopper 18 via the DC bus 14 into AC power of a predetermined frequency and supplies it to the AC transmission line 4. The inverter 20 will be described in more detail later.

[0031] The control device 22 controls switches S1 to S3, converter 12, bidirectional chopper 18, and inverter 20 based on the AC input voltage VI, AC output voltage VO, DC voltage VD, battery voltage VB, AC input current Ii, DC current IB, and AC output current Io. Typically, the control device 22 can be configured by at least one microprocessor with a predetermined program pre-stored in it.

[0032] Figure 2 is a circuit diagram showing the main circuit configuration of converter 12 and inverter 20. As shown in Figure 2, each of converter 12 and inverter 20 is composed of a modular multilevel converter (MMC) in which multiple unit converters (hereinafter also referred to as "converter cells") are connected in a cascade. Note that "converter cells" are also called "submodules," SMs, or "unit converters."

[0033] The converter 12 includes multiple leg circuits 12r, 12s, and 12t. The multiple leg circuits 12r, 12s, and 12t are connected in parallel to each other between the DC positive bus 14p and the DC negative bus 14n. In the following description, when referring to the multiple leg circuits 12r, 12s, and 12t collectively, they will also be referred to as "leg circuit 12x".

[0034] The leg circuits 12x are provided for each of the multiple phases that make up the AC. Figure 2 shows the case where the AC power supply 1 is a three-phase AC power supply, and three leg circuits 12r, 12s, and 12t are provided corresponding to the R phase, S phase, and T phase, respectively. The AC input terminals Nr, Ns, and Nt provided for the leg circuits 12r, 12s, and 12t are connected to the input terminal T1 via the switch S1.

[0035] The leg circuit 12r includes an upper arm 24 from the DC positive busbar 14p to the AC input terminal Nr, and a lower arm 25 from the DC negative busbar 14n to the AC input terminal Nr. Leg circuits 12s and 12t have a similar configuration, so the configuration of leg circuit 12r will be described as representative below.

[0036] The upper arm 24 includes a plurality of cascaded transducer cells 26 and a reactor L1. The plurality of transducer cells 26 and reactor L1 are connected in series. Similarly, the lower arm 25 includes a plurality of cascaded transducer cells 26 and a reactor L2. The plurality of transducer cells 26 and reactor L2 are connected in series.

[0037] Reactors L1 and L2 are buffer reactors for suppressing short-circuit current. Reactor L1 may be inserted at any position on the upper arm 24, and reactor L2 may be inserted at any position on the lower arm 25. Multiple reactors L1 and L2 may be provided. Alternatively, only reactor L1 on the upper arm 24 or only reactor L2 on the lower arm 25 may be provided.

[0038] The inverter 20 includes multiple leg circuits 20u, 20v, and 20w. These multiple leg circuits 20u, 20v, and 20w are connected in parallel to each other between the DC positive busbar 14p and the DC negative busbar 14n. In the following description, when referring to the multiple leg circuits 20u, 20v, and 20w collectively, they will also be referred to as "leg circuit 20x".

[0039] The leg circuits 20x are provided for each of the multiple phases that make up the AC. Figure 2 shows the case where the load 6 is a three-phase AC load, and three leg circuits 20u, 20v, and 20w are provided corresponding to the U phase, V phase, and W phase, respectively. The AC output terminals Nu, Nv, and Nw provided for the leg circuits 20u, 20v, and 20w are connected to the output terminal T3 via switch S3. The leg circuits 20u, 20v, and 20w have the same configuration as the leg circuit 12r, so their explanation is omitted.

[0040] Figure 3 is a circuit diagram showing a first configuration example of the converter cell 26 shown in Figure 2. As shown in Figure 3, the converter cell 26 according to the first configuration example has a half-bridge circuit.

[0041] The converter cell 26 comprises a series configuration formed by connecting two semiconductor switching elements SW1 and SW2 in series, an energy storage element 28, and input / output terminals P1 and P2. The series configuration of semiconductor switching elements SW1 and SW2 and the energy storage element 28 are connected in parallel.

[0042] Both terminals of the semiconductor switching element SW2 are connected to the input / output terminals P1 and P2, respectively. The converter cell 26 outputs the voltage Vc of the energy storage element 28 or zero voltage between the input / output terminals P1 and P2 by the switching operation of the semiconductor switching elements SW1 and SW2. When semiconductor switching element SW1 is ON and semiconductor switching element SW2 is OFF, the converter cell 26 outputs the voltage Vc of the energy storage element 28. When semiconductor switching element SW1 is OFF and semiconductor switching element SW2 is ON, the converter cell 26 outputs zero voltage.

[0043] Figure 4 is a circuit diagram showing a second configuration example of the converter cell 26 shown in Figure 2. As shown in Figure 4, the converter cell 26 according to the second configuration example has a full bridge circuit.

[0044] The converter cell 26 includes a first series body formed by connecting two semiconductor switching elements SW1 and SW2 in series, a second series body formed by connecting two semiconductor switching elements SW3 and SW4 in series, a power storage element 28, and input / output terminals P1 and P2. The first series body, the second series body, and the power storage element 28 are connected in parallel.

[0045] The midpoints of the semiconductor switching elements SW1 and SW2 are connected to the input / output terminal P1. Similarly, the midpoints of the semiconductor switching elements SW3 and SW4 are connected to the input / output terminal P2. The converter cell 26 outputs the voltages Vc, -Vc or zero voltage of the power storage element 28 between the input / output terminals P1 and P2 by the switching operations of the semiconductor switching elements SW1 to SW4.

[0046] In FIGS. (3) and (4), the semiconductor switching elements SW1 to SW4 are configured by connecting freewheeling diodes (FWDs) in anti-parallel to self-extinguishing semiconductor switching elements such as IGBTs (Insulated Gate Bipolar Transistors) and MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). A capacitor such as a film capacitor is mainly used as the power storage element 28.

[0047] FIG. 5 is a circuit block diagram showing the configuration of the bidirectional chopper 18. As shown in FIG. 5, the bidirectional chopper 18 includes a plurality of DC / DC converters 30 connected between high voltage side nodes 18a and 18b and low voltage side nodes (18c) and 18d. The configurations of the plurality of DC / DC converters 30 are the same as each other.

[0048] Each DC / DC converter 30 has high-voltage-side DC terminals 30a and 30b, and low-voltage-side DC terminals 30c and 30d. The high-voltage-side DC terminals 30a and 30b of the plurality of DC / DC converters 30 are connected in series between the high-voltage-side nodes 18a and 18b of the bidirectional chopper 18. Specifically, the DC terminal 30a of the first DC / DC converter 30 is connected to the high-voltage-side node 18a, and the DC terminal 30b of the first DC / DC converter 30 is connected to the DC terminal 30a of the second DC / DC converter 30. The DC terminal 30b of the second DC / DC converter 30 is connected to the DC terminal 30a of the third DC / DC converter 30.

[0049] Thus, the DC terminal 30a of the i-th DC / DC converter 30 is connected to the DC terminal of the (i - 1)-th DC / DC converter 30, and the DC terminal 30b of the i-th DC / DC converter is connected to the DC terminal 30a of the (i + 1)-th DC / DC converter 30. The DC terminal 30b of the N-th DC / DC converter is connected to the high-voltage-side node 18b. N represents the number of DC / DC converters 30, and i is an integer of 2 or more and N - 1 or less. That is, the plurality of DC / DC converters 30 are connected in series via the high-voltage-side DC terminals between the high-voltage-side nodes 18a and 18b to the DC bus 14.

[0050] The low-voltage-side DC terminals 30c and 30d of each DC / DC converter 30 are connected to the low-voltage-side nodes 18c and 18d. That is, the plurality of DC / DC converters 30 are connected in parallel via the low-voltage-side DC terminals between the low-voltage-side nodes 18c and 18d to the battery 3.

[0051] Each DC / DC converter 30 performs bidirectional DC voltage conversion between the high-voltage-side DC terminals 30a and 30b and the low-voltage-side DC terminals 30c and 30d. By multi-leveling the high-voltage side of the DC / DC converter 30, the DC voltage applied from the DC bus 14 to each DC / DC converter 30 can be reduced, so that it is possible to use semiconductor switching elements with low breakdown voltage and low on-resistance in the DC / DC converter 30.

[0052] Figure 6 is a circuit diagram showing the main circuit configuration of the DC / DC converter 30 shown in Figure 5. As shown in Figure 6, the DC / DC converter 30 is an isolated DC / DC converter. In the example in Figure 6, the DC / DC converter 30 is composed of a DAB (Dual Active Bridge) converter. Specifically, the DC / DC converter 30 includes a primary bridge circuit 31, a secondary bridge circuit 32, and a transformer Tr.

[0053] The primary bridge circuit 31 constitutes a single-phase full-bridge circuit. Specifically, it has semiconductor switching elements SW5 to SW8 connected between DC terminal 30c and DC terminal 30d. Semiconductor switching elements SW5 and SW6 are connected in series between DC terminal 30c and DC terminal 30d via node N1a connected to AC terminal 31a. Semiconductor switching elements SW7 and SW8 are connected in series between DC terminal 30c and DC terminal 30d via node N1b connected to AC terminal 31b.

[0054] Similarly, the secondary bridge circuit 32 constitutes a single-phase full-bridge circuit. Specifically, it has semiconductor switching elements SW9 to SW12 connected between DC terminal 30a and DC terminal 30b. Semiconductor switching elements SW9 and SW10 are connected in series between DC terminal 30a and DC terminal 30b via node N2a connected to AC terminal 32a. Semiconductor switching elements SW11 and SW12 are connected in series between DC terminal 30a and DC terminal 30b via node N2b connected to AC terminal 32b.

[0055] The semiconductor switching elements SW5 to SW12 each consist of a self-extinguishing switching element and a diode. The switching element can be made up of any self-extinguishing element such as an IGBT or MOSFET. The diode is connected in antiparallel to the switching element to form a freewheeling diode (FWD).

[0056] The transformer Tr has a primary winding connected between the AC terminals 31a and 31b of the primary bridge circuit 31, and a secondary winding connected between the AC terminals 32a and 32b of the secondary bridge circuit 32.

[0057] The control device 22 controls the power conversion in each DC / DC converter 30. Specifically, the control device 22 generates gate signals to control the on / off state of semiconductor switching elements SW5 to SW12 based on output signals from sensors (not shown), etc.

[0058] When the AC power supply 1 is functioning properly, each DC / DC converter 30 converts the DC power input from the DC terminals 30a and 30b into AC power via the secondary bridge circuit 32, and transmits this AC power to the primary bridge circuit 31 via the transformer Tr. The primary bridge circuit 31 converts the AC power back into DC power and transmits it to the DC terminals 30c and 30d. In this case, each DC / DC converter 30 stores the DC power input from the DC bus 14 in the battery 3.

[0059] In the event of a power outage in AC power supply 1, each DC / DC converter 30 converts the DC power input from DC terminals 30c and 30d into AC power via the primary bridge circuit 31, and transmits this AC power to the secondary bridge circuit 32 via the transformer Tr. The secondary bridge circuit 32 converts the AC power back into DC power and transmits it to DC terminals 30a and 30b. In this case, each DC / DC converter 30 supplies DC power from battery 3 to the DC bus 14.

[0060] Next, an example of the application of the uninterruptible power supply 10 according to this embodiment will be described. Figure 7 is a diagram illustrating an example of the application of the uninterruptible power supply 10 according to this embodiment. As shown in Figure 7, the uninterruptible power supply 10 according to this embodiment receives medium-voltage AC power from the AC power source 1, generates medium-voltage AC power, and supplies it to the AC transmission line 4. The battery 3 stores medium-voltage DC voltage.

[0061] As explained in Figure 2, each of the converter 12 and inverter 20 is composed of a modular multilevel converter (MMC). The MMC can output a stepped multilevel voltage waveform by staggering the operating timing of each converter cell 26, and since the output AC voltage can be made approximately sinusoidal, an AC filter is unnecessary. In addition, since the MMC has an energy storage element 28 within the relatively low-voltage converter cell 26, a high-voltage capacitor connected to the high-voltage DC terminal, as is the case with a two-level converter, is unnecessary.

[0062] In this embodiment, by applying MMC suitable for high voltage and large capacity to each of the converter 12 and inverter 20, the uninterruptible power supply 10 can supply medium-voltage AC power to the AC transmission line 4. Therefore, compared to conventional 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. This reduces power loss and voltage drop in the AC transmission line. Furthermore, since the number of AC transmission lines can be reduced, it becomes possible to miniaturize the power supply system and reduce equipment costs.

[0063] Figure 8 shows a first configuration example of a power supply system using an uninterruptible power supply 10 according to this embodiment. The power supply system can be applied, for example, to a large-scale data center.

[0064] As shown in Figure 8, the power supply system includes multiple uninterruptible power supplies 10 connected in parallel between the AC power sources 1 and 1A and the AC transmission line 4. The basic configuration of each uninterruptible power supply 10 is the same as that of the uninterruptible power supply 10 described in Figures 1 to 6. The uninterruptible power supply 10 shown in Figure 8 differs in that it includes a switch S5 instead of a switch S1, and has a transformer 2.

[0065] Switch S5 is controlled by a control device (not shown) and is configured to connect one 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. In other words, the uninterruptible power supply 10 is configured to be switchable between a commercial AC power source and a generator as the AC power source.

[0066] As shown in Figure 8, the converter 12 receives 13.8 kV (medium voltage) AC power from either AC power source 1 or 1A via switch S5 and transformer 2. The AC power is 50 MVA.

[0067] Figure 9 shows the main circuit configuration of the converter 12, inverter 20, and bidirectional chopper 18 shown in Figure 8. As explained in Figures 2 to 6, the converter 12 is composed of a modular multilevel converter (MMC) and converts 13.8 kV AC power (50 MVA) to 22.5 kV (medium voltage) DC power and outputs it to the DC bus 14. The bidirectional chopper 18 is composed of multiple DC / DC converters 30.

[0068] The inverter 20 is composed of a modular multilevel circuit (MMC) and converts 22.5 kV (medium voltage) DC power supplied from the converter 12 or bidirectional chopper 18 via the DC bus 14 into 13.8 kV (medium voltage) AC power which is then supplied to the AC transmission line 4. The AC transmission line 4 is approximately 1,000 feet long. The 13.8 kV (medium voltage) AC power transmitted through the AC transmission line 4 is converted to 415 V (low voltage) AC power by the transformer 5 and supplied to the load.

[0069] Figure 10 shows a second configuration example of a power supply system using an uninterruptible power supply 10 according to this embodiment. The power supply system can be applied, for example, to a large-scale data center. The second configuration example differs from the first configuration example described above in terms of load capacity. Figure 11 shows the main circuit configuration of the converter 12, inverter 20, and bidirectional chopper 18 shown in Figure 10.

[0070] Converter 12 receives 4.16 kV (medium voltage) AC power from either AC power source 1 or 1A via switch S5 and transformer 2. The AC power is 10 MVA. Converter 12 is composed of a modular multilevel converter (MMC) and converts the 4.16 kV AC power to 6.8 kV (medium voltage) DC power and outputs it to the DC bus 14. The bidirectional chopper 18 is composed of multiple DC / DC converters 30.

[0071] The inverter 20 is composed of a modular multilevel circuit (MMC) and converts 6.8kV (medium voltage) DC power supplied from the converter 12 or bidirectional chopper 18 via the DC bus 14 into 4.16kV (medium voltage) AC power and supplies it to the AC transmission line 4. The 4.16kV (medium voltage) AC power transmitted through the AC transmission line 4 is converted to 415V (low voltage) AC power by the transformer 5 and supplied to the load.

[0072] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included.

[0073] 1, 1A AC power supply, 2, 5, Tr transformer, 3 battery, 4 AC transmission line, 6 load, 10 uninterruptible power supply, 12 converter, 12r, 12s, 12t, 20u, 20v, 20w reg circuit, 14 DC bus, 16 capacitor, 18 bidirectional chopper, 20 inverter, 22 control device, 24 upper arm, 25 lower arm, 26 converter cell, 28 energy storage element, 30 DC / DC converter, 31 primary bridge circuit, 32 secondary bridge circuit, L1, L2 reactor, SW1 to SW12 semiconductor switching element, T1 input terminal, T2 DC terminal, T3 output terminal, S1 to S5 switch.

Claims

1. An uninterruptible power supply (UPS) connected between an AC power source and an AC transmission line, comprising: a converter that converts AC power supplied from the AC power source into DC power and supplies it to a DC bus; a bidirectional chopper that exchanges DC power between the DC bus and a power storage device; and an inverter that converts DC power received from the DC bus into AC power and supplies it to the AC transmission line, wherein each of the converter and the inverter includes a plurality of arms for each phase of the AC power source, and each of the plurality of arms has a plurality of converter cells cascaded to each other.

2. The uninterruptible power supply according to claim 1, wherein the bidirectional chopper includes a plurality of isolated DC / DC converters, the plurality of isolated DC / DC converters having high-voltage DC terminals connected in series with the DC bus and low-voltage DC terminals connected in parallel with the power storage device.

3. The uninterruptible power supply according to claim 2, wherein each of the plurality of isolated DC / DC converters is a DAB (Dual Active Bridge) converter.

4. The uninterruptible power supply according to any one of claims 1 to 3, wherein the AC power source is a power system or generator that supplies medium-voltage AC power, and when the AC power source is healthy, the converter converts the medium-voltage AC power supplied from the AC power source into medium-voltage DC power and supplies it to the DC bus, and the inverter converts the medium-voltage DC power received from the DC bus into medium-voltage AC power and supplies it to the AC transmission line.

5. The uninterruptible power supply according to claim 4, wherein the power storage device is configured to store medium-voltage DC power, and in the event of a power outage of the AC power supply, the converter stops operating, and the bidirectional chopper supplies the medium-voltage DC power from the power storage device to the DC bus.

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