Uninterruptible power supply device and power supply system

Abstract

And the uninterruptible power supply device (10) is connected with the alternating current system (1) and the direct current power grid (6). A DC power grid (6) is provided with: a DC bus (7) that is connected to an AC system (1) via an AC / DC converter (5); a distributed power source (61) that outputs DC power generated by power generation to the DC bus; and a DC load (65) that receives DC power from the DC bus (7). An uninterruptible power supply device (10) is provided with: a DC link (12) for transmitting and 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 the 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) configured to have a first DC terminal (T1) connected to the DC link (12), a second DC terminal (T2) connected to the power storage device (9), and a third DC terminal (T3) connected to the DC bus (7), and to exchange DC power between the first to third DC terminals.

Description

Technical Field

[0001] This disclosure relates to uninterruptible power supply devices and power supply systems using the uninterruptible power supply devices. Background Technology

[0002] An uninterruptible power supply (UPS) is connected between an AC system and an AC load. It converts the AC power supplied by the AC system into DC power, then converts the DC power back into AC power and supplies it to the AC load. In the event of an AC system failure, the UPS converts the DC power stored in the UPS back into AC power and supplies it to the AC load. Therefore, even in the event of an AC system failure, the AC load can continue to operate while the UPS stores DC power.

[0003] On the other hand, in recent years, against the backdrop of the introduction of renewable energy sources and the increase of DC loads driven by DC power, DC power grids that connect multiple power sources and multiple DC loads on a DC bus and transmit and receive DC power via the DC bus have attracted attention. While fully DCization is being promoted in data centers and the like, power supply systems where AC systems and DC power grids coexist have been studied in factory equipment and the like, which have a large number of AC loads (see Non-Patent Literature 1).

[0004] Existing technical documents

[0005] Non-patent literature

[0006] Non-patent literature 1: Yukita Kazuto et al., “Technical Trends in DC Power Supply Systems”, Journal of the Institute of Electrical Engineering, Vol. 135, No. 6, pp. 366-369 (2015) Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] In the aforementioned power supply system, the DC grid is interconnected with 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, it is impossible to exchange power between the uninterruptible power supply (UPS) connected to the AC system, the energy storage device connected to the UPS, and the DC grid.

[0009] In order to exchange power between uninterruptible power supply (UPS), energy storage devices, and the DC grid, DC / DC converters are needed for bidirectional DC-DC voltage conversion between the UPS's DC link and the energy storage devices, as well as for bidirectional DC-DC voltage conversion between the DC link and the DC grid. However, with multiple DC / DC converters installed between the UPS, energy storage devices, and the DC grid, there are concerns about increased power loss when transmitting DC power via these multiple converters. Furthermore, there are concerns about the increased size of the power supply system due to the installation of multiple DC / DC converters.

[0010] This disclosure was made to address such a problem. Its main objective is to enable power exchange between an uninterruptible power supply (UPS), an energy storage device, and a DC power grid in a power supply system where AC and DC systems coexist. Another objective of this disclosure is to achieve efficient power exchange between the UPS, the energy storage device, and the DC power grid.

[0011] Methods for solving problems

[0012] One aspect of this disclosure provides an uninterruptible power supply (UPS) device 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 outputting DC power generated by the generator to the DC bus; and a DC load receiving DC power from the DC bus. The UPS device comprises: a DC link for transmitting and receiving DC power; a converter for converting AC power supplied from the AC system to DC power and supplying it to the DC link; an inverter for converting DC power received from the DC link to AC power and supplying it to the AC load; and a DC / DC converter configured to have a first DC terminal connected to the DC link, a second DC terminal connected to an energy storage device, and a third DC terminal connected to the DC bus, exchanging DC power between the first and third DC terminals.

[0013] Invention Effects

[0014] According to this disclosure, in a power supply system where AC and DC power grids coexist, power exchange between an uninterruptible power supply device, an energy storage device, and the DC power grid can be realized. Furthermore, this power exchange can be performed with high efficiency. Attached Figure Description

[0015] Figure 1 This is a diagram showing the overall structure of the power supply system in this embodiment.

[0016] Figure 2 This is a block diagram representing an example of the hardware structure of a control device.

[0017] Figure 3This is a diagram showing an example of the circuit structure of a DC / DC converter.

[0018] Figure 4 This is a diagram illustrating the driving method of a DC / DC converter.

[0019] Figure 5 This is an example of the operating waveform of a bridge circuit.

[0020] Figure 6 This is an example of the operating waveform of a DC / DC converter.

[0021] Figure 7 This is a circuit block diagram used to illustrate the operation of the uninterruptible power supply device in the first power supply mode.

[0022] Figure 8 This is a circuit block diagram used to illustrate the operation of the uninterruptible power supply device in the second power supply mode.

[0023] Figure 9 It is a circuit block diagram used to illustrate the operation of an uninterruptible power supply device in the third power supply mode.

[0024] Figure 10 This is a circuit block diagram used to illustrate the operation of an uninterruptible power supply device in the fourth power supply mode.

[0025] Figure 11 This is a circuit block diagram used to illustrate the operation of the uninterruptible power supply device in the fifth power supply mode.

[0026] Figure 12 It is a block diagram representing the structure of the control device.

[0027] Figure 13 This is a flowchart explaining the selection of the power supply mode in the mode selection section. Detailed Implementation

[0028] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Furthermore, the same or equivalent parts in the drawings will be labeled with the same reference numerals, and their descriptions will generally not be repeated.

[0029] <Example of a power supply system structure>

[0030] Figure 1 This diagram illustrates the overall structure of a power supply system 100 using the uninterruptible power supply device 10 of this embodiment. The power supply system 100 of this embodiment is used to supply power to users such as factory equipment or data centers.

[0031] like Figure 1As shown, the power supply system 100 is connected to an AC bus 3 that transmits AC power supplied from the 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, supplying commercial frequency AC power to the AC bus 3. Furthermore, the power supply system 100 actually receives three-phase AC voltage from the AC system 1 and supplies three-phase AC voltage to the AC load 8, but for the sake of simplicity in the figures and description, [the following is omitted]. Figure 1 Only the portion related to one phase AC voltage is shown.

[0032] The power supply system 100 includes a transformer 4, an AC / DC converter 5, a DC power grid 6, an uninterruptible power supply 10, an AC load 8, and a battery 9.

[0033] Transformer 4 and AD / DC converter 5 are connected in series between AC bus 3 and DC bus 7 in DC power grid 6. AC node 5a of AC / DC converter 5 is connected to AC bus 3 via transformer 4. DC node 5b of AC / DC converter 5 is connected to DC bus 7.

[0034] AC / DC converter 5 is a bidirectional AC / DC converter configured to perform the operations of converting AC power input to AC node 5a into DC power and supplying it to DC bus 7 from DC node 5b, and converting DC power input from DC bus 7 to DC node 5b into AC power and supplying it to AC node 5a.

[0035] The DC power 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, and 64.

[0036] Distributed power source 61 generates electricity using natural energy or fuel, and outputs the generated power to the DC bus 7. Figure 1 In this example, distributed power source 61 is a solar panel that generates electricity using sunlight. Distributed power source 61 is not limited to solar panels, but may also include other power generation devices (such as wind power generation devices or hydropower generation devices).

[0037] The DC / DC converter 60 is connected between the distributed power source 61 and the DC bus 7, converting the DC power generated by the distributed power source 61 into constant voltage DC power and supplying it to the DC bus 7.

[0038] The power storage device 63 stores DC power. The power storage device 63 is, for example, a 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, performing bidirectional DC / DC conversion between the power storage device 63 and the DC bus 7.

[0039] A DC load 65 receives DC power from a DC bus 7. The DC load 65 is an electrical device or the like driven by DC power. A DC / DC converter 64 is connected between the DC bus 7 and the DC load 65, boosting or bucking the DC power supplied from the DC bus 7 and supplying it to the DC load 65. The number of distributed power sources 61, power storage devices 63, and DC loads 65 connected to the DC bus 7 is not limited.

[0040] <Structure Example of an Uninterruptible Power Supply Device>

[0041] An uninterruptible power supply (UPS) 10 is connected between the AC bus 3 and the AC load 8. The UPS 10 is also connected to a battery 9 and a DC power grid 6. Specifically, the UPS 10 has an AC input terminal 10a, an AC output terminal 10b, a battery terminal 10c, and a DC terminal 10d. The UPS 10 also includes a converter 11, a DC link 12, a capacitor 13, an inverter 14, a DC / DC converter 16, and a control device 15.

[0042] AC input terminal 10a is connected to AC bus 3 and receives AC power from AC bus 3. AC output terminal 10b is connected to AC load 8. AC load 8 is driven by AC power supplied from uninterruptible power supply 10.

[0043] Battery terminal 10c is connected to battery 9. Battery 9 corresponds to an embodiment of an "energy storage device" that stores DC power. Battery 9 can be a lead-acid battery or a lithium-ion battery. Alternatively, a double-layer capacitor can be connected to battery terminal 10c instead of battery 9. The instantaneous value of the inter-terminal voltage VB of battery 9 appearing at battery terminal 10c is detected by control device 15.

[0044] DC terminal 10d is connected to DC bus 7. The instantaneous value of the DC voltage VDC appearing at DC terminal 10d is detected by control device 15.

[0045] Converter 11 is a known converter comprising multiple transistors and multiple diodes, and is controlled by control device 15. When AC power is normally supplied from AC system 1 (when AC system 1 is functioning properly), converter 11 essentially converts the AC power supplied from AC bus 3 via AC input terminal 10a into DC power and outputs it to DC link 12. The output voltage of converter 11 can be controlled to a desired value. In the event that AC power cannot be normally supplied from AC system 1 (when AC system 1 experiences a fault), the operation of converter 11 is stopped.

[0046] 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 a fault has occurred in the AC system 1. In addition, the control device 15 controls the converter 11 synchronously with the AC input voltage VI.

[0047] Capacitor 13 is connected to DC link 12 to smooth the voltage (hereinafter also referred to as "DC link voltage") VD of DC link 12. DC link 12 includes a positive DC bus PL and a negative DC bus NL, but... Figure 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 functioning properly, the control device 15 controls the converter 11 to make the DC link voltage VD the reference voltage VDR.

[0048] DC / DC converter 16 is a multi-port DC / DC converter with three ports. 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, serving as the first port, is connected to DC link 12. The second DC terminal T2, serving as the second port, is connected to battery 9 via battery terminal 10c. The third DC terminal T3, serving as the third port, is connected to DC bus 7 via DC terminal 10d.

[0049] DC / DC converter 16 is configured to transmit DC power between the first to third DC terminals T1, T2, and T3. DC / DC converter 16 is a TAB (Triple Active Bridge) type DC / DC converter. DC / DC converter 16 is controlled by control device 15. The circuit configuration and driving method of DC / DC converter 16 will be described in detail later.

[0050] Inverter 14 is a known inverter comprising multiple transistors and multiple diodes, and is controlled by control device 15. Inverter 14 converts the DC power supplied from DC link 12 into AC power and outputs it to AC output terminal 10b. The instantaneous value of the AC output voltage VO appearing at AC output terminal 10b is detected by control device 15. Control device 15 controls inverter 14 to make the AC output voltage VO a sinusoidal reference voltage VOR.

[0051] 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 device 10 based on these detection values. The uninterruptible power supply device 10 has four power supply modes (see reference). Figures 7-10The control device 15 selects one of the four power supply modes based on the status of the AC system 1, the DC power grid 6, and the AC / DC converter 5, and executes the selected power supply mode.

[0052] Figure 2 This is a block diagram illustrating an example of the hardware structure of the control device 15. For example... Figure 2 As shown, the control device 15 is configured to include a CPU (Central Processing Unit) 150, a memory 152, and input / output (I / O) circuitry 154. The CPU 150, memory 152, and I / O circuitry 154 can send and receive data with each other via a bus 156. A program is stored in a portion of the memory 152, and by executing the program through the CPU 150, various functions described later can be implemented. The I / O circuitry 154 inputs and outputs signals and data to and from the outside of the control device 15.

[0053] Or, with Figure 2 Unlike other examples, at least a portion of the control device 15 can be constructed using circuits such as FPGA (Field Programmable Gate Array) or ASIC (Application Specific Integrated Circuit). Alternatively, at least a portion of the control device 15 can also be constructed using analog circuits.

[0054] (Example of a DC / DC converter circuit structure)

[0055] Figure 3 This is a diagram illustrating an example of the circuit structure of the DC / DC converter 16 included in the uninterruptible power supply device 10. Figure 3 In the example, DC / DC converter 16 is a TAB-type DC / DC converter.

[0056] like Figure 3 As shown, the DC / DC converter 16 is configured to include bridge circuits 31 to 33, reactors L1 to L3, capacitors 17 and 18, and transformer 20.

[0057] 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 positive DC bus PL of the DC link 12. The negative DC terminal T1n is connected to the negative DC bus NL of the DC link 12.

[0058] The first bridge circuit 31 constitutes 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. Switching elements Q1 and Q2 are connected in series between the positive DC terminal T1p and the negative DC terminal T1n. Semiconductor switching elements Q3 and Q4 are connected in series between the positive DC terminal T1p and the negative DC terminal T1n.

[0059] The second bridge circuit 32 is connected between the positive DC terminal T2p and the negative DC terminal T2n of the second DC terminal T2. The positive DC terminal T2p is connected to the positive terminal of the battery 9. The negative DC terminal T2n is connected to the negative terminal of the battery 9. A capacitor 17 is connected between the positive DC terminal T2p and the negative DC terminal T2n to smooth the DC voltage V2 between the positive DC terminal T2p and the negative DC terminal T2n.

[0060] The second bridge circuit 32 constitutes a single-phase full-bridge circuit. Specifically, the second bridge circuit 32 has switching elements Q5 to Q8 and diodes D5 to D8. Switching elements Q5 and Q6 are connected in series between the positive DC terminal T2p and the negative DC terminal T2n. Switching elements Q7 and Q8 are connected in series between the positive DC terminal T2p and the negative DC terminal T2n.

[0061] 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 them.

[0062] The third bridge circuit 33 constitutes a single-phase full-bridge circuit. Specifically, the third bridge circuit 33 has switching elements Q9 to Q12 and diodes D9 to D12. Switching elements Q9 and Q10 are connected in series between the positive DC terminal T3p and the negative DC terminal T3n. Switching elements Q11 and Q12 are connected in series between the positive DC terminal T3p and the negative DC terminal T3n.

[0063] Transformer 20 has a primary winding 20a, secondary windings 20b and 20c, and an iron core 21. Reactor L1 and the primary winding 20a are connected in series between node N1 (between switching elements Q1 and Q2) and node N2 (between switching elements Q3 and Q4). Reactor L2 and the secondary winding 20b are connected in series between node N3 (between switching elements Q5 and Q6) and node N4 (between switching elements Q7 and Q8). Reactor L3 and the secondary winding 20c are connected in series between node N5 (between switching elements Q9 and Q10) and node N6 (between switching elements Q11 and Q12). Furthermore, reactors L1 through L3 can each be replaced by the leakage inductance of transformer 20.

[0064] Switching elements Q1 to Q12 can be constructed from any self-extinguishing arc-suppressing 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. Diodes D1 to D12 are connected in reverse parallel with switching elements Q1 to Q12, forming freewheeling diodes (FWD).

[0065] The DC / DC converter 16 is configured 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 to AC power via the first bridge circuit 31. Figure 3 In this example, the AC power is single-phase AC, and this AC power is transmitted via transformer 20 to the second bridge circuit 32 and the third bridge circuit 33. 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.

[0066] On the other hand, 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 via the second bridge circuit 32. Figure 3In this example, the AC power is single-phase AC, and this AC power is transmitted via transformer 20 to the first bridge circuit 31 and the third bridge circuit 33. 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.

[0067] In 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 via the third bridge circuit 33. Figure 3 In this example, the AC power is single-phase AC, and this AC power is transmitted via transformer 20 to the first bridge circuit 31 and the second bridge circuit 32. 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.

[0068] (Driving method of DC / DC converter)

[0069] Next, use Figures 4 to 6 The driving method of DC / DC converter 16 is explained.

[0070] Reference Figure 4 DC power P1 is the DC power input and output to the first DC terminal T1. DC voltage V1 is the DC voltage between DC terminals T1p and T1n. AC voltage u1 is the AC voltage appearing between nodes N1 and N2 of the first bridge circuit 31.

[0071] The alternating current i1 is the alternating current flowing through the first bridge circuit 31. The reactor current iL1 is the current flowing through reactor L1. The reactor current iL2 is the current flowing through reactor L2. The reactor current iL3 is the current flowing through reactor L3. In the following description, the direction of the alternating current i1 and the reactor current iL1 is defined as the direction from the first bridge circuit 31 to the primary winding 20a of the transformer 20. The direction of the reactor currents iL2 and iL3 is defined as the direction from the secondary windings 20b and 20c of the transformer 20 to the second and third bridge circuits 32 and 33, respectively.

[0072] DC power P2 is the DC power input to and output to the second DC terminal T2. DC voltage V2 is the DC voltage between DC terminals T2p and T2n. AC voltage u2 is the AC voltage appearing between nodes N3 and N4 of the second bridge circuit 32.

[0073] DC power P3 is the DC power input and output to the third DC terminal T3. DC voltage V3 is the DC voltage between DC terminals T3p and T3n. AC voltage u3 is the AC voltage appearing between nodes N5 and N6 of the third bridge circuit 33.

[0074] In the following explanation, regarding the transmission direction of DC power P1 to P3, the direction of output from DC terminals T1 to T3 is taken as the positive direction, and the direction of input to DC terminals T1 to T3 is taken as the negative direction.

[0075] Figure 5 These are examples of the operating waveforms of bridge circuits 31 to 33. Figure 5 The waveforms of switching elements Q1, Q4, Q5, Q8, Q9, and Q12 are shown.

[0076] In the first bridge circuit 31, switching elements Q1 and Q2 are switched on and off complementaryly, as are switching elements Q3 and Q4. Furthermore, switching elements Q1 and Q4 are switched on and off in phase, and switching elements Q2 and Q3 are switched on and off in phase. Thus, the switching on and off of switching elements Q1 to Q4 is switched every half of the switching cycle T. The ratio of the on-time length of the switching elements to the switching cycle T, i.e., the duty cycle, is 50%.

[0077] Similarly, in the second bridge circuit 32, switching elements Q5 and Q6 are switched on and off complementaryly, as are switching elements Q7 and Q8. Furthermore, switching elements Q5 and Q8 are switched on and off in the same phase, and switching elements Q6 and Q7 are switched on and off in the same phase. Thus, the switching on and off of switching elements Q5 to Q8 is switched every half of the switching cycle T.

[0078] Similarly, in the third bridge circuit 33, switching elements Q9 and Q10 are switched on and off complementaryly, and switching elements Q11 and Q12 are switched on and off complementaryly. Furthermore, switching elements Q9 and Q12 are switched on and off in the same phase, and switching elements Q10 and Q11 are switched on and off in the same phase. Thus, the switching on and off of switching elements Q9 to Q12 is switched every half of the switching cycle T.

[0079] A phase difference φ is set between the timing of the switching elements Q1 to Q4 in the first bridge circuit 31 and the timing of the switching elements Q5 to Q8 in the second bridge circuit 32.

[0080] 2. If the switching period T is set to 2π, then the phase difference φ2 is equivalent to the time difference φ2 / 2π×T.

[0081] A phase difference φ3 is set between the timing of switching elements Q1 to Q4 being switched on and off in the first bridge circuit 31 and the timing of switching elements Q9 to Q12 being switched on and off in the third bridge circuit 33. If the switching period T is set to 2π, then the phase difference φ3 is equivalent to the time difference φ3 / 2π×T.

[0082] Figure 6 This is an example of the operating waveform of DC / DC converter 16. Figure 6 The diagram shows the waveforms of AC voltages u1-u3, vt, u1-vt, reactor current iL1, and AC current i1. AC voltage vt is the terminal voltage of the primary winding 20a of transformer 20. AC voltage u1-vt is the terminal voltage of reactor L1.

[0083] pass Figure 5 The switching elements Q1 to Q12 in the bridge circuits 31 to 33 shown are controlled to open and close, generating an AC voltage u1 between nodes N1 and N2 in the first bridge circuit 31, an AC voltage u2 between nodes N3 and N4 in the second bridge circuit 32, and an AC voltage u3 between nodes N5 and N6 in the third bridge circuit 33. The AC voltages u1 to u3 respectively become [various components] according to [the circuit's parameters]. Figure 5 The shown switching elements Q1 to Q12 are square wave voltages with pulse widths corresponding to their duty cycles. A reactor current iL1, varying according to the inter-terminal voltage u1-vt, flows through reactor L1. Although not shown in the diagram, a reactor current iL2, varying according to the inter-terminal voltage u2-vt, flows through reactor L2. A reactor current iL1, varying according to the inter-terminal voltage u3-vt, flows through reactor L3.

[0084] A phase difference φ2 is generated between AC voltages u1 and u2. A phase difference φ3 is generated between AC voltages u1 and u3. The inter-terminal voltages u1-vt, u2-vt, and u3-vt of the reactor change according to these phase differences φ2 and φ3, thereby causing changes in the reactor currents iL1, iL2, and iL3. Based on the changes in the reactor currents iL1, iL2, and iL3, the power transmitted between the first DC terminal T1, the second DC terminal T2, and the third DC terminal T3 also changes.

[0085] The DC power P1 input to and output to the first DC terminal T1 is represented by the following formula (1). The first term on the right represents the DC power transmitted between DC terminals T1 and T2, and the second term on the right represents the DC power transmitted between DC terminals T1 and T3.

[0086] [Number 1]

[0087]

[0088] The DC power P2 input to and output to the second DC terminal T2 is represented by the following formula (2). The first term on the right represents the DC power transmitted between DC terminals T2 and T1, and the second term on the right represents the DC power transmitted between DC terminals T2 and T3.

[0089] [Number 2]

[0090]

[0091] The DC power P3 input to and output to the third DC terminal T3 is represented by the following formula (3). The first term on the right represents the DC power transmitted between DC terminals T3 and T1, and the second term on the right represents the DC power transmitted between DC terminals T3 and T2.

[0092] [Number 3]

[0093]

[0094] 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.

[0095] Furthermore, V2, L2, V3, and L3 in equations (1) to (3) are the primary-side conversion values ​​that take into account the transformation ratio of transformer 20 (the winding ratio of primary winding 20a to secondary windings 20b and 20c). The measured value of the DC voltage between DC terminals T2p and T2n is set as V2r, the measured value of the DC voltage between DC terminals T3p and T3n is set as V3r, the measured value of the inductance component of reactor L2 and secondary winding 20b is set as L2r, the measured value of the inductance component of reactor L3 and secondary winding 20c is set as L3r, the winding ratio of secondary winding 20b to primary winding 20a is set as n2, and the winding ratio of secondary winding 20c to primary winding 20a is set as n3. In this case, V2, V3, L2, L3 and V2r, V3r, L2r, L3r have the relationship shown in equation (4).

[0096] [Number 4]

[0097]

[0098] Ideally, the relationship shown in equation (5) holds between DC power P1, P2, and P3.

[0099] [Number 5]

[0100] P1+P2+P3=0 (5)

[0101] When the phase difference φ2 is positive (when the phase of AC voltage u1 leads the phase of AC voltage u2), power is transferred 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 is delayed by the phase of AC voltage u2), power is transferred from the second DC terminal T2 to the first DC terminal T1.

[0102] When the phase difference φ3 is positive (when the phase of AC voltage u1 leads the phase of AC voltage u3), power is transferred 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 is delayed by the phase of AC voltage u3), power is transferred from the third DC terminal T3 to the first DC terminal T1.

[0103] When the difference between phase difference φ3 and phase difference φ2 (φ3-φ2) is positive (when the phase of AC voltage u2 leads the phase of AC voltage u3), power is transferred from the second DC terminal T2 to the third DC terminal T3.

[0104] When the difference between phase difference φ3 and phase difference φ2 (φ3-φ2) is negative (when the phase of AC voltage u2 is delayed compared to the phase of AC voltage u3), power is transferred from the third DC terminal T3 to the second DC terminal T2.

[0105] Operation of Uninterruptible Power Supply Device

[0106] Next, the operation of the uninterruptible power supply device 10 of this embodiment will be explained.

[0107] The uninterruptible power supply 10 has five power supply modes. The control device 15 selects one of the five power supply modes based on the status of the AC system 1, the DC power grid 6, and the AC / DC converter 5, and executes the selected power supply mode.

[0108] (First power supply mode)

[0109] Figure 7 This is a circuit block diagram illustrating the operation of the uninterruptible power supply device 10 in the first power supply mode. Figure 7 In the diagram, solid arrows indicate the path for transmitting power supplied from AC bus 3. Dashed arrows indicate the path for transmitting power supplied from DC bus 7.

[0110] The first power supply mode can be executed when AC system 1 is functioning properly. AC power supplied from AC bus 3 is converted to DC power by converter 11 and supplied to DC link 12. The DC power supplied to DC link 12 is stored in battery 9 via DC / DC converter 16 and then converted back to AC power by inverter 14 before being supplied to AC load 8. DC power supplied from DC bus 7 is stored in battery 9 via DC / DC converter 16.

[0111] In the first power supply mode, the control device 15 controls the converter 11 to make the DC link voltage VD the reference voltage VDR. Additionally, the control device 15 controls the inverter 14 to make the AC output voltage VO the reference voltage VOR.

[0112] The control device 15 also controls the DC / DC converter 16 to transfer 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. Thus, DC power is supplied to the battery 9 from the DC link 12 and the DC bus 7 via the DC / DC converter 16.

[0113] Specifically, the control device 15 generates a command value for DC power P2, namely DC power command value P2*, so that the terminal voltage VB of battery 9 becomes the reference voltage VBR. Next, the control device 15 generates a DC power command value P1* as the command value for DC power P1 and a DC power command value P3* as the command value for DC power P3, such that the sum of the absolute values ​​of DC power P1 and DC power P3 becomes the DC power command value P2*. The ratio of DC power command value P1* to DC power command value P2* can be controlled to a desired value. Based on the generated DC power command values ​​P1*, P2*, and P3*, the control device 15 calculates the phase differences φ2 and φ3, and controls the bridge circuits 31 to 33 to generate the calculated phase differences φ2 and φ3.

[0114] The first power supply mode can be selected under the following conditions: first, the power supplied in the DC grid 6 exceeds the required power; and second, the power supplied by the DC grid 6 to the DC / DC converter 16 is sufficient to charge the battery 9.

[0115] The first condition is met when the power supply and demand balance of DC grid 6 is characterized by oversupply. For example, the first condition is met when the generated power of distributed power source 61 (e.g., the power generated by solar panels) exceeds the power consumed by DC load 65. Conversely, the first condition is not met when the power supply and demand balance of DC grid 6 is characterized by overdemand.

[0116] The second condition is met if the first condition is satisfied and the remaining power supply in the DC power grid 6 is below the DC power command value P2*. The DC power command value P2* is equivalent to the power required to charge the battery 9.

[0117] When the power supply and demand balance of DC grid 6 is in the case of oversupply, the surplus power is supplied from DC grid 6 to battery 9 via DC / DC converter 16 by executing the first power supply mode. This allows for efficient utilization of the surplus power and enables the power supply and demand balance of DC grid 6 to be adjusted to a constant level.

[0118] (Second power supply mode)

[0119] Figure 8 This is a circuit block diagram illustrating the operation of the uninterruptible power supply device 10 in the second power supply mode. Figure 8 In the diagram, solid arrows indicate the path for transmitting power supplied from AC bus 3. Dashed arrows indicate the path for transmitting power supplied from DC bus 7.

[0120] The second power supply mode can be executed when AC system 1 is functioning correctly. AC power supplied from AC bus 3 is converted to DC power by converter 11 and supplied to DC link 12. DC power supplied from DC bus 7 is stored in battery 9 by DC / DC converter 16 and supplied to DC link 12. The DC power supplied to DC link 12 is converted to AC power by inverter 14 and supplied to AC load 8. The second power supply mode is similar to the first power supply mode (see reference). Figure 7 The difference is that DC power is supplied from the DC grid 6 to the DC link 12 via the DC / DC converter 16.

[0121] In the second power supply mode, the control device 15 controls the converter 11 to make the DC link voltage VD the reference voltage VDR. Additionally, the control device 15 controls the inverter 14 to make the AC output voltage VO the reference voltage VOR.

[0122] The control device 15 also controls the DC / DC converter 16 to transfer the DC power P3 input to the third DC terminal T3 to the first DC terminal T1 and the second DC terminal T2. Thus, DC power is supplied from the DC bus 7 to the battery 9 and the DC link 12 via the DC / DC converter 16.

[0123] Specifically, control device 15 generates a DC power command value P1* by using the DC link voltage VD as the reference voltage VDR. Additionally, control device 15 generates a DC power command value P2* by using the inter-terminal voltage VB of battery 9 as the reference voltage VBR. Next, control device 15 generates a DC power command value P3* based on the sum of the absolute values ​​of DC power command values ​​P1* and P2*. Control device 15 calculates the phase differences φ2 and φ3 based on the generated DC power command values ​​P1*, P2*, and P3*, and controls bridge circuits 31 to 33 to generate the calculated phase differences φ2 and φ3.

[0124] The second power supply mode can be selected if the first condition described above and the third condition that the DC grid 6 can supply more power to the DC / DC converter 16 than the power required to charge the battery 9 are met.

[0125] The third condition is met if the first condition is satisfied and the remaining power supply in DC grid 6 is greater than the DC power command value P2*. The DC power command value P2* is equivalent to the power required to charge battery 9.

[0126] When the surplus power supplied to the DC grid 6 exceeds the power required to charge the battery 9, a second power supply mode is executed, supplying the surplus power to the battery 9 and the DC link 12 via the DC / DC converter 16. This allows for efficient utilization of the surplus power and enables the power supply and demand balance of the DC grid 6 to be adjusted to a constant level. For example, by executing the second power supply mode when the generated power of the distributed power source 61 (e.g., the generated power of the solar panels) significantly exceeds the power consumed by the DC load 65, the power supply and demand balance of the DC grid 6 can be rapidly adjusted.

[0127] Alternatively, it can be configured to stop the operation of converter 11 to stop the power supply from AC bus 3 based on the amount of remaining power supplied in DC grid 6, and only supply DC power from DC bus 7 to DC link 12.

[0128] (Third power supply mode)

[0129] Figure 9 This is a circuit block diagram illustrating the operation of the uninterruptible power supply device 10 in the third power supply mode. Figure 9 In the diagram, solid arrows indicate the paths through which power is transmitted from AC bus 3.

[0130] The third power supply mode can be executed when AC system 1 is functioning correctly. AC power supplied from AC bus 3 is converted to DC power by converter 11 and supplied to DC link 12. The DC power supplied to DC link 12 is converted back to AC power by inverter 14 and then supplied to AC load 8. The third power supply mode is similar to the first power supply mode (see reference). Figure 7 ) and the second power supply mode (refer to Figure 8 The difference is that DC power is not supplied from the DC grid 6 to the DC / DC converter 16.

[0131] In the third power supply mode, the control device 15 controls the converter 11 to make the DC link voltage VD the reference voltage VDR. Additionally, the control device 15 controls the inverter 14 to make the AC output voltage VO the reference voltage VOR.

[0132] The control device 15 also controls the DC / DC converter 16 to stop the operation of the third bridge circuit 33 and transfer the DC power P1 input to the first DC terminal T1 to the second DC terminal T2. Thus, DC power is supplied from the DC link 12 to the battery 9 via the DC / DC converter 16, while simultaneously stopping the supply of DC power from the DC bus 7 to the DC / DC converter 16.

[0133] Specifically, the control device 15 generates a DC power command value P2* by using the inter-terminal voltage VB of the battery 9 as a reference voltage VBR. Next, the control device 15 generates a DC power command value P1* by using the absolute value of the DC power P1 as the DC power command value P2*. Based on the generated DC power command values ​​P1* and P2*, the control device 15 calculates the phase difference φ2 and controls the bridge circuits 31 and 32 to generate the calculated phase difference φ2.

[0134] A third power supply mode can be selected even if the first condition described above is not met. That is, when the power supply and demand balance of the DC grid 6 is excessive, the third power supply mode can be selected. When the power supply 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. This prevents the power supply and demand balance of the DC grid 6 from becoming unstable.

[0135] (Fourth power supply mode)

[0136] Figure 10 This is a circuit block diagram illustrating the operation of the uninterruptible power supply device 10 in the fourth power supply mode. Figure 10 In the diagram, a single-dotted arrow indicates the path for transmitting power supplied from battery 9. A dashed arrow indicates the path for transmitting power supplied from DC bus 7.

[0137] The fourth power supply mode can be executed in the event of a failure in AC system 1. In the event of a failure in AC system 1, the operation of converter 11 is stopped. DC power stored in battery 9 is supplied to DC link 12 via DC / DC converter 16. DC power supplied from DC bus 7 is also supplied to DC link 12 via DC / DC converter 16. The DC power supplied to DC link 12 is converted to AC power by inverter 14 and then supplied to AC load 8.

[0138] In the fourth power supply mode, the control device 15 stops the operation of the converter 11 and controls the inverter 14 to make the AC output voltage VO the reference voltage VOR.

[0139] The control device 15 also controls the DC / DC converter 16 to transfer 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. Thus, DC power is supplied from the battery 9 and the DC bus 7 to the DC link 12 via the DC / DC converter 16.

[0140] Specifically, the control device 15 generates a DC power command value P1* by using the DC link voltage VD as the reference voltage VDR. Next, the control device 15 generates DC power command values ​​P2* and P3* such that the sum of the absolute values ​​of DC power P2 and DC power P3 equals the DC power command value P1*. The ratio of power command value P2* to power command value P3* can be controlled to a desired value. Based on the generated DC power command values ​​P1*, P2*, and P3*, the control device 15 calculates the phase differences φ2 and φ3, and controls the bridge circuits 31 to 33 to generate the calculated phase differences φ2 and φ3.

[0141] In the fourth power supply mode, the DC power from battery 9 and DC bus 7 is converted into AC power by inverter 14 and supplied to AC load 8. Therefore, even if an AC system 1 fails, the operation of AC load 8 can continue. Furthermore, even after the remaining capacity of battery 9 decreases and its discharge stops, the operation of AC load 8 can continue using the DC power from DC bus 7. Thus, the reliability of the uninterruptible power supply device 10 can be improved.

[0142] (Fifth power supply mode)

[0143] Figure 11 This is a circuit block diagram illustrating the operation of the uninterruptible power supply device 10 in the fifth power supply mode. Figure 11 In the diagram, a single-dotted arrow indicates the path for transmitting power supplied from battery 9. A dashed arrow indicates the path for transmitting power supplied from DC bus 7.

[0144] The fifth power supply mode can be executed in the event of a fault in the DC power grid 6 or a failure in the AC / DC converter 5. AC power supplied from the AC bus 3 is converted to DC power by converter 11 and supplied to the DC link 12. The DC power supplied to the DC link 12 is converted back to AC power by inverter 14 and supplied to the AC load 8. The DC power from the DC link 12 and the DC power from the battery 9 are supplied to the DC bus 7 via DC / DC converter 16.

[0145] In the fifth power supply mode, the control device 15 controls the converter 11 to make the DC link voltage VD the reference voltage VDR. Additionally, the control device 15 controls the inverter 14 to make the AC output voltage VO the reference voltage VOR.

[0146] The control device 15 also controls the DC / DC converter 16 to transfer 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. Thus, DC power is supplied from the DC link 12 and the battery 9 to the DC bus 7 via the DC / DC converter 16.

[0147] Specifically, the control device 15 generates a DC power command value P3* by using the DC voltage VDC of the DC bus 7 as a reference voltage VDCR. Next, the control device 15 generates DC power command values ​​P1* and P2* such that the sum of the absolute values ​​of DC power P1 and DC power P2 equals the DC power command value P3*. The ratio of power command value P1* to power command value P2* can be controlled to a desired value. Based on the generated DC power command values ​​P1*, P2*, and P3*, the control device 15 calculates the phase differences φ2 and φ3, and controls the bridge circuits 31 to 33 to generate the calculated phase differences φ2 and φ3.

[0148] In the fifth power supply mode, in parallel with the power supply to the AC load 8, DC power from DC link 12 and battery 9 is supplied to DC bus 7 via DC / DC converter 16. Therefore, even in the event of a fault in the DC power grid 6 or a failure of AC / DC converter 5, DC power can still be supplied to DC bus 7. As a result, the operation of DC load 65 can continue. Furthermore, even after the remaining capacity of battery 9 decreases and its discharge stops, the DC power from DC link 12 can still be used to continue the operation of DC load 65. Therefore, the reliability of DC power grid 6 can be improved.

[0149] <Control Structure of Uninterruptible Power Supply Device>

[0150] Figure 12 This is a block diagram showing the structure of the control device 15. For example... Figure 12As shown, the control device 15 is configured to include fault 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. Figure 11 The functions of each module shown can be realized through at least one of the software processing and hardware processing of the control device 15.

[0151] 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 inactive level "H". In the event of a fault in the AC system 1, the detection signal DT1 is set to the active level "L". For example, the fault detector 160 determines that a fault has occurred in the AC system 1 if the AC input voltage VI is below a lower limit.

[0152] The fault detector 162 detects whether a fault has occurred in the DC power grid 6 or 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 power grid 6 is intact and the AC / DC converter 5 is functioning normally, the detection signal DT2 is set to a "H" level. In the event of a fault in the DC power grid 6 or a fault in the AC / DC converter 5, the detection signal DT2 is set to a "L" level. For example, if the AC input voltage VI is higher than a lower limit and the DC voltage VDC is lower than a lower limit, the fault detector 162 determines that a fault has occurred in the DC power grid 6 or the AC / DC converter 5.

[0153] The mode selection unit 164 selects one of 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.

[0154] Figure 13 This is a flowchart illustrating the selection of the power supply mode in the mode selection unit 164. For example... Figure 13 As shown, the mode selection unit 164 determines whether an AC system 1 malfunction has occurred based on the detection signal DT1 from the fault detector 160 in step S01. If the detection signal DT1 is at an "L" level, the mode selection unit 164 determines that an AC system 1 malfunction has occurred (when S01 is "yes"), and selects the fourth power supply mode (see reference) in step S05. Figure 10 ).

[0155] If the detection signal DT1 is at an "H" level, the mode selection unit 164 determines that the AC system 1 is functioning properly (if S01 is "No"), and proceeds to step S02. In step S02, the mode selection unit 164, based on the detection signal DT2 from the fault detector 162, determines whether a fault has occurred in the DC power grid 6 or the AC / DC converter 5. If the detection signal DT2 is at an "L" level, the mode selection unit 164 determines that a fault has occurred in the DC power grid 6 or the AC / DC converter 5 (if S02 is "Yes"), and proceeds to step S06 to select the fifth power supply mode (see reference). Figure 11 ).

[0156] When the detection signal DT2 is at the "H" level, the mode selection unit 164 determines that the DC power grid 6 is healthy and the AC / DC converter 5 is normal (when S02 is "No"), and proceeds to step S03. In step S03, the mode selection unit 164 determines whether the power supplied to the DC power grid 6 exceeds the required power. In S03, the mode selection unit 164 determines whether the power supply and demand balance of the DC power grid 6 is due to oversupply or overdemand. The determination in S03 can use the DC voltage VDC of the DC bus 7. For example, if the DC voltage VDC is higher than a threshold, S03 determines "Yes". Alternatively, by monitoring the power generation of the distributed power source 61, if the power generation exceeds a threshold, S03 determines "Yes".

[0157] If the power supply in DC grid 6 is lower than the power demand (when "No" is determined in S03), the mode selection unit 164 determines that the power supply and demand balance of DC grid 6 is too high, and proceeds to step S07 to select the third power supply mode (refer to...). Figure 9 On the other hand, if the power supplied in the DC grid 6 exceeds the power required (when "yes" is determined in S03), the mode selection unit 164 determines that the power supply and demand balance of the DC grid 6 is oversupplied and proceeds to step S04.

[0158] 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 remaining power supply in the DC grid 6. Furthermore, the mode selection unit 164 generates a DC power command value P2* by using the inter-terminal voltage VB of the battery 9 as a reference voltage VBR. The DC power command value P2* corresponds to the power required to charge the battery 9.

[0159] When the power supplied by the DC grid 6 to the DC / DC converter 16 is greater than the DC power command value P2* (when "yes" is determined in S04), the mode selection unit 164 selects the second power supply mode in step S08 (refer to...). Figure 8 ).

[0160] On the other hand, when the power supplied by the DC grid 6 to the DC / DC converter 16 is less than or equal to the DC power command value P2* (when "No" is determined in S04), the mode selection unit 164 selects the first power supply mode in step S09 (refer to...). Figure 7 ).

[0161] return Figure 12 The mode selection unit 164 outputs a mode signal MD, which indicates the selected power supply mode, to the converter control unit 166, the inverter control unit 168, and the DC / DC control unit 170.

[0162] The converter control unit 166 controls the converter 11 based on the mode signal MD. When the mode signal MD represents 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 to make the DC link voltage VD the reference voltage VDR. When the mode signal MD represents the fourth power supply mode, the converter control unit 166 stops the operation of the converter 11.

[0163] The inverter control unit 168 controls the inverter 14 based on the mode signal MD. When the mode signal MD represents 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.

[0164] The DC / DC control unit 170 controls the DC / DC converter 16 based on the mode signal MD. When the mode signal MD indicates a first power supply mode, the DC / DC control unit 170 controls the DC / DC converter 16 to transfer 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.

[0165] When the mode signal MD indicates the second power supply mode, the DC / DC control unit 170 controls the DC / DC converter 16 to transfer the DC power P3 input to the third DC terminal T3 to the first DC terminal T1 and the second DC terminal T2.

[0166] 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 transfer the DC power P1 input to the first DC terminal T1 to the second DC terminal T2.

[0167] When the mode signal MD indicates the fourth power supply mode, the DC / DC control unit 170 controls the DC / DC converter 16 to transfer 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.

[0168] When the mode signal MD indicates the fifth power supply mode, the DC / DC control unit 170 controls the DC / DC converter 16 to transfer 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.

[0169] <Effects of the Implementation Method>

[0170] As explained above, in this embodiment, the DC / DC converter 16 has a first DC terminal T1 connected to the DC link 12 of the uninterruptible power supply device 10, a second DC terminal T2 connected to the battery 9, and a third DC terminal T3 connected to the DC bus 7, configured to transmit DC power between the first to third DC terminals T1 to T3. Thus, power exchange in three directions is possible between the uninterruptible power supply device 10, the battery 9, and the DC grid 6 via the DC / DC converter 16.

[0171] Specifically, when AC system 1 is functioning properly, if the power supplied in DC grid 6 exceeds the required power, the DC power from DC link 12 and DC grid 6 can be stored in battery 9. In particular, when the surplus power supplied in DC grid 6 exceeds the power required to charge battery 9, the DC power from DC grid 6 can be stored in battery 9 and converted into AC power to supply AC load 8. Thus, when the power supply and demand balance of DC grid 6 is excessive, the DC power of DC grid 6 can be effectively utilized, and the supply and demand balance of DC grid 6 can be adjusted to a constant level.

[0172] In the event of a failure in AC system 1, the operation of AC load 8 can continue by converting the DC power from battery 9 and DC grid 6 into AC power and supplying it to AC load 8. Furthermore, by using both the DC power from battery 9 and DC power from DC grid 6, the operation of AC load 8 can continue even after battery 9 stops discharging. Therefore, the reliability of the uninterruptible power supply device 10 can be improved.

[0173] In the event of a fault in the DC power grid 6 or a failure in the AC / DC converter 5, DC power from the DC link 12 and the battery 9 can be supplied to the DC power grid 6. Thus, even in the event of a fault in the DC power grid 6 or a failure in the AC / DC converter 5, the operation of the DC load 65 can continue using the AC power from the AC system 1.

[0174] Furthermore, according to this embodiment, by employing a TAB-type DC / DC converter for the DC / DC converter 16, DC power can be transmitted between the uninterruptible power supply device 10, the battery 9, and the DC power grid 6 via a single DC / DC converter. Therefore, compared to a power supply system that transmits DC power between the uninterruptible power supply device 10, the battery 9, and the DC power grid 6 via multiple DC / DC converters, power losses generated in the power supply system can be reduced. Thus, high efficiency of the power supply system can be achieved. Additionally, the large size of the power supply system can be prevented.

[0175] The embodiments disclosed herein should be considered illustrative and not restrictive in all respects. This disclosure is not represented by the foregoing description, but by the scope of the claim, and is intended to include the equivalent meaning of the scope of the claim and all modifications within that scope.

[0176] Explanation of reference numerals in the attached figures

[0177] 1. AC system; 2. Transformers 4 and 20; 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. DC terminals T1-T3; 11. Converter; 12. DC link; 13. Capacitor; 14. Inverter; 15. Control device; 20a. Primary winding; 20b. Secondary winding; 20c. Secondary winding; 21. Iron core; 16. 60. 62. 64. DC / DC converter, 31-33 bridge circuit, 61 distributed power supply, 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-Q12 switching elements, D1-D12 diodes, L1-L3 reactors.

Claims

1. An uninterruptible power supply device, connected to an AC system and a DC power grid, wherein, The DC power grid includes: a DC bus connected to the AC system via an AC / DC converter; distributed power sources that output DC power generated by the generator to the DC bus; and DC loads that receive DC power from the DC bus. The uninterruptible power supply device includes: DC link, used for transmitting and receiving DC power; The converter converts the AC power supplied from the AC system into DC power and supplies it to the DC link; The inverter converts the DC power received from the DC link into AC power and supplies it to the AC load; and A DC / DC converter is configured to have a first DC terminal connected to the DC link, a second DC terminal connected to an energy storage device, and a third DC terminal connected to the DC bus, transmitting DC power between the first and third DC terminals.

2. The uninterruptible power supply device according to claim 1, wherein, The uninterruptible power supply device has the following features: In the first power supply mode, power from the AC system is supplied to the AC load and the energy storage device, and power from the DC grid is supplied to the energy storage device. The second power supply mode supplies power from the DC grid to the AC load and the energy storage device; The third power supply mode supplies power from the AC system to the AC load and the energy storage device. The fourth power supply mode supplies power from the energy storage device and the DC grid to the AC load; and The fifth power supply mode supplies power from the AC system and the energy storage device to the DC grid. The uninterruptible power supply device also includes a control device, which selects one of the first to fifth power supply modes based on the state of the AC system, the DC power 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 functioning properly, and the power supplied from the DC grid exceeds the required power, if the power supplied by the DC grid is less than the power required to charge the energy storage device, the control device selects the first power supply mode. 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 from the DC link and the DC bus to the energy storage device, and controls the inverter to convert DC power from the DC link into AC power and supply it to the AC load.

4. The uninterruptible power supply device according to claim 2, wherein, When the AC system is functioning properly, and the power supplied by the DC grid exceeds the required power, if the power supplied by the DC grid is greater than the power required to charge the energy storage device, the control device selects the second power supply mode. 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 from the DC bus to the energy storage device and the DC link, and controls the inverter to convert DC power from 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 functioning properly, and the power supplied from the DC grid is lower than the required power, the control device selects the third power supply mode. 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 DC power from the DC bus to the energy storage device, and controls the inverter to convert DC power from 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 a fault occurs in the AC system. When the fourth power supply mode is selected, the control device stops the operation of the converter, controls the DC / DC converter to supply the DC power of the energy storage device and the DC bus to the DC link, and controls the inverter to convert the DC power of the DC link into AC power and supply it to the AC load.

7. The uninterruptible power supply device according to claim 2, wherein, When a fault occurs in the DC power grid or the AC / DC converter, the control device selects the fifth power supply mode. 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 energy storage device to the DC bus, and controls the inverter to convert DC power from the DC link into AC power and supply it to the AC load.

8. The uninterruptible power supply device according to claim 1, wherein, The DC / DC converter includes a TAB-type DC / DC converter, i.e., a three-active-bridge DC / DC converter.

9. A power supply system, comprising: The uninterruptible power supply device according to any one of claims 1 to 8; The DC power grid; and The AC / DC converter is connected between the AC system and the DC power grid.

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