No power outage device

Abstract

The uninterruptible power supply includes a converter (12), a bidirectional chopper (18), and an inverter (20). Each of the converter (12) and the inverter (20) includes a leg circuit having a plurality of cascaded converter cells (26). The bidirectional chopper (18) includes a plurality of chopper cells (30) connected in series between a DC positive bus (14p) and a DC negative bus (14n). The power storage device includes a plurality of power storage cells connected in parallel to each other and corresponding to the plurality of chopper cells. Each of the plurality of chopper cells (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 charge / discharge circuit for exchanging DC power with the 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 the present disclosure is connected between an AC power source and an AC transmission line. The uninterruptible power supply 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 a power storage device, and vice versa. The inverter converts DC power received from the DC positive bus and the DC negative bus into AC power and supplies it to the AC transmission line. Each of the converter and the inverter includes a leg circuit having a plurality of cascaded converter cells. The bidirectional chopper includes a plurality of chopper cells connected in series between the DC positive bus and the DC negative bus. The power storage device includes a plurality of storage cells provided corresponding to the plurality of chopper cells and connected in parallel to each other. Each of the plurality of chopper cells 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 charge / discharge circuit for exchanging DC power between the capacitor and a 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 a main circuit configuration of a converter, an inverter, and a bidirectional chopper. [Figure 3] FIG. 2 is a circuit diagram showing a first configuration example of a converter cell. [Figure 4] FIG. 10 is a circuit diagram showing a second configuration example of the converter cell. [Figure 5] FIG. 2 is a circuit diagram showing a first configuration example of a chopper cell. [Figure 6] 10 is a flowchart showing control of a chopper 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 the chopper cell. [Figure 9] FIG. 10 is a circuit diagram showing a third configuration example of a chopper cell. [Figure 10] 10 is a flowchart showing control of a chopper cell by a control circuit. [Figure 11] 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 12] 12 is a diagram illustrating the main circuit configuration of the converter, inverter, and bidirectional chopper illustrated in FIG. 11. 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 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. AC input voltage VI is a medium-voltage AC voltage, and its instantaneous value is detected by control device 22. 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 22.

[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 S3 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 S3 connected to each load 6 is turned on or off.

[0019] When switch S3 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 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. When the battery 3 is fully charged, the terminal voltage VB is, for example, several kV.

[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 chopper cells included in the bidirectional chopper 18. The battery cells 3a constitute "storage cells."

[0022] The 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 being supplied normally from the AC power source 1 (when the AC power source 1 is operating normally), 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 is controlled by a control device 22, and when the AC power supply 1 is healthy, converts 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 described in detail later. The instantaneous value of the DC voltage VD of the DC bus 14 is detected by the control device 22.

[0024] When the AC power supply 1 is normal, the control device 22 controls the converter 12 so that the DC voltage VD becomes equal to the reference DC voltage VDR. When the AC power supply 1 experiences a power outage, the control device 22 stops the operation of the converter 12.

[0025] The DC bus 14 is connected to a high-voltage side node 18a of a bidirectional chopper 18, and a low-voltage side node 18c of the bidirectional chopper 18 is connected to a DC terminal T2. The DC bus 14 includes a DC positive bus 14p and a DC negative bus 14n (see FIG. 2).

[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 exchanging DC power between the DC bus 14 and the battery 3. When the AC power supply 1 is operating normally, the control device 22 controls the bidirectional chopper 18 so that the voltage VB between the terminals of the battery 3 becomes equal to the reference DC voltage VBR. When the AC power supply 1 fails, the control device 22 controls the bidirectional chopper 18 so that the DC voltage VD becomes equal to the reference DC voltage VDR. The bidirectional chopper 18 will be described in detail later.

[0027] The DC bus 14 is connected to a DC node of the inverter 20, and the AC node of the inverter 20 is connected to the output terminal T3 via a switch S2. The switch S2 is controlled by a control device 22. When the uninterruptible power supply 10 is in use, the switch S2 is turned on. When maintenance of the inverter 20 is performed, the switch S2 is turned off.

[0028] The current detector CD2 detects the AC output current Io of the inverter 20 and provides a signal Iof indicating the detected value to the control device 22. The instantaneous value of the AC output voltage VO applied to the AC transmission line 4 is detected by the control device 22.

[0029] The inverter 20 is controlled by a control device 22, and converts DC power supplied from the converter 12 or the 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 detail later.

[0030] The control device 22 controls the switches S1 to S3, the converter 12, the bidirectional chopper 18, and the inverter 20 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, the DC current IB, and the AC output current Io.

[0031] The control device 22 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.

[0032] Fig. 2 is a circuit diagram showing the main circuit configuration of the converter 12, the inverter 20, and the bidirectional chopper 18. As shown in Fig. 2, each of the converter 12 and the inverter 20 is configured by a modular multilevel converter (MMC) in which multiple converter cells are connected in cascade.

[0033] 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."

[0034] 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 an input terminal T1 via a switch S1.

[0035] The leg circuit 12r includes an upper arm 24 from the DC positive bus 14p to the AC input terminal Nr, and a lower arm 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.

[0036] The upper arm 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 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.

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

[0038] The inverter 20 includes a plurality of leg circuits 20u, 20v, and 20w. The leg circuits 20u, 20v, and 20w 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 20u, 20v, and 20w are also collectively referred to as "leg circuits 20x."

[0039] A leg circuit 20x 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 20u, 20v, and 20w 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 20u, 20v, and 20w, respectively, are connected to the output terminal T3 via a switch S3. The leg circuits 20u, 20v, and 20w have the same configuration as the leg circuit 12r, and therefore description thereof will be omitted.

[0040] Fig. 3 is a circuit diagram showing a first configuration example of the converter cell 26 shown in Fig. 2. As shown in Fig. 3, the converter cell 26 according to the first configuration example includes a series body formed by connecting two switching elements SW1 and SW2 in series, a capacitor 28, and input / output terminals 26a and 26b.

[0041] To representatively explain the converter cells 26 of the leg circuit 12r, in the upper arm 24, the input / output terminal 26a of the uppermost converter cell 26 is connected to the DC positive bus 14p. 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 AC input terminal Nr.

[0042] In the lower arm 25, the input / output terminal 26a of the uppermost converter cell 26 is connected to the AC input terminal Nr. 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.

[0043] The series circuit of switching elements SW1 and SW2 is connected in parallel with capacitor 28. The series circuit of switching elements SW1 and SW2 forms a half-bridge circuit. Capacitor 28 forms a "storage element" that stores DC power.

[0044] Both terminals of the switching element SW2 are connected to the input / output terminals 26a and 26b, respectively. The converter cell 26 outputs the voltage Vc across the terminals of the capacitor 28 or zero voltage between the input / output terminals 26a and 26b 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 26 outputs the voltage Vc across the terminals of the capacitor 28. When the switching element SW1 is off and the switching element SW2 is on, the converter cell 26 outputs zero voltage.

[0045] Fig. 4 is a circuit diagram showing a second configuration example of the converter cell 26 shown in Fig. 2. As shown in Fig. 4, the converter cell 26 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 28, and input / output terminals 26a and 26b. The first series body, the second series body, and the capacitor 26 are connected in parallel. The first series body and the second series body form a full-bridge circuit.

[0046] The connection point between switching element SW1 and switching element SW2 is connected to input / output terminal 26a. The connection point between switching element SW3 and switching element SW4 is connected to input / output terminal 26b. Converter cell 26 outputs inter-terminal voltage Vc, −Vc, or zero voltage of capacitor 28 between input / output terminals 26a and 26b through the switching operations of switching elements SW1 to SW4.

[0047] 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).

[0048] 2, the bidirectional chopper 18 includes a plurality of chopper cells (BCELLs) 30 connected in series between the DC positive bus 14p and the DC negative bus 14n. Each of the plurality of chopper cells 30 is also called a "battery circuit cell" because it is configured to control the charging and discharging of a corresponding battery cell 3a, as described below.

[0049] Fig. 5 is a circuit diagram showing a first configuration example of the chopper cell 30 shown in Fig. 2. As shown in Fig. 5, the chopper cell 30 according to the first configuration example includes input / output terminals 30a and 30b, DC terminals 30c and 30d, switching elements SW5 and SW6, a capacitor 40, a bypass switch S4, a charge / discharge circuit 45, switches S5 and S6, a resistive element 46, voltage detectors 42 and 48, a current detector CD3, a fuse 50, a power supply 52, and a control circuit 54.

[0050] In the bidirectional chopper 18, the input / output terminal 30a of the uppermost chopper cell 30 is connected to the DC positive bus 14p. The input / output terminal 30b of each chopper cell 30 other than the lowermost chopper cell 30 is connected to the input / output terminal 30a of the adjacent chopper cell 30. The input / output terminal 30b of the lowermost chopper cell 30 is connected to the DC negative bus 14n.

[0051] The DC terminal 30c is connected to the positive terminal of the corresponding battery cell 3a, and the DC terminal 30d is connected to the negative terminal of the corresponding battery cell 3a.

[0052] The positive terminal of the capacitor 40 is connected to the input / output terminal 30a via the DC line PL, and the negative terminal of the capacitor 40 is connected to the input / output terminal 30b via the DC line NL. That is, the same number of capacitors 40 as the number of chopper cells 30 included in the bidirectional chopper 18 are connected in series between the DC positive bus 14p and the DC negative bus 14n.

[0053] A series connection of multiple capacitors 40 constitutes a capacitor for stabilizing and smoothing the DC voltage VD between the DC buses 14p, 14n. The voltage VDc across the terminals of the capacitor 40 of each chopper cell 30 is ideally equal to the DC voltage VD divided by the number of chopper cells 30 included in the bidirectional chopper 18. The voltage detector 42 detects the instantaneous value of the voltage VDc across the terminals of the capacitor 40 and provides a signal indicating the detected value to the control circuit 54.

[0054] The bypass switch S4 is connected between the input / output terminal 30a and the input / output terminal 30b. The bypass switch S4 is configured to be able to short-circuit the input / output terminal 30a and the input / output terminal 30b by turning on in response to a command from the control circuit 54. In one aspect, the bypass switch S4 can be used to short-circuit the chopper cells 30 when the corresponding battery cell 3a fails. In this case, even if the battery cell 3a fails in some of the multiple chopper cells 30, the other chopper cells 30 can be used to continue operating the uninterruptible power supply 10.

[0055] The charge / discharge circuit 45 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 45 includes switching elements SW5 and SW6 and a reactor 44. 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.

[0056] 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 44. A second terminal of the reactor 44 is connected to the DC terminal 30c via the switch S5.

[0057] 5, an example in which the charge / discharge circuit 45 includes a bidirectional chopper has been described, but the charge / discharge circuit 45 is not limited to this. The charge / discharge circuit 45 may include a well-known non-insulated DC / DC converter.

[0058] The charge / discharge circuit 45 is controlled by the control circuit 54. When the AC power supply 1 is operating normally, the charge / discharge circuit 45 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 45 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 45 and the battery cell 3a, and provides the control circuit 54 with a signal indicating the detected value.

[0059] The switch S5 is connected between the second terminal of the reactor 44 and the DC terminal 30c, and is controlled by the control circuit 54. When the chopper cell 30 is used, the switch S5 is turned on. When the uninterruptible power supply 10 is started up and when maintenance of the battery cell 3a is performed, the switch S5 is turned off.

[0060] A fuse 50 is provided between the switch S5 and the DC terminal 30c. When a large current flows between the charge / discharge circuit 45 and the battery cell 3a, the fuse 50 melts.

[0061] Resistance element 46 and switch S6 are connected in series between the first terminal and the second terminal of switch S5. Switch S6 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 46 limits the current flowing from battery cell 3a to capacitor 40 when DC power is not stored in capacitor 40 when uninterruptible power supply 10 starts up.

[0062] 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.

[0063] A first input terminal of the power supply 52 is connected to the DC terminal 30c, and a second input terminal of the power supply 52 is connected to the DC terminal 30d. The power supply 52 steps down the DC voltage supplied from the battery cell 3a via the DC terminals 30c and 30d 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.

[0064] The control circuit 54 is driven by the power supply voltage supplied from the power supply 52, and exchanges signals with the control device 22. The control circuit 54 controls the chopper cell 30 based on signals from the control device 22, output signals from the voltage detectors 42 and 48, and an output signal from the current detector CD3, etc.

[0065] 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.

[0066] Fig. 6 is a flowchart showing the control of the chopper cells 30 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 22 transmits a signal instructing the start up of the uninterruptible power supply 10 to the control circuit 54 of each chopper cell 30. In S01, when the control circuit 54 receives this signal from the control device 22, it determines that a command to start up the uninterruptible power supply 10 has been issued.

[0067] When an instruction to start up the uninterruptible power supply 10 is issued (YES in S01), the control circuit 54 turns on the switch S6 in step S02 to start initial charging of the capacitor 40 (step S03).

[0068] 7 is a circuit block diagram for explaining the initial charging of the capacitor 40. During the initial charging, the bypass switch S4 and the switch S5 are turned off.

[0069] 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 S6, resistor 46, reactor 44, 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 45 so that the voltage across capacitor 40 becomes a predetermined target voltage.

[0070] Returning to FIG. 6, when the initial charging of the capacitor 40 is completed, the control circuit 54 turns off the switch S6 and turns on the switch S5 in step S04.

[0071] 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 22 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 chopper cell 30. 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 22.

[0072] 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 charge / discharge 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 charge / discharge circuit 45 so that the voltage across the terminals of the battery cell 3a detected by the voltage detector 48 becomes the reference DC voltage VBR.

[0073] 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 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 charge / discharge circuit 45 so that the inter-terminal voltage VDc of the capacitor 40 detected by the voltage detector 42 becomes equal to the reference DC voltage VDcR.

[0074] The control circuit 54 obtains the number of normal chopper cells 30 from signals exchanged with the control device 22. The control circuit 54 then obtains the reference DC voltage VDc by dividing the reference DC voltage VDR by the number of normal chopper cells 30 included in the bidirectional chopper 18.

[0075] In step S07, 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 S07, 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.

[0076] If no failure of the battery cell 3a is detected (NO in S07), the control circuit 54 executes the processes of steps S05 to S06 and S11. On the other hand, if a failure of the battery cell 3a is detected (YES in S07), the control circuit 54 proceeds to step S08 and turns off the switch S5 to disconnect the battery cell 3a from the chopper cell 30. The control circuit 54 also short-circuits the chopper cell 30 by turning on the bypass switch S4.

[0077] In step S09, the control circuit 54 turns off the switching elements SW5 and SW6 to stop the operation of the charge / discharge circuit 45. In step S10, the control circuit 54 transmits a fault detection signal indicating a fault in the chopper cell 30 to the control device 22. When the control device 22 receives a fault detection signal from the control circuit 54 of one of the multiple chopper cells 30, the control device 22 identifies the position of the chopper cell 30 based on the received fault detection signal, and notifies the user of the uninterruptible power supply 10 and the control circuits 54 of the other chopper cells 30 of information indicating the identified position.

[0078] This allows the user of the uninterruptible power supply 10 to perform maintenance on the battery cell 3a of the faulty chopper cell 30 based on the acquired information. In addition, the control circuit 54 of each chopper cell 30 can determine the number of normal chopper cells 30 from the acquired information.

[0079] As described above, each of the multiple chopper cells 30 connected in series between the DC buses 14p, 14n includes a smoothing capacitor 40 and a charge / discharge circuit 45 for exchanging DC power between the capacitor 40 and the corresponding battery cell 3a. With this configuration, the voltage applied to each chopper cell 30 can be reduced according to the number of chopper cells 30 included in the bidirectional chopper 18. Therefore, electrical insulation between the capacitor 40 and the battery cell 3a is not required in the charge / discharge circuit 45. This allows the bidirectional chopper 18 to be made smaller, which in turn allows the uninterruptible power supply 10 to be made smaller.

[0080] Furthermore, since a plurality of battery cells 3a are provided corresponding to the plurality of chopper cells 30, even if one of the plurality of battery cells 3a fails, by turning on the bypass switch S4 of the chopper cell 30 corresponding to the failed battery cell 3a and shorting the chopper cell 30, it is possible to perform maintenance on the failed battery cell 3a while continuing to operate the uninterruptible power supply 10 using the other chopper cells 30.

[0081] Next, another example of the configuration of the chopper cell 30 will be described. Fig. 8 is a circuit diagram showing a second configuration example of the chopper cell 30. As shown in Fig. 8, the chopper cell 30 according to the second configuration example differs from the chopper cell 30 according to the first configuration example shown in Fig. 5 in that the chopper cell 30 has a built-in battery cell 3a.

[0082] Since each chopper cell 30 has a built-in battery cell 3a, it is not necessary to install a battery panel including multiple battery cells 3a outside the uninterruptible power supply 10. As a result, the size of the power supply system including the uninterruptible power supply 10 can be reduced.

[0083] Fig. 9 is a circuit diagram showing a third configuration example of the chopper cell 30. As shown in Fig. 9, the chopper cell 30 according to the third configuration example differs from the chopper cell 30 according to the first configuration example shown in Fig. 5 in that it has a built-in battery cell 3a and includes an equalization circuit 56.

[0084] The equalization circuit 56 is provided between the input / output terminals 30a, 30b and the capacitor 40. The equalization circuit 56 is a circuit for equalizing the inter-terminal voltages VDc of the capacitors 40 of the plurality of chopper cells 30.

[0085] When there is variation in the inter-terminal voltages VDc of the capacitors 40 of multiple chopper cells 30, there is also variation in the operation of the charge / discharge circuits 45 of the chopper cells 30. For example, assume that the inter-terminal voltages VDc of the capacitors 40 of some chopper cells 30 exceed the reference DC voltage VDcR. In this case, in that chopper cell 30, in order to lower the inter-terminal voltage VDc of the capacitor 40, the charge / discharge circuit 45 is controlled to supply DC power from the capacitor 40 to the battery cell 3a, i.e., to charge the battery cell 3a.

[0086] Conversely, when the terminal voltage VDc of the capacitor 40 in some chopper cells 30 is lower than the reference DC voltage VDcR, the charge / discharge circuit 45 is controlled to supply DC power from the battery cell 3a to the capacitor 40 in that chopper cell 30, i.e., to discharge the battery cell 3a, in order to increase the terminal voltage VDc of the capacitor 40.

[0087] As described above, in each chopper cell 30, charging and discharging of the battery cell 3a is individually controlled according to the terminal voltage VDc of the capacitor 40. Therefore, if there is a variation in the terminal voltage VDc of the capacitor 40 of the plurality of chopper cells 30, there will be a difference in the number of times the battery cell 3a is charged and discharged among the plurality of chopper cells 30. The battery cell 3a usually gradually deteriorates as it is charged and discharged many times. Therefore, among the plurality of battery cells 3a, a battery cell 3a that has been charged and discharged many times deteriorates more rapidly than a battery cell 3a that has been charged and discharged few times. This variation in the number of times the battery cells 3a are charged and discharged will cause a variation in the lifespan of the plurality of battery cells 3a. The equalization circuit 56 reduces the variation in the terminal voltage VDc of the capacitor 40 of the plurality of chopper cells 30, thereby suppressing the variation in the lifespan of the plurality of battery cells 3a and achieving a longer lifespan.

[0088] The equalization circuit 56 includes switching elements SW7 and SW8. Each of the switching elements SW7 and SW8 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. The switching elements SW7 and SW8 are connected in series between the DC line PL and the DC line NL. The connection point between the switching elements SW7 and SW8 is connected to the input / output terminal 30a. As will be described later, the control circuit 54 controls the on and off of the switching elements SW7 and SW8 based on a signal from the control device 22 and an output signal from the voltage detector 42.

[0089] Fig. 10 is a flowchart showing the control of the chopper cell 30 according to the third configuration example by the control circuit 54. The flowchart in Fig. 10 differs from the flowchart shown in Fig. 6 in that it includes step S04A and step S09A instead of step S09.

[0090] As shown in FIG. 10, during operation of the uninterruptible power supply 10, the control circuit 54 of each chopper cell 30 controls the equalization circuit 56 in step S04A so that the inter-terminal voltages VDc of the capacitors 40 of the plurality of chopper cells 30 are equalized.

[0091] In S04A, the control circuit 54 acquires output signals of the voltage detectors 42 from the other chopper cells 30 via the control device 22. The control circuit 54 calculates an average value VDcave of the inter-terminal voltages VDc of the capacitors 40 of the multiple chopper cells 30 based on the output signal of the voltage detector 42 of its own chopper cell 30 and the acquired output signals of the voltage detectors 42 of the other chopper cells 30. The control circuit 54 calculates a deviation ΔVDc between the calculated average value VDc_ave and the reference DC voltage VDcR (ΔVDc = VDcR - VDc_ave). The control circuit 54 controls the on and off of the switching elements SW7 and SW8 so that the deviation ΔVDc becomes zero.

[0092] 6, if a failure of the battery cell 3a is detected (YES determination in S07), the control circuit 54 proceeds to step S08, and turns off the switch S5 to disconnect the battery cell 3a from the chopper cell 30, and turns on the bypass switch S4 to short-circuit the chopper cell 30. Furthermore, in step S09A, the control circuit 54 turns off the switching elements SW5 and SW6 to stop the operation of the charge / discharge circuit 45, and turns off the switching elements SW7 and SW8 to stop the operation of the equalization circuit 56.

[0093] As described above, in this embodiment, each of the converter 12 and the inverter 20 is configured by a modular multilevel converter (MMC). The MMC can output a stepped multilevel voltage waveform by shifting the operation timing of each converter cell 26, and can make the output AC voltage a substantially sinusoidal wave, eliminating the need for an AC filter.

[0094] By applying MMC suitable for high voltage and large capacity to each of the converter 12 and the 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., 400 V) AC power to AC transmission lines, the current flowing in 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, the power supply system can be made smaller and the equipment costs can be reduced.

[0095] Moreover, in this embodiment, the bidirectional chopper 18 is composed of a plurality of chopper cells 30 connected in series. Each of the plurality of chopper cells 30 includes a smoothing capacitor 40 and a charge / discharge circuit 45 for exchanging DC power between the capacitor 40 and the corresponding battery cell 3a. Since the voltage applied to each chopper cell 30 can be reduced in accordance with the number of chopper cells 30 included in the bidirectional chopper 18, electrical insulation between the capacitor 40 and the battery cell 3a in the charge / discharge circuit 45 is not required. This allows the bidirectional chopper 18 to be miniaturized, which in turn allows the uninterruptible power supply 10 to be miniaturized.

[0096] Furthermore, since a plurality of battery cells 3a are provided corresponding to the plurality of chopper cells 30, even if one of the plurality of battery cells 3a fails, by turning on the bypass switch S4 of the chopper cell 30 corresponding to the failed battery cell 3a and shorting the chopper cell 30, it is possible to perform maintenance on the failed battery cell 3a while continuing to operate the uninterruptible power supply 10 using the other chopper cells 30.

[0097] Furthermore, as described in FIG. 9, by providing each chopper cell 30 with an equalization circuit 56 for equalizing the inter-terminal voltages VDc of the capacitors 40 of the plurality of chopper cells 30, it is possible to suppress the variation in the number of charge / discharge cycles of the plurality of battery cells 3a, thereby realizing a longer life for the plurality of battery cells 3a.

[0098] Next, an application example of uninterruptible power supply 10 according to the present embodiment will be described. 11 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.

[0099] As shown in Fig. 11, 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 10. The uninterruptible power supply 10 shown in Fig. 11 differs in that it includes a switch S7 instead of switch S1 and in that it has a transformer 2.

[0100] Switch S7 is controlled by a control device (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.

[0101] 11, 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.

[0102] Fig. 12 shows the main circuit configuration of the converter 12, inverter 20, and bidirectional chopper 18 shown in Fig. 11. As described with reference to Figs. 2 to 4, the converter 12 is configured by a modular multilevel converter (MMC), and converts 13.8 kV AC power (50 MVA) into 22.5 kV (medium voltage) DC power and outputs it to the DC bus 14.

[0103] As described with reference to FIGS. 2 and 5 to 10, the bidirectional chopper 18 includes a plurality of chopper cells 30 connected in series.

[0104] Inverter 20 is configured with a modular multilevel circuit (MMC) and converts 22.5 kV (medium voltage) DC power supplied from converter 12 or bidirectional chopper 18 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.

[0105] 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]

[0106] 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, 20u, 20v, 20w leg circuit, 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 cell, 26a, 26b, 30a, 30b input / output terminals, 28, 38, 40 capacitor, 30 chopper cell, 30c, 30d, T2 DC terminal, 42, 48 voltage detector, 44, L1, L2 reactor, 45 charge / discharge circuit, 46 resistor element, 50 fuse, 52 power supply, 54 control circuit, 56 Equalization circuit, CD1 to CD3 current detectors, NL, PL DC lines, S1 to S3, S5 to S7 switches, S4 bypass switch, SW1 to SW8 switching elements, 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 between a DC positive bus and a DC negative bus; a bidirectional chopper that converts a DC voltage between the DC positive bus and the DC negative bus and a DC voltage of a power storage device; an inverter that converts DC power received from the DC positive bus and the DC negative bus into AC power and supplies the AC power to the AC transmission line; each of the converter and the inverter includes a leg circuit having a plurality of cascaded converter cells; the bidirectional chopper includes a plurality of chopper cells connected in series between the DC positive bus and the DC negative bus; the power storage device includes a plurality of power storage cells provided corresponding to the plurality of chopper cells, respectively, and connected in parallel to each other; Each of the plurality of chopper cells 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; a charge / discharge circuit for exchanging DC power between the capacitor and a corresponding power storage cell; a control device that controls the converter, the inverter, and the bidirectional chopper, Each of the plurality of chopper cells a control circuit communicatively connected to the control device and controlling the charge / discharge circuit; a power supply that generates a power supply voltage for the control circuit from the DC voltage of the corresponding storage cell.

2. In each of the plurality of chopper cells, the control circuit When the AC power supply is normal, the charging / discharging circuit is controlled so as to supply DC power from the capacitor to the corresponding power storage cell; 2. The uninterruptible power supply according to claim 1, wherein the charge / discharge circuit is controlled so that, when the AC power supply is interrupted, DC power is supplied from the corresponding power storage cell to the capacitor.

3. each of the plurality of chopper cells further includes a resistor element and a switch connected in series between the charge / discharge circuit and the corresponding storage cell; 2. The uninterruptible power supply according to claim 1, 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 capacitor via the resistance element and the charge / discharge circuit.

4. each of the plurality of chopper cells further includes a bypass switch connecting between the first input / output terminal and the second input / output terminal; 2. The uninterruptible power supply according to claim 1, wherein the control circuit stops operation of the charge / discharge circuit and turns on the bypass switch when the corresponding storage cell fails.

5. each of the plurality of chopper cells further includes an equalization circuit including a plurality of semiconductor switching elements; 2. The uninterruptible power supply according to claim 1, wherein the control circuit controls the on and off of the semiconductor switching elements so that the voltages across the terminals of the capacitors of the chopper cells are equalized.

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

7. the AC power source is a power system or a generator that supplies medium-voltage AC power, When the AC power supply is operating normally, 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 between the DC positive bus and the DC negative bus; 7. The uninterruptible power supply according to claim 1, wherein the inverter converts medium-voltage DC power received from the DC positive bus and the DC negative bus into medium-voltage AC power and supplies the medium-voltage AC power to the AC transmission line.

8. the power storage device is configured to store medium-voltage DC power, 8. The uninterruptible power supply according to claim 7, wherein, during a power outage of the AC power supply, the converter stops operation, and the bidirectional chopper supplies medium-voltage DC power from the power storage device to the DC positive bus and the DC negative bus.

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