No power outage device

Abstract

The uninterruptible power supply (10) includes a converter (12) that converts AC power supplied from an AC power source (1) into DC power and supplies the DC power to a DC bus (14), an inverter (18) that converts DC power received from the DC bus (14) into AC power and supplies the AC power to an AC transmission line (4), and a power storage device (3). The converter (12) includes a plurality of cascaded first converter cells. The inverter (18) includes a plurality of cascaded second converter cells. The power storage device (3) includes a plurality of power storage cells (3a) provided corresponding to the plurality of first converter cells, respectively. Each of the plurality of first converter cells includes first and second input / output terminals, a first bridge circuit including a plurality of semiconductor switching elements, a first capacitor connected to the first and second input / output terminals via the first bridge circuit, and a charge / discharge circuit. The charge / discharge circuit transfers DC power between the first capacitor and the corresponding power storage cell.

Description

[Technical Field]

[0001] The present disclosure relates to uninterruptible power supplies. [Background technology]

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

[0003] [Patent Document 1] International Publication No. 2014 / 132452 Summary of the Invention [Problem to be solved by the invention]

[0004] To supply AC power to large-capacity loads ranging from tens to hundreds of MVA, a power supply system is constructed by connecting multiple uninterruptible power supplies in parallel to the load. This power supply system supplies low-voltage AC power (400V AC) to the load via transmission lines.

[0005] In the above power supply system, a large current flows through the power transmission lines, which raises concerns about increased power loss and voltage drops. In addition, a large number of power transmission lines are required to carry the large current, which increases the size of the power supply system and increases the equipment costs.

[0006] Therefore, a primary object of the present disclosure is to provide an uninterruptible power supply that can be made smaller and more efficient. [Means for solving the problem]

[0007] An uninterruptible power supply according to one embodiment of the present disclosure is connected between an AC power source and an AC transmission line. The uninterruptible power supply includes a converter that converts AC power supplied from the AC power source into DC power and supplies the DC power to a DC bus, an inverter that converts DC power received from the DC bus into AC power and supplies the AC power to the AC transmission line, and a power storage device. The converter includes a plurality of first converter cells cascaded for each phase of the AC power source. The inverter includes a plurality of second converter cells cascaded for each phase of the AC power source. The power storage device includes a plurality of storage cells provided corresponding to the plurality of first converter cells, respectively. Each of the plurality of first converter cells includes first and second input / output terminals, a first bridge circuit including a plurality of semiconductor switching elements, a first capacitor connected to the first and second input / output terminals via the first bridge circuit, and a charge / discharge circuit. The charge / discharge circuit is configured to exchange DC power between the first capacitor and the corresponding storage cell. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide an uninterruptible power supply that can be made smaller and more efficient. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a circuit block diagram showing an uninterruptible power supply according to an embodiment of the present invention; [Figure 2] FIG. 2 is a circuit diagram showing the main circuit configuration of a converter and an inverter. [Figure 3] FIG. 2 is a circuit diagram showing a first configuration example of a converter cell included in an inverter. [Figure 4] FIG. 10 is a circuit diagram showing a second configuration example of a converter cell included in the inverter. [Figure 5] FIG. 2 is a circuit diagram showing a first configuration example of a converter cell included in a converter. [Figure 6]10 is a flowchart showing control of a converter cell by a control circuit. [Figure 7] FIG. 10 is a circuit block diagram for explaining initial charging of a capacitor. [Figure 8] FIG. 10 is a circuit diagram showing a second configuration example of a converter cell included in the converter. [Figure 9] FIG. 10 is a circuit diagram showing a third configuration example of a converter cell included in the converter. [Figure 10] 1 is a diagram showing an example of the configuration of a power supply system using an uninterruptible power supply according to an embodiment of the present invention; [Figure 11] FIG. 11 is a diagram showing the main circuit configuration of the converter and inverter shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described in detail 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 description will not be repeated in principle.

[0011] Fig. 1 is a circuit block diagram showing an uninterruptible power supply according to the present embodiment. As shown in Fig. 1, uninterruptible power supply 10 is connected between AC power supply 1 and AC transmission line 4. Uninterruptible power supply 10 receives a three-phase AC voltage from AC power supply 1 and supplies the three-phase AC voltage to AC transmission line 4, but for simplicity of the drawing and explanation, Fig. 1 shows only a circuit for one phase.

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

[0013] In addition, for direct current, voltage classes above 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 extra-high voltage (EHVAC) for voltages of 7kV or higher, high voltage (HVAC) for voltages between 600V and 7kV, and low voltage (LVAC) for voltages below 600V. DC voltages are classified as extra-high voltage (EHVDC) for voltages above 7kV, high voltage (HVDC) for voltages between 750V and 7kV, and low voltage (LVDC) for voltages below 1.5kV.

[0015] The AC power source 1 is a power system that supplies medium-voltage AC power or a generator that generates medium-voltage AC power. The AC transmission line 4 transmits the 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 and S2, a converter 12, current detectors CD1 and CD2, a DC bus 14, a capacitor 16, an inverter 18, and a control device 20.

[0017] Input terminal T1 receives AC power of a predetermined frequency from AC power source 1 via transformer 2. AC input voltage VI is a medium-voltage AC voltage, and its instantaneous value is detected by control device 20. The presence or absence of a power outage is determined based on the instantaneous value of AC input voltage VI. Current detector CD1 detects AC input current Ii flowing through input terminal T1 and provides signal Iif indicating the detected value to control device 20.

[0018] The output terminal T3 is connected to an AC transmission line 4. The AC transmission line 4 transmits medium-voltage AC power. A plurality of loads 6 are electrically connected to the AC transmission line 4. A switch S7 and a transformer 5 are connected in series between the AC transmission line 4 and each of the loads 6. The load capacity of the uninterruptible power supply 10 changes when the switch S7 connected to each of the loads 6 is turned on or off.

[0019] When switch S7 is in the on state, transformer 5 steps down the medium-voltage AC power received 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 a 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. When the battery 3 is fully charged, the terminal voltage VB of the battery 3 is, for example, several kV. The instantaneous value of the terminal voltage VB of the battery 3 is detected by the control device 20.

[0021] The battery 3 is configured to include a plurality of battery cells 3a connected in parallel to one another. As will be described later, the plurality of battery cells 3a are provided corresponding to the plurality of converter cells included in the converter 12, respectively. The battery cells 3a constitute "storage cells."

[0022] The switch S1 is connected between the input terminal T1 and the AC node 12a of the converter 12, and is controlled by the control device 20. When AC power is being supplied normally from the AC power source 1 (when the AC power source 1 is functioning properly), the switch S1 is turned on, and AC power is supplied from the AC power source 1 to the converter 12 via the switch S1. When AC power is not being supplied normally from the AC power source 1 (when the AC power source 1 is experiencing a power outage), the switch S1 is turned off, and the AC power source 1 and the converter 12 are disconnected.

[0023] The converter 12 has an AC node 12a and DC nodes 12b and 12c. The AC node 12a is connected to an input terminal T1 via a switch S1, the DC node 12b is connected to a DC terminal T2, and the DC node 12c is connected to a DC bus 14.

[0024] Converter 12 is controlled by control device 20, and when AC power supply 1 is healthy, converts medium-voltage AC power from AC power supply 1 into medium-voltage DC power and outputs it to DC bus 14. Converter 12 is also configured to perform bidirectional DC voltage conversion between DC bus 14 and battery 3, thereby transmitting and receiving DC power between DC bus 14 and battery 3. Converter 12 will be described in detail later.

[0025] The 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 20. When the AC power supply 1 is operating normally, the control device 20 controls the converter 12 so that the DC voltage VD becomes the reference DC voltage VDR and the voltage VB between the terminals of the battery 3 becomes the reference DC voltage VBR. When the AC power supply 1 fails, the control device 20 controls the converter 12 so that the DC voltage VD becomes the reference DC voltage VDR.

[0026] The DC bus 14 is connected to a DC node 18a of the inverter 18, and an AC node 18b of the inverter 18 is connected to an output terminal T3 via a switch S2. The switch S2 is controlled by a control device 20. When the uninterruptible power supply 10 is in use, the switch S2 is turned on. When maintenance of the inverter 18 is performed, the switch S2 is turned off.

[0027] The current detector CD2 detects the AC output current Io of the inverter 18 and provides a signal Iof indicating the detected value to the control device 20. The instantaneous value of the AC output voltage VO applied to the AC transmission line 4 is detected by the control device 20.

[0028] The inverter 18 is controlled by the control device 20, and converts the DC power supplied from the converter 12 via the DC bus 14 into AC power of a predetermined frequency and supplies it to the AC transmission line 4. The inverter 18 will be described in detail later.

[0029] The control device 20 controls the switches S1, S2, the converter 12, and the inverter 18 based on the AC input voltage VI, the AC output voltage VO, the DC voltage VD, the terminal voltage VB of the battery 3, the AC input current Ii, and the AC output current Io.

[0030] The control device 20 can typically be configured by a microcomputer in which a predetermined program is stored in advance. For example, the control circuit 54 includes a CPU (Central Processing Unit), a memory, and an input / output circuit. A program is stored in advance in a partial area of ​​the memory, and the CPU executes the program to realize various functions described below.

[0031] Fig. 2 is a circuit diagram showing the main circuit configuration of converter 12 and inverter 18. As shown in Fig. 2, each of converter 12 and inverter 18 is configured by a modular multilevel converter (MMC) in which a plurality of converter cells are cascaded.

[0032] The converter 12 includes a plurality of leg circuits 12r, 12s, and 12t. The leg circuits 12r, 12s, and 12t are connected in parallel with one another between a DC positive bus 14p and a DC negative bus 14n. In the following description, the leg circuits 12r, 12s, and 12t are also collectively referred to as "leg circuits 12x."

[0033] A leg circuit 12x is provided for each of the multiple phases constituting the AC. FIG. 2 shows a 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. AC input terminals Nr, Ns, and Nt provided in the leg circuits 12r, 12s, and 12t, respectively, are connected to the input terminal T1 via a switch S1. The AC input terminals Nr, Ns, and Nt correspond to the AC node 12a shown in FIG. 1. In the following description, the AC input terminals Nr, Ns, and Nt are also collectively referred to as "AC input terminal Nx."

[0034] The leg circuit 12r includes an upper arm circuit 24 from the DC positive bus 14p to the AC input terminal Nr, and a lower arm circuit 25 from the DC negative bus 14n to the AC input terminal Nr. The leg circuits 12s and 12t have a similar configuration, so the configuration of the leg circuit 12r will be representatively described below.

[0035] The upper arm circuit 24 includes a plurality of cascaded converter cells (CELL) 26 and a reactor L1. The plurality of converter cells 26 and the reactor L1 are connected in series. Similarly, the lower arm circuit 25 includes a plurality of cascaded converter cells (CELL) 26 and a reactor L2. The plurality of converter cells 26 and the reactor L2 are connected in series. The converter cell 26 corresponds to one example of a "first converter cell."

[0036] The reactors L1 and L2 are buffer reactors for suppressing short-circuit current. The reactor L1 may be inserted at any position in the upper arm circuit 24, and the reactor L2 may be inserted at any position in the lower arm circuit 25. A plurality of reactors L1 and L2 may be provided. Alternatively, only the reactor L1 in the upper arm circuit 24 or only the reactor L2 in the lower arm circuit 25 may be provided.

[0037] The inverter 18 includes a plurality of leg circuits 18u, 18v, and 18w. The leg circuits 18u, 18v, and 18w are connected in parallel with one another between the DC positive bus 14p and the DC negative bus 14n. In the following description, the leg circuits 18u, 18v, and 18w are also collectively referred to as "leg circuits 18x."

[0038] A leg circuit 18x ​​is provided for each of the multiple phases constituting the AC. FIG. 2 shows a case where the load 6 is a three-phase AC load, and three leg circuits 18u, 18v, and 18w are provided corresponding to the U phase, V phase, and W phase, respectively. AC output terminals Nu, Nv, and Nw provided in the leg circuits 18u, 18v, and 18w, respectively, are connected to the output terminal T3 via a switch S2. The AC output terminals Nu, Nv, and Nw correspond to the AC node 18b shown in FIG. 1. In the following description, the AC output terminals Nu, Nv, and Nw are also collectively referred to as "AC output terminal Nx."

[0039] The leg circuit 18u includes an upper arm circuit 34 from the DC positive bus 14p to the AC output terminal Nu, and a lower arm circuit 35 from the DC negative bus 14n to the AC output terminal Nu. The leg circuits 18v and 18w have a similar configuration, so the configuration of the leg circuit 18u will be representatively described below.

[0040] The upper arm circuit 34 includes a plurality of cascaded converter cells (CELL) 36 and a reactor L1. The plurality of converter cells 36 and the reactor L1 are connected in series. Similarly, the lower arm circuit 35 includes a plurality of cascaded converter cells (CELL) 36 and a reactor L2. The plurality of converter cells 36 and the reactor L2 are connected in series. The converter cell 36 corresponds to one example of a "second converter cell."

[0041] The reactors L1 and L2 are buffer reactors for suppressing short-circuit current. The reactor L1 may be inserted at any position in the upper arm circuit 34, and the reactor L2 may be inserted at any position in the lower arm circuit 35. A plurality of reactors L1 and a plurality of reactors L2 may be provided. Alternatively, only the reactor L1 in the upper arm circuit 34 or only the reactor L2 in the lower arm circuit 35 may be provided.

[0042] Fig. 3 is a circuit diagram showing a first configuration example of a converter cell 36 included in the inverter 18. As shown in Fig. 3, the converter cell 36 according to the first configuration example includes a series body formed by connecting two switching elements SW1 and SW2 in series, a capacitor 38, and input / output terminals 36a and 36b.

[0043] In the upper arm circuit 34, the input / output terminal 36a of the top converter cell 36 is connected to the DC positive bus 14p. The input / output terminal 36b of each converter cell 36 other than the bottom one is connected to the input / output terminal 36a of the adjacent converter cell 36. The input / output terminal 36b of the bottom converter cell 36 is connected to the AC output terminal Nx.

[0044] In the lower arm circuit 35, the input / output terminal 36a of the uppermost converter cell 36 is connected to the AC output terminal Nx. The input / output terminal 36b of each converter cell 36 other than the lowermost converter cell 36 is connected to the input / output terminal 36a of the adjacent converter cell 36. The input / output terminal 36b of the lowermost converter cell 36 is connected to the DC negative bus 14n.

[0045] The series connection of switching elements SW1 and SW2 and capacitor 38 are connected in parallel. The series connection of switching elements SW1 and SW2 constitutes a half-bridge circuit. Switching elements SW1 and SW2 correspond to an embodiment of a "second semiconductor switching element," and the half-bridge circuit corresponds to an embodiment of a "second bridge circuit." Capacitor 38 constitutes a "storage element" that stores DC power. Capacitor 38 corresponds to an embodiment of a "second capacitor."

[0046] Both terminals of the switching element SW2 are connected to input / output terminals 36a and 36b, respectively. The converter cell 36 outputs the voltage Vc across the terminals of the capacitor 38 or zero voltage between the input / output terminals 36a and 36b through the switching operations of the switching elements SW1 and SW2. When the switching element SW1 is on and the switching element SW2 is off, the converter cell 36 outputs the voltage Vc across the terminals of the capacitor 38. When the switching element SW1 is off and the switching element SW2 is on, the converter cell 36 outputs zero voltage.

[0047] FIG. 4 is a circuit diagram showing a second configuration example of a converter cell 36 included in the inverter 18. As shown in FIG. 4, the converter cell 36 according to the second configuration example includes a first series body formed by connecting two switching elements SW1 and SW2 in series, a second series body formed by connecting two switching elements SW3 and SW4 in series, a capacitor 38, and input / output terminals 36a and 36b. The first series body, the second series body, and the capacitor 38 are connected in parallel. The first series body and the second series body form a full bridge circuit. The full bridge circuit corresponds to an example of a "second bridge circuit."

[0048] The connection point between switching elements SW1 and SW2 is connected to input / output terminal 36a. Similarly, the connection point between switching elements SW3 and SW4 is connected to input / output terminal 36b. Converter cell 36 outputs the inter-terminal voltage Vc, −Vc, or zero voltage of capacitor 38 between input / output terminals 36a and 36b through the switching operations of switching elements SW1 to SW4.

[0049] The 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).

[0050] Fig. 5 is a circuit diagram showing a first configuration example of the converter cell 26 included in the converter 12. As shown in Fig. 5, the converter cell 26 according to the first configuration example includes input / output terminals 26a and 26b, DC terminals 26c and 26d, switching elements SW1 and SW2, a capacitor 40, a bypass switch S3, a charge / discharge circuit 44, switches S4 and S5, a resistive element R1, voltage detectors 42 and 48, a current detector CD3, a fuse 50, a power supply 52, and a control circuit 54.

[0051] In the upper arm circuit 24, the input / output terminal 26a of the top converter cell 26 is connected to the DC positive bus 14p. The input / output terminal 26b of each converter cell 26 other than the bottom one is connected to the input / output terminal 26a of the adjacent converter cell 26. The input / output terminal 26b of the bottom converter cell 26 is connected to the AC input terminal Nx.

[0052] In the lower arm circuit 25, the input / output terminal 26a of the uppermost converter cell 26 is connected to the AC input terminal Nx. The input / output terminal 26b of each converter cell 26 other than the lowermost converter cell 26 is connected to the input / output terminal 26a of the adjacent converter cell 26. The input / output terminal 26b of the lowermost converter cell 26 is connected to the DC negative bus 14n.

[0053] The DC terminal 26c is connected to the positive terminal of the corresponding battery cell 3a, and the DC terminal 26d is connected to the negative terminal of the corresponding battery cell 3a.

[0054] The switching elements SW1 and SW2 are connected in series between the DC line PL and the DC line NL. The connection point between the switching elements SW1 and SW2 is connected to the input / output terminal 26a. The connection point between the switching element SW2 and the DC line NL is connected to the input / output terminal 26b and the DC terminal 26d.

[0055] The series connection of switching elements SW1 and SW2 forms a half-bridge circuit. The half-bridge circuit corresponds to an embodiment of a "first bridge circuit." The switching elements SW1 and SW2 correspond to an embodiment of a "first semiconductor switching element." The capacitor 40 is connected between the DC line PL and the DC line NL. That is, the capacitor 40 is connected in parallel with the series connection of switching elements SW1 and SW2 and forms a "storage element" that stores DC power. The capacitor 40 corresponds to an embodiment of a "first capacitor." The voltage detector 42 detects the instantaneous value of the voltage across the terminals of the capacitor 40 and provides a signal indicating the detected value to the control circuit 54.

[0056] The converter cell 26 outputs the voltage across the terminals of the capacitor 40 or zero voltage between the input / output terminal 26a and the input / output terminal 26b through the switching operation of the switching elements SW1 and SW2. The on and off of the switching elements SW1 and SW2 is controlled by the control circuit 54. The switching elements SW1 and SW2 are turned on and off complementarily. When the switching element SW1 is turned on and the switching element SW2 is turned off, the converter cell 26 outputs the voltage across the terminals of the capacitor 40. When the switching element SW1 is turned off and the switching element SW2 is turned on, the converter cell 26 outputs zero voltage.

[0057] The bypass switch S3 is connected between the input / output terminal 26a and the input / output terminal 26b. The bypass switch S3 is configured to be able to short-circuit the input / output terminal 26a and the input / output terminal 26b by turning on in response to a command from the control circuit 54. In one aspect, the bypass switch S3 can be used to short-circuit the converter cells 26 when the corresponding battery cell 3a fails. In this case, even if the battery cell 3a fails in some of the multiple converter cells 26, the other converter cells 26 can be used to continue operating the uninterruptible power supply 10.

[0058] The charge / discharge circuit 44 is configured to exchange DC power between the capacitor 40 and the battery cell 3a by performing bidirectional DC voltage conversion between the capacitor 40 and the battery cell 3a. Specifically, the charge / discharge circuit 44 includes switching elements SW5 and SW6 and a reactor 46. Each of the switching elements SW5 and SW6 is configured by connecting a free wheel diode in anti-parallel to a self-extinguishing semiconductor switching element such as an IGBT or a MOSFET.

[0059] The switching elements SW5 and SW6 are connected in series between the DC line PL and the DC line NL. A connection point between the switching elements SW5 and SW6 is connected to a first terminal of the reactor 46. A second terminal of the reactor 46 is connected to the DC terminal 26c via the switch S4.

[0060] 3, the charge / discharge circuit 44 includes a bidirectional chopper, but is not limited to this. The charge / discharge circuit 44 may include a well-known non-isolated DC / DC converter.

[0061] The charge / discharge circuit 44 is controlled by a control circuit 54. When the AC power supply 1 is operating normally, the charge / discharge circuit 44 stores DC power supplied from the capacitor 40 via the DC line PL in the battery cell 3a. When the AC power supply 1 experiences a power outage, the charge / discharge circuit 44 supplies 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 charge / discharge circuit 44 and the battery cell 3a, and provides the control circuit 54 with a signal indicating the detected value.

[0062] The switch S4 is connected between the second terminal of the reactor 46 and the DC terminal 26c, and is controlled by the control circuit 54. When the converter cell 26 is in use, the switch S4 is turned on. When the uninterruptible power supply 10 is started up and when maintenance of the battery cell 3a is performed, the switch S4 is turned off.

[0063] A fuse 50 is provided between the switch S4 and the DC terminal 26c. When a large current flows between the charge / discharge circuit 44 and the battery cell 3a, the fuse 50 melts.

[0064] Resistance element R1 and switch S5 are connected in series between the first and second terminals of switch S4. Switch S5 is controlled by control circuit 54 and is turned on when uninterruptible power supply 10 starts up, and is turned off during normal operation and maintenance of battery cell 3a. Resistance element R1 limits the current flowing from battery cell 3a to capacitor 40 when no DC power is stored in capacitor 40 when uninterruptible power supply 10 starts up.

[0065] The voltage detector 48 detects the instantaneous value of the voltage between the terminals of the corresponding battery cell 3 a, and provides the control circuit 54 with a signal indicating the detected value.

[0066] A first input terminal of the power supply 52 is connected to the DC terminal 26c, and a second input terminal of the power supply 52 is connected to the DC terminal 26d. The power supply 52 steps down the DC voltage supplied from the battery cell 3a via the DC terminals 26c and 26d to generate a power supply voltage for the control circuit 54. This allows the control circuit 54 to operate even when the uninterruptible power supply 10 is stopped.

[0067] The control circuit 54 is driven by the power supply voltage supplied from the power supply 52, and exchanges signals with the control device 20. The control circuit 54 controls the converter cell 36 based on signals from the control device 20, output signals from the voltage detectors 42 and 48, and output signals from the current detector CD3, etc.

[0068] The control circuit 54 can typically be configured by a microcomputer in which a predetermined program is stored in advance. For example, the control circuit 54 includes a CPU, a memory, and an input / output circuit. A program is stored in advance in a partial area of ​​the memory, and the CPU executes the program to realize various functions described below.

[0069] Fig. 6 is a flowchart showing the control of the converter cells 26 by the control circuit 54. As shown in Fig. 6, the control circuit 54 determines in step S01 whether or not a command to start up the uninterruptible power supply 10 has been issued. When a command to start up the uninterruptible power supply 10 is issued by the user of the uninterruptible power supply 10, the control device 20 transmits a signal instructing the start up of the uninterruptible power supply 10 to the control circuit 54 of each converter cell 26. In S01, when the control circuit 54 receives this signal from the control device 20, it determines that a command to start up the uninterruptible power supply 10 has been issued.

[0070] When an instruction to start up the uninterruptible power supply 10 is issued (YES in S01), the control circuit 54 turns on the switch S5 in step S02 to start initial charging of the capacitor 40 (step S03).

[0071] 7 is a circuit block diagram for explaining the initial charging of the capacitor 40. During the initial charging, the bypass switch S3 and the switch S4 are turned off, and the switching elements SW1 and SW2 are turned off.

[0072] If the voltage across capacitor 40 is lower than the voltage across battery cell 3a, when switch S5 is turned on in step S02 of Fig. 6, a current flows through a path from battery cell 3a to capacitor 40 via switch S5, resistor R1, reactor 46, switching element SW5, and DC line PL, as shown by the arrows in Fig. 7. This current charges capacitor 40, and the voltage across capacitor 40 increases. In step S03, control circuit 54 controls charge / discharge circuit 44 so that the voltage across capacitor 40 becomes a predetermined target voltage.

[0073] Returning to FIG. 6, when the initial charging of the capacitor 40 is completed, the control circuit 54 turns off the switch S5 and turns on the switch S4 in step S04.

[0074] During operation of the uninterruptible power supply 10, the control circuit 54 determines in step S05 whether a power outage has occurred in the AC power supply 1. The control device 20 determines whether a power outage has occurred in the AC power supply 1 based on the AC input voltage VI supplied from the AC power supply 1, and transmits a power outage detection signal indicating the determination result to the control circuit 54 of each converter cell 26. In S05, the control circuit 54 determines whether a power outage has occurred in the AC power supply 1 based on the power outage detection signal from the control device 20.

[0075] If it is determined that no power outage has occurred in the AC power supply 1 and that the AC power supply 1 is healthy (NO in S05), the control circuit 54 controls the half-bridge circuit in step S06 to convert the AC power input between the input / output terminals 26a and 26b from the AC power supply 1 into DC power. Furthermore, the control circuit 54 controls the charge / discharge circuit 44 in step S07 to supply the DC power stored in the capacitor 40 to the battery cell 3a.

[0076] On the other hand, if it is determined that a power outage has occurred in the AC power supply 1 (YES in S05), the control circuit 54 controls the charge / discharge circuit 44 in step S12 to supply DC power from the battery cell 3a to the capacitor 40. Furthermore, the control circuit 54 controls the half-bridge circuit in step S13 to output the DC power stored in the capacitor 40 between the input / output terminals 26a and 26b.

[0077] In step S08, the control circuit 54 detects a failure of the battery cell 3a based on the output signals of the voltage detector 48 and the current detector CD3. In S08, if at least one of the voltage across the terminals of the battery cell 3a detected by the voltage detector 48 and the current of the battery cell 3a detected by the current detector CD3 is outside the allowable range, a failure of the battery cell 3a is detected.

[0078] If no failure of the battery cell 3a is detected (NO in S08), the control circuit 54 executes the processes of steps S05 to S07, S12, and S13. On the other hand, if a failure of the battery cell 3a is detected (YES in S08), the control circuit 54 proceeds to step S09 and turns off the switch S4 to disconnect the battery cell 3a from the converter cell 26. The control circuit 54 also short-circuits the converter cell 26 by turning on the bypass switch S3.

[0079] In step S10, the control circuit 54 stops the operation of the half-bridge circuit by turning off the switching elements SW1 and SW2. The control circuit 54 also stops the operation of the charge / discharge circuit 44 by turning off the switching elements SW5 and SW6.

[0080] In step S11, the control circuit 54 transmits a failure detection signal indicating a failure of the converter cell 26 to the control device 20. When the control device 20 receives a failure detection signal from the control circuit 54 of one of the multiple converter cells 26, it identifies the position of the converter cell 26 based on the received failure detection signal and notifies the user of the uninterruptible power supply 10 of information indicating the identified position. This allows the user of the uninterruptible power supply 10 to perform maintenance on the battery cell 3a of the failed converter cell 26 based on the obtained information.

[0081] The control device 20 may further short-circuit one converter cell 26 in each leg circuit other than the leg circuit including the failed converter cell 26. For example, if one converter cell 26 fails in the upper arm circuit 24 of the leg circuit 12r, the control circuit 54 short-circuits the converter cell 26, and also selects one of the multiple converter cells 26 included in the upper arm circuit 24 of the leg circuit 12s and one of the multiple converter cells 26 included in the upper arm circuit 24 of the leg circuit 12t, and short-circuits the selected two converter cells 26. In this way, the number of converter cells 26 in operation can be made the same among the leg circuits 12r, 12s, and 12t.

[0082] As described above, each of the multiple converter cells 26 included in the converter 12 includes a capacitor 40, which is a power storage element, and a charge / discharge circuit 44 that exchanges DC power with the corresponding battery cell 3a. Therefore, in the uninterruptible power supply 10 shown in FIG. 1, it is not necessary to install a bidirectional DC / DC converter for exchanging DC power between the DC bus 14 and the battery 3.

[0083] Furthermore, because multiple converter cells 26 are cascade-connected for each phase of the AC power supply 1, the peak value of the voltage applied to each converter cell 26 can be reduced according to the number of converter cells 26 included in each phase. This eliminates the need for electrical insulation between the capacitor 40 and the battery cell 3a in the charge / discharge circuit 44. For these reasons, it is possible to reduce the size of the uninterruptible power supply 10.

[0084] Furthermore, since multiple battery cells 3a are provided corresponding to the multiple converter cells 26, even if one of the multiple battery cells 3a fails, the bypass switch S3 of the converter cell 26 corresponding to the failed battery cell 3a is turned on to short-circuit the converter cell 26, thereby allowing the operation of the uninterruptible power supply 10 to continue using the other converter cells 26 while maintenance of the failed battery cell 3a can be performed.

[0085] Next, another example of the configuration of the converter cell 26 included in the converter 12 will be described. Fig. 8 is a circuit diagram showing a second configuration example of the converter cell 26 included in the converter 12. The converter cell 26 according to the second configuration example differs from the converter cell 26 according to the first configuration example shown in Fig. 5 in that the converter cell 26 includes switching elements SW3 and SW4.

[0086] As shown in Fig. 8, in a converter cell 26 according to the second configuration example, switching elements SW1 and SW2 are connected in series between a DC line PL and a DC line NL. A connection point between the switching element SW1 and the switching element SW2 is connected to an input / output terminal 26a. A connection point between the switching element SW2 and the DC line NL is connected to an input / output terminal 26b and a DC terminal 26d. Switching elements SW3 and SW4 are connected in series between the DC line PL and the DC line NL. A connection point between the switching element SW3 and the switching element SW4 is connected to an input / output terminal 26b.

[0087] The first series body of the switching elements SW1 and SW2 and the second series body of the switching elements SW3 and SW4 form a full bridge circuit, which corresponds to one example of a "first bridge circuit."

[0088] In the second configuration example, the full-bridge circuit is controlled by a control circuit 54, and outputs the voltage across the terminals of the capacitor 40, a voltage with the polarity of the voltage across the terminals of the capacitor 40 reversed, or zero voltage between the input / output terminals 26a and 26b through the switching operations of the switching elements SW1 to SW4. The other configurations of the second configuration example are the same as those of the first configuration example.

[0089] FIG. 9 is a circuit diagram showing a third configuration example of the converter cell 26 included in the converter 12. The converter cell 26 according to the third configuration example differs from the converter cell 26 according to the first configuration example shown in FIG. 5 in that a battery cell 3a is built in. Since each converter cell 26 has a built-in battery cell 3a, it is not necessary to install a storage battery panel including multiple battery cells 3a outside the uninterruptible power supply 10. This makes it possible to reduce the size of the power supply system including the uninterruptible power supply 10. Although not shown, the converter cell 26 according to the second configuration example shown in FIG. 8 can also be configured to have a built-in battery cell 3a.

[0090] In the above-described embodiment, a configuration has been described in which each of the multiple converter cells 26 included in the converter 12 has a charge / discharge circuit 44, but the same effects as those of the above-described embodiment can be obtained even if each of the multiple converter cells 36 included in the inverter 18 has a charge / discharge circuit 44 instead of the multiple converter cells 26. In this case, each of the multiple converter cells 36 has the circuit configuration shown in Fig. 5, Fig. 8 or Fig. 9, and each of the multiple converter cells 26 has the circuit configuration shown in Fig. 3 or Fig. 4.

[0091] Next, an application example of uninterruptible power supply 10 according to the present embodiment will be described. 10 is a diagram showing an example of the configuration of a power supply system using uninterruptible power supply 10 according to this embodiment. The power supply system can be applied to, for example, a large-scale data center.

[0092] As shown in Fig. 10, the power supply system includes a plurality of uninterruptible power supplies 10 connected in parallel between AC power supplies 1, 1A and an AC transmission line 4. The basic configuration of each uninterruptible power supply 10 is the same as the configuration of the uninterruptible power supply 10 described with reference to Figs. 1 to 9. The uninterruptible power supply 10 shown in Fig. 10 differs in that it includes a switch S6 instead of switch S1 and in that it has a transformer 2.

[0093] Switch S6 is controlled by a control device 20 (not shown) and is configured to connect one of the two AC power supplies 1, 1A to the primary side of transformer 2. AC power supply 1 is, for example, a commercial AC power supply, and AC power supply 1A is, for example, a generator. In other words, uninterruptible power supply 10 is configured to be able to switch between the commercial AC power supply and the generator as the AC power supply.

[0094] 10, converter 12 receives AC power of 13.8 kV (medium voltage) from one of AC power sources 1 and 1A via switch S5 and transformer 2. The AC power is 50 MVA.

[0095] Fig. 11 shows the main circuit configuration of the converter 12 and inverter 18 shown in Fig. 10. As described in Fig. 2, the converter 12 is configured by a modular multilevel converter (MMC), converts 13.8 kV AC power (50 MVA) into 22.5 kV (medium voltage) DC power and outputs it to the DC bus 14, and also exchanges DC power between the DC bus 14 and the battery 3. The battery 3 stores 1.5 kV (medium voltage) DC power. The battery 3 has a plurality of battery cells 3a connected in parallel.

[0096] As described in Figures 5 to 9, each of the multiple converter cells 26 that make up the converter 12 includes a bridge circuit, a capacitor 40, and a charge / discharge circuit 44 provided between the capacitor 40 and the corresponding battery cell 3a.

[0097] Inverter 18 is composed of a modular multilevel converter (MMC) and converts 22.5 kV (medium voltage) DC power supplied from converter 12 via DC bus 14 into 13.8 kV (medium voltage) AC power and supplies it to AC transmission line 4. AC transmission line 4 is approximately 1,000 feet long. The 13.8 kV (medium voltage) AC power transmitted through AC transmission line 4 is converted by transformer 5 into 415 V (low voltage) AC power and supplied to the load.

[0098] In this embodiment, each of converter 12 and inverter 18 is configured by a modular multilevel converter (MMC). An MMC can output a stepped multilevel voltage waveform by shifting the operation timing of each converter cell, and can output an AC voltage that is a substantially sinusoidal wave, eliminating the need for an AC filter.

[0099] In this embodiment, by applying MMC suitable for high voltage and large capacity to each of converter 12 and inverter 18, uninterruptible power supply 10 can supply medium-voltage AC power to AC transmission line 4. Therefore, compared to conventional uninterruptible power supplies that supply low-voltage (e.g., 400 V) AC power to AC transmission lines, the current flowing through AC transmission line 4 can be reduced. This makes it possible to reduce power loss and voltage drop in AC transmission line 4. Furthermore, since the number of AC transmission lines can be reduced, it becomes possible to downsize the power supply system and reduce facility costs.

[0100] Furthermore, in this embodiment, as described above, each of the multiple converter cells 26 included in the converter 12 is configured to include a charge / discharge circuit 44 that exchanges DC power between the capacitor 40 and the corresponding battery cell 3a. This eliminates the need to install a bidirectional DC / DC converter for exchanging DC power between the DC bus 14 and the battery 3, allowing the power supply system to be made smaller.

[0101] Furthermore, since multiple battery cells 3a are provided corresponding to the multiple converter cells 26, even if one of the multiple battery cells 3a fails, the bypass switch S3 of the converter cell 26 corresponding to the failed battery cell 3a is turned on to short-circuit the converter cell 26, thereby allowing the operation of the uninterruptible power supply 10 to continue using the other converter cells 26 while maintenance of the failed battery cell 3a can be performed.

[0102] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0103] 1,1A AC power supply, 2,5 transformer, 3 battery, 3a battery cell, 4 AC transmission line, 6 load, 10 uninterruptible power supply, 12 converter, 12r, 12s, 12t, 18u, 18v, 18w leg circuit, 14 DC bus, 14p DC positive bus, 14n DC negative bus, 16, 38, 40 capacitor, 18 inverter, 20 control device, 24, 34 upper arm circuit, 25, 35 lower arm circuit, 26a, 26b, 36a, 26b input / output terminals, 26, 36 converter cell, 26c, 26d, T2 DC terminal, 42, 48 voltage detector, 44 charge / discharge circuit, 46, L1, L2 reactor, 50 fuse, 52 power supply, 54 control circuit, CD1 to CD3 current detector, PL, NL DC line, SW1 to SW6 switching elements, R1 resistor element, S1 to S2, S4 to S7 switches, S3 bypass switch, T1 input terminal, T3 output terminal.

Claims

1. An uninterruptible power supply connected between an AC power source and an AC power transmission line, a converter that converts AC power supplied from the AC power supply into DC power and supplies the DC power to a DC bus; an inverter that converts DC power received from the DC bus into AC power and supplies the AC power to the AC transmission line; a power storage device, the converter includes a plurality of cascaded first converter cells; the inverter includes a plurality of cascaded second converter cells; the power storage device includes a plurality of power storage cells provided corresponding to the plurality of first converter cells, respectively; Each of the plurality of first converter cells comprises: a first input / output terminal and a second input / output terminal; a first bridge circuit including a plurality of first semiconductor switching elements; a first capacitor connected to the first input / output terminal and the second input / output terminal via the first bridge circuit; an uninterruptible power supply including a charge / discharge circuit for supplying and receiving DC power between the first capacitor and the corresponding power storage cell;

2. a control device for controlling the converter and the inverter, Each of the plurality of first converter cells comprises: a control circuit connected to the control device for communication therewith and controlling the first bridge circuit and the charge / discharge circuit; 2. The uninterruptible power supply according to claim 1, further comprising: a power supply that generates a power supply voltage for the control circuit from the DC voltage of the corresponding power storage cell.

3. In each of the plurality of first converter cells, the control circuit when the AC power supply is normal, the first bridge circuit is controlled to convert AC power input between the first input / output terminal and the second input / output terminal from the AC power supply into DC power, and the charging / discharging circuit is controlled to supply DC power from the first capacitor to the corresponding power storage cell; 3. The uninterruptible power supply according to claim 2, wherein, during a power outage of the AC power supply, the charge / discharge circuit is controlled to supply DC power from the corresponding storage cell to the first capacitor, and the first bridge circuit is controlled to output the DC power of the first capacitor between the first input / output terminal and the second input / output terminal.

4. each of the plurality of first converter cells further includes a resistor element and a switch connected in series between the charge / discharge circuit and the corresponding storage cell; 3. The uninterruptible power supply according to claim 2, wherein, at the time of startup of the uninterruptible power supply, the control circuit turns on the switch and supplies DC power from the corresponding storage cell to the first capacitor via the resistance element and the charge / discharge circuit.

5. each of the plurality of first converter cells further includes a bypass switch connected between the first input / output terminal and the second input / output terminal; 3. The uninterruptible power supply according to claim 2, wherein, when the corresponding storage cell fails, the control circuit stops operation of the charge / discharge circuit and the first bridge circuit and turns on the bypass switch.

6. The uninterruptible power supply according to claim 1 , wherein each of the plurality of first converter cells incorporates the corresponding storage cell.

7. Each of the plurality of second converter cells comprises: a third input / output terminal and a fourth input / output terminal; a second bridge circuit including a plurality of second semiconductor switching elements; 2. The uninterruptible power supply according to claim 1, further comprising: a second capacitor connected to the third input / output terminal and the fourth input / output terminal via the second bridge circuit.

8. the AC power source is a power system or a generator that supplies medium-voltage AC power, the converter converts medium-voltage AC power supplied from the AC power supply into medium-voltage DC power and supplies the medium-voltage DC power to the DC bus when the AC power supply is operating normally, and when the AC power supply is in a power outage, supplies the medium-voltage DC power stored in the power storage device to the DC bus; 8. The uninterruptible power supply according to claim 1, wherein the inverter converts medium-voltage DC power received from the DC bus into medium-voltage AC power and supplies the medium-voltage AC power to the AC transmission line.

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