No power outage device

Abstract

The uninterruptible power supply (10) is connected between the AC power source (1) and the DC transmission line (4). The uninterruptible power supply (10) comprises a converter (12), a DC bus (14), and a bidirectional chopper (18). The converter (12) converts the AC power supplied from the AC power source (1) into DC power. The DC bus (14) supplies the DC power received from the converter (12) to the DC transmission line (4). The bidirectional chopper (18) exchanges DC power between the DC bus (14) and the power storage device (3). The converter (12) includes multiple power converters that convert the AC power input to the AC terminals into DC power and output it from the DC terminals. The multiple power converters have their AC terminals connected in series to the AC power source (1) and their DC terminals connected in parallel to the DC bus (14).

Description

Technical Field

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

Background Art

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

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

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

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

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

[0007] An uninterruptible power supply (UPS) according to this disclosure is connected between an AC power source and a DC transmission line. The UPS comprises a converter, a DC bus, and a bidirectional chopper. The converter converts AC power supplied from the AC power source into DC power. The DC bus supplies the DC power received from the converter to the DC transmission line. The bidirectional chopper exchanges DC power between the DC bus and the power storage device. The converter includes a plurality of power converters that convert AC power input to AC terminals into DC power and output from DC terminals. The plurality of power converters have their AC terminals connected in series to the AC power source and their DC terminals connected in parallel to the DC bus. [Effects of the Invention]

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

[0009] [Figure 1] This is a circuit block diagram showing the configuration of an uninterruptible power supply according to this embodiment. [Figure 2] This is a block diagram showing the main circuit configuration of the converter. [Figure 3] Figure 2 is a circuit diagram showing the main circuit configuration of the power converter. [Figure 4] This is a circuit diagram showing the main circuit configuration of a bidirectional chopper. [Figure 5] This figure illustrates an example of an application of an uninterruptible power supply according to this embodiment. [Figure 6] This diagram illustrates an example of applying an uninterruptible power supply according to a comparative example. [Figure 7] This figure shows an example configuration of a power supply system using an uninterruptible power supply according to this embodiment. [Figure 8] Figure 7 is a circuit diagram showing the main circuit configuration of the converter. [Modes for carrying out the invention]

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

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

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

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

[0014] In Japan, currently, for alternating current, voltage classes of 7 kV or higher are classified as extra-high voltage (EHVAC), voltage classes of 600 V to 7 kV are classified as high voltage (HVAC), and voltage classes of less than 600 V are classified as low voltage (LVAC). For direct current, voltage classes exceeding 7 kV are classified as extra-high voltage (EHVDC), voltage classes of 750 V to 7 kV are classified as high voltage (HVDC), and voltage classes of less than 1.5 kV are classified as low voltage (LVDC).

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

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

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

[0018] The output terminal T3 is connected to the DC transmission line 4. The DC transmission line 4 transmits medium-voltage DC power. A plurality of loads 6 are electrically connected to the DC transmission line 4. A switch S4 and an inverter 5 are connected in series between the DC transmission line 4 and each load 6. By turning on or off the switch S4 connected to each load 6, the load capacity of the uninterruptible power supply device 10 changes.

[0019] The inverter 5 converts the medium-voltage DC power supplied from the DC transmission line 4 into low-voltage AC power and supplies it to the load 6 when the switch S4 is in the on state. The load 6 is driven by the low-voltage AC power supplied from the inverter 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 voltage VB between the terminals of the battery 3 is detected by the control device 20. In the following description, the voltage VB between the terminals of the battery 3 is also referred to as the "battery voltage VB". The battery voltage VB when the battery 3 is fully charged is, for example, several kV.

[0021] 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 20. When AC power is being normally supplied from the AC power source 1 (when the AC power source 1 is healthy), 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 normally supplied from the AC power source 1 (when there is a power outage of the AC power source 1), the switch S1 is turned off, and the connection between the AC power source 1 and the converter 12 is interrupted.

[0022] The converter 12 is controlled by the control device 20 and, when the AC power source 1 is healthy, converts medium-voltage AC power from the AC power source 1 into medium-voltage DC power and outputs it to the DC bus 14. The converter 12 will be described in detail later.

[0023] The capacitor 16 is connected to the DC bus 14 and smoothes 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.

[0024] When the AC power source 1 is healthy, the control device 20 controls the converter 12 so that the DC voltage VD becomes the reference DC voltage VDR. When there is a power outage of the AC power source 1, the control device 20 stops the operation of the converter 12.

[0025] The DC bus 14 is connected to the DC terminal T2 via the bidirectional chopper 18 and switch S2. Switch S2 is controlled by the control device 20. When the uninterruptible power supply 10 is in use, switch S2 is turned on. When the battery 3 or the bidirectional chopper 18 is being maintained, switch S2 is turned off.

[0026] The bidirectional chopper 18 is controlled by the control device 20 and performs DC voltage conversion between the DC bus 14 and the battery 3, thereby transferring DC power between the DC bus 14 and the battery 3. The current detector CD2 detects the DC current IB flowing between the battery 3 and the bidirectional chopper 18 and provides the control device 20 with a signal IBf indicating the detected value.

[0027] When AC power supply 1 is functioning properly, the control device 20 controls the bidirectional chopper 18 so that the battery voltage VB becomes the reference DC voltage VBR. When AC power supply 1 fails, the control device 20 controls the bidirectional chopper 18 so that the DC voltage VD becomes the reference DC voltage VDR. The bidirectional chopper 18 will be explained in more detail later.

[0028] The DC bus 14 is connected to the output terminal T3 via switch S3. Switch S3 is controlled by the control device 20. When the uninterruptible power supply 10 is in use, switch S3 is turned on. During maintenance of the converter 12, switch S3 is turned off.

[0029] The current detector CD3 detects the DC output current Io of the converter 12 and provides a signal Iof indicating the detected value to the control device 20. The instantaneous value of the DC output voltage VO applied to the DC transmission line 4 is detected by the control device 20.

[0030] The control device 20 controls switches S1 to S3, the converter 12, and the bidirectional chopper 18 based on the AC input voltage VI, DC output voltage VO, DC voltage VD, battery voltage VB, AC input current Ii, DC current IB, DC output current Io, etc. Typically, the control device 20 can be configured by at least one microprocessor with a predetermined program pre-stored in it.

[0031] Figure 2 is a block diagram showing the main circuit configuration of converter 12. As shown in Figure 2, converter 12 is composed of multiple power converters 30 connected between AC nodes 12a, 12b and DC nodes 12c, 12d. The configurations of the multiple power converters 30 are identical to each other.

[0032] Each power converter 30 includes AC terminals 30a, 30b, DC terminals 30c, 30d, an AC / DC converter 32, a DC / DC converter 34, and capacitors C1, C2.

[0033] The AC terminals 30a and 30b of multiple power converters 30 are connected in series between the AC nodes 12a and 12b of converter 12. Specifically, the AC terminal 30a of the first power converter 30 is connected to the AC node 12a, the AC terminal 30b of the first power converter 30 is connected to the AC terminal 30a of the second power converter 30, and the AC terminal 30b of the second power converter 30 is connected to the AC terminal 30a of the third power converter 30.

[0034] Thus, the AC terminal 30a of the i-th power converter 30 is connected to the AC terminal 30b of the (i-1)th power converter 30, and the AC terminal 30b of the i-th power converter 30 is connected to the AC terminal 30a of the (i+1)th power converter 30. The AC terminal 30b of the Nth power converter 30 is connected to the AC node 12b. N represents the number of power converters 30, and i is an integer between 2 and N-1. In other words, the AC terminals 30a and 30b of the multiple power converters 30 are connected in series to the AC power source 1 via the AC nodes 12a and 12b.

[0035] The DC terminals 30c and 30d of each power converter 30 are connected to the DC nodes 12c and 12d. In other words, the DC terminals 30c and 30d of multiple power converters 30 are connected in parallel to the DC bus 14 via the DC nodes 12c and 12d.

[0036] In each power converter 30, the AC / DC converter 32 converts the AC power input to the AC terminals 30a and 30b into DC power. By making the AC side of the power converter 30 a multi-stage DC converter, the AC voltage applied to the AC / DC converter 32 can be reduced, making it possible to use semiconductor switching elements with low voltage resistance and low on-resistance in the AC / DC converter 32.

[0037] The DC / DC converter 34 transmits the DC power generated by the AC / DC converter 32 to the DC terminals 30c and 30d. The DC / DC converter 34 is an isolated DC / DC converter.

[0038] Capacitor C1 is connected between DC buses PL1 and NL1, which connect AC / DC converter 32 and DC / DC converter 34, to smooth and stabilize the DC voltage between DC buses PL1 and NL1. Capacitor C2 is connected between DC buses PL2 and NL2, which connect DC converter 34 and DC terminals 30c and 30d, to smooth and stabilize the DC voltage between DC buses PL2 and NL2.

[0039] Figure 3 is a circuit diagram showing the main circuit configuration of the power converter 30 shown in Figure 2. As shown in Figure 3, a solid-state transformer (SST) is used in the power converter 30. The SST uses a high-frequency transformer to perform both isolation and voltage transformation, and the volume and weight of the transformer can be significantly reduced compared to a commercial frequency transformer.

[0040] As shown in Figure 3, the AC / DC converter 32 includes semiconductor switching elements SW1 to SW4. The semiconductor switching elements SW1 to SW4 constitute a single-phase full-bridge circuit. The single-phase full-bridge circuit is driven by a gate signal from the control device 20 and converts the AC power input to AC terminals 30a and 30b into DC power, which is output to DC buses PL1 and NL1. Capacitor C1 smooths the DC voltage between DC buses PL1 and NL1.

[0041] The isolated DC / DC converter 34 is a DAB (Dual Active Bridge) converter. Specifically, the isolated DC / DC converter 34 includes a primary bridge circuit 35, a secondary bridge circuit 36, and a high-frequency transformer Tr.

[0042] The primary bridge circuit 35 constitutes a single-phase full-bridge circuit. Specifically, it has semiconductor switching elements SW5 to SW8 connected between the DC positive busbar PL1 and the DC negative busbar NL1. Semiconductor switching elements SW5 and SW6 are connected in series between the DC positive busbar PL1 and the DC negative busbar NL1 via node N1a, which is connected to AC terminal 35a. Semiconductor switching elements SW7 and SW8 are connected in series between the DC positive busbar PL1 and the DC negative busbar NL1 via node N1b, which is connected to AC terminal 35b.

[0043] Similarly, the secondary bridge circuit 36 ​​constitutes a single-phase full-bridge circuit. Specifically, it has semiconductor switching elements SW9 to SW12 connected between the DC positive busbar PL2 and the DC negative busbar NL2. Semiconductor switching elements SW9 and SW10 are connected in series between the DC positive busbar PL2 and the DC negative busbar NL2 via node N2a, which is connected to AC terminal 36a. Semiconductor switching elements SW11 and SW12 are connected in series between the DC positive busbar PL2 and the DC negative busbar NL2 via node N2b, which is connected to AC terminal 36b.

[0044] Each of the semiconductor switching elements SW1 to SW12 comprises a self-extinguishing switching element and a diode. The switching element can be made up of any self-extinguishing element such as an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal Oxide Semiconductor Fielded Effect Transistor). The diode is connected in antiparallel to the switching element to form a free-wheeling diode (FWD).

[0045] The high-frequency transformer Tr has a primary winding connected between the AC terminals 35a and 35b of the primary bridge circuit 35, and a secondary winding connected between the AC terminals 36a and 36b of the secondary bridge circuit 36.

[0046] The control device 20 controls the power conversion in the isolated DC / DC converter 34. Specifically, the control device 20 generates gate signals to control the on / off state of semiconductor switching elements SW5 to SW12 based on output signals from current sensors and voltage sensors (not shown).

[0047] The isolated DC / DC converter 34 converts the DC power input from the DC buses PL1 and NL1 into AC power via the primary bridge circuit 35. This AC power is transmitted to the secondary bridge circuit 36 ​​via the high-frequency transformer Tr. The secondary bridge circuit 36 ​​converts the transmitted AC power back into DC power and outputs it to the DC buses PL2 and NL2. As a result, the DC power generated by the AC / DC converter 32 is transmitted to the DC bus 14 via the DC terminals 30c and 30d.

[0048] Figure 4 is a circuit diagram showing an example of the main circuit configuration of the bidirectional chopper 18. As shown in Figure 4, the bidirectional chopper 18 is composed of a non-isolated type bidirectional chopper. Specifically, the bidirectional chopper 18 is composed of semiconductor switching elements SW13, SW14, a reactor L1, and a capacitor C3.

[0049] The semiconductor switching elements SW13 and SW14 are connected in series between the high-voltage nodes 18a and 18b. The reactor L1 is connected between the connection node of the semiconductor switching elements SW13 and SW14 and the low-voltage node 18c. The capacitor C3 is connected between the high-voltage nodes 5a and 5b to stabilize the DC voltage VD between the high-voltage nodes 5a and 5b.

[0050] When AC power supply 1 is functioning properly, semiconductor switching element SW3 is switched on and off at a predetermined frequency, storing DC power from DC bus 14 in battery 3. When AC power supply 1 fails, semiconductor switching element SW4 is switched on and off at a predetermined frequency, supplying DC power from battery 3 to DC bus 14.

[0051] Next, we will describe an example of how the uninterruptible power supply 10 according to this embodiment can be applied. Figure 5 illustrates an example of the application of the uninterruptible power supply 10 according to this embodiment. As shown in Figure 5, the uninterruptible power supply 10 according to this embodiment receives medium-voltage AC power from the AC power source 1. The converter 12 converts the medium-voltage AC power into medium-voltage DC power and supplies it to the DC transmission line 4.

[0052] As described in Figures 2 and 3, the converter 12 includes multiple power converters 30, the AC side of which is connected in series with the AC power source 1, and the DC side of which is connected in parallel with the DC bus 14. With this configuration, the converter 12 can generate medium-voltage DC power from medium-voltage AC power. The medium-voltage DC power transmitted through the DC transmission line 4 is converted to low-voltage (e.g., 415V) AC power by the inverter 5 and supplied to the load 6.

[0053] Figure 6 illustrates an example of the application of an uninterruptible power supply (UPS) 10A according to the comparative example. As shown in Figure 6, the UPS 10A according to the comparative example is a conventional UPS and comprises a converter 12, a bidirectional chopper 18, a DC bus 14, a capacitor 16, and an inverter 22A.

[0054] The uninterruptible power supply (UPS) 10A receives low-voltage (e.g., 480V) AC power from the AC power source 1. The converter 12 converts the low-voltage (e.g., 480V) AC power to low-voltage (e.g., 600V) DC power and outputs it to the DC bus 14. The inverter 22A converts the low-voltage (e.g., 600V) DC power to low-voltage (e.g., 480V) AC power and supplies it to the AC transmission line 7. The low-voltage (e.g., 480V) AC power transmitted through the AC transmission line 7 is stepped down to low-voltage (e.g., 415V) AC power by the transformer 8 and supplied to the load 6.

[0055] The uninterruptible power supply 10 according to this embodiment does not have an inverter 22A compared to the uninterruptible power supply 10A according to the comparative example, and therefore the size of the device can be reduced.

[0056] Furthermore, since the uninterruptible power supply (UPS) 10 generates medium-voltage DC power from medium-voltage AC power and supplies it to the DC transmission line 4, it can reduce the current flowing through the DC transmission line 4 compared to the UPS 10A that supplies low-voltage AC power. This reduces power loss and voltage drop in the DC transmission line 4. In addition, since the number of DC transmission lines 4 can be reduced, it becomes possible to miniaturize the power supply system and reduce equipment costs.

[0057] Figure 7 shows an example configuration of a power supply system using an uninterruptible power supply 10 according to this embodiment. The power supply system can be applied, for example, to a large-scale data center.

[0058] As shown in Figure 7, the power supply system includes multiple uninterruptible power supplies 10 connected in parallel between the AC power supply 1,1A and the DC transmission line 4. The basic configuration of each uninterruptible power supply 10 is the same as that of the uninterruptible power supply 10 described in Figures 1 to 4. The uninterruptible power supply 10 shown in Figure 7 differs in that it includes a switch S5 instead of switch S1, and has a transformer 2.

[0059] Switch S5 is controlled by a control device (not shown) and is configured to connect one of the two AC power sources 1 and 1A to the primary side of transformer 2. AC power source 1 is, for example, a commercial AC power source, and AC power source 1A is, for example, a generator. In other words, the uninterruptible power supply 10 is configured to be switchable between a commercial AC power source and a generator as the AC power source.

[0060] As shown in Figure 7, the converter 12 receives 13.8kV (medium voltage) AC power from either AC power source 1 or 1A via switch S5 and transformer 2. The AC power is 10MVA.

[0061] Figure 8 shows the main circuit configuration of the converter 12 shown in Figure 7. As described in Figures 2 and 3, the converter 12 comprises multiple power converters 30. The converter 12 converts 13.8kV AC power (10MVA) to 1.5kV (medium voltage) DC power and supplies it to the DC transmission line 4. The DC transmission line 4 is approximately 1,000 feet long. The 1.5kV DC power transmitted through the DC transmission line 4 is converted to 415V (low voltage) AC power by the inverter 5 and supplied to the load.

[0062] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims and not by the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included. [Explanation of Symbols]

[0063] 1.1A AC power supply, 2.8 transformer, 3 battery, 4 DC transmission line, 5.22A inverter, 6 load, 7 AC transmission line, 10.10A uninterruptible power supply, 12 converter, 14.PL1,NL1,PL2,NL2 DC bus, 16.C1~C3 capacitors, 18 bidirectional chopper, 20 control device, 30 power converter, 32 AC / DC converter, 34 DC / DC converter, 35 primary bridge circuit, 36 secondary bridge circuit, SW1~SW14 semiconductor switching elements, T1 input terminal, T2 DC terminal, T3 output terminal, Tr high-frequency transformer, S1~S5 switches.

Claims

1. An uninterruptible power supply connected between an AC power source and a DC transmission line, A converter that converts AC power supplied from the aforementioned AC power source into DC power, A DC bus that supplies DC power received from the converter to the DC transmission line, The system includes a bidirectional chopper that exchanges DC power between the DC bus and the power storage device, The aforementioned AC power source is a power system or generator that supplies medium-voltage AC power. The aforementioned power storage device is configured to store medium-voltage DC power, The converter includes a plurality of power converters that convert AC power input to AC terminals into DC power and output it from DC terminals. The plurality of power converters are configured such that the AC terminals are connected in series with the AC power supply, and the DC terminals are connected in parallel with the DC busbar. When the AC power supply is functioning properly, the converter converts the medium-voltage AC power supplied from the AC power supply into medium-voltage DC power and supplies it to the DC bus. An uninterruptible power supply (UPS) in which, in the event of a power outage in the AC power supply, the converter stops operating, and the bidirectional chopper supplies medium-voltage DC power from the power storage device to the DC bus.

2. Each of the aforementioned plurality of power converters is An AC / DC converter that converts AC power input to the aforementioned AC terminal into DC power, The uninterruptible power supply according to claim 1, further comprising an isolated DC / DC converter that transmits DC power from the AC / DC converter to the DC terminal.

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

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