Uninterruptible power supply device and power supply system

Abstract

The uninterruptible power supply device (10) is connected to an AC system (1) and a DC grid (6). The DC grid (6) includes a DC bus (7) connected to the AC system (1) via an AC / DC converter (5), a distributed power source (61) that outputs the generated DC power to the DC bus, and a DC load (65) that receives the DC power of the DC bus (7). The uninterruptible power supply device (10) includes a DC link (12) for exchanging DC power, a converter (11) that converts the AC power supplied from the AC system (1) into DC power and supplies it to the DC link (12), an inverter (14) that converts the DC power received from the DC link (12) into AC power and supplies it to an AC load (8), a first DC terminal (T1) connected to the DC link (12), a second DC terminal (T2) connected to a power storage device (9), and a third DC terminal (T3) connected to the DC bus (7), and a DC / DC converter (16) configured to transfer DC power among the first to third DC terminals.

Description

Technical Field

[0001] The present disclosure relates to an uninterruptible power supply device and a power supply system using the same.

Background Art

[0002] An uninterruptible power supply device is connected between an AC system and an AC load, converts AC power supplied from the AC system into DC power, and converts the DC power into AC power to supply it to the AC load. When an accident occurs in the AC system, the DC power of the energy storage device is converted into AC power and supplied to the AC load. Therefore, even when an accident occurs in the AC system, the time during which DC power is stored in the energy storage device allows the operation of the AC load to continue.

[0003] On the other hand, in recent years, against the background of the introduction of renewable energy sources and the increase in DC loads driven by DC power, a DC grid that connects a plurality of power sources and a plurality of DC loads to a DC bus and exchanges DC power via the DC bus has attracted attention. While full DC conversion is progressing in data centers and the like, in factory facilities with many AC loads, a power supply system in which an AC system and a DC grid coexist has been studied (see Non-Patent Document 1).

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the above-described power supply system, the DC grid is connected to the AC system by an AC / DC converter. However, the power supply of AC power in the AC system and the power supply of DC power in the DC grid are independent of each other. Therefore, power cannot be exchanged between the uninterruptible power supply device connected to the AC system, the energy storage device connected to the uninterruptible power supply device, and the DC grid.

[0006] Here, in order to exchange power among the uninterruptible power supply device, the energy storage device, and the DC grid, a DC / DC converter for performing bidirectional DC voltage conversion between the DC link of the uninterruptible power supply device and the energy storage device, and a DC / DC converter for performing bidirectional DC voltage conversion between the DC link and the DC grid are required. However, when a plurality of DC / DC converters are provided among the uninterruptible power supply device, the energy storage device, and the DC grid in this way, DC power will be transmitted via the plurality of DC / DC converters, and there is a concern about an increase in power loss. In addition, there is a concern that the power supply system will be enlarged by providing a plurality of DC / DC converters.

[0007] The present disclosure has been made to solve such problems, and the main object of the present disclosure is to realize power exchange among the uninterruptible power supply device, the energy storage device, and the DC grid in a power supply system in which an AC system and a DC grid coexist. Another object of the present disclosure is to perform power exchange among the uninterruptible power supply device, the energy storage device, and the DC grid with high efficiency.

Means for Solving the Problems

[0008] An uninterruptible power supply device according to one aspect of the present disclosure is connected to an AC system and a DC grid. The DC grid includes a DC bus connected to the AC system via an AC / DC converter, a distributed power source that outputs generated DC power to the DC bus, and a DC load that receives the DC power of the DC bus. The uninterruptible power supply device includes a DC link for exchanging DC power, a converter that converts AC power supplied from the AC system into DC power and supplies it to the DC link, an inverter that converts DC power received from the DC link into AC power and supplies it to an AC load, a first DC terminal connected to the DC link, a second DC terminal connected to a power storage device, and a third DC terminal connected to the DC bus, and a DC / DC converter configured to transfer DC power among the first to third DC terminals.

Effect of the Invention

[0009] According to the present disclosure, in a power supply system in which an AC system and a DC grid coexist, power transfer among the uninterruptible power supply device, the power storage device, and the DC grid can be realized. Further, this power transfer can be performed with high efficiency.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Embodiments for Carrying Out the Invention

[0011] 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 are denoted by the same reference numerals, and the description thereof will not be repeated in principle.

[0012] <Configuration Example of Power Supply System> FIG. 1 is a diagram showing the overall configuration of a power supply system 100 using an uninterruptible power supply 10 according to the present embodiment. The power supply system 100 according to the present embodiment is a system for supplying power to a customer such as factory equipment or a data center.

[0013] As shown in FIG. 1, the power supply system 100 is connected to an AC bus 3 that transmits AC power supplied from an AC system 1. The AC bus 3 is connected to the AC system 1 via a transformer 2. The AC system 1 is typically a commercial AC power system and supplies AC power of a commercial frequency to the AC bus 3. In practice, the power supply system 100 receives a three-phase AC voltage from the AC system 1 and supplies a three-phase AC voltage to the AC load 8. However, for the sake of simplicity of the drawings and description, only the part related to the single-phase AC voltage is shown in FIG. 1.

[0014] The power supply system 100 includes a transformer 4, an AC / DC converter 5, a DC grid 6, an uninterruptible power supply device 10, an AC load 8, and a battery 9.

[0015] The transformer 4 and the AC / DC converter 5 are connected in series between the AC bus 3 and the DC bus 7 in the DC grid 6. The AC node 5a of the AC / DC converter 5 is connected to the AC bus 3 via the transformer 4. The DC node 5b of the AC / DC converter 5 is connected to the DC bus 7.

[0016] The AC / DC converter 5 is a bidirectional AC / DC converter, and is configured to be capable of performing an operation of converting AC power input to the AC node 5a into DC power and supplying it from the DC node 5b to the DC bus 7, and an operation of converting DC power input from the DC bus 7 to the DC node 5b into AC power and supplying it to the AC node 5a.

[0017] The DC grid 6 includes a DC bus 7 for transmitting DC power, a distributed power source 61, a power storage device 63, a DC load 65, and DC / DC converters 60, 62, 64.

[0018] The distributed power source 61 generates electricity using natural energy or fuel, and outputs the generated power to the DC bus 7. In the example of FIG. 1, the distributed power source 61 is a solar panel that generates electricity using sunlight. The distributed power source 61 is not limited to a solar panel, and may include other power generation devices (for example, a wind power generation device or a hydro power generation device).

[0019] The DC / DC converter 60 is connected between the distributed power source 61 and the DC bus 7, and converts the DC power generated by the distributed power source 61 into DC power of a constant voltage and supplies it to the DC bus 7.

[0020] The power storage device 63 stores DC power. The power storage device 63 is, for example, a storage battery capable of charging and discharging DC power. The DC / DC converter 62 is connected between the power storage device 63 and the DC bus 7, and performs bidirectional DC / DC conversion between the power storage device 63 and the DC bus 7.

[0021] The DC load 65 receives power supply from the DC bus 7. The DC load 65 is an electrical device or the like driven by DC power. The DC / DC converter 64 is connected between the DC bus 7 and the DC load 65, boosts or steps down the DC power supplied from the DC bus 7, and supplies it to the DC load 65. The number of each of the distributed power source 61, the power storage device 63, and the DC load 65 connected to the DC bus 7 is not limited.

[0022] <Configuration example of uninterruptible power supply> The uninterruptible power supply 10 is connected between the AC bus 3 and the AC load 8. The uninterruptible power supply 10 is further connected to the battery 9 and the DC grid 6. Specifically, the uninterruptible power supply 10 includes an AC input terminal 10a, an AC output terminal 10b, a battery terminal 10c, and a DC terminal 10d. The uninterruptible power supply 10 further includes a converter 11, a DC link 12, a capacitor 13, an inverter 14, a DC / DC converter 16, and a control device 15.

[0023] The AC input terminal 10a is connected to the AC bus 3 and receives AC power from the AC bus 3. The AC output terminal 10b is connected to the AC load 8. The AC load 8 is driven by the AC power supplied from the uninterruptible power supply 10.

[0024] The battery terminal 10c is connected to the battery 9. The battery 9 corresponds to an example of a "power storage device" that stores DC power. The battery 9 may be a lead-acid battery or a lithium-ion battery. Also, instead of the battery 9, an electric double-layer capacitor may be connected to the battery terminal 10c. The instantaneous value of the inter-terminal voltage VB of the battery 9 appearing at the battery terminal 10c is detected by the control device 15.

[0025] The DC terminal 10d is connected to the DC bus 7. The instantaneous value of the DC voltage VDC appearing at the DC terminal 10d is detected by the control device 15.

[0026] Converter 11 is a well-known device that includes a plurality of transistors and a plurality of diodes, and is controlled by a control device 15. When AC power is normally supplied from the AC system 1 (when the AC system 1 is healthy), converter 11 basically converts the AC power supplied from the AC bus 3 via the AC input terminal 10a into DC power and outputs it to the DC link 12. The output voltage of converter 11 can be controlled to a desired value. When the AC power from the AC system 1 stops being normally supplied (when an accident occurs in the AC system 1), the operation of converter 11 is stopped.

[0027] The instantaneous value of the AC input voltage VI that appears at the AC input terminal 10a is detected by the control device 15. Based on the detected value of the AC input voltage VI, the control device 15 determines whether an accident has occurred in the AC system 1. Also, the control device 15 controls converter 11 in synchronization with the AC input voltage VI.

[0028] Capacitor 13 is connected to the DC link 12 and smoothes the voltage of the DC link 12 (hereinafter also referred to as the "DC link voltage" VD). The DC link 12 includes a DC positive bus PL and a DC negative bus NL, but in FIG. 1, only the DC positive bus PL is shown. The instantaneous value of the DC link voltage VD is detected by the control device 15. When the AC system 1 is healthy, the control device 15 controls converter 11 so that the DC link voltage VD becomes the reference voltage VDR.

[0029] The DC / DC converter 16 is a multi-port DC / DC converter having three ports. The DC / DC converter 16 has a first DC terminal T1, a second DC terminal T2, and a third DC terminal T3. The first DC terminal T1, which is the first port, is connected to the DC link 12. The second DC terminal T2, which is the second port, is connected to the battery 9 via the battery terminal 10c. The third DC terminal T3, which is the third port, is connected to the DC bus 7 via the DC terminal 10d.

[0030] The DC / DC converter 16 is configured to be able to transmit DC power between the first to third DC terminals T1, T2, and T3. The DC / DC converter 16 is a DC / DC converter of the Triple Active Bridge (TAB) type. The DC / DC converter 16 is controlled by the control device 15. The circuit configuration and drive method of the DC / DC converter 16 will be described in detail later.

[0031] The inverter 14 is a well-known one including a plurality of transistors and a plurality of diodes, and is controlled by the control device 15. The inverter 14 converts the DC power supplied from the DC link 12 into AC power and outputs it to the AC output terminal 10b. The instantaneous value of the AC output voltage VO appearing at the AC output terminal 10b is detected by the control device 15. The control device 15 controls the inverter 14 so that the AC output voltage VO becomes a sinusoidal reference voltage VOR.

[0032] The control device 15 receives detection values from various sensors included in the power supply system 100, and based on the detection values, controls the power converters (converter 11, inverter 14, and DC / DC converter 16) included in the uninterruptible power supply device 10. The uninterruptible power supply device 10 has four power supply modes (see FIGS. 7 to 10). The control device 15 selects one of these four power supply modes according to the states of the AC system 1, the DC grid 6, and the AC / DC converter 5, and executes the selected power supply mode.

[0033] FIG. 2 is a block diagram showing an example of the hardware configuration of the control device 15. As shown in FIG. 2, the control device 15 includes a CPU (Central Processing Unit) 150, a memory 152, and an input / output (I / O) circuit 154. The CPU 150, the memory 152, and the I / O circuit 154 can exchange data with each other via a bus 156. A program is stored in a partial area of the memory 152, and by executing the program by the CPU 150, various functions described later can be realized. The I / O circuit 154 inputs and outputs signals and data to and from the outside of the control device 15.

[0034] Alternatively, different from the example of FIG. 2, at least a part of the control device 15 can be configured using a circuit such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). Also, at least a part of the control device 15 can be configured by an analog circuit.

[0035] (Circuit configuration example of DC / DC converter) FIG. 3 is a diagram showing an example of the circuit configuration of the DC / DC converter 16 included in the uninterruptible power supply device 10. In the example of FIG. 3, the DC / DC converter 16 is a TAB type DC / DC converter.

[0036] As shown in FIG. 3, the DC / DC converter 16 includes bridge circuits 31 to 33, reactors L1 to L3, capacitors 17 and 18, and a transformer 20.

[0037] The first bridge circuit 31 is connected between the positive DC terminal T1p and the negative DC terminal T1n of the first DC terminal T1. The positive DC terminal T1p is connected to the DC positive bus PL of the DC link 12. The negative DC terminal T1n is connected to the DC negative bus NL of the DC link 12.

[0038] The first bridge circuit 31 constitutes a single-phase full-bridge circuit. Specifically, the first bridge circuit 31 includes semiconductor switching elements Q1 to Q4 (hereinafter also referred to as "switching elements") and diodes D1 to D4. The switching elements Q1 and Q2 are connected in series between the positive-side DC terminal T1p and the negative-side DC terminal T1n. The semiconductor switching elements Q3 and Q4 are connected in series between the positive-side DC terminal T1p and the negative-side DC terminal T1n.

[0039] The second bridge circuit 32 is connected between the positive-side DC terminal T2p and the negative-side DC terminal T2n of the second DC terminal T2. The positive-side DC terminal T2p is connected to the positive terminal of the battery 9. The negative-side DC terminal T2n is connected to the negative terminal of the battery 9. A capacitor 17 for smoothing the DC voltage V2 between the positive-side DC terminal T2p and the negative-side DC terminal T2n is connected between the positive-side DC terminal T2p and the negative-side DC terminal T2n.

[0040] The second bridge circuit 32 constitutes a single-phase full-bridge circuit. Specifically, the second bridge circuit 32 includes switching elements Q5 to Q8 and diodes D5 to D8. The switching elements Q5 and Q6 are connected in series between the positive-side DC terminal T2p and the negative-side DC terminal T2n. The switching elements Q7 and Q8 are connected in series between the positive-side DC terminal T2p and the negative-side DC terminal T2n.

[0041] The third bridge circuit 33 is connected between the positive-side DC terminal T3p and the negative-side DC terminal T3n of the third DC terminal T3. The positive-side DC terminal T3p is connected to the DC positive bus of the DC bus 7. The negative-side DC terminal T3n is connected to the DC negative bus of the DC bus 7. A capacitor 18 for smoothing the DC voltage V3 between the positive-side DC terminal T3p and the negative-side DC terminal T3n is connected between the positive-side DC terminal T3p and the negative-side DC terminal T3n.

[0042] The third bridge circuit 33 constitutes a single-phase full-bridge circuit. Specifically, the third bridge circuit 33 includes switching elements Q9 to Q12 and diodes D9 to D12. The switching elements Q9 and Q10 are connected in series between the positive-side DC terminal T3p and the negative-side DC terminal T3n. The switching elements Q11 and Q12 are connected in series between the positive-side DC terminal T3p and the negative-side DC terminal T3n.

[0043] The transformer 20 includes a primary winding 20a, secondary windings 20b and 20c, and an iron core 21. The reactor L1 and the primary winding 20a are connected in series between the node N1 between the switching elements Q1 and Q2 and the node N2 between the switching elements Q3 and Q4. The reactor L2 and the secondary winding 20b are connected in series between the node N3 between the switching elements Q5 and Q6 and the node N4 between the switching elements Q7 and Q8. The reactor L3 and the secondary winding 20c are connected in series between the node N5 between the switching elements Q9 and Q10 and the node N6 between the switching elements Q11 and Q12. Each of the reactors L1 to L3 can be substituted by the leakage inductance of the transformer 20.

[0044] The switching elements Q1 to Q12 can be constituted by any self-extinguishing type element such as an IGBT (Insulated Gate Bipolar Transistor), a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), or a GCT (Gate Commutated Turn-off) thyristor. The diodes D1 to D12 are respectively connected in anti-parallel to the switching elements Q1 to Q12 to constitute free-wheeling diodes (FWD).

[0045] The DC / DC converter 16 is configured to be able to transmit DC power between a first DC terminal T1, a second DC terminal T2, and a third DC terminal T3. In one aspect, the DC / DC converter 16 transmits the DC power input to the first DC terminal T1 to the second DC terminal T2 and the third DC terminal T3. In this case, the DC / DC converter 16 converts the DC power into AC power (single-phase AC power in the example of FIG. 3) by the first bridge circuit 31, and transmits the AC power to the second bridge circuit 32 and the third bridge circuit 33 via the transformer 20. The second bridge circuit 32 converts the AC power back into DC power and transmits it to the second DC terminal T2. The third bridge circuit 33 converts the AC power back into DC power and transmits it to the third DC terminal T3.

[0046] In another aspect, the DC / DC converter 16 is also capable of transmitting DC power from the second DC terminal T2 to the first DC terminal T1 and the third DC terminal T3. In this case, the DC / DC converter 16 converts the DC power input to the second DC terminal T2 into AC power (single-phase AC power in the example of FIG. 3) by the second bridge circuit 32, and transmits the AC power to the first bridge circuit 31 and the third bridge circuit 33 via the transformer 20. The first bridge circuit 31 converts the AC power back into DC power and transmits it to the first DC terminal T1. The third bridge circuit 33 converts the AC power back into DC power and transmits it to the third DC terminal T3.

[0047] In yet another aspect, the DC / DC converter 16 is also capable of transmitting DC power from the third DC terminal T3 to the first DC terminal T1 and the second DC terminal T2. In this case, the DC / DC converter 16 converts the DC power input to the third DC terminal T3 into AC power (single-phase AC power in the example of FIG. 3) by the third bridge circuit 33, and transmits the AC power to the first bridge circuit 31 and the second bridge circuit 32 via the transformer 20. The first bridge circuit 31 converts the AC power back into DC power and transmits it to the first DC terminal T1. The second bridge circuit 32 converts the AC power back into DC power and transmits it to the second DC terminal T2.

[0048] (Drive method of the DC / DC converter) Next, the drive method of the DC / DC converter 16 will be described with reference to FIGS. 4 to 6.

[0049] Referring to FIG. 4, the DC power P1 is the DC power input and output to the first DC terminal T1. The DC voltage V1 is the DC voltage between the DC terminals T1p and T1n. The AC voltage u1 is the AC voltage that appears between the nodes N1 and N2 of the first bridge circuit 31.

[0050] The AC current i1 is the AC current flowing through the first bridge circuit 31. The reactor current iL1 is the current flowing through the reactor L1. The reactor current iL2 is the current flowing through the reactor L2. The reactor current iL3 is the current flowing through the reactor L3. In the following description, regarding the directions of the AC current i1 and the reactor current iL1, the direction from the first bridge circuit 31 to the primary winding 20a of the transformer 20 is treated as the positive direction. Regarding the directions of the reactor currents iL2 and iL3, the directions flowing from the secondary windings 20b and 20c of the transformer 20 to the second and third bridge circuits 32 and 33, respectively, are treated as the positive directions.

[0051] The DC power P2 is the DC power input and output to the second DC terminal T2. The DC voltage V2 is the DC voltage between the DC terminals T2p and T2n. The AC voltage u2 is the AC voltage that appears between the nodes N3 and N4 of the second bridge circuit 32.

[0052] The DC power P3 is the DC power input and output to the third DC terminal T3. The DC voltage V3 is the DC voltage between the DC terminals T3p and T3n. The AC voltage u3 is the AC voltage that appears between the nodes N5 and N6 of the third bridge circuit 33.

[0053] In the following description, regarding the transmission directions of the DC powers P1 to P3, the directions output from the DC terminals T1 to T3 are treated as the positive directions, and the directions input to the DC terminals T1 to T3 are treated as the negative directions.

[0054] FIG. 5 is an example of the operation waveforms of the bridge circuits 31 to 33. FIG. 5 shows the operation waveforms of the switching elements Q1, Q4, the switching elements Q5, Q8, and the switching elements Q9, Q12.

[0055] In the first bridge circuit 31, the switching elements Q1, Q2 are turned on and off complementarily, and the switching elements Q3, Q4 are turned on and off complementarily. Further, the switching elements Q1, Q4 are turned on and off in the same phase, and the switching elements Q2, Q3 are turned on and off in the same phase. As a result, the on and off of the switching elements Q1 to Q4 are switched every half of the switching period T. The duty ratio, which is the ratio of the on period length of the switching element to the switching period T, is 50%.

[0056] Similarly, in the second bridge circuit 32, the switching elements Q5, Q6 are turned on and off complementarily, and the switching elements Q7, Q8 are turned on and off complementarily. Further, the switching elements Q5, Q8 are turned on and off in the same phase, and the switching elements Q6, Q7 are turned on and off in the same phase. As a result, the on and off of the switching elements Q5 to Q8 are switched every half of the switching period T.

[0057] Similarly, in the third bridge circuit 33, the switching elements Q9, Q10 are turned on and off complementarily, and the switching elements Q11, Q12 are turned on and off complementarily. Further, the switching elements Q9, Q12 are turned on and off in the same phase, and the switching elements Q10, Q11 are turned on and off in the same phase. As a result, the on and off of the switching elements Q9 to Q12 are switched every half of the switching period T.

[0058] A phase difference φ2 is provided between the timing at which the on and off of the switching elements Q1 to Q4 are switched in the first bridge circuit 31 and the timing at which the on and off of the switching elements Q5 to Q8 are switched in the second bridge circuit 32. Assuming the switching period T is 2π, the phase difference φ2 corresponds to a time difference φ2 / 2π×T.

[0059] In the first bridge circuit 31, a phase difference φ3 is provided between the timing at which the on / off states of the switching elements Q1 to Q4 change and the timing at which the on / off states of the switching elements Q9 to Q12 change in the third bridge circuit 33. Assuming the switching period T is 2π, the phase difference φ3 corresponds to a time difference φ3 / 2π×T.

[0060] FIG. 6 is an example of the operation waveforms of the DC / DC converter 16. FIG. 6 shows the waveforms of the AC voltages u1 to u3, vt, u1 - vt, the reactor current iL1, and the AC current i1. The AC voltage vt is the voltage across the terminals of the primary winding 20a of the transformer 20. The AC voltage u1 - vt is the voltage across the terminals of the reactor L1.

[0061] By controlling the on / off states of the switching elements Q1 to Q12 in the bridge circuits 31 to 33 shown in FIG. 5, an AC voltage u1 is generated between the nodes N1 and N2 of the first bridge circuit 31, an AC voltage u2 is generated between the nodes N3 and N4 of the second bridge circuit 32, and an AC voltage u3 is generated between the nodes N5 and N6 of the third bridge circuit 33. Each of the AC voltages u1 to u3 becomes a square-wave voltage having a pulse width according to the duty of the switching elements Q1 to Q12 shown in FIG. 5. A reactor current iL1 that changes in accordance with the change in the terminal voltage u1 - vt flows through the reactor L1. Although not shown, a reactor current iL2 that changes in accordance with the change in the terminal voltage u2 - vt flows through the reactor L2. A reactor current iL1 that changes in accordance with the change in the terminal voltage u3 - vt flows through the reactor L3.

[0062] A phase difference φ2 occurs between the AC voltage u1 and the AC voltage u2. A phase difference φ3 occurs between the AC voltage u1 and the AC voltage u3. The terminal voltages u1 - vt, u2 - vt, u3 - vt of the reactors change according to these phase differences φ2 and φ3, thereby changing the reactor currents iL1, iL2, iL2. In response to the changes in the reactor currents iL1, iL2, iL3, the power transmitted between the first DC terminal T1, the second DC terminal T2, and the third DC terminal T3 also changes.

[0063] The DC power P1 input and output to the first DC terminal T1 is represented by the following equation (1). The first term on the right side indicates the DC power transmitted between the DC terminals T1 and T2, and the second term on the right side indicates the DC power transmitted between the DC terminals T1 and T3.

[0064]

Number

[0065] The DC power P2 input and output to the second DC terminal T2 is represented by the following equation (2). The first term on the right side indicates the DC power transmitted between the DC terminals T2 and T1, and the second term on the right side indicates the DC power transmitted between the DC terminals T2 and T3.

[0066]

Number

[0067] The DC power P3 input and output to the third DC terminal T3 is represented by the following equation (3). The first term on the right side indicates the DC power transmitted between the DC terminals T3 and T1, and the second term on the right side indicates the DC power transmitted between the DC terminals T3 and T2.

[0068]

Number

[0069] In equations (1) to (3), V1 is the DC voltage between the DC terminals T1p and T1n, V2 is the DC voltage between the DC terminals T2p and T2n, and V3 is the DC voltage between the DC terminals T3p and T3n. L1 is the inductance component of the reactor L1 and the primary winding 20a, L2 is the inductance component of the reactor L2 and the secondary winding 20b, and L3 is the inductance component of the reactor L3 and the secondary winding 20c.

[0070] In addition, each of V2, L2, V3, and L3 in formulas (1) to (3) is a value converted to the primary side considering the turns ratio of transformer 20 (the turns ratio between primary winding 20a and secondary windings 20b and 20c). Let the measured value of the DC voltage between DC terminals T2p and T2n be V2r, the measured value of the DC voltage between DC terminals T3p and T3n be V3r, the measured value of the inductance component of reactor L2 and secondary winding 20b be L2r, the measured value of the inductance component of reactor L3 and secondary winding 20c be L3r, the turns ratio of secondary winding 20b with respect to primary winding 20a be n2, and the turns ratio of secondary winding 20c with respect to primary winding 20a be n3. In this case, V2, V3, L2, L3 and V2r, V3r, L2r, L3r have the relationship shown in the following formula (4).

[0071]

Number

[0072] Ideally, the following relationship shown in formula (5) holds among DC powers P1, P2, and P3.

[0073]

Number

[0074] When the phase difference φ2 is positive (when the phase of AC voltage u1 leads the phase of AC voltage u2), power is transmitted from the first DC terminal T1 to the second DC terminal T2. When the phase difference φ2 is negative (when the phase of AC voltage u1 lags the phase of AC voltage u2), power is transmitted from the second DC terminal T2 to the first DC terminal T1.

[0075] When the phase difference φ3 is positive (when the phase of AC voltage u1 leads the phase of AC voltage u3), power is transmitted from the first DC terminal T1 to the third DC terminal T3. When the phase difference φ3 is negative (when the phase of AC voltage u1 lags the phase of AC voltage u3), power is transmitted from the third DC terminal T3 to the first DC terminal T1.

[0076] When the difference (φ3 - φ2) between the phase difference φ3 and the phase difference φ2 is positive (when the phase of the AC voltage u2 leads the phase of the AC voltage u3), power is transmitted from the second DC terminal T2 to the third DC terminal T3.

[0077] When the difference (φ3 - φ2) between the phase difference φ3 and the phase difference φ2 is negative (when the phase of the AC voltage u2 lags behind the phase of the AC voltage u3), power is transmitted from the third DC terminal T3 to the second DC terminal T2.

[0078] <Operation of the uninterruptible power supply device> Next, the operation of the uninterruptible power supply device 10 according to the present embodiment will be described.

[0079] The uninterruptible power supply device 10 has five power supply modes. The control device 15 selects one of the five power supply modes according to the states of the AC system 1, the DC grid 6, and the AC / DC converter 5, and executes the selected power supply mode.

[0080] (First power supply mode) FIG. 7 is a circuit block diagram for explaining the operation of the uninterruptible power supply device 10 in the first power supply mode. In FIG. 7, the solid arrows indicate the paths through which the power supplied from the AC bus 3 is transmitted. The dashed arrows indicate the paths through which the power supplied from the DC bus 7 is transmitted.

[0081] The first power supply mode can be executed when the AC system 1 is healthy. The AC power supplied from the AC bus 3 is converted into DC power by the converter 11 and supplied to the DC link 12. The DC power supplied to the DC link 12 is stored in the battery 9 via the DC / DC converter 16 and is also converted into AC power by the inverter 14 and supplied to the AC load 8. The DC power supplied from the DC bus 7 is stored in the battery 9 by the DC / DC converter 16.

[0082] In the first power supply mode, the control device 15 controls the converter 11 so that the DC link voltage VD becomes the reference voltage VDR. Further, the control device 15 controls the inverter 14 so that the AC output voltage VO becomes the reference voltage VOR.

[0083] The control device 15 further controls the DC / DC converter 16 so as to transmit the DC power P1 input to the first DC terminal T1 and the DC power P3 input to the third DC terminal T3 to the second DC terminal T2. As a result, DC power is supplied from the DC link 12 and the DC bus 7 to the battery 9 via the DC / DC converter 16.

[0084] Specifically, the control device 15 generates a DC power command value P2* which is a command value of the DC power P2 so that the voltage VB between the terminals of the battery 9 becomes the reference voltage VBR. Next, the control device 15 generates a DC power command value P1* which is a command value of the DC power P1 and a DC power command value P3* which is a command value of the DC power P3 so that the sum of the absolute value of the DC power P1 and the absolute value of the DC power P3 becomes the DC power command value P2*. The ratio between the DC power command value P1* and the DC power command value P2* can be controlled to a desired value. The control device 15 calculates the phase differences φ2 and φ3 based on the generated DC power command values P1*, P2*, and P3*, and controls the bridge circuits 31 to 33 so as to generate the calculated phase differences φ2 and φ3.

[0085] The first power supply mode can be selected when the first condition that the supply power in the DC grid 6 exceeds the demand power and the second condition that the power that the DC grid 6 can supply to the DC / DC converter 16 is equal to or less than the power required for charging the battery 9 are satisfied.

[0086] The first condition is satisfied when the power supply-demand balance in the DC grid 6 is in an oversupply state. For example, when the generated power of the distributed power source 61 (for example, the generated power of a solar panel) exceeds the power consumption of the DC load 65, the first condition is satisfied. On the contrary, when the power supply-demand balance in the DC grid 6 is in an overdemand state, the first condition is not satisfied.

[0087] The second condition is satisfied when the first condition is satisfied and the surplus of the supply power in the DC grid 6 is equal to or less than the DC power command value P2*. The DC power command value P2* corresponds to the power required for charging the battery 9.

[0088] When the power supply-demand balance of the DC grid 6 is in an oversupply state, by executing the first power supply mode, the surplus of the supply power is supplied from the DC grid 6 to the battery 9 via the DC / DC converter 16. Thereby, the surplus can be effectively utilized, and the power supply-demand balance of the DC grid 6 can be adjusted to be constant.

[0089] (Second power supply mode) FIG. 8 is a circuit block diagram for explaining the operation of the uninterruptible power supply device 10 in the second power supply mode. In FIG. 8, the solid arrows indicate the paths through which the power supplied from the AC bus 3 is transmitted. The dashed arrows indicate the paths through which the power supplied from the DC bus 7 is transmitted.

[0090] The second power supply mode can be executed when the AC system 1 is healthy. The AC power supplied from the AC bus 3 is converted into DC power by the converter 11 and supplied to the DC link 12. The DC power supplied from the DC bus 7 is stored in the battery 9 by the DC / DC converter 16 and supplied to the DC link 12. The DC power supplied to the DC link 12 is converted into AC power by the inverter 14 and supplied to the AC load 8. The second power supply mode is different from the first power supply mode (see FIG. 7) in that DC power is supplied from the DC grid 6 to the DC link 12 via the DC / DC converter 16.

[0091] During the second power supply mode, the control device 15 controls the converter 11 so that the DC link voltage VD becomes the reference voltage VDR. Also, the control device 15 controls the inverter 14 so that the AC output voltage VO becomes the reference voltage VOR.

[0092] The control device 15 further controls the DC / DC converter 16 so as to transmit the DC power P3 input to the third DC terminal T3 to the first DC terminal T1 and the second DC terminal T2. Thereby, DC power is supplied from the DC bus 7 to the battery 9 and the DC link 12 via the DC / DC converter 16.

[0093] Specifically, the control device 15 generates a DC power command value P1* such that the DC link voltage VD becomes the reference voltage VDR. Further, the control device 15 generates a DC power command value P2* such that the voltage VB between the terminals of the battery 9 becomes the reference voltage VBR. Next, the control device 15 generates a DC power command value P3* based on the sum of the absolute value of the DC power command value P1* and the absolute value of the DC power command value P2*. The control device 15 calculates the phase differences φ2 and φ3 based on the generated DC power command values P1*, P2*, and P3*, and controls the bridge circuits 31 to 33 so as to generate the calculated phase differences φ2 and φ3.

[0094] The second power supply mode can be selected when the above-described first condition and a third condition that the power that the DC grid 6 can supply to the DC / DC converter 16 is greater than the power required for charging the battery 9 are satisfied.

[0095] The third condition is satisfied when the first condition is satisfied and the surplus of the supply power in the DC grid 6 is greater than the DC power command value P2*. The DC power command value P2* corresponds to the power required for charging the battery 9.

[0096] When the surplus of the power supplied in the DC grid 6 is greater than the power required for charging the battery 9, by executing the second power supply mode, the surplus of the supplied power is supplied to the battery 9 and the DC link 12 via the DC / DC converter 16. Thereby, the surplus can be effectively utilized, and the power supply-demand balance of the DC grid 6 can be adjusted constantly. For example, when the generated power of the distributed power source 61 (for example, the generated power of a solar panel) greatly exceeds the power consumption of the DC load 65, by executing the second power supply mode, the power supply-demand balance of the DC grid 6 can be adjusted quickly.

[0097] Note that depending on the magnitude of the surplus of the power supplied in the DC grid 6, it may be configured to stop the operation of the converter 11 to stop the power supply from the AC bus 3 and supply only the DC power of the DC bus 7 to the DC link 12.

[0098] (Third power supply mode) FIG. 9 is a circuit block diagram for explaining the operation of the uninterruptible power supply device 10 in the third power supply mode. In FIG. 9, the solid arrows indicate the paths through which the power supplied from the AC bus 3 is transmitted.

[0099] The third power supply mode can be executed when the AC system 1 is healthy. The AC power supplied from the AC bus 3 is converted into DC power by the converter 11 and supplied to the DC link 12. The DC power supplied to the DC link 12 is converted into AC power by the inverter 14 and supplied to the AC load 8. The third power supply mode is different from the first power supply mode (see FIG. 7) and the second power supply mode (see FIG. 8) in that no DC power is supplied from the DC grid 6 to the DC / DC converter 16.

[0100] In the third power supply mode, the control device 15 controls the converter 11 so that the DC link voltage VD becomes the reference voltage VDR. Also, the control device 15 controls the inverter 14 so that the AC output voltage VO becomes the reference voltage VOR.

[0101] The control device 15 further controls the DC / DC converter 16 to stop the operation of the third bridge circuit 33 and transmit the DC power P1 input to the first DC terminal T1 to the second DC terminal T2. As a result, while DC power is supplied from the DC link 12 to the battery 9 via the DC / DC converter 16, the supply of DC power from the DC bus 7 to the DC / DC converter 16 is stopped.

[0102] Specifically, the control device 15 generates a DC power command value P2* such that the voltage VB across the terminals of the battery 9 becomes the reference voltage VBR. Next, the control device 15 generates a DC power command value P1* such that the absolute value of the DC power P1 becomes the DC power command value P2*. The control device 15 calculates the phase difference φ2 based on the generated DC power command values P1* and P2*, and controls the bridge circuits 31 and 32 to generate the calculated phase difference φ2.

[0103] The third power supply mode can be selected when the above-described first condition is not satisfied. That is, the third power supply mode can be selected when the power supply-demand balance of the DC grid 6 is in excess of demand. When the supply power in the DC grid 6 is insufficient, by executing the third power supply mode, the supply of DC power from the DC grid 6 to the DC / DC converter 16 is stopped. Thereby, it is possible to suppress the power supply-demand balance of the DC grid 6 from becoming unstable.

[0104] (Fourth power supply mode) FIG. 10 is a circuit block diagram for explaining the operation of the uninterruptible power supply device 10 in the fourth power supply mode. In FIG. 10, the dashed-dotted arrow indicates the path through which the power supplied from the battery 9 is transmitted. The broken arrow indicates the path through which the power supplied from the DC bus 7 is transmitted.

[0105] The fourth power supply mode can be executed when an accident occurs in the AC system 1. When an accident occurs in the AC system 1, the operation of the converter 11 is stopped. The DC power stored in the battery 9 is supplied to the DC link 12 by the DC / DC converter 16. The DC power supplied from the DC bus 7 is supplied to the DC link 12 by the DC / DC converter 16. The DC power supplied to the DC link 12 is converted into AC power by the inverter 14 and supplied to the AC load 8.

[0106] During the fourth power supply mode, the control device 15 stops the operation of the converter 11 and controls the inverter 14 so that the AC output voltage VO becomes the reference voltage VOR.

[0107] The control device 15 further controls the DC / DC converter 16 so as to transmit the DC power P2 input to the second DC terminal T2 and the DC power P3 input to the third DC terminal T3 to the first DC terminal T1. Thereby, DC power is supplied from the battery 9 and the DC bus 7 to the DC link 12 via the DC / DC converter 16.

[0108] Specifically, the control device 15 generates a DC power command value P1* such that the DC link voltage VD becomes the reference voltage VDR. Next, the control device 15 generates a DC power command value P2* and a DC power command value P3* such that the sum of the absolute value of the DC power P2 and the absolute value of the DC power P3 becomes the DC power command value P1*. The ratio between the power command value P2* and the power command value P3* can be controlled to a desired value. The control device 15 calculates the phase differences φ2 and φ3 based on the generated DC power command values P1*, P2*, and P3*, and controls the bridge circuits 31 to 33 so as to generate the calculated phase differences φ2 and φ3.

[0109] In the fourth power supply mode, the DC power of the battery 9 and the DC bus 7 is converted into AC power by the inverter 14 and supplied to the AC load 8. Therefore, even when an accident occurs in the AC power system 1, the operation of the AC load 8 can be continued. Further, even after the remaining capacity of the battery 9 decreases and the discharge of the battery 9 stops, the operation of the AC load 8 can be continued using the DC power of the DC bus 7. Thus, the reliability of the uninterruptible power supply device 10 can be improved.

[0110] (Fifth power supply mode) FIG. 11 is a circuit block diagram for explaining the operation of the uninterruptible power supply device 10 in the fifth power supply mode. In FIG. 11, the dash-dotted arrow indicates the path through which the power supplied from the battery 9 is transmitted. The broken-line arrow indicates the path through which the power supplied from the DC bus 7 is transmitted.

[0111] The fifth power supply mode can be executed when an accident occurs in the DC grid 6 or when the AC / DC converter 5 fails. The AC power supplied from the AC bus 3 is converted into DC power by the converter 11 and supplied to the DC link 12. The DC power supplied to the DC link 12 is converted into AC power by the inverter 14 and supplied to the AC load 8. The DC power of the DC link 12 and the DC power of the battery 9 are supplied to the DC bus 7 by the DC / DC converter 16.

[0112] In the fifth power supply mode, the control device 15 controls the converter 11 so that the DC link voltage VD becomes the reference voltage VDR. Also, the control device 15 controls the inverter 14 so that the AC output voltage VO becomes the reference voltage VOR.

[0113] The control device 15 further controls the DC / DC converter 16 so as to transmit the DC power P1 input to the first DC terminal T1 and the DC power P2 input to the second DC terminal T2 to the third DC terminal T3. Thereby, DC power is supplied from the DC link 12 and the battery 9 to the DC bus 7 via the DC / DC converter 16.

[0114] Specifically, the control device 15 generates a DC power command value P3* such that the DC voltage VDC of the DC bus 7 becomes the reference voltage VDCR. Next, the control device 15 generates a DC power command value P1* and a DC power command value P2* such that the sum of the absolute value of the DC power P1 and the absolute value of the DC power P2 becomes the DC power command value P3*. The ratio between the power command value P1* and the power command value P2* can be controlled to a desired value. The control device 15 calculates the phase differences φ2 and φ3 based on the generated DC power command values P1*, P2*, and P3*, and controls the bridge circuits 31 to 33 to generate the calculated phase differences φ2 and φ3.

[0115] In the fifth power supply mode, in parallel with the power supply to the AC load 8, the DC power of the DC link 12 and the battery 9 is supplied to the DC bus 7 by the DC / DC converter 16. Therefore, even when an accident occurs in the DC grid 6 or when the AC / DC converter 5 fails, DC power can be supplied to the DC bus 7. As a result, the operation of the DC load 65 can be continued. Furthermore, even after the remaining capacity of the battery 9 decreases and the discharge of the battery 9 stops, the operation of the DC load 65 can be continued using the DC power of the DC link 12. Thus, the reliability of the DC grid 6 can be improved.

[0116] <Control Configuration of the Uninterruptible Power Supply Device> FIG. 12 is a block diagram showing the configuration of the control device 15. As shown in FIG. 12, the control device 15 includes accident detectors 160 and 162, a mode selection unit 164, a converter control unit 166, an inverter control unit 168, and a DC / DC control unit 170. The functions of each block shown in FIG. 11 can be realized by at least one of software processing and hardware processing by the control device 15.

[0117] The accident detector 160 detects whether an accident has occurred in the AC system 1 based on the AC input voltage VI supplied from the AC bus 3, and outputs a signal DT1 indicating the detection result. When the AC system 1 is healthy, the detection signal DT1 is set to the "H" level of the deactivation level. When an accident occurs in the AC system 1, the detection signal DT1 is set to the "L" level of the activation level. For example, the accident detector 160 determines that an accident has occurred in the AC system 1 when the AC input voltage VI drops below the lower limit value.

[0118] The accident detector 162 detects whether an accident has occurred in the DC grid 6 or a failure has occurred in the AC / DC converter 5 based on the AC input voltage VI and the DC voltage VDC of the DC bus 7, etc., and outputs a signal DT2 indicating the detection result. When the DC grid 6 is healthy and the AC / DC converter 5 is normal, the detection signal DT2 is set to the "H" level. When an accident occurs in the DC grid 6 or a failure occurs in the AC / DC converter 5, the detection signal DT2 is set to the "L" level. For example, the accident detector 162 determines that an accident has occurred in the DC grid 6 or a failure has occurred in the AC / DC converter 5 when the DC voltage VDC drops below the lower limit value while the AC input voltage VI is higher than the lower limit value.

[0119] The mode selection unit 164 selects one of the five power supply modes based on the detection signal DT1 from the accident detector 160, the detection signal DT2 from the accident detector 162, the DC voltage VDC of the DC bus 7, etc.

[0120] FIG. 13 is a flowchart for explaining the selection of the power supply mode in the mode selection unit 164. As shown in FIG. 13, in step S01, the mode selection unit 164 determines whether an accident has occurred in the AC system 1 based on the detection signal DT1 from the accident detector 160. When the detection signal DT1 is at the "L" level, the mode selection unit 164 determines that an accident has occurred in the AC system 1 (when the determination in S01 is YES), and selects the fourth power supply mode (see FIG. 10) in step S05.

[0121] When the detection signal DT1 is at the "H" level, the mode selection unit 164 determines that the AC system 1 is sound (when the NO determination is made in S01), and proceeds to step S02. Based on the detection signal DT2 from the accident detector 162, the mode selection unit 164 determines, in step S02, whether an accident in the DC grid 6 or a failure of the AC / DC converter 5 has occurred. When the detection signal DT2 is at the "L" level, the mode selection unit 164 determines that an accident in the DC grid 6 or a failure of the AC / DC converter 5 has occurred (when the YES determination is made in S02), and selects the fifth power supply mode (see Fig. 11) in step S06.

[0122] When the detection signal DT2 is at the "H" level, the mode selection unit 164 determines that the DC grid 6 is sound and the AC / DC converter 5 is normal (when the NO determination is made in S02), and proceeds to step S03. In step S03, the mode selection unit 164 determines whether the supply power in the DC grid 6 exceeds the demand power. In S03, the mode selection unit 164 determines whether the power supply and demand balance in the DC grid 6 is in oversupply or undersupply. For the determination in S03, the DC voltage VDC of the DC bus 7 can be used. For example, when the DC voltage VDC is higher than the threshold value, S03 is determined as YES. Or, by monitoring the power generation amount of the distributed power source 61, when the power generation amount exceeds the threshold value, S03 is determined as YES.

[0123] When the supply power in the DC grid 6 is lower than the demand power (when the NO determination is made in S03), the mode selection unit 164 determines that the power supply and demand balance in the DC grid 6 is in undersupply, proceeds to step S07, and selects the third power supply mode (see Fig. 9). On the other hand, when the supply power in the DC grid 6 exceeds the demand power (when the YES determination is made in S03), the mode selection unit 164 determines that the power supply and demand balance in the DC grid 6 is in oversupply and proceeds to step S04.

[0124] The mode selection unit 164 compares, in step S04, the power that the DC grid 6 can supply to the DC / DC converter 16 with the power required for charging the battery 9. In S04, the mode selection unit 164 calculates the power that the DC grid 6 can supply to the DC / DC converter 16 based on the surplus of the supply power in the DC grid 6. Further, the mode selection unit 164 generates a DC power command value P2* such that the terminal voltage VB of the battery 9 becomes the reference voltage VBR. The DC power command value P2* corresponds to the power required for charging the battery 9.

[0125] When the power that the DC grid 6 can supply to the DC / DC converter 16 is greater than the DC power command value P2* (when the determination in S04 is YES), the mode selection unit 164 selects, in step S08, the second power supply mode (see FIG. 8).

[0126] On the other hand, when the power that the DC grid 6 can supply to the DC / DC converter 16 is less than or equal to the DC power command value P2* (when the determination in S04 is NO), the mode selection unit 164 selects, in step S09, the first power supply mode (see FIG. 7).

[0127] Returning to FIG. 12, the mode selection unit 164 outputs a mode signal MD indicating the selected power supply mode to the converter control unit 166, the inverter control unit 168, and the DC / DC control unit 170.

[0128] The converter control unit 166 controls the converter 11 based on the mode signal MD. When the mode signal MD indicates any one of the first power supply mode, the second power supply mode, the third power supply mode, and the fifth power supply mode, the converter control unit 166 controls the converter 11 such that the DC link voltage VD becomes the reference voltage VDR. When the mode signal MD indicates the fourth power supply mode, the converter control unit 166 stops the operation of the converter 11.

[0129] The inverter control unit 168 controls the inverter 14 based on the mode signal MD. When the mode signal MD indicates any one of the first power supply mode, the second power supply mode, the third power supply mode, the fourth power supply mode, and the fifth power supply mode, the inverter control unit 168 controls the inverter 14 so that the AC output voltage VO becomes the reference voltage VOR.

[0130] The DC / DC control unit 170 controls the DC / DC converter 16 based on the mode signal MD. When the mode signal MD indicates the first power supply mode, the DC / DC control unit 170 controls the DC / DC converter 16 to transmit the DC power P1 input to the first DC terminal T1 and the DC power P3 input to the third DC terminal T3 to the second DC terminal T2.

[0131] When the mode signal MD indicates the second power supply mode, the DC / DC control unit 170 controls the DC / DC converter 16 to transmit the DC power P3 input to the third DC terminal T3 to the first DC terminal T1 and the second DC terminal T2.

[0132] When the mode signal MD indicates the third power supply mode, the DC / DC control unit 170 stops the operation of the third bridge circuit 33 and controls the DC / DC converter 16 to transmit the DC power P1 input to the first DC terminal T1 to the second DC terminal T2.

[0133] When the mode signal MD indicates the fourth power supply mode, the DC / DC control unit 170 controls the DC / DC converter 16 to transmit the DC power P2 input to the second DC terminal T2 and the DC power P3 input to the third DC terminal T3 to the first DC terminal T1.

[0134] When the mode signal MD indicates the fifth power supply mode, the DC / DC control unit 170 controls the DC / DC converter 16 to transmit the DC power P1 input to the first DC terminal T1 and the DC power P2 input to the second DC terminal T2 to the third DC terminal T3.

[0135] <Effects of the Embodiment> As described above, in the present embodiment, the DC / DC converter 16 has a first DC terminal T1 connected to the DC link 12 of the uninterruptible power supply 10, a second DC terminal T2 connected to the battery 9, and a third DC terminal T3 connected to the DC bus 7, and is configured to transmit DC power among the first to third DC terminals T1 to T3. According to this, it is possible to perform three-way power sharing among the uninterruptible power supply 10, the battery 9, and the DC grid 6 via the DC / DC converter 16.

[0136] Specifically, when the AC system 1 is normal and the supply power in the DC grid 6 exceeds the demand power, the DC power of the DC link 12 and the DC grid 6 can be stored in the battery 9. In particular, when the surplus of the supply power in the DC grid 6 is larger than the power required for charging the battery 9, the DC power of the DC grid 6 can be stored in the battery 9, and the DC power of the DC grid 6 can be converted into AC power and supplied to the AC load 8. According to this, when the power supply-demand balance of the DC grid 6 becomes oversupply, the DC power of the DC grid 6 can be effectively utilized, and the power supply-demand balance of the DC grid 6 can be adjusted to be constant.

[0137] When an accident occurs in the AC system 1, the operation of the AC load 8 can be continued by converting the DC power of the battery 9 and the DC grid 6 into AC power and supplying it to the AC load 8. By using the DC power of the battery 9 and the DC power of the DC grid 6 in combination, the operation of the AC load 8 can be continued even after the discharge of the battery 9 stops. Therefore, the reliability of the uninterruptible power supply 10 can be improved.

[0138] When an accident occurs in the DC grid 6 or a failure occurs in the AC / DC converter 5, the DC power of the DC link 12 and the battery 9 can be supplied to the DC grid 6. Thereby, even when an accident occurs in the DC grid 6 or a failure occurs in the AC / DC converter 5, the operation of the DC load 65 can be continued using the AC power of the AC system 1.

[0139] Furthermore, according to the present embodiment, by adopting a TAB type DC / DC converter for the DC / DC converter 16, DC power can be transmitted among the uninterruptible power supply device 10, the battery 9, and the DC grid 6 through a single DC / DC converter. According to this, compared with a power supply system that transmits DC power among the uninterruptible power supply device 10, the battery 9, and the DC grid 6 through a plurality of DC / DC converters, the power loss generated in the power supply system can be reduced. Therefore, the power supply system can be made more efficient. In addition, the enlargement of the power supply system can be suppressed.

[0140] The embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. The present disclosure is shown not by the above description but by the scope of the claims, and it is intended that all modifications within the meaning and scope equivalent to the scope of the claims are included.

Explanation of Reference Numerals

[0141] 1 AC system, 2, 4, 20 transformers, 3 AC bus, 5 AC / DC converter, 6 DC grid, 7 DC bus, 8 AC load, 9 battery, 10 uninterruptible power supply device, 10a AC input terminal, 10b AC output terminal, 10c battery terminal, 10d, T1 to T3 DC terminals, 11 converter, 12 DC link, 13 capacitor, 14 inverter, 15 control device, 20a primary winding, 20b, 20c secondary windings, 21 iron core, 16, 60, 62, 64 DC / DC converters, 31 to 33 bridge circuits, 61 distributed power source, 63 power storage device, 65 DC load, 100 power supply system, 150 CPU, 152 memory, 154 I / O circuit, 156 bus, 160, 162 accident detectors, 164 mode selection unit, 166 converter control unit, 168 inverter control unit, 170 DC / DC control unit, PL DC positive busbar, NL DC negative busbar, Q1 to Q12 switching elements, D1 to D12 diodes, L1 to L3 reactors.

Claims

1. An uninterruptible power supply connected to an AC grid and a DC grid, the DC grid includes a DC bus connected to the AC system via an AC / DC converter, a distributed power source that outputs generated DC power to the DC bus, and a DC load that receives the DC power of the DC bus; The uninterruptible power supply device is A DC link for transmitting and receiving DC power; a converter that converts AC power supplied from the AC system into DC power and supplies the DC power to the DC link; an inverter that converts DC power received from the DC link into AC power and supplies the AC power to an AC load; an uninterruptible power supply comprising: a DC / DC converter having a first DC terminal connected to the DC link, a second DC terminal connected to a power storage device, and a third DC terminal connected to the DC bus, the DC / DC converter being configured to transmit DC power between the first to third DC terminals.

2. The uninterruptible power supply device is a first power supply mode in which power from the AC system is supplied to the AC load and the power storage device, and power from the DC grid is supplied to the power storage device; a second power supply mode in which power from the DC grid is supplied to the AC load and the power storage device; a third power supply mode in which power from the AC system is supplied to the AC load and the power storage device; a fourth power supply mode in which power from the power storage device and the DC grid is supplied to the AC load; a fifth power supply mode in which power from the AC system and the power storage device is supplied to the DC grid, 2. The uninterruptible power supply device according to claim 1, further comprising a control device that selects one of the first to fifth power supply modes based on states of the AC system, the DC grid, and the AC / DC converter, and executes the selected power supply mode.

3. When the AC system is healthy and the supply power of the DC grid exceeds the demand power, if the power that the DC grid can supply is equal to or less than the power required for charging the power storage device, the control device selects the first power supply mode, When the first power supply mode is selected, the control device Controlling the converter so as to convert AC power from the AC system into DC power and output the DC power to the DC link; controlling the DC / DC converter to supply DC power from the DC link and the DC bus to the power storage device; 3. The uninterruptible power supply according to claim 2, wherein the inverter is controlled so as to convert DC power of the DC link into AC power and supply the AC power to the AC load.

4. When the supply power of the DC grid exceeds the demand power while the AC system is healthy, if the power that the DC grid can supply is greater than the power required to charge the power storage device, the control device selects the second power supply mode; When the second power supply mode is selected, the control device Controlling the converter so as to convert AC power from the AC system into DC power and output the DC power to the DC link; controlling the DC / DC converter to supply DC power of the DC bus to the power storage device and the DC link; 3. The uninterruptible power supply according to claim 2, wherein the inverter is controlled so as to convert DC power of the DC link into AC power and supply the AC power to the AC load.

5. When the AC system is healthy, if the supply power in the DC grid falls below the demand power, the control device selects the third power supply mode; When the third power supply mode is selected, the control device Controlling the converter so as to convert AC power from the AC system into DC power and output the DC power to the DC link; controlling the DC / DC converter so as to supply DC power of the DC link to the power storage device; 3. The uninterruptible power supply according to claim 2, wherein the inverter is controlled so as to convert DC power of the DC link into AC power and supply the AC power to the AC load.

6. The control device selects the fourth power supply mode when a fault occurs in the AC system, When the fourth power supply mode is selected, the control device Stopping the operation of the converter; controlling the DC / DC converter to supply DC power from the power storage device and the DC bus to the DC link; 3. The uninterruptible power supply according to claim 2, wherein the inverter is controlled so as to convert DC power of the DC link into AC power and supply the AC power to the AC load.

7. The control device selects the fifth power supply mode when an accident occurs in the DC grid or a failure occurs in the AC / DC converter; When the fifth power supply mode is selected, the control device Controlling the converter so as to convert AC power from the AC system into DC power and output the DC power to the DC link; controlling the DC / DC converter to supply DC power from the DC link and the power storage device to the DC bus; 3. The uninterruptible power supply according to claim 2, wherein the inverter is controlled so as to convert DC power of the DC link into AC power and supply the AC power to the AC load.

8. 2. The uninterruptible power supply according to claim 1, wherein the DC / DC converter includes a TAB (Triple Active Bridge) DC / DC converter.

9. An uninterruptible power supply device according to any one of claims 1 to 8; the DC grid; and the AC / DC converter connected between the AC system and the DC grid.

Images