Uninterruptible power source device and power supply system

Abstract

An uninterruptible power source 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) through 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 source device (10) comprises: a DC link (12) for transmitting / receiving DC power; a converter (11) that converts AC power supplied from the AC system (1) into DC power and supplies the DC power to the DC link (12); an inverter (14) that converts DC power received from the DC link (12) into AC power and supplies the AC power to an AC load (8); and a DC / DC converter (16) that has 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 is configured to redistribute DC power between the first to third DC terminals.

Description

Uninterruptible Power Supplies and Power Distribution Systems

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

[0002] An uninterruptible power supply is connected between an AC system and an AC load, converts AC power supplied from the AC system into DC power, and then converts the DC power back into AC power to supply to the AC load. In the event of an AC system accident, the uninterruptible power supply converts DC power from the power storage device into AC power to supply to the AC load. Therefore, even if an AC system accident occurs, the operation of the AC load can continue for as long as DC power is stored in the power storage device.

[0003] Meanwhile, in recent years, with the introduction of renewable energy sources and an increase in DC loads driven by DC power, attention has been focused on DC grids, in which multiple power sources and multiple DC loads are connected to a DC bus and DC power is exchanged via the DC bus. While data centers and the like are moving toward full DC power, power supply systems in which AC systems and DC grids coexist are being considered for factory facilities and the like with many AC loads (see Non-Patent Document 1).

[0004] Kazuto Yukida et al., "Technological Trends in DC Power Supply Systems," Journal of the Institute of Electrical Engineers of Japan, Vol. 135, No. 6, pp. 366-369 (2015)

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

[0006] To exchange power among the uninterruptible power supply, the power storage device, and the DC grid, a DC / DC converter is required to perform bidirectional DC voltage conversion between the DC link of the uninterruptible power supply and the power storage device, and another DC / DC converter is required to perform bidirectional DC voltage conversion between the DC link and the DC grid. However, if multiple DC / DC converters are provided between the uninterruptible power supply, the power storage device, and the DC grid, DC power will be transmitted via multiple DC / DC converters, which may increase power loss. Furthermore, providing multiple DC / DC converters may increase the size of the power supply system.

[0007] The present disclosure has been made to solve such problems, and a primary object of the present disclosure is to realize power interchange between an uninterruptible power supply, a power storage device, and a 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 interchange between an uninterruptible power supply, a power storage device, and a DC grid with high efficiency.

[0008] An uninterruptible power supply 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, distributed power sources that generate DC power and output it to the DC bus, and DC loads that receive the DC power from the DC bus. The uninterruptible power supply includes a DC link for receiving and sending 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 the AC load, and 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, and configured to exchange DC power between the first and third DC terminals.

[0009] According to the present disclosure, in a power supply system in which an AC system and a DC grid coexist, it is possible to realize power interchange between an uninterruptible power supply, a power storage device, and a DC grid. Furthermore, this power interchange can be performed with high efficiency.

[0010] 1 is a diagram showing the overall configuration of a power supply system according to the present embodiment. FIG. 2 is a block diagram showing an example of the hardware configuration of a control device. FIG. 3 is a diagram showing an example of the circuit configuration of a DC / DC converter. FIG. 4 is a diagram explaining a drive method for a DC / DC converter. FIG. 4 is an example of the operating waveforms of a bridge circuit. FIG. 5 is an example of the operating waveforms of a DC / DC converter. FIG. 6 is a circuit block diagram for explaining the operation of an uninterruptible power supply in a first power supply mode. FIG. 7 is a circuit block diagram for explaining the operation of an uninterruptible power supply in a second power supply mode. FIG. 8 is a circuit block diagram for explaining the operation of an uninterruptible power supply in a third power supply mode. FIG. 9 is a circuit block diagram for explaining the operation of an uninterruptible power supply in a fourth power supply mode. FIG. 10 is a circuit block diagram for explaining the operation of an uninterruptible power supply in a fifth power supply mode. FIG. 11 is a block diagram showing the configuration of a control device. FIG. 12 is a flowchart for explaining the selection of a power supply mode in a mode selection unit.

[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 will be denoted by the same reference numerals, and their description will not be repeated in principle.

[0012] 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 consumers such as factory facilities or data centers.

[0013] As shown in Fig. 1 , a 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. Note that the power supply system 100 actually receives a three-phase AC voltage from the AC system 1 and supplies the three-phase AC voltage to an AC load 8, but for the sake of simplicity of the drawing and explanation, only a portion related to a one-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 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 a DC bus 7 in a DC grid 6. An AC node 5a of the AC / DC converter 5 is connected to the AC bus 3 via the transformer 4. A 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 that is configured to be able to convert AC power input to the AC node 5a into DC power and supply it from the DC node 5b to the DC bus 7, and convert DC power input from the DC bus 7 to the DC node 5b into AC power and supply it to the AC node 5a.

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

[0018] The distributed power sources 61 generate power using natural energy or fuel and output the generated power to the DC bus 7. In the example of Fig. 1 , the distributed power sources 61 are solar panels that generate power using sunlight. The distributed power sources 61 are not limited to solar panels and may include other power generation devices (for example, wind power generation devices or hydroelectric power generation devices).

[0019] The DC / DC converter 60 is connected between the distributed power source 61 and the DC bus 7 , 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 that can charge and discharge 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 loads 65 receive DC power from the DC bus 7. The DC loads 65 are electrical devices or the like that are driven by DC power. The DC / DC converters 64 are connected between the DC bus 7 and the DC loads 65, and boost or lower the DC power supplied from the DC bus 7 and supply it to the DC loads 65. The number of each of the distributed power sources 61, the power storage devices 63, and the DC loads 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 a battery 9 and a 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 an AC load 8. The AC load 8 is driven by 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. Alternatively, an electric double layer capacitor may be connected to the battery terminal 10c instead of the battery 9. The instantaneous value of the terminal voltage VB of the battery 9 that appears 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] The converter 11 is a well-known device including 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 functioning properly), the converter 11 basically converts AC power supplied from the AC bus 3 via the AC input terminal 10a into DC power and outputs the DC power to the DC link 12. The output voltage of the converter 11 can be controlled to a desired value. When AC power is no longer normally supplied from the AC system 1 (when a fault occurs in the AC system 1), the operation of the converter 11 is stopped.

[0027] The instantaneous value of the AC input voltage VI appearing 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 or not a fault has occurred in the AC system 1. The control device 15 also controls the converter 11 in synchronization with the AC input voltage VI.

[0028] The capacitor 13 is connected to the DC link 12 and smoothes the voltage VD of the DC link 12 (hereinafter also referred to as the "DC link voltage"). The DC link 12 includes a DC positive bus PL and a DC negative bus NL, but only the DC positive bus PL is shown in FIG. 1. The instantaneous value of the DC link voltage VD is detected by a control device 15. When the AC system 1 is healthy, the control device 15 controls the converter 11 so that the DC link voltage VD becomes equal to 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 a battery terminal 10c. The third DC terminal T3, which is the third port, is connected to the DC bus 7 via a DC terminal 10d.

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

[0031] The inverter 14 is a well-known device including a plurality of transistors and a plurality of diodes, and is controlled by a 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 equal to the sinusoidal reference voltage VOR.

[0032] The control device 15 receives detection values ​​from various sensors included in the power supply system 100, and controls the power converters (converter 11, inverter 14, and DC / DC converter 16) included in the uninterruptible power supply 10 based on the detection values. The uninterruptible power supply 10 has four power supply modes (see FIGS. 7 to 10). The control device 15 selects one of these four power supply modes depending on 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. Programs are stored in a partial area of ​​the memory 152, and the CPU 150 executes these programs to realize various functions described below. The I / O circuit 154 inputs and outputs signals and data to and from the outside of the control device 15.

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

[0035] (Circuit Configuration Example of DC / DC Converter) Fig. 3 is a diagram showing a circuit configuration example of the DC / DC converter 16 included in the uninterruptible power supply 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 side DC terminal T1p and the negative side DC terminal T1n of the first DC terminal T1. The positive side DC terminal T1p is connected to the positive DC bus PL of the DC link 12. The negative side DC terminal T1n is connected to the negative DC bus NL of the DC link 12.

[0038] The first bridge circuit 31 forms a single-phase full-bridge circuit. Specifically, the first bridge circuit 31 has 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 is connected between the positive side DC terminal T2p and the negative side DC terminal T2n to smooth the DC voltage V2 between the positive side DC terminal T2p and the negative side DC terminal T2n.

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

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

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

[0043] The transformer 20 has 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 a node N1 between the switching elements Q1 and Q2 and a node N2 between the switching elements Q3 and Q4. The reactor L2 and the secondary winding 20b are connected in series between a node N3 between the switching elements Q5 and Q6 and a node N4 between the switching elements Q7 and Q8. The reactor L3 and the secondary winding 20c are connected in series between a node N5 between the switching elements Q9 and Q10 and a 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 configured with any self-extinguishing element such as an insulated gate bipolar transistor (IGBT), a metal oxide semiconductor field effect transistor (MOSFET), or a gate commutated turn-off thyristor (GCT). The diodes D1 to D12 are connected in antiparallel to the switching elements Q1 to Q12, respectively, to configure free wheeling diodes (FWD).

[0045] The DC / DC converter 16 is configured to transmit DC power among the first DC terminal T1, the second DC terminal T2, and the third DC terminal T3. In one aspect, the DC / DC converter 16 transmits 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 ) using 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 can also transmit 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 DC power input to the second DC terminal T2 into AC power (single-phase AC power in the example of FIG. 3 ) using 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 can also transmit 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 DC power input to the third DC terminal T3 into AC power (single-phase AC power in the example of FIG. 3 ) using 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 System of DC / DC Converter) Next, a drive system of the DC / DC converter 16 will be described with reference to FIGS. 4 to 6. FIG.

[0049] 4, DC power P1 is DC power input / output to / from the first DC terminal T1. DC voltage V1 is DC voltage across DC terminals T1p and T1n. AC voltage u1 is AC voltage appearing across 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, the direction of the AC current i1 and the reactor current iL1 from the first bridge circuit 31 to the primary winding 20a of the transformer 20 is treated as the positive direction. The directions of the reactor currents iL2 and iL3 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 DC power input / output to the second DC terminal T2. The DC voltage V2 is DC voltage between the DC terminals T2p and T2n. The AC voltage u2 is AC voltage appearing between the nodes N3 and N4 of the second bridge circuit 32.

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

[0053] In the following description, the direction of transmission of DC powers P1 to P3 is assumed to be the positive direction when output from DC terminals T1 to T3, and the negative direction when input to DC terminals T1 to T3.

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

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

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

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

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

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

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

[0061] By controlling the on / off 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 is 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 flows through the reactor L1, which changes in response to changes in the inter-terminal voltage u1-vt. Although not shown, a reactor current iL2 flows through the reactor L2, which changes in response to changes in the inter-terminal voltage u2-vt. A reactor current iL1 flows through the reactor L3, which changes in response to changes in the inter-terminal voltage u3-vt.

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

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

[0064]

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

[0066]

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

[0068]

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

[0070] Note that V2, L2, V3, and L3 in equations (1) to (3) are primary-side converted values ​​that take into account the transformation ratio of the transformer 20 (the turns ratio between the primary winding 20a and the secondary windings 20b and 20c). Let V2r be the measured value of the DC voltage between the DC terminals T2p and T2n, V3r be the measured value of the DC voltage between the DC terminals T3p and T3n, L2r be the measured value of the inductance component of the reactor L2 and the secondary winding 20b, and L3r be the measured value of the inductance component of the reactor L3 and the secondary winding 20c. Let n2 be the turns ratio of the secondary winding 20b to the primary winding 20a, and n3 be the turns ratio of the secondary winding 20c to the primary winding 20a. In this case, V2, V3, L2, and L3 have the relationship shown in the following equation (4) with V2r, V3r, L2r, and L3r.

[0071]

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

[0073]

[0074] When the phase difference φ2 is positive (when the phase of the AC voltage u1 leads the phase of the 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 the AC voltage u1 lags the phase of the 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 the AC voltage u1 leads the phase of the 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 the AC voltage u1 lags the phase of the 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 Uninterruptible Power Supply> Next, the operation of uninterruptible power supply 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 depending on 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 10 in the first power supply mode. In Fig. 7, solid arrows indicate paths along which power supplied from the AC bus 3 is transmitted. Dashed arrows indicate paths along which 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. 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. 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, and also 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 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 to the battery 9 from the DC link 12 and the DC bus 7 via the DC / DC converter 16.

[0084] Specifically, the control device 15 generates a DC power command value P2* that is a command value for the DC power P2 so that the terminal voltage VB of the battery 9 becomes equal to the reference voltage VBR. Next, the control device 15 generates a DC power command value P1* that is a command value for the DC power P1 and a DC power command value P3* that is a command value for the DC power P3 so that the sum of the absolute values ​​of the DC power P1 and 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 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.

[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 to charge the battery 9 are satisfied.

[0086] The first condition is satisfied when the balance of power supply and demand in the DC grid 6 is in excess of supply. For example, the first condition is satisfied when the power generated by the distributed power source 61 (for example, the power generated by a solar panel) exceeds the power consumption of the DC load 65. Conversely, when the balance of power supply and demand in the DC grid 6 is in excess of demand, the first condition is not satisfied.

[0087] The second condition is satisfied when the first condition is satisfied and the surplus power supplied from 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 to charge the battery 9.

[0088] When the balance between power supply and demand in the DC grid 6 is in excess of supply, the first power supply mode is executed to supply the surplus power from the DC grid 6 to the battery 9 via the DC / DC converter 16. This makes it possible to effectively utilize the surplus power and to adjust the balance between power supply and demand in the DC grid 6 to a constant level.

[0089] (Second power supply mode) Fig. 8 is a circuit block diagram for explaining the operation of the uninterruptible power supply 10 in the second power supply mode. In Fig. 8, solid arrows indicate paths along which power supplied from the AC bus 3 is transmitted. Dashed arrows indicate paths along which 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. AC power supplied from the AC bus 3 is converted into DC power by the converter 11 and supplied to the DC link 12. 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 differs from the first power supply mode (see FIG. 7 ) in that DC power is supplied to the DC link 12 from the DC grid 6 via the DC / DC converter 16.

[0091] In 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, and also 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 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 supplying DC power from the DC bus 7 via the DC / DC converter 16 to the battery 9 and the DC link 12.

[0093] Specifically, the control device 15 generates a DC power command value P1* so that the DC link voltage VD becomes equal to the reference voltage VDR. The control device 15 also generates a DC power command value P2* so that the inter-terminal voltage VB of the battery 9 becomes equal to 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 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.

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

[0095] The third condition is satisfied when the first condition is satisfied and the surplus power supplied from the DC grid 6 is greater than the DC power command value P2*. The DC power command value P2* corresponds to the power required to charge the battery 9.

[0096] When the surplus power supplied in the DC grid 6 is greater than the power required to charge the battery 9, the second power supply mode is executed, and the surplus power is supplied to the battery 9 and the DC link 12 via the DC / DC converter 16. This makes it possible to effectively utilize the surplus power and to adjust the balance of power supply and demand in the DC grid 6 to a constant level. For example, when the power generated by the distributed power source 61 (e.g., the power generated by a solar panel) greatly exceeds the power consumption of the DC load 65, the second power supply mode is executed, thereby making it possible to quickly adjust the balance of power supply and demand in the DC grid 6.

[0097] Depending on the amount of excess power supplied in the DC grid 6, the operation of the converter 11 may be stopped to stop the power supply from the AC bus 3, and only the DC power from the DC bus 7 may be supplied 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 10 in the third power supply mode. In Fig. 9, solid arrows indicate paths along which 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. 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 differs from the first power supply mode (see FIG. 7 ) and the second power supply mode (see FIG. 8 ) in that DC power is not 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, and also controls the inverter 14 so that the AC output voltage VO becomes the reference voltage VOR.

[0101] The control device 15 further 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. As a result, DC power is supplied from the DC link 12 to the battery 9 via the DC / DC converter 16, while 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* so that the inter-terminal voltage VB of the battery 9 becomes equal to the reference voltage VBR. Next, the control device 15 generates a DC power command value P1* so that the absolute value of the DC power P1 becomes the DC power command value P2*. The control device 15 calculates a 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 first condition described above is not satisfied. That is, the third power supply mode can be selected when the power supply and demand balance of the DC grid 6 is in excess of demand. When the supply of power in the DC grid 6 is insufficient, the third power supply mode is executed to stop the supply of DC power from the DC grid 6 to the DC / DC converter 16. This makes it possible to prevent the power supply and 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 10 in the fourth power supply mode. In Fig. 10, the dashed-dotted arrows indicate the paths along which power supplied from the battery 9 is transmitted. The dashed-dotted arrows indicate the paths along which power supplied from the DC bus 7 is transmitted.

[0105] The fourth power supply mode can be executed when a fault occurs in the AC system 1. When a fault 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] In 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 equal to the reference voltage VOR.

[0107] The control device 15 further 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. As a result, 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* so that the DC link voltage VD becomes equal to the reference voltage VDR. Next, the control device 15 generates a DC power command value P2* and a DC power command value P3* so 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 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.

[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 system 1, the operation of the AC load 8 can be continued. Furthermore, even after the remaining capacity of the battery 9 decreases and discharging of the battery 9 stops, the operation of the AC load 8 can be continued using the DC power of the DC bus 7. Therefore, the reliability of the uninterruptible power supply 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 10 in the fifth power supply mode. In Fig. 11, the dashed-dotted arrows indicate the paths along which power supplied from the battery 9 is transmitted. The dashed-dotted arrows indicate the paths along which 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 loads 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, and also 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 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. As a result, 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* so that the DC voltage VDC of the DC bus 7 becomes equal to the reference voltage VDCR. Next, the control device 15 generates a DC power command value P1* and a DC power command value P2* so 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 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 loads 8, DC power from the DC link 12 and the battery 9 is supplied to the DC bus 7 by the DC / DC converter 16. Therefore, even if an accident occurs in the DC grid 6 or the AC / DC converter 5 fails, DC power can be supplied to the DC bus 7. As a result, the operation of the DC loads 65 can be continued. Furthermore, even after the remaining capacity of the battery 9 decreases and discharging of the battery 9 stops, the operation of the DC loads 65 can be continued using the DC power from the DC link 12. Therefore, the reliability of the DC grid 6 can be improved.

[0116] <Control Configuration of Uninterruptible Power Supply> Fig. 12 is a block diagram showing the configuration of the control device 15. As shown in Fig. 12, the control device 15 is configured to include fault detectors 160, 162, a mode selection unit 164, a converter control unit 166, an inverter control unit 168, and a DC / DC control unit 170. The function 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 fault detector 160 detects whether a fault 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, which is an inactivation level. When a fault has occurred in the AC system 1, the detection signal DT1 is set to the "L" level, which is an activation level. For example, the fault detector 160 determines that a fault has occurred in the AC system 1 when the AC input voltage VI drops below a lower limit value.

[0118] The fault detector 162 detects whether a fault 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, 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 "H" level. When a fault has occurred in the DC grid 6 or a failure has occurred in the AC / DC converter 5, the detection signal DT2 is set to "L" level. For example, when the DC voltage VDC falls below the lower limit value while the AC input voltage VI is higher than the lower limit value, the fault detector 162 determines that a fault has occurred in the DC grid 6 or a failure has occurred in the AC / DC converter 5.

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

[0120] Fig. 13 is a flowchart illustrating the selection of a power supply mode by the mode selection unit 164. As shown in Fig. 13, in step S01, the mode selection unit 164 determines whether or not an accident has occurred in the AC system 1 based on the detection signal DT1 from the accident detector 160. If 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 (YES in S01), and selects the fourth power supply mode (see Fig. 10) in step S05.

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

[0122] If the detection signal DT2 is at the "H" level, the mode selection unit 164 determines that the DC grid 6 is healthy and the AC / DC converter 5 is normal (NO in S02), and proceeds to step S03. In step S03, the mode selection unit 164 determines whether the supplied power in the DC grid 6 exceeds the demanded power. In S03, the mode selection unit 164 determines whether the balance between supply and demand of power in the DC grid 6 is an excess supply or an excess demand. The DC voltage VDC of the DC bus 7 can be used for the determination in S03. For example, if the DC voltage VDC is higher than a threshold, a YES determination is made in S03. Alternatively, the amount of power generated by the distributed power sources 61 is monitored, and if the amount of power generated exceeds a threshold, a YES determination is made in S03.

[0123] If the supplied power in the DC grid 6 is lower than the demanded power (NO in S03), the mode selection unit 164 determines that the balance between supply and demand of power in the DC grid 6 is in excess of demand, and proceeds to step S07 to select the third power supply mode (see FIG. 9 ). On the other hand, if the supplied power in the DC grid 6 exceeds the demanded power (YES in S03), the mode selection unit 164 determines that the balance between supply and demand of power in the DC grid 6 is in excess of supply, and proceeds to step S04.

[0124] In step S04, the mode selection unit 164 compares the power that the DC grid 6 can supply to the DC / DC converter 16 with the power required to charge 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 power supplied by the DC grid 6. The mode selection unit 164 also generates a DC power command value P2* such that the inter-terminal voltage VB of the battery 9 becomes equal to the reference voltage VBR. The DC power command value P2* corresponds to the power required to charge the battery 9.

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

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

[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, second, third, and fifth power supply modes, the converter control unit 166 controls the converter 11 so 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, second, third, fourth, and fifth power supply modes, the inverter control unit 168 controls the inverter 14 so that the AC output voltage VO becomes equal to 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 between the first to third DC terminals T1 to T3. This makes it possible to exchange power in three directions between 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 healthy 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 supply power in the DC grid 6 is greater than the power required to charge the battery 9, the DC power of the DC grid 6 can be stored in the battery 9 and can be converted into AC power to supply to the AC loads 8. This makes it possible to effectively utilize the DC power of the DC grid 6 and adjust the supply and demand balance of the DC grid 6 to a constant level when the power supply and demand balance of the DC grid 6 is in an oversupply state.

[0137] In the event of an accident in the AC system 1, the DC power of the battery 9 and the DC grid 6 is converted into AC power and supplied to the AC loads 8, thereby allowing the operation of the AC loads 8 to continue. 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 loads 8 can be continued even after the discharge of the battery 9 has stopped. This improves the reliability of the uninterruptible power supply 10.

[0138] In the event of a fault in the DC grid 6 or a failure 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. As a result, even in the event of a fault in the DC grid 6 or a failure 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 this embodiment, by employing a TAB type DC / DC converter for DC / DC converter 16, DC power can be transmitted between uninterruptible power supply 10, battery 9, and DC grid 6 via a single DC / DC converter. This reduces power loss in the power supply system compared to a power supply system that transmits DC power between uninterruptible power supply 10, battery 9, and DC grid 6 via multiple DC / DC converters. This enables the power supply system to be made more efficient. Also, it is possible to prevent the power supply system from becoming larger.

[0140] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The present disclosure is defined by the scope of the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0141] 1 AC system, 2, 4, 20 transformer, 3 AC bus, 5 AC / DC converter, 6 DC grid, 7 DC bus, 8 AC load, 9 battery, 10 uninterruptible power supply, 10a AC input terminal, 10b AC output terminal, 10c battery terminal, 10d, T1 to T3 DC terminal, 11 converter, 12 DC link, 13 capacitor, 14 inverter, 15 control device, 20a primary winding, 20b, 20c secondary winding, 21 iron core, 16, 60, 62, 64 DC / DC converter, 31 to 33 bridge circuit, 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 fault detector, 164 Mode selection unit, 166 converter control unit, 168 inverter control unit, 170 DC / DC control unit, PL DC positive bus, NL DC negative bus, Q1 to Q12 switching elements, D1 to D12 diodes, L1 to L3 reactors.

Claims

1. An uninterruptible power supply connected to an AC system and a DC grid, wherein the DC grid includes a DC bus connected to the AC system via an AC / DC converter, distributed power sources that output generated DC power to the DC bus, and DC loads that receive the DC power from the DC bus, the uninterruptible power supply comprising: a DC link for receiving and sending 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 the AC load; and 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, and configured to transmit DC power between the first to third DC terminals.

2. The uninterruptible power supply 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. The uninterruptible power supply device according to claim 2, wherein when the AC system is healthy and the supply power of the DC grid exceeds the demand power, and the power that the DC grid can supply is equal to or less than the power required to charge the power storage device, the control device selects the first power supply mode, and when the first power supply mode is selected, the control device: controls the converter to convert AC power from the AC system into DC power and output it to the DC link; controls the DC / DC converter to supply DC power of the DC link and the DC bus to the power storage device; and controls the inverter to convert DC power of the DC link into AC power and supply it to the AC load.

4. The uninterruptible power supply system according to claim 2, wherein when the supply power of the DC grid exceeds the demand power while the AC system is healthy, and when 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, and when the second power supply mode is selected, the control device: controls the converter to convert AC power from the AC system into DC power and output it to the DC link; controls the DC / DC converter to supply DC power of the DC bus to the power storage device and the DC link; and controls the inverter to convert DC power of the DC link into AC power and supply it to the AC load.

5. The uninterruptible power supply device according to claim 2, wherein when the AC system is healthy and the supply power in the DC grid is lower than the demand power, the control device selects the third power supply mode, and when the third power supply mode is selected, the control device: controls the converter to convert AC power from the AC system into DC power and output it to the DC link; controls the DC / DC converter to supply the DC power of the DC bus to the power storage device; and controls the inverter to convert the DC power of the DC link into AC power and supply it to the AC load.

6. The uninterruptible power supply device according to claim 2, wherein the control device selects the fourth power supply mode when an accident occurs in the AC system, and when the fourth power supply mode is selected, the control device stops operation of the converter, controls the DC / DC converter to supply DC power from the storage device and the DC bus to the DC link, and controls the inverter to convert the DC power from the DC link into AC power and supply it to the AC load.

7. The uninterruptible power supply device according to claim 2, wherein 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, and when the fifth power supply mode is selected, the control device controls the converter to convert AC power from the AC system into DC power and output it to the DC link, controls the DC / DC converter to supply DC power from the DC link and the power storage device to the DC bus, and controls the inverter to convert the DC power of the DC link into AC power and supply it to the AC load.

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

9. A power supply system comprising: the uninterruptible power supply 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.

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