Uninterruptible power supply system

Abstract

To provide an uninterruptible power supply system capable of responding to a request to reduce AC power received from an AC power supply.SOLUTION: An uninterruptible power supply device U1 in an uninterruptible power supply system converts AC power from an AC power supply 2 into DC power and stores the DC power in a battery B1 during a normal operation mode, and converts DC power of the battery B1 into AC power and supplies the AC power to an uninterruptible power supply device U2 during a regeneration operation mode. The uninterruptible power supply device U2 drives a load 3 using AC power supplied from the AC power supply 2 and the uninterruptible power supply device U1. Therefore, by causing the uninterruptible power supply device U1 to execute the regeneration operation mode, it is possible to respond to a request to reduce AC power received from the AC power supply 2.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present disclosure relates to an uninterruptible power supply system, and more particularly to an uninterruptible power supply system including a plurality of uninterruptible power supply devices. [Background technology]

[0002] For example, Japanese Patent Application Laid-Open Publication No. 2020-5410 (Patent Document 1) discloses an uninterruptible power supply system including multiple uninterruptible power supplies. The multiple uninterruptible power supplies are connected in parallel between an AC power source and a load. The appropriate number of operating units required to supply the load current is determined, and the appropriate number of operating uninterruptible power supplies among the multiple uninterruptible power supplies are put into operation to supply the load current, while the remaining uninterruptible power supplies are put into standby mode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-5410 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, conventional uninterruptible power supply systems have to constantly receive AC power equivalent to the power consumption of the load from the AC power source, and there has been a problem in that even if there is a request to reduce the AC power received from the AC power source (for example, peak cutting), it is not possible to meet this request.

[0005] Therefore, a main object of the present disclosure is to provide an uninterruptible power supply system that can meet the demand for reducing AC power received from an AC power supply. [Means for solving the problem]

[0006] The uninterruptible power supply system according to the present disclosure includes a first uninterruptible power supply device including a first input terminal and a first output terminal, and a second uninterruptible power supply device including a second input terminal and a second output terminal, the first and second input terminals being connected to each other to receive AC power from an AC power source, and the second output terminal being connected to a load.

[0007] The first uninterruptible power supply executes an operation mode selected from a normal operation mode in which, when the AC power supply is normal, the first uninterruptible power supply converts AC power received at a first input terminal into DC power and uses the DC power to charge the first power storage device and generate AC power to output to the first output terminal, and a regenerative operation mode in which the first uninterruptible power supply converts DC power from the first power storage device into AC power and outputs it to the first input terminal. Furthermore, when the AC power supply fails, the first uninterruptible power supply converts DC power from the first power storage device into AC power and outputs it to the first output terminal.

[0008] When the AC power supply is normal, the second uninterruptible power supply converts AC power received at a second input terminal from the AC power supply and the first uninterruptible power supply into DC power, charges the second power storage device using the DC power, and generates AC power to output to a second output terminal. Furthermore, when the AC power supply is out of service, the second uninterruptible power supply converts DC power from the second power storage device into AC power and outputs it to the second output terminal. [Effects of the Invention]

[0009] In the uninterruptible power supply system according to the present disclosure, in a normal operation mode, a first uninterruptible power supply converts AC power from an AC power source into DC power and stores it in a first power storage device, and in a regenerative operation mode, converts the DC power from the first power storage device into AC power and supplies it to a second uninterruptible power supply. The second uninterruptible power supply drives a load using the AC power source and the AC power supplied from the first uninterruptible power supply. Therefore, by operating the first uninterruptible power supply in the regenerative operation mode, it is possible to meet the demand for reducing the AC power received from the AC power source. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a circuit block diagram showing an overall configuration of an uninterruptible power supply system according to a first embodiment of the present disclosure. [Figure 2] 2 is a circuit block diagram showing the configuration of the uninterruptible power supply device shown in FIG. 1. FIG. [Figure 3] FIG. 3 is a block diagram showing the configuration of the control device shown in FIG. 2. [Figure 4] 4 is a block diagram showing the configuration of a portion of the control circuit shown in FIG. 3 that is related to converter control. FIG. [Figure 5] 4 is a block diagram showing the configuration of a portion of the control circuit shown in FIG. 3 that is related to the control of the bidirectional chopper. FIG. [Figure 6] 4 is a block diagram showing the configuration of a portion of the control circuit shown in FIG. 3 that is related to inverter control. FIG. [Figure 7] 4 is a block diagram showing the configuration of a portion of the control circuit shown in FIG. 3 that is related to switch control. FIG. [Figure 8] 8 is a circuit block diagram showing the operation of the uninterruptible power supply system shown in FIGS. 1 to 7. FIG. [Figure 9] 8 is a circuit block diagram showing another operation of the uninterruptible power supply system shown in FIGS. 1 to 7. FIG. [Figure 10] 8 is a circuit block diagram showing still another operation of the uninterruptible power supply system shown in FIGS. 1 to 7. FIG. [Figure 11] 8 is a circuit block diagram showing still another operation of the uninterruptible power supply system shown in FIGS. 1 to 7. FIG. [Figure 12] 3 is a waveform diagram showing the operation of the uninterruptible power supply U shown in FIG. 2. [Figure 13] 13 is a time chart for explaining the effect of the uninterruptible power supply system shown in FIGS. 1 to 12. [Figure 14] FIG. 10 is a circuit block diagram showing a main part of an uninterruptible power supply system according to a second embodiment of the present disclosure. [Figure 15] FIG. 11 is a circuit block diagram showing an overall configuration of an uninterruptible power supply system according to a third embodiment of the present disclosure. [Figure 16]FIG. 16 is a block diagram showing a main part of the uninterruptible power supply shown in FIG. [Figure 17] FIG. 17 is a circuit block diagram showing the operation of the uninterruptible power supply system shown in FIGS. 15 and 16. [Figure 18] FIG. 17 is a circuit block diagram showing another operation of the uninterruptible power supply system shown in FIGS. 15 and 16. [Figure 19] FIG. 17 is a circuit block diagram showing still another operation of the uninterruptible power supply system shown in FIGS. 15 and 16. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Embodiment 1] Figure 1 is a circuit block diagram showing the overall configuration of an uninterruptible power supply system according to a first embodiment of the present disclosure. In Figure 1, the uninterruptible power supply system includes multiple (two in the figure) uninterruptible power supply devices U1 and U2. Each of the uninterruptible power supply devices U1 and U2 includes a bypass terminal T1, an AC input terminal T2, a DC terminal T3, and an AC output terminal T4.

[0012] A bypass terminal T1 of the uninterruptible power supply U1 (first uninterruptible power supply) receives AC power of a predetermined frequency (for example, commercial frequency) from a bypass AC power supply 1. The AC input terminals T2 of the uninterruptible power supplies U1 and U2 are connected to each other and receive AC power of a predetermined frequency (for example, commercial frequency) from an AC power supply 2. Each of the AC power supplies 1 and 2 may be a commercial AC power supply or a private generator. Both the AC power supplies 1 and 2 may be commercial AC power supplies.

[0013] The DC terminals T3 of the uninterruptible power supplies U1 and U2 are connected to batteries B1 and B2, respectively. The batteries B1 and B2 store DC power. Capacitors may be connected instead of the batteries.

[0014] Although the uninterruptible power supply U1 and the uninterruptible power supply U2 have the same configuration, in the present embodiment 1, the uninterruptible power supply U1 is used as a backup device and the uninterruptible power supply U2 is used as a power supply device. The configurations of the uninterruptible power supplies U1 and U2 will be described later.

[0015] An AC output terminal T4 (first output terminal) of the uninterruptible power supply U1 is connected to a bypass terminal T1 of the uninterruptible power supply U2. An AC output terminal T4 (second output terminal) of the uninterruptible power supply U2 (second uninterruptible power supply) is connected to a load 3. The load 3 is driven by AC power supplied from the uninterruptible power supply U2.

[0016] The uninterruptible power supply U1 and the uninterruptible power supply U2 are connected to each other by a communication line 4. The uninterruptible power supplies U1 and U2 exchange various information via the communication line 4. For example, the uninterruptible power supply U2 transmits information indicating the AC power being supplied to the load 3 to the uninterruptible power supply U1 via the communication line 4.

[0017] The communication line 4 is also connected to a central control room 5. When AC power is being supplied normally from the AC power source 2 (when the AC power source 2 is healthy), and when the central control room 5 wants to reduce the AC power that the uninterruptible power supply system receives from the AC power source 2 (for example, during peak cutting), the central control room 5 generates a regeneration command signal CMD and sends it to the uninterruptible power supplies U1 and U2 via the communication line 4.

[0018] In the first embodiment, the uninterruptible power supply U1 used as a standby device operates in accordance with the regeneration command signal CMD, and the uninterruptible power supply U2 used as a power supply device does not operate in accordance with the regeneration command signal CMD.

[0019] When the uninterruptible power supply U1 does not receive a regeneration command signal CMD while the AC power supply 2 is healthy, it executes a normal operation mode, converts AC power supplied from the AC power supply 2 via an AC input terminal T2 (first input terminal) into DC power, uses the DC power to charge a battery B1 (first power storage device), and generates AC power of a predetermined frequency (for example, a commercial frequency), which is output to the bypass terminal T1 of the uninterruptible power supply U2 via an AC output terminal T4.

[0020] Furthermore, when the uninterruptible power supply U1 receives a regeneration command signal CMD while the AC power supply 2 is healthy, it executes a regeneration operation mode for a predetermined time Td (for example, 10 minutes), converts the DC power of the battery B1 into AC power of a predetermined frequency (for example, commercial frequency), and outputs the AC power to the AC input terminal T2.

[0021] At this time, uninterruptible power supply U1 outputs to AC input terminal T2 AC power of a value corresponding to the power consumption of load 3 indicated by information provided from uninterruptible power supply U2 via communication line 4. This AC power is supplied to AC input terminal T2 of uninterruptible power supply U2.

[0022] Uninterruptible power supply U2 converts the AC power supplied from uninterruptible power supply U1 into DC power, uses the DC power to charge battery B2 (second power storage device), and also generates AC power of a predetermined frequency (for example, commercial frequency), which is supplied to load 3 via AC output terminal T4. Therefore, the AC power that the uninterruptible power supply system receives from AC power supply 2 is reduced, and peak cutting is achieved.

[0023] After the regenerative operation mode ends, the uninterruptible power supply U1 executes the charge stop operation mode until a predetermined time ts, converts the AC power supplied from the AC power supply 2 via the AC input terminal T2 into DC power, uses the DC power to generate AC power of a predetermined frequency, and outputs the AC power to the bypass terminal T1 of the uninterruptible power supply U2 via the AC output terminal T4.

[0024] The uninterruptible power supply U1 does not charge battery B1 in charge stop mode, and after charge stop mode ends, it operates in normal operation mode. When normal operation mode is resumed, the AC power received from AC power source 2 increases until the terminal voltage VB of battery B1 returns to the reference DC voltage VBR. However, by resuming normal operation mode at night when electricity rates are low, electricity rates can be reduced. This technique is called peak shifting.

[0025] Furthermore, when the supply of AC power from the AC power supply 2 is stopped (during a power outage of the AC power supply 2), the uninterruptible power supply U1 converts the DC power of the battery B1 into AC power of a predetermined frequency (for example, a commercial frequency) and outputs it to the AC output terminal T4.

[0026] Furthermore, if the inverter of the uninterruptible power supply U1 that converts DC power to AC power fails, the uninterruptible power supply U1 connects the bypass terminal T1 to the AC output terminal T4, and supplies AC power supplied from the bypass AC power supply U1 to the bypass terminal T1 of the uninterruptible power supply U2 via the AC output terminal T4. The inverter will be described later.

[0027] The uninterruptible power supply U2 does not respond to the regeneration command signal CMD, and when the AC power supply 2 is normal, converts the AC power supplied from the AC power supply 2 and the uninterruptible power supply U1 via the AC input terminal T2 into DC power, uses the DC power to charge the battery B2 (second power storage device), and also generates AC power of a predetermined frequency (for example, the commercial frequency), which is supplied to the load 3 via the output terminal T4.

[0028] Furthermore, when a power outage occurs in the AC power supply 2, the uninterruptible power supply U2 converts the DC power of the battery B2 into AC power of a predetermined frequency (for example, a commercial frequency) and supplies the AC power to the load 3 via the AC output terminal T4. Therefore, even when a power outage occurs in the AC power supply 2, the operation of the load 3 can be continued.

[0029] Furthermore, if the inverter in the uninterruptible power supply U2 that converts DC power to AC power fails, the uninterruptible power supply U2 connects the bypass terminal T1 to the AC output terminal T4, and supplies the AC power supplied from the uninterruptible power supply U1 to the load 3 via the AC output terminal T4. The inverter will be described later.

[0030] Fig. 2 is a circuit block diagram showing the configuration of the uninterruptible power supply U shown in Fig. 1. In this disclosure, the uninterruptible power supplies U1 and U2 may be representatively and collectively referred to as the uninterruptible power supply U. Furthermore, the batteries B1 and B2 may be representatively and collectively referred to as the battery B.

[0031] 2, the uninterruptible power supply U includes a bypass terminal T1, an AC input terminal T2, a DC terminal T3, and an AC output terminal T4, as well as switches S1 to S4, a converter 11, current detectors CD1 to CD4, a DC line 12, capacitors 13 and 16, a bidirectional chopper 14, an inverter 15, a semiconductor switch 17, an operation unit 18, and a control device 19. A battery B is connected to the DC terminal T3.

[0032] The switch S1 is connected between the AC input terminal T2 and the AC node of the converter 11, and is controlled by the control device 19. When the AC power supply 2 is normal, the switch S1 is turned on, and AC power is supplied from the AC power supply 2 to the converter 11 via the switch S1. When the AC power supply 2 experiences a power outage, the switch S1 is turned off, and the AC power supply 2 and the converter 11 are disconnected.

[0033] The instantaneous value of the AC input voltage Vi supplied from the AC power supply 2 is detected by the control device 19. Based on the instantaneous value of the AC input voltage Vi, the control device 19 determines whether the AC voltage Vi is being normally supplied from the AC power supply 2. The current detector CD1 detects the AC input current Ii flowing between the AC power supply 2 and the converter 11, and provides the control device 19 with a signal Iif indicating the detected value.

[0034] Converter 11 is controlled by control device 19. During AC-DC conversion operation, converter 11 converts AC power received at AC input terminal T2 into DC power and outputs it to DC line 12. During DC-AC conversion operation, converter 11 converts DC power received at DC line 12 into AC power and outputs it to AC input terminal T2. Converter 11 is a well-known device that includes multiple sets of IGBTs (Insulated Gate Bipolar Transistors) and diodes.

[0035] The capacitor 6 is connected to the DC line 12 and smooths and stabilizes the DC voltage VD of the DC line 12. The instantaneous value of the DC voltage VD of the DC line 12 is detected by the control device 19.

[0036] When the uninterruptible power supply U is set as a standby device, the control device 19 controls the converter 11 in accordance with the regeneration command signal CMD. That is, in a normal operation mode in which the regeneration command signal CMD is not received while the AC power supply 2 is normal, the control device 19 controls the converter 11 to perform AC-DC conversion operation so that the DC voltage VD of the DC line 12 becomes the reference DC voltage VDR.

[0037] Furthermore, in a regeneration operation mode in which a regeneration command signal CMD is received when the AC power supply 2 is healthy, the control device 19 controls the converter 11 to perform a DC-AC conversion operation and to output a predetermined AC power from the converter 11 to the AC input terminal T2.

[0038] At this time, the control device 19 transmits and receives information to the other uninterruptible power supply devices U via the communication line 4, and determines the value of the AC power that the uninterruptible power supply system is supplying to the load 3 based on the information from the uninterruptible power supply device U. The control device 19 then controls the converter 11 so that the determined value of AC power is output from the converter 11 to the AC input terminal T2. When a power outage occurs in the AC power source 2, the control device 19 stops the operation of the converter 11.

[0039] Furthermore, when the uninterruptible power supply U is set as a power supply device, the control device 19 controls the converter 11 regardless of the regeneration command signal CMD. That is, when the AC power supply 2 is normal, the control device 19 controls the converter 11 to perform AC-DC conversion operation so that the DC voltage VD of the DC line 12 becomes the reference DC voltage VDR. When the AC power supply 2 experiences a power outage, the control device 19 stops the operation of the converter 11.

[0040] The DC line 12 is connected to the DC terminal T3 via the bidirectional chopper 14 and the switch S2. The switch S2 is controlled by the control device 19. When the uninterruptible power supply U is used, the switch S2 is turned on. When maintenance of the battery B and the bidirectional chopper 14 is performed, the switch S2 is turned off.

[0041] The instantaneous value of the voltage VB between the terminals of battery B is detected by the control device 19. The current detector CD2 detects the DC current IB flowing between battery B and the bidirectional chopper 14, and provides the control device 19 with a signal IBf indicating the detected value.

[0042] The bidirectional chopper 14 is controlled by a control device 19. During charging operation, the bidirectional chopper 14 stores DC power supplied from the converter 11 via the DC line 12 in the battery B1. During discharging operation, the bidirectional chopper 14 supplies DC power from the battery B to the DC line 12. The bidirectional chopper 14 is a well-known device that includes multiple sets of IGBTs and diodes, and a reactor.

[0043] When the uninterruptible power supply U is set as a standby device, the control device 19 controls the bidirectional chopper 14 in accordance with the regeneration command signal CMD. That is, when the AC power supply 2 is normal and the regeneration command signal CMD is not received, the control device 19 causes the bidirectional chopper 14 to perform a charging operation and causes the battery B1 to store the DC power supplied to the bidirectional chopper 14 from the converter 11 via the DC line 12. At this time, the control device 19 controls the bidirectional chopper 14 so that the battery voltage VB becomes the reference DC voltage VBR.

[0044] Furthermore, when the regeneration command signal CMD is received while the AC power supply 2 is normal, or during a power outage of the AC power supply 2, the control device 19 causes the bidirectional chopper 14 to perform a discharge operation and supplies DC power from the battery B1 to the DC line 12. At this time, the control device 19 controls the bidirectional chopper 14 so that the DC voltage VD of the DC line 12 becomes the reference DC voltage VDR. Furthermore, during a charge stop mode after the regeneration operation mode ends, the control device 19 stops the charging operation of the bidirectional chopper 14.

[0045] Furthermore, when the uninterruptible power supply U is set as a power supply device, the control device 19 controls the bidirectional chopper 14 regardless of the regeneration command signal CMD. That is, when the AC power supply 2 is normal, the control device 19 causes the bidirectional chopper 14 to perform a charging operation and causes the battery B1 to store the DC power supplied to the bidirectional chopper 14 from the converter 11 via the DC line 12. At this time, the control device 19 controls the bidirectional chopper 14 so that the battery voltage VB becomes the reference DC voltage VBR.

[0046] The DC line 12 is connected to a DC node of an inverter 15, the AC node of the inverter 15 is connected to one terminal of a switch S3, and the other terminal of the switch S3 is connected to an AC output terminal T4. A capacitor 16 is connected to one terminal of the switch S3 and removes signals of the switching frequency generated in the inverter 15.

[0047] The switch S3 is controlled by the control device 19. In the inverter power supply mode in which the output voltage of the inverter 15 is output to the output terminal T4, the switch S3 is turned on. If the inverter 15 fails in the inverter power supply mode, the switch S3 is turned off. Furthermore, in the bypass power supply mode in which the AC voltage VI of the bypass AC power supply 1 is output to the output terminal T4, the switch S3 is turned off.

[0048] Current detector CD3 detects AC output current IO of inverter 15 and provides a signal IOf indicating the detected value to control device 19. Current detector CD4 detects current IL flowing through AC output terminal T4 and provides a signal ILf indicating the detected value to control device 19. In addition, the instantaneous value of AC output voltage VO appearing at AC output terminal T4 is detected by control device 19.

[0049] The inverter 15 is controlled by a control device 19. During DC-AC conversion operation, the inverter 15 converts DC power supplied from the converter 11 and the bidirectional chopper 14 via the DC line 12 into AC power of a predetermined frequency (for example, a commercial frequency) and outputs the AC power to an output terminal T4. The inverter 15 is a well-known device that includes multiple sets of IGBTs and diodes.

[0050] When the uninterruptible power supply U is set as a standby device, the control device 19 controls the inverter 15 in accordance with the regeneration command signal CMD. That is, during normal operation when the AC power supply 2 is healthy and no regeneration command signal CMD is received, and during a power outage of the AC power supply 2, the control device 19 causes the inverter 15 to perform DC-AC conversion operation and controls the inverter 15 so that the AC output voltage VO becomes the reference AC voltage VOR of a predetermined frequency. Furthermore, during regeneration operation when the AC power supply 2 is healthy and the regeneration command signal CMD is received, the control device 19 stops the operation of the inverter 15.

[0051] Furthermore, when the uninterruptible power supply U is set as a power supply device, the control device 19 controls the inverter 15 regardless of the regeneration command signal CMD. That is, the control device 19 controls the inverter 15 to perform a DC-AC conversion operation so that the AC output voltage VO becomes the reference AC voltage VOR of a predetermined frequency.

[0052] The switch S4 is connected between the bypass terminal T1 and the other terminal of the switch S3 (the terminal on the AC output terminal T4 side), and is controlled by the control device 19. In the inverter power supply mode in which the output voltage of the inverter 15 is output to the output terminal T4, the switch S4 is turned off. If the inverter 15 fails in the inverter power supply mode, the switch S4 is turned on. Furthermore, in the bypass power supply mode in which the AC voltage VI of the bypass AC power supply 1 is output to the output terminal T4, the switch S4 is turned on.

[0053] Semiconductor switch 17 is connected in parallel to switch S4. Semiconductor switch 17 includes a pair of thyristors connected in anti-parallel to each other, and is controlled by control device 19. If inverter 15 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.

[0054] The operation unit 18 includes a plurality of buttons, a plurality of switches, and an image display unit. By operating the operation unit 18, a user of the uninterruptible power supply U can turn the power of the uninterruptible power supply U on and off, operate the uninterruptible power supply U automatically or manually, and set the uninterruptible power supply U as a standby device or a power supply device.

[0055] Furthermore, the user of the uninterruptible power supply U can set the regeneration rate Rr (%), the time Td for which the regenerative operation mode is executed, and the time ts for canceling the charging stop mode by operating the operation unit 18. The regeneration rate Rr (%) is approximately equal to the ratio of the AC power supplied from the standby device to the power supply device in the regenerative operation mode to the AC power supplied from the power supply device to the load 3. The regeneration rate Rr is set to a desired value between 0% and 100%. The operation unit 18 outputs a signal indicating the content of the operation performed by the user to the control device 19.

[0056] In this embodiment 1, a user of the uninterruptible power supply system operates the operation unit 18 of the uninterruptible power supply U1 to set the uninterruptible power supply U1 as a backup device, and operates the operation unit 18 of the uninterruptible power supply U2 to set the uninterruptible power supply U2 as a power supply device.

[0057] In addition, the user of the uninterruptible power supply system operates the operation unit 18 of the uninterruptible power supply device U1 to set the regeneration rate Rr (%), the execution time Td of the regeneration operation mode, and the time ts at which the charge stop operation mode is released.

[0058] The control device 19 controls the switches S1 to S4, the converter 11, the bidirectional chopper 14, the inverter 15, and the semiconductor switch 17 based on signals from the operation unit 18, the regeneration command signal CMD from the central control room 5, the AC input voltages VI and Vi, the AC output voltage VO, the DC voltage VD, the battery voltage VB, the AC input current Ii, the battery current IB, and the AC output currents IO and IL.

[0059] 3 is a block diagram showing the configuration of the control device 19. In FIG. 3, the control device 19 includes voltage detectors 21-25, reference voltage generators 26-28, a power failure detector 29, a fault detector 30, a communication circuit 31, and a control circuit 32.

[0060] The voltage detector 21 detects the instantaneous value of the AC voltage VI appearing at the bypass terminal T1 and outputs a signal VIf indicating the detected value. The voltage detector 22 detects the instantaneous value of the AC input voltage Vi appearing at the AC input terminal T2 and outputs a signal Vif indicating the detected value.

[0061] Voltage detector 23 detects the instantaneous value of AC output voltage VO appearing at AC output terminal T4 and outputs signal VOf indicating the detected value. Voltage detector 24 detects the instantaneous value of DC voltage VD on DC line 12 and outputs signal VDf indicating the detected value. Voltage detector 25 detects the instantaneous value of voltage VB between the terminals of battery B and outputs signal VBf indicating the detected value.

[0062] The reference voltage generator 26 outputs a reference DC voltage VDR. The reference voltage generator 27 outputs a reference DC voltage VBR. The reference voltage generator 28 outputs a reference AC voltage VOR synchronized with the AC voltage VI indicated by the output signal φVI of the voltage detector 21.

[0063] The power failure detector 29 determines whether a power failure has occurred in the AC power supply 2 based on the output signal Vif of the voltage detector 22, and outputs a signal φ29 indicating the determination result. For example, if the AC input voltage Vi indicated by the output signal Vif of the voltage detector 22 is higher than a predetermined voltage, the power failure detector 29 determines that the AC power supply 2 is healthy and sets the signal φ29 to an inactivation level of "L". Conversely, if the AC input voltage Vi indicated by the output signal Vif of the voltage detector 22 is lower than the predetermined voltage, the power failure detector 29 determines that a power failure has occurred in the AC power supply 2 and sets the signal φ29 to an activation level of "H".

[0064] The fault detector 30 determines whether the inverter 15 has failed and outputs a signal φ30 indicating the determination result. For example, when the inverter 15 is operating normally, the signal φ30 is set to the inactive "L" level. When the inverter 15 has failed, the signal φ30 is set to the active "H" level.

[0065] The communication circuit 31 transmits and receives various signals between the central command room 5, the control circuit 32 of the other devices, and the control circuit 32 of its own device via the communication line 4 (FIG. 1).

[0066] The control circuit 32 controls the switches S1 to S4, the converter 11, the bidirectional chopper 14, the inverter 15, and the semiconductor switch 17 based on the output signals VIf, Vif, VOf, VDf, and VBf of the voltage detectors 21 to 25, the output voltages VDR, VBR, and VOR of the reference voltage generators 26 to 28, the output signal φ29 of the power failure detector 29, the output signal φ30 of the fault detector 30, and a signal from the communication circuit 31.

[0067] Fig. 4 is a block diagram showing the configuration of a portion of control circuit 32 that is related to the control of converter 11. In Fig. 4, control circuit 32 includes a voltage control unit 41, a current control unit 42, a calculation unit 43, a regenerative power command unit 44, a signal generation unit 45, a selector 46, a limiter 47, and a PWM (Pulse Width Modulation) control unit 48.

[0068] The voltage control unit 41 determines the deviation ΔVD=VDR−VD between the reference DC voltage VDR and the DC voltage VD indicated by the signal VDf, and generates the current control value Iic so that the deviation ΔVD is eliminated.

[0069] The current control unit 42 calculates the deviation ΔIi=Iic-Ii between the current control value Iic and the AC input current Ii indicated by the output signal Iif of the current detector CD1, generates a phase control value θc1 so as to eliminate the deviation ΔIi, and provides the phase control value θc1 to the first input terminal 46a of the selector 46.

[0070] Here, the phase control value θc1 will be explained. When the DC voltage VD of the DC line 12 reaches the reference DC voltage VDR, the converter 11 (FIG. 2) converts the DC voltage VD into an AC voltage Vc having the same frequency and amplitude as the AC input voltage Vi, and outputs the AC voltage Vc to the AC input terminal T2. The phase of the AC voltage Vc is controllable.

[0071] When the phase of the AC voltage Vc is made to lead the phase of the AC input voltage Vi, power flows from the DC line 12 to the AC input terminal T2 via the converter 11, and the DC voltage VD of the DC line 12 drops. Conversely, when the phase of the AC voltage Vc is made to lag the phase of the AC input voltage Vi, power flows from the AC input terminal T2 to the DC line 12 via the converter 11, and the DC voltage VD of the DC line 12 rises. Therefore, by adjusting the phase control value θc1, the DC voltage VD of the DC line 12 can be made to coincide with the reference DC voltage VDR.

[0072] Also, from the perspective of the control device 19, the uninterruptible power supply U that includes the control device 19 is referred to as the "own device," and the other uninterruptible power supply U that does not include the control device 19 is referred to as the "other device." The calculation unit 43 calculates the AC output power PL1 of its own device based on the output signal VOf of the voltage detector 23 and the output signal ILf of the current detector CD4, and transmits a signal indicating the calculated AC output power PL1 to the other device via the communication circuit 31 (FIG. 3).

[0073] Furthermore, calculation unit 43 calculates AC output power PL2 being supplied from the uninterruptible power supply system to load 3, based on AC output power PL1 of the device itself and AC output power PL1 of the other device indicated by a signal transmitted from the other device via communication circuit 31. Then, calculation unit 43 calculates AC power PL3 to be output to AC input terminal T2 in the regenerative operation mode, based on the calculated AC output power PL2 and the regeneration rate Rr (%) set using operation unit 18.

[0074] The AC power PL3 is calculated by multiplying the AC output power PL2 by Rr / 100 and adding a loss Pα generated in the power supply device to the multiplied value, and is therefore expressed as PL3=Pα+PL2×Rr / 100.

[0075] The regenerative power command unit 44 generates a phase control value θc2 required to output the AC power PL3 calculated by the calculation unit 43 from the converter 11 to the AC input terminal T2, and supplies the phase control value θc2 to the second input terminal 46b of the selector 46.

[0076] When the device itself is set as a backup device using the operation unit 18, the signal generating unit 45 responds to the regeneration command signal CMD by raising the signal φ45 from the inactivation level “L” to the activation level “H” for the time Td set using the operation unit 18.

[0077] Furthermore, when the device itself is set as a power supply device using the operation unit 18, the signal generating unit 45 maintains the signal φ45 at the inactivation level “L” regardless of the regeneration command signal CMD. The signal φ45 is provided to a control terminal 46c of the selector 46.

[0078] When the signal φ45 is at the inactivation level “L”, the selector 46 establishes conduction between the first input terminal 46a and the output terminal 46d, and provides the phase control value θc1 generated by the current control unit 42 to the limiter 47 as the phase control value θc3.

[0079] Furthermore, when the signal φ45 is at the activated "H" level, the selector 46 connects the second input terminal 46b and the output terminal 46d, and provides the phase control value θc2 generated by the regenerative power command unit 44 to the limiter 47 as the phase control value θc3.

[0080] The limiter 47 limits the phase control value θc3 from the selector 46 to a value between the positive maximum value (+θm) and the negative maximum value (-θm) to generate a phase control value θc4. If θc3<-θm, then θc4=-θm. If -θm≦θc3≦+θm, then θc4=θc3. If +θm<θc3, then θc4=+θm.

[0081] When the output signal φ29 of the power failure detector 29 (FIG. 3) is at the inactivation level “L” (when the AC power supply 2 is healthy), the PWM control unit 48 controls the converter 11 based on the AC input voltage Vi indicated by the output signal Vif of the voltage detector 22 and the phase control value θc4 from the limiter 47.

[0082] The converter 11 generates an AC voltage Vc having the same frequency and amplitude as the AC input voltage Vi and outputs the AC voltage Vc to the AC input terminal T2. The phase of the AC voltage Vc is adjusted in accordance with a phase control value θc4.

[0083] When the phase control value θc4 is a positive value, the phase of the AC voltage Vc is delayed from the phase of the AC input voltage Vi by an angle corresponding to the phase control value θc4, and power is supplied from the AC input terminal T2 to the DC line 12 via the converter 11.

[0084] Conversely, when the phase control value θc4 is a negative value, the phase of the AC voltage Vc is advanced from the phase of the AC input voltage Vi by an angle corresponding to the phase control value θc4, and power is supplied from the DC line 12 to the AC input terminal T2 via the converter 11.

[0085] Furthermore, when the output signal φ29 of the power failure detector 29 is at the "H" level, which is the activation level (when the AC power supply 2 is in a power failure state), the PWM control unit 48 stops the operation of the converter 11.

[0086] 5 is a block diagram showing the configuration of a portion of the control circuit 32 (FIG. 3) that is related to the control of the bidirectional chopper 14. In FIG. 5, the control circuit 32 includes a timer 51, a signal generating unit 52, and a control unit 53.

[0087] The timer 51 outputs a signal φ51 indicating the current time tn. In response to receiving a regeneration command signal CMD from the central control room 5 (FIG. 1) via the communication circuit 31 (FIG. 3), the signal generating unit 52 raises the signal φ52 from an inactive "L" level to an active "H" level.

[0088] Furthermore, the signal generating unit 52 causes the signal φ52 to fall from the activated "H" level to the inactivated "L" level in response to the time tn indicated by the output signal φ51 of the timer 51 reaching the time ts set using the operation unit 18. When the signal φ52 is at the activated "H" level, the charging operation of the bidirectional chopper 14 is stopped. When the signal φ52 is at the inactivated "L" level, the charging operation of the bidirectional chopper 14 is permitted.

[0089] The control unit 53 controls the bidirectional chopper 14 based on a signal from the operation unit 18, the output signal φ52 of the signal generating unit 52, the power failure detector 29 (FIG. 3), the output signal φ45 of the signal generating unit 45 (FIG. 4), the output signals VDf and VBf of the voltage detectors 24 and 25 (FIG. 3), the output voltages VDR and VBR of the reference voltage generators 26 and 27, and the output signal IBf of the current detector CD2 (FIG. 2).

[0090] First, we will explain the operation of the control unit 53 when the device itself is set as a standby device using the operation unit 18. When the AC power supply 2 is healthy (φ29=L) and in the normal operation mode (φ45=L), the control unit 53 controls the bidirectional chopper 14 so that the inter-terminal voltage VB of battery B becomes the reference DC voltage VBR.

[0091] When the AC power supply 2 is healthy (φ29=L) and in the regenerative operation mode (φ45=H), the control unit 53 controls the bidirectional chopper 14 so that the DC voltage VD of the DC line 12 becomes the reference DC voltage VDR.

[0092] When the AC power supply 2 is in a normal state (φ29=L) and in a charge stop mode (φ52=H), the control unit 53 stops the charging operation of the bidirectional chopper 14. When the AC power supply 2 is in a power outage (φ29=H), the control unit 53 controls the bidirectional chopper 14 so that the DC voltage VD of the DC line 12 becomes the reference DC voltage VDR.

[0093] Next, the operation of the control unit 53 when the device itself is set as a power supply device using the operation unit 18 will be described. When the AC power supply 2 is healthy (φ29=L), the control unit 53 controls the bidirectional chopper 14 so that the voltage VB between the terminals of the battery B becomes the reference DC voltage VBR. When the AC power supply 2 is in a power outage (φ29=H), the control unit 53 controls the bidirectional chopper 14 so that the DC voltage VD of the DC line 12 becomes the reference DC voltage VDR. When the device itself is set as a power supply device, the control unit 53 does not execute the regenerative operation mode or the charge stop mode.

[0094] Fig. 6 is a block diagram showing the configuration of a portion of control circuit 32 (Fig. 3) that is related to the control of inverter 15. In Fig. 6, control circuit 32 includes a control unit 55. Control unit 55 controls inverter 15 based on a signal from operation unit 18, signal φ30 from fault detector 30 (Fig. 3), output signal φ45 from signal generating unit 45 (Fig. 4), output signal VOf from voltage detector 23 (Fig. 3), output voltage VOR from reference voltage generator 28, and output signal IOf from current detector CD3 (Fig. 2).

[0095] First, the operation of the control unit 55 when the device itself is set as a standby device using the operation unit 18 will be described. In the normal operation mode (φ45=L) and when the inverter 15 is operating normally (φ30=L), the control unit 55 controls the inverter 15 so that the AC output voltage VO becomes the reference AC voltage VOR. In the regenerative operation mode (φ45=H), the control unit 55 stops the operation of the inverter 15. If the inverter 15 fails (φ30=H), the control unit 55 stops the operation of the inverter 15.

[0096] Next, the operation of the control unit 53 when the device itself is set as a power supply device using the operation unit 18 will be described. When the inverter 15 is operating normally (φ30=L) in the normal operation mode (φ45=L), the control unit 55 controls the inverter 15 so that the AC output voltage VO becomes the reference AC voltage VOR. When the inverter 15 fails (φ30=H), the control unit 55 stops the operation of the inverter 15. When the device itself is set as a power supply device, the control unit 55 does not execute the regenerative operation mode.

[0097] Fig. 7 is a block diagram showing the configuration of the portion of control circuit 32 (Fig. 3) that is related to the control of switches S1 to S4 and 17. In Fig. 7, control circuit 32 includes a control unit 56. Control unit 56 controls switches S1 to S4 and semiconductor switch 17 based on a signal from operation unit 18, a signal φ29 from power failure detector 29 (Fig. 3), and a signal φ30 from failure detector 30 (Fig. 3).

[0098] First, a description will be given of the operation of the control unit 55 when the uninterruptible power supply U is set as a standby device using the operation unit 18. Here, it is assumed that the uninterruptible power supply U is set to the automatic operation mode using the operation unit 18.

[0099] When the AC power supply 2 is healthy (φ29=L) and the inverter 15 is operating normally (φ30=L), the control unit 56 turns on the switches S1 to S3 and turns off the switch S4 and the semiconductor switch 17. When a power outage occurs in the AC power supply 2 (φ29=H), the control unit 56 turns off the switch S1.

[0100] When the inverter 15 fails (φ30=H) while the AC power supply 2 is healthy (φ29=L), the control unit 56 turns on the switch S4 and the semiconductor switch 17 and turns off the switch S3, and turns off the semiconductor switch 17 after a predetermined time.

[0101] Figure 8 is a circuit block diagram showing the operation of the uninterruptible power supply system shown in Figures 1 to 7. However, for simplicity of the drawing and explanation, only the switches S1 to S4, converter 11, bidirectional chopper 14, inverter 15, and semiconductor switch 17 are shown in each uninterruptible power supply U. Figure 8 shows the flow of power in the normal operation mode (φ29=L, φ30=L, φ45=L).

[0102] In this case, in each of the uninterruptible power supplies U1 and U2, the switches S1 to S3 are turned on, and the switch S4 and the semiconductor switch 17 are turned off. The AC power supplied from the AC power supply 2 is supplied to the converter 11 via the switch S1, and the AC power is converted by the converter 11 into DC power and supplied to the DC line 12.

[0103] The voltage control unit 41 (FIG. 4) generates a current control value Iic so that the deviation ΔVD=VDR−VD between the reference DC voltage VDR generated by the reference voltage generator 26 (FIG. 3) and the DC voltage VD of the DC line 12 indicated by the output signal VDf of the voltage detector 24 is eliminated.

[0104] A current control unit 42 generates a phase control value θc1 so as to eliminate the deviation ΔIi between the current control value Iic and the AC input current Ii indicated by the current detector CD1 (FIG. 2). The phase control value θc1 passes through a selector 46 and a limiter 47 to become a phase control value θc4, which is then provided to a PWM control unit 48. The converter 11 is controlled by the PWM control unit 48, and converts the DC voltage VD of the DC line 12 into an AC voltage Vc, and outputs it to an AC input terminal T2.

[0105] The phase difference between the AC voltage Vc and the AC input voltage Vi from the AC power supply 2 is adjusted according to the phase control value θc4. When the DC voltage VD is lower than the reference DC voltage VDR, the phase control value θc4 becomes a positive value, the phase of the AC voltage Vc lags behind the phase of the AC input voltage Vi, power is transferred from the AC input terminal T2 to the DC line 12 via the converter 11, and the DC voltage VD of the DC line 12 increases.

[0106] Conversely, when the DC voltage VD is higher than the reference DC voltage VDR, the phase control value θc4 becomes a negative value, the phase of the AC voltage Vc leads the phase of the AC input voltage Vi, power is transferred from the DC line 12 to the AC input terminal T2 via the converter 11, and the DC voltage VD of the DC line 12 drops. In this way, the DC voltage VD is maintained at the reference DC voltage VDR.

[0107] Furthermore, the DC power generated by the converter 11 is supplied to the battery B by the bidirectional chopper 14. The terminal voltage VB of the battery B is detected by the voltage detector 25 (FIG. 3). The control unit 53 (FIG. 4) controls the bidirectional chopper 14 so that the DC voltage VB becomes equal to the reference DC voltage VBR generated by the reference voltage generator 27.

[0108] Furthermore, DC power generated by converter 11 is converted into AC power by inverter 15. An AC output voltage V0 of inverter 15 is detected by voltage detector 23 (FIG. 3). A control unit 55 (FIG. 6) controls inverter 15 so that AC output voltage V0 coincides with a reference AC voltage V0 generated by reference voltage generator 28.

[0109] The AC power generated by inverter 15 of uninterruptible power supply U1, which is the standby device, is output to bypass terminal T1 of uninterruptible power supply U2. Because switch S4 and semiconductor switch 17 of uninterruptible power supply U2 are turned off, the value of the AC power generated by inverter 15 of uninterruptible power supply U1 is sufficiently small. Furthermore, when battery B1 is sufficiently charged and VB=VBR, the power flowing through converter 11 and bidirectional chopper 14 of uninterruptible power supply U1 becomes sufficiently small.

[0110] AC power generated by inverter 15 of uninterruptible power supply U2, which is a power supply device, is supplied to load 3. Therefore, a large amount of power flows from AC power source 2 to load 3 via converter 11 and inverter 15 of uninterruptible power supply U2. Furthermore, when battery B2 is sufficiently charged and VB=VBR, the power flowing to bidirectional chopper 14 of uninterruptible power supply U2 becomes sufficiently small.

[0111] 8, paths through which small power flows are indicated by dotted lines, and paths through which large power flows are indicated by solid lines. When batteries B1 and B2 are fully charged, almost 100% of the power supplied from AC power supply 2 is supplied to load 3 via converter 11 and inverter 15 of uninterruptible power supply U2.

[0112] Fig. 9 is a circuit block diagram showing another operation of the uninterruptible power supply system shown in Fig. 1 to Fig. 7. Fig. 9 shows the flow of power when inverter 15 of uninterruptible power supply U2 fails in the state shown in Fig. 8.

[0113] In this case, the output signal φ30 of the failure detector 30 (FIG. 3) of the uninterruptible power supply U2 is set to the "H" level, which is the activation level, and the control unit 56 (FIG. 7) instantly turns on the semiconductor switch 17, turns off the switch S3, turns on the switch S4, and then turns off the semiconductor switch 17, and the control unit 55 (FIG. 6) stops the operation of the inverter 15.

[0114] As a result, AC power generated by inverter 15 of uninterruptible power supply U1 is supplied to load 3 via switch S3 of uninterruptible power supply U1 and switch S4 of uninterruptible power supply U2, and operation of load 3 continues.

[0115] 9, paths through which small amounts of power flow are indicated by dotted lines, and paths through which large amounts of power flow are indicated by solid lines. When batteries B1 and B2 are fully charged, almost 100% of the power supplied from AC power supply 2 is supplied to load 3 via converter 11 and inverter 15 of uninterruptible power supply U1.

[0116] Fig. 10 is a circuit block diagram showing still another operation of the uninterruptible power supply system shown in Figs. 1 to 7. Fig. 10 shows the flow of power in regenerative operation mode (φ29=L, φ30=L, φ45=H). In other words, Fig. 10 shows the flow of power when a regenerative command signal CMD is given in the state shown in Fig. 8. The regeneration rate Rr is set to 100%.

[0117] In the uninterruptible power supply U1, which is a standby device, the calculation unit 43 (Figure 4) calculates the AC output power PL3 supplied from the uninterruptible power supply system to the load 3, and the regenerative power command unit 44 calculates a phase control value θ2c corresponding to the AC output power PL3.

[0118] Furthermore, a discharge time Td is set using the operation unit 18. When the regeneration command signal CMD is given, the signal generating unit 45 raises the signal φ45 from the inactive level “L” to the active level “H” for the discharge time Td. When the signal φ45 is set to the “H” level, a state of conduction is established between the second input terminal 46b and the output terminal 46d of the selector 46.

[0119] As a result, the phase control value θc2 generated by the regenerative power command unit 44 passes through the selector 46 and the limiter 47 to become the phase control value θc4, which is then given to the PWM control unit 48. The converter 11 is controlled by the PWM control unit 48, and converts the DC voltage VD of the DC line 12 into an AC voltage Vc, and outputs it to the AC input terminal T2.

[0120] The phase of the AC voltage Vc is advanced by an angle corresponding to the phase control value θc4 relative to the phase of the AC voltage Vi supplied from the AC power supply 2. As a result, AC power is output from the converter 11 to the AC input terminal T2.

[0121] 10 again, in uninterruptible power supply U1, DC power from battery B1 is supplied to converter 11 via switch S2, bidirectional chopper 14, and DC line 12, and is converted into AC power by converter 11. Bidirectional chopper 14 is controlled by control unit 53 (FIG. 5) so that DC voltage VD of DC line 12 becomes reference DC voltage VDR. Also, operation of inverter 15 is stopped by control unit 55 (FIG. 6).

[0122] The AC power generated by the converter 11 of the uninterruptible power supply U1 is supplied to the AC input terminal T2 of the uninterruptible power supply U2 via the switch S1 and the AC input terminal T2 of the uninterruptible power supply U1.

[0123] In the uninterruptible power supply U2, the normal operation mode described in FIG. 8 is performed, and the AC power supplied from the converter 11 of the uninterruptible power supply U1 is converted into DC power by the converter 11 of the uninterruptible power supply U2, and the DC power is stored in the battery B2 by the bidirectional chopper 14 and is also converted into AC power by the inverter 15 and supplied to the load 3.

[0124] 10, paths through which small power flows are indicated by dotted lines, and paths through which large power flows are indicated by solid lines. When battery B2 is fully charged, almost 100% of the power supplied from converter 11 of uninterruptible power supply U1 is supplied to load 3 via converter 11 and inverter 15 of uninterruptible power supply U2.

[0125] In the uninterruptible power supply U1, which is the standby device, when the regenerative operation mode ends, the charging stop operation mode is performed. From the time when the regenerative command signal CMD is given until the time ts set using the operation unit 18, the signal generating unit 52 (FIG. 5) sets the signal φ52 to the "H" level, which is the activation level, and the control unit 53 stops the charging operation of the bidirectional chopper 14. This prevents a sudden increase in AC power received from the AC power source 2 immediately after the regenerative operation mode ends.

[0126] Fig. 11 is a circuit block diagram showing still another operation of the uninterruptible power supply system shown in Fig. 1 to Fig. 7. Fig. 11 shows the flow of power when a power outage occurs in AC power supply 2 in the state shown in Fig. 8.

[0127] In this case, in each uninterruptible power supply U, switch S1 is turned off to disconnect the AC power supply 2 from converter 11 and stop operation of converter 11. Also, DC power from battery B is supplied to inverter 15 via switch S2, bidirectional chopper 14, and DC line 12, where it is converted into AC power and output to AC output terminal T4 via switch S3. The AC output power of uninterruptible power supply U1 is supplied to bypass terminal T1 of uninterruptible power supply U2, but is not consumed by load 3. The AC output power of uninterruptible power supply U2 is supplied to load 3 and consumed.

[0128] 11, paths through which small power flows are indicated by dotted lines, and paths through which large power flows are indicated by solid lines. The power flowing from battery B1 via uninterruptible power supply U1 to uninterruptible power supply U2 is sufficiently small. Nearly 100% of the power supplied from battery B2 is supplied to load 3 via uninterruptible power supply U2.

[0129] Fig. 12 is a waveform diagram showing the operation of the uninterruptible power supply U shown in Fig. 2. In reality, the uninterruptible power supply U receives three-phase AC voltages from each of the AC power supplies 1 and 2, but for the sake of simplicity of the drawing and explanation, Fig. 2 shows only the portion related to one phase of AC voltage.

[0130] Fig. 12 shows the waveforms of AC input voltages Vi1 and Vi2 of two of the three phases and the waveforms of AC input currents Ii1 and Ii2 of the two phases. In particular, Fig. 12(A) shows the waveforms of AC input voltages Vi1 and Vi2 and AC input currents Ii1 and Ii2 in the normal operation mode, and Fig. 12(B) shows the waveforms of AC input voltages Vi1 and Vi2 and AC input currents Ii1 and Ii2 in the regenerative operation mode.

[0131] 12(A) and 12(B), when the waveforms of the AC input currents Ii1 and Ii2 are viewed with reference to the AC input voltages Vi1 and Vi2, the phases of the AC input currents Ii1 and Ii2 in the normal operation mode and the regenerative operation mode are shifted by 180 degrees. This indicates that the flow directions of the AC input currents Ii1 and Ii2 are reversed in the normal operation mode and the regenerative operation mode.

[0132] Figure 13 is a time chart for explaining the effects of the uninterruptible power supply system shown in Figures 1 to 12. In particular, Figure 13(A) shows the change over time in the amount of DC power EDC (%) stored in battery B1, and Figure 13(B) shows the AC power PAC (kVA) that the uninterruptible power supply system receives from AC power supply 2. Figure 13(A) shows that the amount of DC power EDC when battery B1 is fully charged is 100%.

[0133] In Fig. 13, from 6:00 to 11:00, each of uninterruptible power supplies U1 and U2 is operating in the normal operation mode (Fig. 8). At this time, battery B1 is fully charged by uninterruptible power supply U1, and the DC power amount EDC of battery B1 is maintained at 100%. In addition, uninterruptible power supply U2 receives 300 kVA AC power PAC from AC power supply 2 and supplies approximately 300 kVA AC power to load 3.

[0134] When a regeneration command signal CMD is sent from the central control room 5 (Fig. 1) at 11:00, the uninterruptible power supply U1 operates in regeneration mode for the set discharge time Td (four hours in Fig. 13), converting the DC power of battery B1 into AC power and supplying it to the uninterruptible power supply U2. The uninterruptible power supply U2 is driven by the AC power from the uninterruptible power supply U1 and continues in normal operation mode.

[0135] Therefore, the DC power amount EDC of battery B1 gradually decreases from 100% from 11:00 to 15:00, and reaches 75% at 15:00. In addition, the AC power PAC that the uninterruptible power supply system receives from AC power supply 2 is maintained at 0 kVA from 11:00 to 15:00.

[0136] In uninterruptible power supply U1, the regenerative operation mode is stopped at 3:00 PM, and the charging suspension operation mode is executed until time ts (midnight in FIG. 13) preset using operation unit 18 (FIG. 5). Uninterruptible power supply U2 is driven by AC power PAC supplied from AC power supply 2 and continues in normal operation mode. Therefore, the DC power amount EDC of battery B1 is maintained at 75% from 3:00 PM to midnight. In addition, the AC power PAC supplied from AC power supply 2 is 300 kVA from 3:00 PM to midnight.

[0137] In uninterruptible power supply U1, the charge stop operation mode is stopped at midnight and the normal operation mode is resumed. This causes charging of battery B1 to resume and the DC power amount EDC of battery B1 gradually increases from 75% and reaches 100% at 3:00. In addition, the AC power PAC from AC power supply 2 increases to 600kVA when charging of battery B1 resumes at midnight, decreases to 300kVA when charging of battery B1 finishes at 3:00, and is maintained at 300kVA from 3:00 onwards.

[0138] In this way, in this uninterruptible power supply system, the regenerative operation mode is executed in response to the regenerative command signal CMD, and the load 3 is driven using the DC power of the battery B1 instead of the AC power PAC from the AC power supply 2. Therefore, in the regenerative operation mode, the AC power PAC received from the AC power supply 2 can be reduced, thereby achieving peak cutting.

[0139] In addition, the regenerative operation mode is executed by discharging battery B1 during the daytime (11:00 to 15:00) when electricity rates are high, and the normal operation mode is resumed and battery B1 is charged during the nighttime (12:00 to 3:00) when electricity rates are low, thereby reducing electricity rates. This method is called peak shifting.

[0140] As described above, in the first embodiment, uninterruptible power supply U1 converts AC power from AC power supply 2 into DC power and stores it in battery B1 in the normal operation mode, and converts DC power from battery B1 into AC power and supplies it to uninterruptible power supply U2 in the regenerative operation mode. Uninterruptible power supply U2 drives load 3 using AC power supplied from AC power supply 2 and uninterruptible power supply U1. Therefore, by operating uninterruptible power supply U1 in the regenerative operation mode, it is possible to meet the demand for reducing the AC power received from AC power supply 2 (for example, peak shaving).

[0141] When the regeneration rate Rr is greater than 0% and less than 100%, AC power is supplied to the uninterruptible power supply U2 from both the AC power source 2 and the uninterruptible power supply U1 during the regenerative operation mode. The uninterruptible power supply U2 is driven by AC power supplied from both the AC power source 2 and the uninterruptible power supply U1.

[0142] [Embodiment 2] Fig. 14 is a block diagram showing a main part of an uninterruptible power supply system according to a second embodiment of the present disclosure, and is a diagram to be compared with Fig. 4. Referring to Fig. 14, the second embodiment differs from the first embodiment in that a regeneration command signal CMDA is received from central control room 5 (Fig. 1) instead of a regeneration command signal CMD, and in that calculation unit 43 and signal generation unit 45 are replaced with calculation unit 43A and signal generation unit 45A, respectively.

[0143] The central control room 5 outputs a regeneration command signal CMDA when it is desired to reduce the AC power received by the uninterruptible power supply system from the AC power supply 2. The regeneration command signal CMDA includes information indicating the regeneration rate Rr (%). The regeneration rate Rr is set to a desired value between 0% and 100%.

[0144] The calculation unit 43A calculates the AC output power PL2 supplied from the uninterruptible power supply system to the load 3 based on the AC output power PL1 of the device itself and the AC output power PL1 of the other device indicated by a signal transmitted from the other device via the communication circuit 31 (FIG. 3). The calculation unit 43A then multiplies the calculated AC output power PL2 by Rr / 100 and adds a loss Pα generated in the power supply device to calculate the AC output power PL3. Therefore, the AC output power PL3 is expressed as PL3 = (PL2 × Rr / 100) + Pα. A signal indicating the AC output power PL3 is provided to the regenerative power command unit 44.

[0145] When the device itself is set as a standby device using the operation unit 18, if the regeneration rate R (%) included in the regeneration command signal CMDA is greater than 0, the signal generating unit 45A responds to the regeneration command signal CMDA by raising the signal φ45 from the inactive level "L" to the active level "H" for the time Td set using the operation unit 18. If the regeneration rate R (%) is 0, the signal φ45 is maintained at the "L" level.

[0146] Furthermore, signal generating unit 45A maintains signal φ45 at the inactivation level of “L” regardless of regeneration command signal CMDA when the device itself is set as a power supply device using operation unit 18. The other configurations and operations are the same as those of the first embodiment, and therefore description thereof will not be repeated.

[0147] In this second embodiment, the central control room 5 can instruct the regeneration rate Rr (%) of the uninterruptible power supply system.

[0148] [Embodiment 3] 15 is a circuit block diagram showing an overall configuration of an uninterruptible power supply system according to a third embodiment of the present disclosure. In FIG. 15, the uninterruptible power supply system includes a plurality of (three in the figure) uninterruptible power supplies U11-U13 and switches S11-S13. Each of the uninterruptible power supplies U11-U12 includes a bypass terminal T1, an AC input terminal T2, a DC terminal T3, and an AC output terminal T4.

[0149] Bypass terminals T1 of uninterruptible power supplies U11 to U13 are connected to each other and receive AC power of a predetermined frequency (for example, commercial frequency) from bypass AC power supply 1. AC input terminals T2 of uninterruptible power supplies U11 to U13 are connected to each other and receive AC power of a predetermined frequency (for example, commercial frequency) from AC power supply 2.

[0150] The DC terminals T3 of the uninterruptible power supplies U11 to U13 are connected to batteries B1 to B3, respectively. Each of the batteries B1 to B3 stores DC power. A capacitor may be connected instead of a battery.

[0151] The uninterruptible power supplies U11 to U13 have the same configuration, but in this embodiment 3, the uninterruptible power supply U11 is used as a standby device, and the uninterruptible power supplies U12 and U13 are used as power supply devices. The configuration of each of the uninterruptible power supplies U11 to U13 will be described later.

[0152] An AC output terminal T4 (first output terminal) of the uninterruptible power supply U11 (first uninterruptible power supply) is connected to the load 3 via a switch S11. An AC output terminal T4 (second output terminal) of the uninterruptible power supply U12 (second uninterruptible power supply) is connected to the load 3 via a switch S12. An AC output terminal T4 of the uninterruptible power supply U13 is connected to the load 3 via a switch S13.

[0153] The switches S11 to S13 are turned on when the uninterruptible power supplies U11 to U13 are used, and are turned off when the uninterruptible power supplies U11 to U13 fail or are undergoing maintenance. The load 3 is driven by AC power supplied from the uninterruptible power supplies U11 to U13.

[0154] The uninterruptible power supplies U11 to U13 are connected to one another by a communication line 4. The uninterruptible power supplies U11 to U13 exchange various information via the communication line 4. For example, each uninterruptible power supply U (its own device) transmits information indicating the AC current being supplied to the load 3 to the other uninterruptible power supplies U (other devices) via the communication line 4.

[0155] The communication line 4 is also connected to a central control room 5. When AC power is being supplied normally from the AC power source 2 (when the AC power source 2 is healthy), and when the central control room 5 wants to reduce the AC power that the uninterruptible power supply system receives from the AC power source 2 (for example, during peak cutting), the central control room 5 generates a regeneration command signal CMD and sends it to the uninterruptible power supplies U11 to U13 via the communication line 4.

[0156] In the third embodiment, the uninterruptible power supply U11 used as a standby device operates in accordance with the regeneration command signal CMD, while the uninterruptible power supply U12 used as a power supply device does not operate in accordance with the regeneration command signal CMD.

[0157] When the uninterruptible power supply U11 has not received a regeneration command signal CMD while the AC power supply 2 is healthy, it executes a normal operation mode, converts AC power supplied from the AC power supply 2 via the AC input terminal T2 (first input terminal) into DC power, uses the DC power to charge the battery B1 (first power storage device), and generates AC power of a predetermined frequency (for example, commercial frequency), which is supplied to the load 3 via the AC output terminal T4 and the switch S11.

[0158] At this time, the uninterruptible power supply U11 adds up the AC output current IL1 of its own device to the AC output currents IL2 and IL3 of the uninterruptible power supplies U12 and U13 indicated by information provided from the uninterruptible power supplies U12 and U13 via communication line 4, and then divides this by the number n of uninterruptible power supplies U operating in the normal operation mode to obtain the shared current Is=(IL1+IL2+IL3) / n. The uninterruptible power supply U11 then supplies the shared current Is to the load 3 via the AC output terminal T4 and switch S11.

[0159] Furthermore, when the uninterruptible power supply U11 receives a regeneration command signal CMD while the AC power supply 2 is healthy, it executes a regeneration operation mode for a predetermined time Td, converts the DC power of the battery B1 into AC power of a predetermined frequency (for example, the commercial frequency), and outputs the AC power to the AC input terminal T2.

[0160] At this time, the uninterruptible power supply U11 outputs to the AC input terminal T2 AC power of a value corresponding to the power consumption of the load 3 indicated by information provided from the uninterruptible power supplies U12 and U13 via the communication line 4. This AC power is supplied to the AC input terminals T2 of the uninterruptible power supplies U12 and U13, and is supplied to the load 3 via the uninterruptible power supplies U12 and U13. Therefore, the AC power that the uninterruptible power supply system receives from the AC power supply 2 is reduced, achieving peak shaving.

[0161] After the regenerative operation mode ends, the uninterruptible power supply U11 executes the charge suspension operation mode until a predetermined time ts, converts the AC power supplied from the AC power supply 2 via the AC input terminal T2 into DC power, uses the DC power to generate AC power of a predetermined frequency, and supplies the AC power to the load 3 via the AC output terminal T4 and the switch S11.

[0162] In the charge stop mode, the uninterruptible power supply U11 does not charge battery B1, but ends the charge stop mode at the set time ts and enters normal operation mode. When the normal operation mode is resumed, the AC power received from AC power source 2 increases until the terminal voltage VB of battery B1 returns to the reference DC voltage VBR. However, by resuming the normal operation mode at night when electricity rates are low, electricity rates can be reduced. This technique is called peak shifting.

[0163] Furthermore, when the supply of AC power from the AC power supply 2 is stopped (during a power outage of the AC power supply 2), the uninterruptible power supply U11 converts the DC power of the battery B1 into AC power of a predetermined frequency (for example, the commercial frequency) and supplies the AC power to the load 3 via the AC output terminal T4 and the switch S11. When the uninterruptible power supply U11 fails, the operation of the uninterruptible power supply U11 is stopped and the switch S11 is turned off.

[0164] The uninterruptible power supply U12 does not respond to the regeneration command signal CMD, and when the AC power supply 2 is normal, converts the AC power supplied from the AC power supply 2 and the uninterruptible power supply U11 via the AC input terminal T2 into DC power, uses the DC power to charge the battery B2 (second power storage device), and also generates AC power of a predetermined frequency (for example, the commercial frequency), which is supplied to the load 3 via the AC output terminal T4 and the switch S12.

[0165] At this time, the uninterruptible power supply U12 adds up the AC output current IL2 of its own device to the AC output currents IL2 and IL3 of the uninterruptible power supplies U12 and U13 indicated by information provided from the uninterruptible power supplies U11 and U13 via communication line 4, and then divides this by the number n of uninterruptible power supplies U operating in the normal operation mode to obtain the shared current Is=(IL1+IL2+IL3) / n. The uninterruptible power supply U12 then supplies the shared current Is to the load 3 via the AC output terminal T4 and switch S11.

[0166] Furthermore, in the event of a power outage in AC power supply 2, uninterruptible power supply U12 converts the DC power of battery B2 into AC power of a predetermined frequency (for example, the commercial frequency) and supplies the AC power to load 3 via AC output terminal T4 and switch S12. Therefore, even in the event of a power outage in AC power supply 2, operation of load 3 can continue. In the event of a failure in uninterruptible power supply U11, operation of uninterruptible power supply U12 is stopped and switch S12 is turned off. Uninterruptible power supply U13 operates in the same manner as uninterruptible power supply U12, and therefore its description will not be repeated.

[0167] Fig. 16 is a block diagram showing the main parts of the uninterruptible power supply U11, and is to be compared with Fig. 6. Referring to Fig. 16, the uninterruptible power supply U11 differs from the uninterruptible power supply U1 in that a calculation unit 57 is added and control unit 55 is replaced with control unit 55A.

[0168] The calculation unit 57 calculates the AC current ILa supplied from the uninterruptible power supplies U1 to U3 to the load 3 and the number n of uninterruptible power supplies U operating in the normal operation mode, based on the output signal ILf of the current detector CD4 of its own device and the output signals ILf of the current detector CD4 provided from the other uninterruptible power supplies U12, U13 via the communication line 4. The calculation unit 57 then divides the AC current ILa by the number n to calculate the shared current Is=ILa / n.

[0169] When the control unit 55A is set as a standby device using the operation unit 18, the control unit 55A controls the inverter 15 to output the shared current Is in the normal operation mode and the charge stop mode, and stops the operation of the inverter 15 in the regenerative operation mode. When the control unit 55A is set as a power supply device using the operation unit 18, the control unit 55A controls the inverter 15 to output the shared current Is. The other configurations and operations are the same as those of the uninterruptible power supply U1, so the description thereof will not be repeated. Each of the uninterruptible power supplies U12 and U13 has the same configuration as the uninterruptible power supply U11.

[0170] Figure 17 is a circuit block diagram showing the operation of the uninterruptible power supply system shown in Figures 15 and 16. However, for simplicity of the drawing and explanation, only the switches S1 to S4, converter 11, bidirectional chopper 14, inverter 15, and semiconductor switch 17 are shown in each uninterruptible power supply U. Figure 17 shows the flow of power in the normal operation mode.

[0171] In this case, in each uninterruptible power supply U, switches S1 to S3 are turned on, and switch S4 and semiconductor switch 17 are turned off. AC power supplied from AC power supply 2 is supplied to converter 11, and the AC power is converted by converter 11 into DC power and supplied to DC line 12.

[0172] The DC power received by the DC line 12 is stored in the battery B by the bidirectional chopper 14, and is also converted to AC power by the inverter 15 and supplied to the load 3. At this time, the shared current Is is calculated by the calculation unit 57 (FIG. 16), and the shared current Is is supplied from each uninterruptible power supply U to the load 3. When the battery B is sufficiently charged and VB=VBR, the power flowing to the bidirectional chopper 14 of each uninterruptible power supply U becomes sufficiently small.

[0173] In Fig. 17, paths through which small power flows are indicated by dotted lines, and paths through which large power flows are indicated by solid lines. When batteries B1 to B3 are fully charged, AC power supplied from AC power supply 2 is divided into three equal parts among three uninterruptible power supplies U11 to U13 and supplied to load 3. In Fig. 17, 100% of the AC power supplied from AC power supply 2 is divided into three equal parts among three uninterruptible power supplies U11 to U13, and 33.3% of the AC power is supplied from each uninterruptible power supply U to load 3.

[0174] Fig. 18 is a circuit block diagram showing another operation of the uninterruptible power supply system shown in Fig. 15 and Fig. 16. Fig. 18 shows the flow of power in a regenerative operation mode. In other words, Fig. 18 shows the flow of power when a regenerative command signal CMD is given in the state shown in Fig. 17. The regeneration rate Rr is set to 100%.

[0175] In the uninterruptible power supply U11, which is a standby device, the AC output power PL2 supplied from the uninterruptible power supply system to the load 3 is calculated by the calculation unit 43 (FIG. 4), and the AC power PL3 to be output to the AC input terminal T2 is calculated.

[0176] In uninterruptible power supply U11, the operation of inverter 15 is stopped, and DC power from battery B1 is supplied to converter 11 via bidirectional chopper 14, converted into AC power PL3 by converter 11, and output to AC input terminal T2. This AC power PL3 is supplied to uninterruptible power supplies U12 and U13.

[0177] In each of the uninterruptible power supplies U12 and U13, AC power supplied from the uninterruptible power supply U11 is supplied to a converter 11 via an AC input terminal T2, converted into DC power, and supplied to a DC line 12.

[0178] The DC power received by the DC line 12 is stored in the battery B by the bidirectional chopper 14, and is also converted to AC power by the inverter 15 and supplied to the load 3. At this time, the shared current Is is calculated by the calculation unit 57 (FIG. 16), and the shared current Is is supplied from each of the uninterruptible power supplies U12 and U13 to the load 3. When the battery B is sufficiently charged and VB=VBR holds, the power flowing to the bidirectional choppers 14 of the uninterruptible power supplies U12 and U13 becomes sufficiently small.

[0179] In Figure 18, paths through which small power flows are indicated by dotted lines, and paths through which large power flows are indicated by solid lines. When batteries B2 and B3 are fully charged, the AC power supplied from uninterruptible power supply U11 is divided equally between the two uninterruptible power supplies U12 and U13 and supplied to load 3. In Figure 18, 100% of the AC power supplied from uninterruptible power supply U11 is divided equally between the two uninterruptible power supplies U12 and U13, and 50% of the AC power is supplied to load 3 from each uninterruptible power supply U11.

[0180] In the uninterruptible power supply U11, which is the standby device, when the regenerative operation mode ends, the charging stop operation mode is performed. The charging operation of the bidirectional chopper 14 is stopped from when the regenerative command signal CMD is given until the time ts set using the operation unit 18. This prevents a sudden increase in AC power received from the AC power source 2 immediately after the regenerative operation mode ends.

[0181] Fig. 19 is a circuit block diagram showing still another operation of the uninterruptible power supply system shown in Fig. 15 and Fig. 16. Fig. 19 shows the flow of power when a power outage occurs in AC power supply 2 in the state shown in Fig. 17.

[0182] In this case, in each uninterruptible power supply U, switch S1 is turned off to disconnect the AC power supply 2 and converter 11, and operation of converter 11 is stopped. Also, DC power from battery B is supplied to inverter 15 via bidirectional chopper 14 and DC line 12, where it is converted into AC power and supplied to load 3 via AC output terminal T4. At this time, a shared current Is is calculated by calculation unit 57 (FIG. 16), and each uninterruptible power supply U supplies shared current Is to load 3. Each of the three uninterruptible power supplies U11 to U13 supplies 33.3% of the AC power to load 3, and a total of 100% of the AC power is supplied to load 3 from the uninterruptible power supply system.

[0183] As described above, in the third embodiment, the uninterruptible power supply U11 converts AC power from the AC power supply 2 into DC power and stores it in the battery B1 in the normal operation mode, and converts DC power from the battery B1 into AC power and supplies it to the uninterruptible power supplies U12 and U13 in the regenerative operation mode. The uninterruptible power supplies U12 and U13 drive the load 3 using the AC power supplied from the AC power supply 2 and the uninterruptible power supply U11. Therefore, by operating the uninterruptible power supply U11 in the regenerative operation mode, it is possible to meet the demand for reducing the AC power received from the AC power supply 2 (for example, peak shaving).

[0184] 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]

[0185] U1, U2, U11 to U13 uninterruptible power supply, T1 bypass terminal, T2 AC input terminal, T3 DC terminal, T4 AC output terminal, 1 bypass AC power supply, 2 AC power supply, B1 to B3 battery, 3 load, 4 communication line, 5 central control room, S1 to S4, S11 to S13 switches, 11 converter, CD1 to CD4 current detector, 12 DC line, 13, 16 capacitor, 14 bidirectional chopper, 15 inverter, 17 semiconductor switch, 18 operation unit, 19 control device, 21 to 25 voltage detector, 26 to 28 reference voltage generator, 29 power failure detector, 30 fault detector, 31 communication circuit, 32 control circuit, 41 voltage control unit, 42 current control unit, 43, 43A, 57 calculation unit, 44 regenerative power command unit, 45, 45A, 52 signal generation unit, 46 Selector, 47 limiter, 48 PWM control unit, 51 timer, 53, 55, 55A, 56 control unit.

Claims

1. a first uninterruptible power supply including a first input terminal and a first output terminal; a second uninterruptible power supply including a second input terminal and a second output terminal; the first and second input terminals are connected to each other to receive AC power from an AC power source; the second output terminal is connected to a load; The first uninterruptible power supply When the AC power supply is healthy, an operation mode selected from a normal operation mode in which AC power received at the first input terminal is converted into DC power, and a first power storage device is charged using the DC power, and AC power is generated and output to the first output terminal, and a regenerative operation mode in which DC power of the first power storage device is converted into AC power and output to the first input terminal are executed; When the AC power supply is out of service, the DC power of the first power storage device is converted into AC power and output to the first output terminal; The second uninterruptible power supply When the AC power supply is healthy, AC power received by the second input terminal from the AC power supply and the first uninterruptible power supply device is converted into DC power, and the DC power is used to charge a second power storage device, and AC power is generated and output to the second output terminal; When the AC power supply is interrupted, the DC power of the second power storage device is converted into AC power and output to the second output terminal.

2. 2. The uninterruptible power supply system according to claim 1, wherein the first uninterruptible power supply device outputs, to the first input terminal, AC power of a value corresponding to the power consumption of the load in the regenerative operation mode.

3. When the AC power supply is healthy, the first uninterruptible power supply device Execute the normal operation mode; Executing the regenerative operation mode in response to a regenerative command signal; After the regenerative operation mode ends, the AC power received by the first input terminal is converted into DC power, the DC power is converted into AC power and output to the first output terminal, and a charge stop mode is executed in which the first power storage device is not charged; 2. The uninterruptible power supply system according to claim 1, wherein the normal operation mode is resumed after the charging suspension mode ends.

4. The second uninterruptible power supply a bypass terminal connected to the first output terminal; an inverter that converts DC power into AC power; 2. The uninterruptible power supply system according to claim 1, further comprising: a switching circuit that applies AC power generated by said inverter to said second output terminal when said inverter is normal, and that connects said bypass terminal to said second output terminal when said inverter fails.

5. 2. The uninterruptible power supply system according to claim 1, wherein the first output terminal is connected to the load together with the second output terminal.

6. 6. The uninterruptible power supply system according to claim 5, wherein in the normal operation mode, the first and second uninterruptible power supplies supply AC power of the same value to the load.

7. the first uninterruptible power supply includes a first converter, a first DC line, a first bidirectional chopper, and a first inverter; the first converter converts AC power received at the first input terminal into DC power and outputs the DC power to the first DC line in the normal operation mode, and converts DC power received from the first DC line into AC power and outputs the AC power to the first input terminal in the regenerative operation mode, and is stopped from operating when a power outage occurs in the AC power supply; the first bidirectional chopper supplies DC power received by the first DC line to the first power storage device in the normal operation mode, and outputs DC power of the first power storage device to the first DC line in the regenerative operation mode and during a power outage of the AC power supply; the first inverter converts DC power received from the DC line into AC power and outputs the AC power to the first output terminal during the normal operation mode and during a power outage of the AC power supply, and stops its operation during the regenerative operation mode; the second uninterruptible power supply includes a second converter, a second DC line, a second bidirectional chopper, and a second inverter; the second converter converts AC power received at the second input terminal into DC power and outputs the DC power to the second DC line when the AC power supply is normal, and stops operation when the AC power supply is in a power outage; the second bidirectional chopper supplies DC power received by the second DC line to the second power storage device when the AC power supply is normal, and outputs DC power of the second power storage device to the second DC line when the AC power supply is in a power outage; 2. The uninterruptible power supply system according to claim 1, wherein the second inverter converts DC power received from the second DC line into AC power and outputs the AC power to the second output terminal.

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