UPS system

Abstract

To improve reliability of load power feeding of a regular UPS at system switching in a UPS system including the regular UPS and a backup UPS.SOLUTION: An input switching device 3S in a UPS system executes a switching operation of changing a connection destination of a backup UPS 8 from a first power supply 2A to a second power supply 2B at system switching. A second power converter 13S executes a self-propelled operation during the switching operation of the input switching device 3S, and shifts from the self-propelled operation to a second synchronous operation after the switching operation. When a phase of a second AC voltage is synchronized with a phase of an AC voltage of a second bypass circuit 18S in the second synchronous operation after the switching operation of the input switching device 3S, a first power converter 13A shifts from a first synchronous operation to a third synchronous operation in which a phase of a first AC voltage is synchronized with a phase of an output voltage of the second power converter 13S. During execution of the third synchronous operation, the input switching device 3A executes a switching operation of changing a connection destination of a regular UPS 7A from the first power supply 2A to the second power supply 2B.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure is a UPS system that includes a main UPS and a standby UPS. [Background technology]

[0002] For example, Japanese Patent Laid-Open Publication No. 2008-67491 (Patent Document 1) discloses a UPS system that includes multiple regular UPS (Uninterruptible Power Supplies) that constantly supply power to a load, and a backup UPS that is provided to supply power to the load in the unlikely event that a malfunction occurs in the regular UPS or when inspection is required. The regular UPS and the backup UPS have the same configuration.

[0003] Each UPS is configured to supply stable AC power to a load by converting AC power supplied from an AC power source into DC power using a converter and then converting it back into AC power using an inverter. In addition, each UPS is provided with a bypass circuit that supplies AC power from the AC power source to the load and a switching circuit that switches between power supply from the inverter and power supply from the bypass circuit, so that power can be continuously supplied to the load even in the unlikely event that the converter or inverter fails.

[0004] In the above configuration, in order to perform power supply switching in the switching circuit without momentary interruption, each UPS performs synchronous operation in which the phase of the AC voltage output from the inverter is synchronized with the phase of the AC voltage of the bypass circuit. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-67491 Summary of the Invention [Problem to be solved by the invention]

[0006] In the UPS system described above, system switching may be performed to switch the AC power source to which each UPS is connected in order to perform maintenance and inspection of the power transmission line, etc. This system switching involves switching the switches provided between the AC power source and each UPS.

[0007] During this switching operation, the AC voltage input to each UPS is temporarily cut off, causing a temporary power outage of the AC power supply. If this temporary power outage causes the AC voltage in the bypass circuit to become abnormal, each UPS will operate independently at a fixed frequency (commercial frequency of 50 Hz or 60 Hz) instead of synchronous operation.

[0008] When the restoration of the AC power supply is detected after the switching operation of the switches is completed, each UPS shifts from independent operation to synchronous operation. In this synchronous operation, the phase of the AC voltage output from the inverter is adjusted so that it is synchronized with the phase of the AC voltage input to the bypass circuit from the AC power supply after the switchover.

[0009] However, because the phase of the inverter's output voltage during free-running operation is asynchronous with the phase of the bypass circuit's AC voltage, it can take up to 10 seconds from the point at which synchronous operation is resumed until the phase of the inverter's output voltage and the phase of the bypass circuit's AC voltage are synchronized. During this time, the bypass circuit's AC voltage and the inverter's output voltage are asynchronous, so in the unlikely event of a failure, power supply switching cannot be performed without interruption, raising concerns that this could affect the load.

[0010] The present disclosure has been made to solve such problems, and its purpose is to improve the reliability of load power supply from a regular UPS when switching systems in a UPS system that includes a regular UPS and a standby UPS. [Means for solving the problem]

[0011] A UPS system according to one embodiment of the present disclosure is connected between an AC power source and a load. The AC power source includes a first power source and a second power source connected to a higher-level system. The UPS system includes a service UPS, a backup UPS, a first input switching device for connecting the service UPS to either the first power source or the second power source, a second input switching device for connecting the backup UPS to either the first power source or the second power source, and an output switching device for connecting either the service UPS or the backup UPS to the load.

[0012] The normal UPS includes a first power converter that converts an AC voltage supplied from a first input switching device into a first AC voltage, a first bypass circuit connected in parallel with the first power converter between the first input switching device and the output switching device, and a first switching circuit for outputting either the first AC voltage of the first power converter or the AC voltage of the first bypass circuit to the output switching device. The standby UPS includes a second power converter that converts an AC voltage supplied from a second input switching device into a second AC voltage, a second bypass circuit connected in parallel with the second power converter between the second input switching device and the output switching device, and a second switching circuit for outputting either the second AC voltage of the second power converter or the AC voltage of the second bypass circuit to the output switching device.

[0013] When the service UPS and the standby UPS are connected to the first power supply and the service UPS is connected to a load, the first power converter performs a first synchronous operation in which the phase of the first AC voltage is synchronized with the phase of the AC voltage of the first bypass circuit, and the second power converter performs a second synchronous operation in which the phase of the second AC voltage is synchronized with the phase of the AC voltage of the second bypass circuit.

[0014] When the connection destinations of the main UPS and the standby UPS are switched from the first power source to the second power source, the second input switching device performs a switching operation to change the connection destination of the standby UPS from the first power source to the second power source. The second power converter performs free-running operation at a fixed frequency in response to a temporary abnormality in the AC voltage of the second bypass circuit during the switching operation of the second input switching device, and transitions from free-running operation to second synchronous operation after the switching operation. The first power converter transitions from first synchronous operation to third synchronous operation in which the phase of the first AC voltage is synchronized with the phase of the AC voltage of the second bypass circuit during the second synchronous operation after the switching operation of the second input switching device. The first input switching device performs a switching operation to change the connection destination of the main UPS from the first power source to the second power source during the third synchronous operation. [Effects of the Invention]

[0015] According to the present disclosure, in a UPS system including a regular UPS and a standby UPS, it is possible to improve the reliability of the regular UPS's power supply to the load when switching between systems. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a circuit block diagram showing an overall configuration of a UPS system according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a circuit block diagram showing the configuration of a standby UPS and a regular UPS. [Figure 3] FIG. 2 is a block diagram showing the configuration of a control device. [Figure 4] 4 is a time chart for explaining the operation of each UPS during system switching. [Figure 5] FIG. 4 is a diagram for explaining the operation of each UPS when switching systems. [Figure 6] FIG. 4 is a diagram for explaining the operation of each UPS when switching systems. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and their description will not be repeated.

[0018] <Configuration of UPS System> FIG. 1 is a circuit block diagram showing the overall configuration of a UPS system according to an embodiment of the present disclosure. As shown in FIG. 1, a UPS system 100 according to the present embodiment is connected between an AC power supply and loads 5A to 5C.

[0019] The AC power supply includes an A-system power supply 2A and a B-system power supply 2B connected to the upper-level system 1. Loads (not shown) are connected to each of the A-system power supply 2A and the B-system power supply 2B. Since both the A-system power supply 2A and the B-system power supply 2B are connected to the upper-level system 1, the AC voltage of the A-system power supply 2A and the AC voltage of the B-system power supply 2B are ideally in the same phase. However, due to differences in the loads connected to each AC power supply, etc., the AC voltage of the A-system power supply 2A and the AC voltage of the B-system power supply 2B may be slightly out of phase. The A-system power supply 2A corresponds to an example of the "first power supply", and the B-system power supply 2B corresponds to an example of the "second power supply".

[0020] The UPS system 100 includes a plurality of UPSs 8, 7A to 7C, switches 3S, 3A to 3C, and switches 4A to 4C. Each of the UPSs 8, 7A to 7C includes an AC input terminal T1, a DC terminal T2, and an AC output terminal T3. The UPSs 8, 7A to 7C basically have the same configuration, but the UPS 8 is used as a "standby UPS", and the UPSs 7A to 7C are used as "main UPSs". The configuration of each UPS will be described later. In the following description, the UPS 8 may be referred to as the "standby UPS 8", and the UPSs 7A to 7C may be referred to as the "main UPSs 7A to 7C". Also, the UPSs 7A to 7C may be collectively referred to as the "main UPSs 7". Note that the number of main UPSs 7 is not limited to three and may be one or more.

[0021] The switch 3S is connected between the A system power supply 2A and the B system power supply 2B and the AC input terminal T1 of the standby UPS 8. The switch 3S is controlled by the user of the UPS system 100 or the like to connect the AC input terminal T1 of the standby UPS 8 to either the A system power supply 2A or the B system power supply 2B. When the switch 3S connects the AC input terminal T1 to the A system power supply 2A, the AC input terminal T1 receives an AC voltage of a predetermined frequency (for example, the commercial frequency) from the A system power supply 2A. When the switch 3S connects the AC input terminal T1 to the B system power supply 2B, the AC input terminal T1 receives an AC voltage of a predetermined frequency (for example, the commercial frequency) from the B system power supply 2B. The switch 3S corresponds to one embodiment of a "second input switching device."

[0022] The switches 3A to 3C are provided corresponding to the service UPSs 7A to 7C, respectively. Each of the switches 3A to 3C is connected between the A system power supply 2A and the B system power supply 2B and the AC input terminal T1 of the corresponding service UPS 7. Each of the switches 3A to 3C is controlled by the user of the UPS system 100 or the like to connect the AC input terminal T1 of the corresponding service UPS 7 to either the A system power supply 2A or the B system power supply 2B. For example, when the AC input terminal T1 of the service UPS 7A is connected to the A system power supply 2A by the switch 3A, the AC input terminal T1 receives an AC voltage of a predetermined frequency (for example, the commercial frequency) from the A system power supply 2A. When the AC input terminal T1 of the service UPS 7A is connected to the B system power supply 2B by the switch 3A, the AC input terminal T1 receives an AC voltage of a predetermined frequency (for example, the commercial frequency) from the B system power supply 2B. The switches 3A to 3C correspond to one embodiment of a "first input switching device." In the example of FIG. 1, all of the AC input terminals T1 of the regular UPSs 7A to 7C are connected to the A system power supply 2A, but some of the AC input terminals T1 of the regular UPSs 7A to 7C may be connected to the B system power supply 2B.

[0023] The DC terminal T2 of each of the UPS 8, 7A to 7C is connected to a battery B. The battery B stores DC power. A capacitor may be connected instead of the battery.

[0024] The switches 4A to 4C are provided corresponding to the regular UPSs 7A to 7C, respectively. The switches 4A to 4C are connected between the AC output terminals T3 of the regular UPSs 7A to 7C and the loads 5A to 5C, respectively. Each of the switches 4A to 4C is controlled by the user of the UPS system 100 or the like, and connects either the AC output terminal T3 of the corresponding regular UPS 7 or the AC output terminal T3 of the backup UPS 8 to the corresponding load. The switches 4A to 4C are, for example, static transfer switches (STS). Each of the switches 4A to 4C switches between the output of the corresponding regular UPS 7 and the output of the backup UPS 8 with or without momentary interruption, thereby continuing to supply power to the corresponding load. The switches 4A to 4C correspond to an embodiment of an "output switching device."

[0025] In the UPS system 100, the regular UPSs 7A to 7C are normally in regular operation, and the backup UPS 8 is in backup operation. The switches 4A to 4C connect the AC output terminals T3 of the regular UPSs 7A to 7C to the loads 5A to 5C, respectively. This supplies the outputs of the regular UPSs 7A to 7C to the loads 5A to 5C, respectively. However, if the regular UPS 7A stops due to maintenance or a malfunction, for example, the switch 4A connects the AC output terminal T3 of the backup UPS 8 to the load 5A, thereby supplying the output of the backup UPS 8 to the load 5A. The backup UPS 8 is also called a "common backup UPS" because it functions as a backup UPS shared by multiple regular UPSs 7A to 7C.

[0026] The regular UPSs 7A to 7C and the standby UPS 8 are connected to each other via a communication line 6. The regular UPSs 7A to 7C and the standby UPS 8 exchange various information via the communication line 6. The information transmitted from the standby UPS 8 to the regular UPSs 7A to 7C includes information relating to synchronization in the standby UPS 8.

[0027] Fig. 2 is a circuit block diagram showing the configuration of the backup UPS 8 and the regular UPS 7A shown in Fig. 1. Although not shown, each of the regular UPSs 7B and 7C has the same configuration as the regular UPS 7A.

[0028] The standby UPS 8 includes switches 10, 14 to 16, a converter 11, a DC line 12, an inverter 13S, a semiconductor switch 17, a bypass circuit 18S, voltage detectors 28, 36, and a control device 20, in addition to an AC input terminal T1, a DC terminal T2, and an AC output terminal T3.

[0029] The switch 10 is connected between the AC input terminal T1 and the AC node of the converter 11, and is controlled by the control device 20. When the AC power supply (A-system power supply 2A in FIG. 2) connected to the AC input terminal T1 via the switch 3S is normal, the switch 10 is turned on, and an AC voltage is supplied from the AC power supply to the converter 11 via the switch 10. When the AC power supply experiences a power outage, the switch 10 is turned off, and the AC power supply and the converter 11 are disconnected.

[0030] The converter 11 is controlled by a control device 20. When the AC power supply is normal, the converter 11 converts the AC voltage received at the AC input terminal T1 into a DC voltage and outputs it to the DC line 12. When the AC power supply fails, the control device 20 stops the operation of the converter 11. The converter 11 is a well-known device that includes multiple sets of IGBTs (Insulated Gate Bipolar Transistors) and diodes.

[0031] The DC line 12 is connected to the DC terminal T2. The battery B stores DC power supplied from the converter 11 via the DC line 12. The DC line 12 is connected to a DC node of the inverter 13S, and an AC node of the inverter 13S is connected to a first terminal of a switch 14. A second terminal of the switch 14 is connected to the AC output terminal T3. The switch 14 is controlled by the control device 20. In an inverter power supply mode in which the output voltage of the inverter 13S is output to the AC output terminal T3, the switch 14 is turned on. If the inverter 13S fails in the inverter power supply mode, the switch 14 is turned off. In addition, in a bypass power supply mode in which the AC voltage of the AC power supply is output to the AC output terminal T3, the switch 14 is turned off.

[0032] The inverter 13S is controlled by the control device 20. The inverter 13S converts the DC voltage supplied from the converter 11 or the battery B via the DC line 12 into AC power and outputs it to the AC output terminal T3. The inverter 13 is a well-known device including multiple sets of IGBTs and diodes. The instantaneous value of the AC voltage VIS appearing at the AC node of the inverter 13S is detected by the control device 20. The converter 11 and the inverter 13S correspond to an example of a "second power converter" that converts the AC voltage supplied from the switch 3S (second input switching device) into the AC voltage VIS (second AC voltage).

[0033] The switch 15 is connected between the AC input terminal T1 and a first terminal of the bypass circuit 18S, and is controlled by the control device 20. When the AC power supply is normal, the switch 15 is turned on, and when the AC power supply is interrupted, the switch 15 is turned off.

[0034] Switch 16 is connected between the second terminal of bypass circuit 18S and the second terminal of switch 14 (the terminal on the AC output terminal T3 side), and is controlled by control device 20. In inverter power supply mode, switch 16 is turned off. If inverter 13 fails in inverter power supply mode, switch 16 is turned on. In bypass power supply mode, switch 16 is turned on. Bypass circuit 18S corresponds to one embodiment of a "second bypass circuit."

[0035] Semiconductor switch 17 is connected in parallel to switch 16. Semiconductor switch 17 includes a pair of thyristors connected in anti-parallel to each other and is controlled by control device 20. If inverter 13S fails in inverter power supply mode, semiconductor switch 17 is instantaneously turned on for a predetermined time. The reason for turning on semiconductor switch 17 for only the predetermined time is to prevent semiconductor switch 17 from being damaged by heat generated by current. Switch 14 and the parallel circuit of switch 16 and semiconductor switch 17 constitute a "second switching circuit."

[0036] The voltage detector 28 detects the instantaneous value of the AC voltage VCS appearing in the bypass circuit 18S and provides a signal indicating the detected value to the control device 20. The AC voltage VCS is equal to the AC voltage received at the AC input terminal T1 from the AC power supply. The voltage detector 26 detects the instantaneous value of the AC voltage VOS appearing at the AC output terminal T3 and provides a signal indicating the detected value to the control device 30 of the service UPS 7A.

[0037] The control device 20 controls the switches 10, 14 to 16, the converter 11, the inverter 13S, and the semiconductor switch 17. Fig. 2 shows the configuration of the part of the control device 20 that is related to the control of the inverter 13S.

[0038] During standby operation of the standby UPS 8, the control device 20 controls the inverter 13S to synchronize the phase of the output voltage VIS of the inverter 13S with the phase of the AC voltage VCS of the bypass circuit 18S. By synchronizing the phase of the output voltage VIS of the inverter 13S with the phase of the AC voltage VCS of the bypass circuit 18S, it becomes possible to switch from the inverter power supply mode to the bypass power supply mode without momentary interruption if the inverter 13S fails.

[0039] The control device 20 includes a synchronization detection unit 22 and a synchronization control unit 24. The synchronization detection unit 22 generates a free-running signal S1 and a synchronization signal S2 based on the output signal of the voltage detector 28, and outputs the generated signals S1 and S2 to the synchronization control unit 24. The synchronization control unit 24 controls the inverter 13S based on the signals S1 and S2 from the synchronization detection unit 22, thereby adjusting the phase of the AC voltage VIS output from the inverter 13S.

[0040] Furthermore, after system switching of the standby UPS 8 is completed, if it is determined that the phase of the AC voltage VIS output from the inverter 13S is synchronized with the phase of the AC voltage VCS of the bypass circuit 18S, the synchronization control unit 24 generates a synchronization completion signal S4 indicating that synchronization in the standby UPS 8 is completed. The synchronization control unit 24 outputs the generated synchronization completion signal S4 to the control device 30 of the regular UPS 7A via the communication line 6. Control of the inverter 13S by the control device 20 will be described later.

[0041] In addition to an AC input terminal T1, a DC terminal T2, and an AC output terminal T3, the regular UPS 7A includes switches 10, 14 to 16, a converter 11, a DC line 12, an inverter 13A, a semiconductor switch 17, a bypass circuit 18A, a voltage detector 36, and a control device 30. The configuration of the regular UPS 7A differs from the configuration of the standby UPS 8 in that it includes an inverter 13A instead of the inverter 13S, a bypass circuit 18A instead of the bypass circuit 18S, a voltage detector 36 instead of the voltage detectors 26 and 28, and a control device 30 instead of the control device 20.

[0042] The switch 10 is connected between the AC input terminal T1 and the AC node of the converter 11, and is controlled by the control device 30. When the AC power supply (A-system power supply 2A in FIG. 2) connected to the AC input terminal T1 via the switch 3A is normal, the switch 10 is turned on, and an AC voltage is supplied from the AC power supply to the converter 11 via the switch 10. When the AC power supply experiences a power outage, the switch 10 is turned off, and the AC power supply and the converter 11 are disconnected.

[0043] Converter 11 is controlled by control device 30. When the AC power supply is normal, converter 11 converts the AC voltage received at AC input terminal T1 into a DC voltage and outputs it to DC line 12. When the AC power supply fails, control device 30 stops the operation of converter 11.

[0044] The DC line 12 is connected to the DC terminal T2. The battery B stores DC power supplied from the converter 11 via the DC line 12. The DC line 12 is connected to a DC node of the inverter 13A, and an AC node of the inverter 13A is connected to a first terminal of a switch 14. A second terminal of the switch 14 is connected to the AC output terminal T3. The switch 14 is controlled by the control device 30. In an inverter power supply mode in which the output voltage of the inverter 13A is output to the AC output terminal T3, the switch 14 is turned on. If the inverter 13A fails in the inverter power supply mode, the switch 14 is turned off. In addition, in a bypass power supply mode in which the AC voltage of the AC power supply is output to the AC output terminal T3, the switch 14 is turned off.

[0045] Inverter 13A is controlled by control device 30. Inverter 13A converts the DC voltage supplied from converter 11 or battery B via DC line 12 into AC power and outputs it to AC output terminal T3. Converter 11 and inverter 13A correspond to an example of a "first power converter" that converts the AC voltage supplied from switch 3A (first input switching device) into AC voltage VIA (first AC voltage).

[0046] The switch 15 is connected between the AC input terminal T1 and a first terminal of the bypass circuit 18A, and is controlled by the control device 30. When the AC power supply is normal, the switch 15 is turned on, and when the AC power supply is interrupted, the switch 15 is turned off.

[0047] Switch 16 is connected between the second terminal of bypass circuit 18A and the second terminal of switch 14 (the terminal on the AC output terminal T3 side), and is controlled by control device 30. In inverter power supply mode, switch 16 is turned off. If inverter 13A fails in inverter power supply mode, switch 16 is turned on. In bypass power supply mode, switch 16 is also turned on. Bypass circuit 18A corresponds to one embodiment of a "first bypass circuit."

[0048] Semiconductor switch 17 is connected in parallel to switch 16. Semiconductor switch 17 is controlled by control device 30. If inverter 13A fails in inverter power supply mode, semiconductor switch 17 is instantaneously turned on for a predetermined period of time. Switch 14 and the parallel circuit of switch 16 and semiconductor switch 17 constitute a "first switching circuit."

[0049] Voltage detector 36 detects the instantaneous value of AC voltage VCA appearing in bypass circuit 18A and provides a signal indicating the detected value to control device 30. AC voltage VCA is equal to the AC voltage received at AC input terminal T1 from the AC power supply (system A power supply 2A in FIG. 2).

[0050] Control device 30 controls switches 10, 14 to 16, converter 11, inverter 13A, and semiconductor switch 17. Fig. 2 shows the configuration of a portion of control device 30 that is related to the control of inverter 13A.

[0051] During normal operation of the normal UPS 7A, the control device 30 controls the inverter 13A so that the phase of the output voltage VIA of the inverter 13 is synchronized with the phase of the AC voltage VCA of the bypass circuit 18A. By synchronizing the phase of the output voltage VIA of the inverter 13A with the phase of the AC voltage VCA of the bypass circuit 18A, if the inverter 13A fails, it becomes possible to switch from the inverter power supply mode to the bypass power supply mode without momentary interruption.

[0052] The control device 30 includes a synchronization detection unit 32 and a synchronization control unit 34. The synchronization detection unit 32 generates a free-running signal S5 and synchronization signals S6 and S7 based on the output signals of the voltage detector 36 and the voltage detector 26, and outputs the generated signals S5 to S7 to the synchronization control unit 24. The synchronization control unit 24 controls the inverter 13A based on the signals S5 to S7 from the synchronization detection unit 22 and the synchronization completion signal S4 from the synchronization control unit 24, thereby adjusting the phase of the AC voltage VIA output from the inverter 13A. Control of the inverter 13A by the control device 30 will be described later. In the following description, the inverters 13S and 13A may be collectively referred to as the "inverter 13." Furthermore, the bypass circuits 18S and 18A may be collectively referred to as the "bypass circuit 18."

[0053] <System switching> Returning to Fig. 1, in the UPS system 100, system switching may be performed to switch the AC power source to which each UPS is connected in order to perform maintenance inspection of the power transmission line, etc. In the example of Fig. 1, it is assumed that the AC power source to which each UPS is connected is switched from the A system power source 2A to the B system power source 2B in order to perform maintenance inspection of the power transmission line of the A system power source 2A.

[0054] In this system switching, the user of the UPS system 100 or the like performs a switching operation on each of the switches 3S, 3A to 3C. However, while this switching operation is being performed, the input of AC voltage to the AC input terminal T1 of each UPS is temporarily interrupted, causing a temporary power outage of the AC power supply. If this temporary power outage of the AC power supply causes an abnormality in the AC voltage of the bypass circuit 18, each UPS will be unable to synchronize the output voltage of the inverter 13 with the phase of the AC voltage of the bypass circuit 18. Therefore, each UPS will perform free-running operation at a fixed frequency (commercial frequency of 50 Hz or 60 Hz) instead of synchronous operation.

[0055] Then, when the temporary power outage is resolved in response to the completion of the switching operation of the corresponding switch and the restoration of the AC power supply (here, the B-system power supply 2B) is detected, each UPS shifts from independent operation to synchronous operation. In this synchronous operation, the phase of the AC voltage output from the inverter 13 is adjusted so as to be synchronized with the phase of the AC voltage input to the bypass circuit 18 from the B-system power supply 2B after switching.

[0056] However, because the phase of the output voltage of inverter 13 during free-running operation is asynchronous with the phase of the AC voltage of bypass circuit 18 (the voltage of system B power supply 2B), it may take up to about 10 seconds from the time synchronous operation is resumed until synchronization is established between the phase of the output voltage of inverter 13 and the phase of the AC voltage of bypass circuit 18. Because the AC voltage of bypass circuit 18 (i.e., the AC voltage of the AC power supply) and the output voltage of inverter 13 are asynchronous during this time, in the unlikely event of a failure of inverter 13, switching from inverter power supply mode to bypass power supply mode cannot be performed without interruption, raising concerns that this may affect the load.

[0057] To address these concerns, the UPS system 100 according to this embodiment switches the system of the regular UPSs 7A to 7C using the standby UPS 8 that does not contribute to power supply to the load. This shortens the time during which the output voltage of the inverter 13 in the regular UPSs 7A to 7C becomes asynchronous with the AC voltage of the bypass circuit 18 as a result of the system switching.

[0058] Fig. 3 is a block diagram showing the configuration of the control devices 20 and 30 shown in Fig. 2. As shown in Fig. 3, the control device 20 of the standby UPS 8 includes a synchronization detection unit 22 and a synchronization control unit .

[0059] The synchronization detection unit 22 includes a power outage detector 220 and a phase detector 224. The power outage detector 220 determines whether a power outage has occurred in the AC power supply based on the output signal of the voltage detector 28, and generates a free-running signal S1 based on the determination result. For example, if the AC voltage VCS indicated by the output signal of the voltage detector 28 is higher than a predetermined voltage, the power outage detector 220 determines that the AC power supply is healthy and sets the free-running signal S1 to a deactivation level of "L." On the other hand, if the AC voltage VCS indicated by the output signal of the voltage detector 28 is lower than the predetermined voltage, the power outage detector 220 determines that a power outage has occurred in the AC power supply and sets the free-running signal S1 to a deactivation level of "H."

[0060] The phase detector 224 detects the phase of the AC voltage VCS based on the output signal of the voltage detector 28, and generates a synchronization signal S2 that indicates the detected value.

[0061] The synchronization control unit 24 controls the inverter 13 based on the free-running signal S1 and the synchronization signal S2 from the synchronization detection unit 22. Specifically, when the free-running signal S1 is at the "H" level, that is, when a power outage occurs in the AC power supply, the synchronization control unit 24 controls the inverter 13S to perform free-running operation at a fixed frequency (commercial frequency of 50 Hz or 60 Hz).

[0062] On the other hand, when the free-running signal S1 is at the "L" level, i.e., when the AC power supply is healthy, the synchronization control unit 24 adjusts the phase of the AC voltage VIS output from the inverter 13S based on the synchronization signal S2. Specifically, the synchronization control unit 24 includes a PLL (Phase Locked Loop) circuit, and uses the PLL circuit to adjust the phase shift between the AC voltage VCS of the bypass circuit 18S and the AC voltage VIS output from the inverter 13S. The PLL circuit adjusts the phase of the AC voltage VIS output from the inverter 13S to synchronize the phase of the AC voltage VIS with the phase of the AC voltage VCS of the bypass circuit 18S.

[0063] The synchronization control unit 24 receives a switching signal S3 from the switch 3S. The switching signal S3 is normally maintained at an inactive "L" level, and is set to an active "H" level for a predetermined period of time when the switching operation of the switch 3S is performed. When the synchronization control unit 24 determines based on the switching signal S3 that the switching operation of the switch 3S is complete, it determines whether the phase of the AC voltage VIS output from the inverter 13S and the phase of the AC voltage VCS of the bypass circuit 18S are synchronized, and generates a synchronization completion signal S4 based on the determination result.

[0064] Specifically, if it is determined that the phase of the AC voltage VIS output from the inverter 13S and the phase of the AC voltage VCS of the bypass circuit 18S are not synchronized, the synchronization control unit 24 sets the synchronization completion signal S4 to the inactivation level "L." Then, if it is determined that the phase of the AC voltage VIS output from the inverter 13S and the phase of the AC voltage VCS of the bypass circuit 18S are synchronized, the synchronization control unit 24 sets the synchronization completion signal S4 to the activation level "H" for a predetermined period of time. The synchronization control unit 24 outputs the synchronization completion signal S4 to the control device 30 of the regular UPS 7A via the communication line 6.

[0065] The control device 30 of the regular UPS 7A includes a synchronization detection unit 32 and a synchronization control unit .

[0066] The synchronization detection unit 32 includes a power failure detector 320 and phase detectors 324 and 326. The power failure detector 320 determines whether a power failure has occurred in the AC power supply based on the output signal of the voltage detector 36, and generates a free-running signal S5 based on the determination result. For example, if the AC voltage VCA indicated by the output signal of the voltage detector 36 is higher than a predetermined voltage, the power failure detector 320 determines that the AC power supply is healthy and sets the free-running signal S5 to a deactivation level of "L." On the other hand, if the AC voltage VCA indicated by the output signal of the voltage detector 36 is lower than the predetermined voltage, the power failure detector 320 determines that a power failure has occurred in the AC power supply and sets the free-running signal S5 to a deactivation level of "H."

[0067] The phase detector 324 detects the phase of the AC voltage VCA based on the output signal of the voltage detector 36, and generates a synchronization signal S6 that indicates the detected value.

[0068] The phase detector 326 detects the phase of the AC voltage VOS appearing at the AC output terminal T3 of the standby UPS 8 based on the output signal of the voltage detector 26, and generates a synchronization signal S7 indicating the detected value.

[0069] The synchronization control unit 34 controls the inverter 13A based on the free-running signal S5 and synchronization signals S6 and S7 provided by the synchronization detection unit 32, and the synchronization completion signal S4 provided by the synchronization control unit 24.

[0070] Specifically, when the synchronization completion signal S4 provided from the synchronization control unit 34 is at the "L" level, that is, when system switching has not been performed in the standby UPS 8, or when system switching has been performed in the standby UPS 8 but the phase of the output voltage VIS of the inverter 13A and the phase of the AC voltage VCS of the bypass circuit 18A in the standby UPS 8 are not synchronized, the synchronization control unit 34 controls the inverter 13A based on the free-running signal S5 and the synchronization signal S6.

[0071] At this time, if the free-running signal S5 is at "H" level, i.e., if a power outage has occurred in the AC power supply, the synchronization control unit 34 controls the inverter 13A to perform free-running operation at a fixed frequency (commercial frequency of 50 Hz or 60 Hz). On the other hand, if the free-running signal S5 is at "L" level, i.e., if the AC power supply is healthy, the synchronization control unit 34 adjusts the phase of the AC voltage VIA output from the inverter 13A based on the synchronization signal S6.

[0072] Specifically, synchronization control unit 34 includes a PLL circuit and uses the PLL circuit to adjust the phase shift between AC voltage VCA of bypass circuit 18A and AC voltage VIA output from inverter 13A. The PLL circuit adjusts the phase of AC voltage VIA output from inverter 13A to synchronize the phase of AC voltage VIA with the phase of AC voltage VCA of bypass circuit 18A.

[0073] On the other hand, when the synchronization completion signal S4 provided from the synchronization control unit 24 changes from the "L" level to the "H" level, that is, when synchronization between the phase of the output voltage VIS of the inverter 13S and the phase of the AC voltage VCS of the bypass circuit 18S is ensured after the system switching in the standby UPS 8 is completed, the synchronization control unit 34 adjusts the phase of the AC voltage VIA output from the inverter 13A based on the synchronization signal S7.

[0074] Specifically, the synchronization control unit 34 adjusts the phase shift between the AC voltage VOS appearing at the AC output terminal T3 of the backup UPS 8 and the AC voltage VIA output from the inverter 13A using a PLL circuit. The PLL circuit adjusts the phase of the AC voltage VIA output from the inverter 13A to synchronize the phase of the AC voltage VIA with the phase of the AC voltage VOS output from the backup UPS 8.

[0075] The synchronization control unit 34 receives a switching signal S8 from the switch 3A. The switching signal S8 is normally maintained at a deactivation level of "L" and is set to an activation level of "H" for a predetermined period of time when the switching operation of the switch 3A is performed. When the synchronization control unit 34 determines that the switching operation of the switch 3A is complete based on the switching signal S8, it again controls the inverter 13A based on the free-running signal S5 and the synchronization signal S6. In response to the completion of system switching of the service UPS 7A, the synchronization control unit 34 synchronizes the phase of the AC voltage VIA output from the inverter 13A with the phase of the AC voltage VCA of the bypass circuit 18A.

[0076] Next, the operation of each UPS during system switching will be described with reference to FIGS. Fig. 4 is a time chart for explaining the operation of each UPS when switching systems, showing the AC power supplies to which the standby UPS 8 and the regular UPS 7A are connected, and the operating and synchronized states of each UPS.

[0077] As shown in Fig. 4, at time t1 before the system switching, the backup UPS 8 and the regular UPS 7A are connected to the A-system power supply 2A by the switches 3S and 3A, respectively. Fig. 5(A) shows the backup UPS 8 and the regular UPS 7A at time t1.

[0078] When the A-system power supply 2A is healthy, the backup UPS 8 converts the AC power supplied from the A-system power supply 2A into DC power, uses that DC power to charge the battery B, and also converts it back into AC power, which is then output to the AC output terminal T3.

[0079] The control device 20 of the standby UPS 8 synchronizes the phase of the output voltage VIS of the inverter 13S with the phase of the AC voltage VCS of the bypass circuit 18S. Specifically, the synchronization control unit 24 controls the inverter 13S based on the synchronization signal S2 from the synchronization detection unit 22. The phase of the AC voltage VIS output from the inverter 13S is adjusted so as to be synchronized with the phase of the AC voltage VCS input from the A system power supply 2A to the bypass circuit 18S (i.e., the AC voltage of the A system power supply 2A).

[0080] When the A-system power supply 2A is operating normally, the normal UPS 7A converts the AC power supplied from the A-system power supply 2A into DC power, uses that DC power to charge the battery B, and also converts it back into AC power, which is then supplied to the load 5A via the AC output terminal T3 and the switch 4A.

[0081] The control device 30 of the normal UPS 7A synchronizes the phase of the output voltage VIA of the inverter 13A with the phase of the AC voltage VCA of the bypass circuit 18A. Specifically, the synchronization control unit 34 controls the inverter 13A based on the synchronization signal S6 from the synchronization detection unit 32. The phase of the AC voltage VIA output from the inverter 13A is adjusted so as to be synchronized with the phase of the AC voltage VIA input from the A system power supply 2A to the bypass circuit 18A (i.e., the AC voltage of the A system power supply 2A).

[0082] When the UPS system 100 switches between systems, the standby UPS 8 is switched first at time t2. When a user of the UPS system 100 or the like performs a switching operation on the switch 3S, this switching operation causes a temporary power outage of the AC power supply in the standby UPS 8. When the AC power supply has been powered down, the synchronization control unit 24 of the control device 20 controls the inverter 13S to perform free-running operation at a fixed frequency (commercial frequency of 50 Hz or 60 Hz) based on the free-running signal S1 of "H" level from the synchronization detection unit 22. During free-running operation, the phase of the output voltage VIS of the inverter 13S becomes asynchronous with the phase of the AC voltage VCS of the bypass circuit 18S.

[0083] At time t3, when the switching operation of the switch 3S is completed and the standby UPS 8 is connected to the B-system power supply 2B, the control device 20 again synchronizes the phase of the output voltage VIS of the inverter 13S with the phase of the AC voltage VCS of the bypass circuit 18S (i.e., the AC voltage of the B-system power supply 2B). Figure 5(B) shows the standby UPS 8 and the regular UPS 7A at time t3. In the standby UPS 8, the synchronization control unit 24 controls the inverter 13S based on the synchronization signal S2 from the synchronization detection unit 22.

[0084] Since the phase of the output voltage VIS of the inverter 13S during free-running operation is asynchronous with the phase of the AC voltage VCS of the bypass circuit 18S (the AC voltage of the B-system power supply 2B), it may take up to about 10 seconds from the time t3 when synchronous operation is resumed until the phase of the output voltage VIS of the inverter 13S and the phase of the AC voltage VCS of the bypass circuit 18S are synchronized.

[0085] Thus, in the standby UPS 8, the output voltage VIS of the inverter 13S and the AC voltage VCS of the bypass circuit 18S (AC voltage of the AC power supply) are asynchronous from time t2 when a power outage occurs in the AC power supply due to system switching until time t4 when synchronization between the phase of the output voltage VIS of the inverter 13S and the phase of the AC voltage VCS of the bypass circuit 18S is ensured after the system switching is completed (corresponding to T1 in the diagram). However, because the standby UPS 8 is in standby operation and is not supplying power to the load 5A, it is considered unlikely that this asynchronous period will affect the load 5A.

[0086] At time t4, when synchronization is established between the phase of the output voltage VIS of the inverter 13S in the standby UPS 8 and the phase of the AC voltage VCS (AC voltage of the B-system power supply 2B) of the bypass circuit 18S, the synchronization control unit 24 transmits an "H" level synchronization completion signal S4 to the control device 30 of the regular UPS 7A.

[0087] In the normal UPS 7A, when the control device 30 receives an "H" level synchronization completion signal S4 from the control device 20 of the standby UPS 8, it starts synchronous operation to synchronize the phase of the output voltage VIA of the inverter 13A with the phase of the AC voltage VOS output from the standby UPS 8. The phase of the AC voltage VOC output from the standby UPS 8 is synchronized with the phase of the AC voltage VCS of the bypass circuit 18S, i.e., the phase of the AC voltage of the B-system power supply 2B.

[0088] 6(C) shows the backup UPS 8 and the regular UPS 7A at time t4. The synchronization control unit 34 controls the inverter 13A based on the synchronization signal S7 from the synchronization detection unit 32. This adjusts the phase of the AC voltage VIA output from the inverter 13A so that it is synchronized with the phase of the AC voltage VOS (i.e., the AC voltage of the B-system power supply 2B) appearing at the AC output terminal T3 of the backup UPS 8.

[0089] Here, because both the A-system power supply 2A and the B-system power supply 2B are connected to the higher-level system 1, the AC voltage of the A-system power supply 2A and the AC voltage of the B-system power supply 2B are ideally in phase. However, due to differences in the loads connected to each AC power supply, there may be a slight phase difference between the AC voltage of the A-system power supply 2A and the AC voltage of the B-system power supply 2B.

[0090] In such a case, at time t4, the synchronization target of the output voltage VIA of the inverter 13A is switched from the AC voltage VCS of the bypass circuit 18A (the AC voltage of the A-system power supply 2A) to the output voltage VOS of the backup UPS 8 (the AC voltage of the B-system power supply 2B), resulting in a period of time during which the phase of the output voltage VIA of the inverter 13A and the phase of the output voltage VOS of the backup UPS 8 are asynchronous.

[0091] However, the phase difference between the AC voltage of the A-system power supply 2A and the AC voltage of the B-system power supply 2B is usually smaller than the phase difference between the output voltage of the inverter 13A and the AC voltage of the B-system power supply 2B when free-running operation at a fixed frequency is performed. Therefore, the time from time t4 to time t5 when synchronization is ensured between the phase of the output voltage VIA of the inverter 13A and the phase of the output voltage VOS of the backup UPS 8 (corresponding to T2 in the figure) is approximately 1 to 3 seconds, which is shorter than the time T1 when the phase of the output voltage VIS of the inverter 13S in the backup UPS 8 becomes asynchronous with the phase of the AC voltage VCS of the bypass circuit.

[0092] Next, at time t6, the system of the regular UPS 7A is switched while the phase of the output voltage VIA of the inverter 13A is synchronized with the phase of the output voltage VOS of the backup UPS 8. When a user of the UPS system 100 or the like performs a switching operation of the switch 3A, this switching operation causes a temporary power outage of the AC power supply in the regular UPS 7A.

[0093] However, the synchronization control unit 34 continues to control the inverter 13A based on the synchronization signal S7 from the synchronization detection unit 32. As a result, even after time t6, the inverter 13A does not perform free-running operation, but outputs the AC voltage VIA synchronized with the phase of the output voltage VOS of the standby UPS 8 (the AC voltage of the B-system power supply 2B).

[0094] When the switching operation of the switch 3A is completed at time t7, the synchronization control unit 34 again controls the inverter 13A based on the synchronization signal S6. FIG. 6(D) shows the backup UPS 8 and the main UPS 7A at time t7. The synchronization control unit 34 synchronizes the phase of the AC voltage VIA output from the inverter 13A with the phase of the AC voltage VCA of the bypass circuit 18A (i.e., the AC voltage of the B-system power supply 2B). As shown in FIG. 4, around time t7, the phase of the AC voltage VIA output from the inverter 13A is synchronized with the phase of the AC voltage of the B-system power supply 2B. Therefore, there is no time after time t7 when the phase of the output voltage VIA of the inverter 13A is out of phase with the phase of the AC voltage VCA of the bypass circuit 18A.

[0095] In addition, in the normal UPSs 7B and 7C, system switching is also performed during synchronous operation in which the phase of the output voltage of the inverter 13 is synchronized with the phase of the output voltage VOS of the standby UPS 8. In this way, the time during which the phase of the output voltage of the inverter 13 becomes asynchronous with the AC voltage of the AC power supply can be shortened in the normal UPSs 7B and 7C due to system switching.

[0096] As described above, in this embodiment, when switching systems in the UPS system 100 including the standby UPS 8 and the regular UPS 7, the standby UPS 8 is switched first, and the regular UPS 7 performs synchronous operation to synchronize the phase of the output voltage of the inverter 13 of the regular UPS 7 with the phase of the output voltage VOS of the standby UPS 8 after the system switching is completed. Then, when the phase of the output voltage of the inverter 13 of the regular UPS 7 is synchronized with the phase of the output voltage VOS of the standby UPS 8, the regular UPS 7 is switched.

[0097] According to this, in the service UPS 7, the time during which the phase of the output voltage of the inverter 13 becomes asynchronous with the phase of the AC voltage of the AC power supply corresponds to the phase difference between the AC voltage of the A-system power supply 2A and the AC voltage of the B-system power supply 2B. With this configuration, the time during which the phase of the output voltage of the inverter 13 becomes asynchronous with the phase of the AC voltage of the AC power supply due to system switching can be shortened compared to a configuration in which the phase of the output voltage of the inverter 13 is synchronized with the phase of the AC voltage after system switching from free-running operation due to a temporary power outage at system switching. Therefore, the reliability of load power supply by the service UPS 7 at system switching can be improved.

[0098] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The present invention is defined by the claims rather than the above description, and it is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0099] 1 Upper system, 2A A system power supply, 2B B system power supply, 3A to 3C, 3S, 4A to 4C, 10, 14 to 16 Switch, 5A to 5C Load, 6 Communication line, 7A to 7C Regular UPS, 8 Standby UPS, 11 Converter, 12 DC line, 13A, 13S Inverter, 17 Semiconductor switch, 18A, 18S Bypass circuit, 20, 30 Control device, 22, 32 Synchronous detection unit, 24, 34 Synchronous control unit, 26, 28, 36 Voltage detector, 100 UPS system, 220, 320 Power outage detector, 224, 324, 326 Phase detector, B Battery, T1 AC input terminal, T2 DC terminal, T3 AC output terminal.

Claims

1. An uninterruptible power supply (UPS) system connected between an AC power supply and a load, the AC power supply including a first power supply and a second power supply connected to a higher-level system; Regular UPS and A spare UPS and a first input switching device for connecting the service UPS to either the first power source or the second power source; a second input switching device for connecting the standby UPS to either the first power source or the second power source; an output switching device for connecting either the regular UPS or the standby UPS to the load, The commonly used UPS is a first power converter that converts the AC voltage supplied from the first input switching device into a first AC voltage; a first bypass circuit connected in parallel with the first power converter between the first input switching device and the output switching device; a first switching circuit for outputting either the first AC voltage of the first power converter or the AC voltage of the first bypass circuit to the output switching device; The backup UPS is a second power converter that converts the AC voltage supplied from the second input switching device into a second AC voltage; a second bypass circuit connected in parallel with the second power converter between the second input switching device and the output switching device; a second switching circuit for outputting either the second AC voltage of the second power converter or the AC voltage of the second bypass circuit to the output switching device; When the service UPS and the backup UPS are connected to the first power source and the service UPS is connected to the load, the first power converter performs a first synchronous operation in which a phase of the first AC voltage is synchronized with a phase of an AC voltage of the first bypass circuit; the second power converter performs a second synchronous operation in which a phase of the second AC voltage is synchronized with a phase of the AC voltage of the second bypass circuit; When the connection destination of the regular UPS and the standby UPS is switched from the first power source to the second power source, the second input switching device performs a switching operation to change the connection destination of the standby UPS from the first power source to the second power source; the second power converter performs a free-running operation at a fixed frequency in response to a temporary abnormality in the AC voltage of the second bypass circuit during a switching operation of the second input switching device, and after the switching operation, transitions from the free-running operation to the second synchronous operation; the first power converter transitions from the first synchronous operation to a third synchronous operation in which the phase of the first AC voltage is synchronized with the phase of the AC voltage of the second bypass circuit in the second synchronous operation after the switching operation of the second input switching device, and The UPS system is configured such that the first input switching device performs a switching operation to change the connection destination of the regular UPS from the first power source to the second power source while the third synchronous operation is being performed.

2. 2. The UPS system according to claim 1, wherein the first power converter shifts from the third synchronous operation to the first synchronous operation after the switching operation of the first input switching device.

3. the first switching circuit outputs the first AC voltage to the output switching device when the first power converter is normal, and outputs the AC voltage of the first bypass circuit to the output switching device when the first power converter fails; the second switching circuit outputs the second AC voltage to the output switching device when the second power converter is normal, and outputs the AC voltage of the second bypass circuit to the output switching device when the second power converter fails; 3. The UPS system according to claim 1, wherein the output switching device connects the service UPS to the load when the service UPS is normal, and connects the spare UPS to the load when the service UPS fails.

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