Uninterruptible power supply device

Abstract

This uninterruptible power supply includes a semiconductor switch (1) connected between a bypass AC power supply (11) and a load (14), which is turned on when the bypass AC power supply is normal and turned off when the bypass AC power supply fails, and an inverter (8) which converts DC power supplied from an AC power supply (12) or a battery (13) into AC power and supplies it to the load when the bypass AC power supply fails, and which supplies an assist current (Ia) that is the difference between the load current and the threshold current to the load when a load current (IL) is greater than a threshold current (Ith) when the bypass AC power supply is normal. Therefore, even if the load current increases due to a load fluctuation, the current flowing through the semiconductor switch can be maintained at or below the threshold current.

Description

[Technical field]

[0001] The present disclosure relates to an uninterruptible power supply, and more particularly to an uninterruptible power supply including a semiconductor switch and an inverter. [Background technology]

[0002] For example, International Publication No. 2017 / 009998 (Patent Document 1) discloses an uninterruptible power supply including a bypass switch, a small semiconductor switch, and a power converter connected in parallel between an AC power source and a load. The power converter includes a converter that converts AC power supplied from the AC power source into DC power, and an inverter that converts the DC power into AC power and supplies it to the load.

[0003] When the AC power supply is normal, the inverter power supply mode is executed and the bypass switch and the semiconductor switch are turned off. The converter converts AC power from the AC power supply into DC power. This DC power is stored in the battery and is provided to the inverter. The inverter converts the DC power into AC power and supplies it to the load.

[0004] When the inverter fails, the bypass power supply mode is executed, the operation of the power converter is stopped, and the bypass switch and the semiconductor switch are turned on. To prevent the semiconductor switch from overheating due to a current, the semiconductor switch is turned off after a predetermined time has elapsed. AC power is supplied from the AC power source to the load via the bypass switch.

[0005] In the event of a power outage in the AC power supply, the battery power supply mode is executed, the operation of the converter is stopped, and the inverter converts the DC power of the battery into AC power and supplies it to the load. Therefore, even if a power outage occurs in the AC power supply, the operation of the load can be continued as long as DC power is stored in the battery. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2017 / 009998 Summary of the Invention [Problem to be solved by the invention]

[0007] However, such uninterruptible power supplies have a problem in that losses occur mainly in the power converter, resulting in low efficiency of about 96%. As a solution to this problem, uninterruptible power supplies with a bypass ECO power supply mode have attracted attention. This uninterruptible power supply has a large semiconductor switch and a power converter connected in parallel between the AC power supply and the load.

[0008] When the AC power supply is healthy, the bypass ECO power supply mode is executed, the semiconductor switch is turned on, and AC power from the AC power supply is supplied to the load via the semiconductor switch. When a power outage occurs in the AC power supply, the battery power supply mode is executed, the semiconductor switch is turned off, and the inverter included in the power converter converts the battery's DC power to AC power and supplies it to the load. In this uninterruptible power supply, losses occur mainly in the semiconductor switch, but because the losses in the semiconductor switch are smaller than the losses in the power converter, a high efficiency of 99% can be achieved.

[0009] In this uninterruptible power supply, a semiconductor switch with a capacity required to supply the rated current of the load is normally used, but when the load current increases above a predetermined current due to a load fluctuation, the semiconductor switch is turned off after a predetermined time has elapsed to prevent the semiconductor switch from overheating, and the operation of the load is stopped.

[0010] One possible solution to this problem is to use a large-capacity semiconductor switch capable of supplying a current significantly larger than the rated current of the load, but this method has the problem of increasing the size and cost of the device.

[0011] Therefore, a primary object of the present disclosure is to provide a small, low-cost uninterruptible power supply that is resistant to load fluctuations. [Means for solving the problem]

[0012] The uninterruptible power supply of the present disclosure includes a semiconductor switch and an inverter. The semiconductor switch is connected between a first AC power source and a load, and is turned on when the first AC power source is normal and turned off when the first AC power source is out of service. The inverter converts DC power supplied from a DC power source into AC power and supplies the AC power to the load when the first AC power source is out of service, and supplies an assist current equal to the difference between the load current and the threshold current to the load when the first AC power source is normal and the load current is greater than a threshold current. Effect of the Invention

[0013] In the uninterruptible power supply of the present disclosure, when the load current is greater than the threshold current when the first AC power supply is healthy, an assist current equal to the difference between the load current and the threshold current is supplied from the inverter to the load. Therefore, even if the load current increases due to a load fluctuation, the current flowing through the semiconductor switch can be maintained at or below the threshold current, and overheating of the semiconductor switch can be prevented. This makes it possible to prevent the semiconductor switch from being turned off and the operation of the load from being stopped, thereby realizing an uninterruptible power supply that is resistant to load fluctuations. In addition, since there is no need to use a large-capacity semiconductor switch in preparation for an increase in the load current, the device can be made smaller and less expensive. [Brief description of the drawings]

[0014] [Figure 1] 1 is a circuit block diagram showing a configuration of an uninterruptible power supply according to an embodiment of the present disclosure. [Diagram 2] 2 is a block diagram showing a main part of the control device shown in FIG. 1. [Diagram 3] 3 is a block diagram showing a configuration of a portion of the control circuit shown in FIG. 2 that is related to the control of a semiconductor switch. [Figure 4] 4 is a time chart showing the operation of the control unit shown in FIG. 3. [Diagram 5]3 is a block diagram showing a configuration of a portion of the control circuit shown in FIG. 2 that is related to inverter control. [Figure 6] 6 is a flowchart showing the operation of the uninterruptible power supply device shown in FIGS. 1 to 5. [Figure 7] FIG. 4 is a circuit block diagram for explaining the operation of the uninterruptible power supply device in an inverter-assisted power supply mode. [Figure 8] 4 is a circuit block diagram for explaining the operation of the uninterruptible power supply device in a battery power supply mode. FIG. [Figure 9] FIG. 11 is a circuit block diagram for explaining the operation of the comparative example. [Figure 10] FIG. 11 is a circuit block diagram for explaining another operation of the comparative example. [Figure 11] 11A and 11B are diagrams for explaining the effects of the embodiment; [Figure 12] FIG. 13 is a circuit block diagram showing a modified example of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Fig. 1 is a circuit block diagram showing a configuration of an uninterruptible power supply according to an embodiment of the present disclosure. In Fig. 1, the uninterruptible power supply includes a bypass input terminal T1, an input terminal T2, a DC terminal T3, an output terminal T4, a semiconductor switch 1, switches S1 to S3, a converter 4, current detectors CD1 to CD4, a DC line 5, a capacitor 6, a bidirectional chopper 7, an inverter 8, an operation unit 9, and a control device 10.

[0016] The bypass input terminal T1 receives AC power of a predetermined frequency (for example, commercial frequency) from a bypass AC power supply 11 (first AC power supply). The input terminal T2 receives AC power of a predetermined frequency (for example, commercial frequency) from an AC power supply 12 (second AC power supply). Each of the AC power supplies 11 and 12 may be a commercial AC power supply or a generator. Both the AC power supplies 11 and 12 may be commercial AC power supplies.

[0017] The DC terminal T3 is connected to a battery 13. The battery 13 (power storage device) stores DC power. A capacitor may be connected instead of the battery 13. The output terminal T4 is connected to a load 14. The load 14 is driven by AC power of a predetermined frequency (for example, a commercial frequency) supplied from an uninterruptible power supply.

[0018] The semiconductor switch 1 is connected between an input terminal T1 and an output terminal T4. The semiconductor switch 1 includes a pair of thyristors 2 and 3 connected in anti-parallel to each other, and is controlled by a control device 10.

[0019] When AC power is normally supplied from the bypass AC power supply 11 (when the bypass AC power supply 11 is healthy), the semiconductor switch 1 is turned on, and AC power is supplied from the bypass AC power supply 11 to the load 14 via the semiconductor switch 1.

[0020] When AC power is not normally supplied from the bypass AC power supply 11 (when the bypass AC power supply 11 experiences a power outage), the semiconductor switch 1 is turned off, and the bypass AC power supply 11 and the load 14 are disconnected.

[0021] The instantaneous value of the AC input voltage VI supplied from the bypass AC power supply 11 is detected by the control device 10. The control device 10 determines whether or not the AC voltage VI is being normally supplied from the bypass AC power supply 11 based on the instantaneous value of the AC input voltage VI.

[0022] The switch S1 is connected between the input terminal T2 and the AC node of the converter 4, and is controlled by the control device 10. When AC power is normally supplied from the AC power source 12 (when the AC power source 12 is healthy), the switch S1 is turned on, and AC power is supplied from the AC power source 12 to the converter 4 via the switch S1. When AC power is not normally supplied from the AC power source 12 (when the AC power source 12 has a power outage), the switch S1 is turned off, and the AC power source 12 and the converter 4 are disconnected.

[0023] The instantaneous value of the AC input voltage Vi supplied from the AC power source 12 is detected by the control device 10. Based on the instantaneous value of the AC input voltage Vi, the control device 10 determines whether or not the AC voltage Vi is normally supplied from the AC power source 12. The current detector CD1 detects the AC input current Ii flowing between the AC power source 12 and the converter 4, and provides the control device 10 with a signal Iif indicating the detected value.

[0024] The converter 4 (forward converter) is controlled by the control device 10, and when the AC power source 12 is healthy, converts AC power from the AC power source 12 into DC power and outputs it to the DC line 5. The converter 4 is a well-known device that includes multiple sets of IGBTs (Insulated Gate Bipolar Transistors) and diodes.

[0025] The capacitor 6 is connected to the DC line 5 and smoothes and stabilizes the DC voltage VD of the DC line 5. The instantaneous value of the DC voltage VD of the DC line 5 is detected by the control device 10.

[0026] When the AC power supply 12 is healthy, the control device 10 controls the converter 4 so that the DC voltage VD of the DC line 5 becomes the reference DC voltage VDR. When the AC power supply 12 experiences a power outage, the control device 10 stops the operation of the converter 4.

[0027] The DC line 5 is connected to the DC terminal T3 via the bidirectional chopper 7 and the switch S2. The switch S2 is controlled by the control device 10. When the uninterruptible power supply is used, the switch S2 is turned on. During maintenance of the battery 13 and the bidirectional chopper 7, the switch S2 is turned off.

[0028] The instantaneous value of the terminal voltage VB of the battery 13 is detected by the control device 10. The current detector CD2 detects a DC current IB flowing between the battery 13 and the bidirectional chopper 7, and provides the control device 10 with a signal IBf indicating the detected value.

[0029] The bidirectional chopper 7 is controlled by the control device 10, and exchanges DC power between the DC line 5 and the battery 13. The bidirectional chopper 7 is a well-known device that includes a plurality of sets of IGBTs and diodes, and a reactor.

[0030] When the AC power supply 12 is healthy, the control device 10 controls the bidirectional chopper 7 so that the battery voltage VB becomes equal to the reference DC voltage VBR. When the AC power supply 12 experiences a power outage, the control device 10 controls the bidirectional chopper 7 so that the DC voltage VD of the DC line 5 becomes equal to the reference DC voltage VDR. The converter 4, the bidirectional chopper 7, and the battery 13 constitute one embodiment of a “DC power supply” that supplies DC power to the inverter 8.

[0031] Furthermore, the DC line 5 is connected to a DC node of an inverter 8, and an AC node of the inverter 8 is connected to a node N1 between the semiconductor switch 1 and the output terminal T4 via a switch S3.

[0032] The switch S3 is controlled by the control device 10. When the uninterruptible power supply is used, the switch S3 is turned on. When maintenance of the inverter 8 is performed, the switch S3 is turned off.

[0033] The current detector CD3 detects the AC output current IO of the inverter 8, and provides a signal IOf indicating the detected value to the control device 10. The current detector CD4 detects the load current IL flowing from the node N1 to the load 14, and provides a signal ILf indicating the detected value to the control device 10. In addition, the instantaneous value of the AC output voltage VO applied to the load 14 is detected by the control device 10.

[0034] The inverter 8 (inverse converter) is controlled by the control device 10, and converts the DC power supplied from the converter 4 and the bidirectional chopper 7 via the DC line 5 into AC power of a predetermined frequency (for example, commercial frequency) and supplies it to the load 14. The inverter 8 is a well-known one that includes multiple sets of IGBTs and diodes.

[0035] When the bypass AC power supply 11 experiences a power outage, the inverter 8 converts the DC power supplied from the converter 4 or the bidirectional chopper 7 into AC power and supplies it to the load 14. At this time, the control device 10 controls the inverter 8 so that the AC output voltage VO is maintained at the AC input voltage VI before the power outage occurred.

[0036] When the load current IL is equal to or less than the threshold current Ith while the bypass AC power supply 11 is healthy, the inverter 8 is put into a standby state in which it does not exchange current with the bypass AC power supply 11 and the load 14. The threshold current Ith is, for example, the rated current of the semiconductor switch 1. At this time, the control device 10 controls the inverter 8 so that the AC output current IO of the inverter 8 becomes 0 A.

[0037] When the load current IL is larger than the threshold current Ith while the bypass AC power supply 11 is healthy, the inverter 8 supplies an assist current Ia=IL-Ic, which is the difference between the load current IL and the threshold current Ith, to the load 14. At this time, the control device 10 controls the inverter 8 so that the AC output current IO becomes the assist current Ia.

[0038] The operation unit 9 includes a plurality of buttons, a plurality of switches, and an image display unit. By operating the operation unit 9, a user of the uninterruptible power supply can turn the power of the uninterruptible power supply on and off, operate the uninterruptible power supply automatically or manually, and set the threshold current Ith to a desired value. The operation unit 9 outputs signals and information indicating the contents of operations performed by the user to the control device 10.

[0039] The control device 10 controls the semiconductor switch 1, the switches S1 to S3, the converter 4, the bidirectional chopper 7, and the inverter 8 based on signals from the operation unit 9, the AC input voltages VI, Vi, the AC output voltage VO, the DC voltage VD, the battery voltage VB, the AC input current Ii, the battery current IB, the AC output current IO, and the load current IL.

[0040] 2 is a block diagram showing a main part of the control device 10. In FIG. 2, the control device 10 includes voltage detectors 21-25, power failure detectors 26 and 27, a synchronization detector 28, and a control circuit 29.

[0041] The voltage detector 21 detects an instantaneous value of the AC input voltage VI supplied from the bypass AC power supply 11, and outputs a signal VIf indicating the detected value to the power failure detector 26 and the control circuit 29. The voltage detector 22 detects an instantaneous value of the AC input voltage Vi supplied from the AC power supply 12, and outputs a signal Vif indicating the detected value to the power failure detector 27 and the control circuit 29. The voltage detector 23 detects an instantaneous value of the AC output voltage VO applied to the load 14, and outputs a signal VOf indicating the detected value to the control circuit 29.

[0042] The voltage detector 24 detects the instantaneous value of the DC voltage VD of the DC line 5, and outputs a signal VDf indicating the detected value to the control circuit 29. The voltage detector 25 detects the instantaneous value of the terminal voltage VB of the battery 13, and outputs a signal VBf indicating the detected value to the control circuit 29. Output signals Iif, IBf, IOf, and ILf of the current detectors CD1 to CD4 (FIG. 1) are provided to the control circuit 29.

[0043] The power failure detector 26 detects whether or not a power failure has occurred in the bypass AC power supply 11 based on the output signal VIf of the voltage detector 21, and outputs a power failure detection signal φ26 indicating the detection result to the control circuit 29. When the bypass AC power supply 11 is healthy, the power failure detection signal φ26 is set to an inactivation level of "H" level. When a power failure has occurred in the bypass AC power supply 11, the power failure detection signal φ26 is set to an activation level of "L" level.

[0044] For example, when the AC input voltage VI is higher than a lower limit, the power failure detector 26 determines that the bypass AC power supply 11 is healthy and sets the power failure detection signal φ26 to the inactivation level "H" level. When the AC input voltage VI is lower than a lower limit, the power failure detector 26 determines that a power failure has occurred in the bypass AC power supply 11 and sets the power failure detection signal φ26 to the activation level "L" level.

[0045] The power failure detector 27 detects whether or not a power failure has occurred in the AC power supply 12 based on the output signal Vif of the voltage detector 22, and outputs a power failure detection signal φ27 indicating the detection result to the control circuit 29. When the AC power supply 12 is healthy, the power failure detection signal φ27 is set to an inactivation level of "H" level. When a power failure has occurred in the AC power supply 12, the power failure detection signal φ27 is set to an activation level of "L" level.

[0046] For example, when the AC input voltage Vi is higher than the lower limit, the power failure detector 27 determines that the AC power supply 12 is healthy and sets the power failure detection signal φ27 to the inactivation level "H" level. When the AC input voltage Vi is lower than the lower limit, the power failure detector 27 determines that a power failure has occurred in the AC power supply 12 and sets the power failure detection signal φ27 to the activation level "L" level.

[0047] The synchronous detector 28 determines whether or not the frequency and phase of the AC input voltage VI match those of the AC output voltage VO, and outputs a signal φ28 indicating the determination result. When the frequency and phase of the AC input voltage VI match those of the AC output voltage VO, the signal φ28 is set to "H" level, and when they do not match, the signal φ28 is set to "L" level.

[0048] The control circuit 29 controls the entire uninterruptible power supply based on output signals VIf, Vif, VOf, VDf, and VBf of the voltage detectors 21-25, output signals Iif, IBf, IOf, and ILf of the current detectors CD1-CD4, signals φ26, φ27, φ28, and signals from the operation unit 9.

[0049] That is, when the AC power supplies 11, 12 are healthy (φ26=H, φ27=H), the control circuit 29 turns on the semiconductor switch 1 and the switches S1 to S3, controls the converter 4 so that the DC voltage VD of the DC line 5 becomes the reference DC voltage VDR, and controls the bidirectional chopper 7 so that the battery voltage VB becomes the reference DC voltage VBR.

[0050] When the load current IL is equal to or less than the threshold current Ith, the control circuit 29 executes the bypass power supply mode and puts the inverter 8 into a standby state. In this case, AC power is supplied from the bypass AC power supply 11 to the load 14 via the semiconductor switch 1, and the load 14 is operated.

[0051] Moreover, when the load current IL is larger than the threshold current Ith, the control circuit 29 executes the inverter assisted power supply mode and controls the inverter 8 so that the AC output current IO of the inverter 8 becomes the assist current Ia=IL-Ith.

[0052] In this case, the threshold current Ith is supplied from the bypass AC power supply 11 to the load 14 via the semiconductor switch 1, and the assist current Ia is supplied from the inverter 8 to the load 14, so that the load 14 is operated by the load current IL=Ith+Ia, which is the sum of the threshold current Ith and the assist current Ia.

[0053] Therefore, even if the load current IL increases due to a load fluctuation, the current flowing through the semiconductor switch 1 is maintained at or below the threshold current Ith, so there is no need to turn off the semiconductor switch 1 to prevent overheating of the semiconductor switch 1. This makes it possible to realize an uninterruptible power supply that is resistant to load fluctuations. Also, since there is no need to use a large-capacity semiconductor switch 1 in preparation for an increase in the load current IL, the device can be made smaller and less expensive.

[0054] When a power outage occurs in the bypass AC power supply 11 (φ26=L), the control circuit 29 executes the battery power supply mode, turns off the semiconductor switch 1, and controls the inverter 8 so that the AC output voltage VO of the inverter 8 is maintained at the AC input voltage VI before the power outage. In this case, a load current IL is supplied from the inverter 8 to the load 14, and the load 14 is operated. Therefore, even when a power outage occurs in the bypass AC power supply 11, the operation of the load 14 can be continued as long as the AC power supply 12 is healthy.

[0055] When the bypass AC power supply 11 recovers from a power outage and becomes healthy, the control circuit 29 synchronizes the AC output voltage VO of the inverter 8 with the AC input voltage VI from the bypass AC power supply 11. When the frequency and phase of the AC output voltage VO match those of the AC input voltage VI and the output signal φ28 of the synchronization detector 28 is set to the “H” level, the control circuit 29 turns on the semiconductor switch 1.

[0056] When a power outage occurs in the AC power supply 12 (φ27=L), the control circuit 29 turns off the switch S1, stops the operation of the converter 4, and controls the bidirectional chopper 7 so that the DC voltage VD of the DC line 5 becomes the reference DC voltage VDR. Therefore, even if a power outage occurs in the AC power supplies 11 and 12, the operation of the load 14 can be continued for as long as DC power is stored in the battery 13.

[0057] When the AC power supply 12 recovers from a power outage and returns to a healthy state (φ27=L), the control circuit 29 turns on the switch S1 to start the operation of the converter 4 and controls the converter 4 so that the DC voltage VD of the DC line 5 becomes the reference DC voltage VD, and also controls the bidirectional chopper 7 so that the battery voltage VB becomes the reference DC voltage VBR.

[0058] Fig. 3 is a block diagram showing a portion of the control circuit 29 that is related to the control of the semiconductor switch 1. In Fig. 3, the control circuit 29 includes a control unit 31. The control unit 31 controls the semiconductor switch 1 and generates a control signal φ31 based on the output signal φ26 of the power failure detector 26 (Fig. 2), the output signal φ28 of the synchronous detector 28, and the output signal VIf of the voltage detector 21.

[0059] That is, when the bypass AC power supply 11 (FIG. 1) is healthy (φ26=H), the control unit 31 controls the thyristors 2 and 3 in synchronization with the AC input voltage VI indicated by the output signal VIf of the voltage detector 21 to turn on the semiconductor switch 1. When a power outage occurs in the bypass AC power supply 11 (FIG. 1) (φ26=L), the control unit 31 turns off the semiconductor switch 1.

[0060] When the bypass AC power supply 11 recovers from a power outage to a healthy state (φ26=H) and the frequency and phase of the AC output voltage VO of the inverter 8 match the frequency and phase of the AC input voltage VI from the bypass AC power supply 11 (φ28=H), the control unit 31 turns on the semiconductor switch 1.

[0061] The control signal φ31 is a signal that indicates the state of the semiconductor switch 1. When the semiconductor switch 1 is off, the control signal φ31 is set to an "H" level. When the semiconductor switch 1 is on, the control signal φ31 is set to an "L" level. The control signal φ31 will be described later.

[0062] 4(A) to (C) are time charts showing the operation of the control unit 31. In Fig. 4, (A) shows the waveform of the output signal φ26 of the power failure detector 26 (Fig. 2), (B) shows the waveform of the output signal φ28 of the synchronous detector 28 (Fig. 2), and (C) shows the waveform of the control signal φ31.

[0063] At a certain time t0, it is assumed that the bypass AC power supply 11 is healthy and the semiconductor switch 1 is on. At this time, the output signal φ26 of the power failure detector 26 is at the "H" level. Also, since the semiconductor switch 1 is on, the frequency and phase of the AC input voltage VI and the frequency and phase of the AC output voltage VO match, and the output signal φ28 of the synchronous detector 28 is at the "H" level. Also, since the semiconductor switch 1 is on, the control signal φ31 is at the "L" level.

[0064] Next, when a power outage occurs in the bypass AC power supply 11 at time t1, the signals φ26 and φ28 both fall from the "H" level to the "L" level, the semiconductor switch 1 is turned off, and the control signal φ31 rises to the "H" level.

[0065] Then, at time t2, when the bypass AC power supply 11 recovers from a power outage to a healthy state, the signal φ26 rises from the "L" level to the "H" level. Next, at time t3, when the frequency and phase of the AC output voltage VO of the inverter 8 match the frequency and phase of the AC input voltage VI from the bypass AC power supply 11, the signal φ28 rises from the "L" level to the "H" level. This turns on the semiconductor switch 1, and the control signal φ31 falls from the "H" level to the "L" level.

[0066] Fig. 5 is a block diagram showing a portion of control circuit 29 related to the control of inverter 8. In Fig. 5, control circuit 29 includes a phase synchronization control unit 40, a voltage command unit 41, current control units 42 and 53, voltage control units 43 and 52, PWM (Pulse Width Modulation) control units 44 and 54, a selector 45, a calculation unit 50, and a current command unit 51.

[0067] When the bypass AC power supply 11 is healthy (φ26=H), the phase synchronization control unit 40 outputs an AC signal vac having the same frequency and phase as the AC input voltage VI indicated by the output signal VIf of the voltage detector 21 (FIG. 2).

[0068] When a power outage occurs in the bypass AC power supply 11 (φ26=L), the phase synchronization control unit 40 continues to output the AC signal vac before the power outage. When the bypass AC power supply 11 recovers from the power outage to a normal state, the phase synchronization control unit 40 controls the frequency and phase of the AC signal vac so that the frequency and phase of the AC signal vac match the frequency and phase of the AC input voltage VI.

[0069] The voltage command unit 41 outputs a voltage command value Vc having the same frequency and phase as the AC signal vac. The current control unit 42 obtains a deviation ΔV=Vc-VO between the voltage command value Vc and the AC output voltage VO indicated by the output signal VOf of the voltage detector 23 (FIG. 2), and generates a current control value Ic so that the deviation ΔV is eliminated.

[0070] The voltage control unit 43 determines the deviation ΔI=Ic-IO between the current control value Ic from the current control unit 42 and the AC output current IO indicated by the output signal IOf of the current detector CD3 (Figure 1), and generates a voltage control value Vc1 so that the deviation ΔI is eliminated.

[0071] When the control signal φ31 (FIGS. 3 and 4) is at the “H” level, the selector 45 connects the PWM control unit 44 to the inverter 8, and when the control signal φ31 is at the “L” level, the selector 45 connects the PWM control unit 54 to the inverter 8.

[0072] When the control signal φ31 is at the “H” level, the PWM control unit 44 is coupled to the inverter 8 by the selector 45. The PWM control unit 44 generates a PWM signal in accordance with the voltage control value Vc1, and controls the inverter 8 by the PWM signal.

[0073] The calculation unit 50 compares the load current IL indicated by the output signal ILf of the current detector CD4 with the threshold current Ith. If IL>Ith, the calculation unit 50 subtracts the threshold current Ith from the load current IL to obtain an assist current Ia=IL-Ic, and outputs a signal Iaf indicating the assist current Ia to the current command unit 51. If IL≦Ith, the calculation unit 50 sets the assist current Ia to 0 A, and outputs a signal Iaf indicating that the assist current Ia is 0 A to the current command unit 51.

[0074] The current command unit 51 generates a current command value Ic1 having a value corresponding to the assist current Ia indicated by the signal Iaf. The current command value Ic1 is a sine wave signal having the same frequency and phase as the load current IL.

[0075] The voltage control unit 52 determines the deviation ΔI=Ic1-IO between the current command value Ic1 from the current command unit 51 and the AC output current IO of the inverter 8 indicated by the output signal IOf of the current detector CD3, and generates a voltage control value Vc2 so that the deviation ΔI is eliminated.

[0076] Current control unit 53 determines the deviation ΔV=Vc2-VO between voltage control value Vc2 and AC output voltage VO indicated by output signal VOf of voltage detector 23 (FIG. 2), and generates current control value Ic2 so that the deviation ΔV is eliminated.

[0077] When the control signal φ31 is at the “L” level, the PWM control unit 54 is coupled to the inverter 8 by the selector 45. The PWM control unit 54 generates a PWM signal in accordance with the current command value Ic2, and controls the inverter 8 by the PWM signal.

[0078] Here, a description will be given of the operation of the control circuit 29 shown in Fig. 5. When the semiconductor switch 1 is turned on by the control unit 31 (Fig. 3) and the control signal φ31 is set to the "L" level, the PWM control unit 54 and the inverter 8 are connected by the selector 45.

[0079] The calculation unit 50 compares the load current IL with the threshold current Ith, and if IL>Ith, generates a signal Iaf indicating the assist current Ia=IL-Ith, and if IL≦Ith, generates a signal Iaf indicating that the assist current Ia is 0 A.

[0080] A current command value Ic1 having a value corresponding to the assist current Ia is generated by a current command unit 51, and a voltage control unit 52 generates a voltage command value Vc2 having a value corresponding to a deviation ΔI=Ic1-IO between the current command value Ic1 and the output current IO of the inverter 8. In addition, a current control unit 53 generates a current command value Ic2 having a value corresponding to a deviation ΔV=Vc2-VO between the voltage command value Vc2 and the AC output voltage VO. A PWM control unit 54 controls the output current IO of the inverter 8 according to the current command value Ic2. As a result, an assist current Ia is supplied from the inverter 8 to the load 14.

[0081] When the semiconductor switch 1 is turned off by the control unit 31 (FIG. 3) and the control signal φ31 is set to the “H” level, the PWM control unit 44 and the inverter 8 are connected by the selector 45.

[0082] A phase synchronization control unit 40 generates an AC signal vac having the same frequency and phase as the AC input voltage VI, and a voltage command unit 41 generates a voltage command value Vc having the same frequency and phase as the AC signal vac.

[0083] Further, a current command value Ic having a value corresponding to the deviation ΔV=Vc-VO between the voltage command value Vc and the AC output voltage VO is generated by a current control unit 42. A voltage control unit 43 generates a voltage command value Vc1 having a value corresponding to the deviation ΔI=Ic-IO between the current command value Ic and the output current IO of the inverter 8. A PWM control unit 44 controls the output voltage VO of the inverter 8 in accordance with the voltage command value Vc1. As a result, even if a power outage occurs in the bypass AC power supply 11, the AC voltage VO is supplied from the inverter 8 to the load 14, and the operation of the load 14 continues.

[0084] Fig. 6 is a flowchart showing the operation of the uninterruptible power supply shown in Fig. 1 to Fig. 5. However, for the sake of simplicity of explanation, it is assumed that AC power sources 11 and 12 are both commercial AC power sources.

[0085] When the power supply of the uninterruptible power supply is turned on using the operation unit 9 while the bypass AC power supply 11 is healthy, the inverter-assisted power supply mode is executed in step ST1. That is, the semiconductor switch 1 is turned on, the converter 4 is controlled so that the DC voltage VD of the DC line 5 becomes the reference DC voltage VDR, and the bidirectional chopper 7 is controlled so that the battery voltage VB becomes the reference DC voltage VBR.

[0086] When the load current IL is equal to or less than the threshold current Ith, the inverter 8 is placed in a standby state. When the load current IL exceeds the threshold current Ith, the inverter 8 supplies the assist current Ia=IL-Ith to the load 14.

[0087] In step ST2, it is determined whether or not a power outage has occurred in the bypass AC power supply 11, i.e., whether or not the power outage detection signal φ36 is at the “L” level. If the signal φ36 is not at the “L” level, the inverter-assisted power supply mode is continued in step ST1.

[0088] When the signal φ36 is at the “L” level, the battery power supply mode is executed in step ST3. That is, the semiconductor switch 1 is turned off, the switch S1 is turned off, and the operation of the converter 4 is stopped. Also, the bidirectional chopper 7 is controlled so that the DC voltage VD of the DC line 5 becomes the reference DC voltage VDR, and the AC voltage VO is supplied from the inverter 8 to the load 14 to operate the load 14.

[0089] In step ST4, it is determined whether the bypass AC power supply 11 has recovered to a healthy state, i.e., whether the power failure detection signal φ36 is at the “H” level. If the signal φ36 is not at the “H” level, the battery power supply mode is continued in step ST3. If the signal φ36 is at the “H” level, the inverter-assisted power supply mode is executed in step ST1.

[0090] Fig. 7 is a circuit block diagram for explaining the operation of the uninterruptible power supply device in the inverter-assisted power supply mode. In Fig. 7, for the sake of simplicity of the drawing and explanation, the terminals T1 to T4, the current detectors CD1 to CD4, the operation unit 9, and the control device 10 (Fig. 1) are omitted. In Fig. 7, the arrows indicate the paths through which power is supplied.

[0091] In the inverter-assisted power supply mode, the semiconductor switch 1 is turned on, and AC power is supplied from the bypass AC power supply 11 to the load 14 via the semiconductor switch 1. In addition, the switches S1 to S3 are turned on, and the AC power supplied from the AC power supply 12 is converted to DC power by the converter 4. The DC power is stored in the battery 13 by the bidirectional chopper 7 and is supplied to the inverter 8.

[0092] When the load current IL is equal to or less than the threshold current Ith, the inverter 8 is placed in a standby state, and the AC output current IO of the inverter 8 is maintained at 0 A. When the load current IL exceeds the threshold current Ith, the excess assist current Ia=IL-Ith is supplied from the inverter 8 to the load 14.

[0093] Here, it is assumed that the capacitance of the semiconductor switch 1, the capacitance of the converter 4, the capacitance of the bidirectional chopper 7, and the capacitance of the inverter 8 are set to the same value. Also, it is assumed that the power that can be supplied by each of the semiconductor switch 1, the converter 4, the bidirectional chopper 7, and the inverter 8 is 100%, and the power consumption of the load 14 varies from 100% to 200%.

[0094] When the power consumption of the load 14 is 100%, 100% of the power is supplied to the load 14 from the bypass AC power supply 11 via the semiconductor switch 1. In this case, the power supplied from the inverter 8 to the load 14 is maintained at 0%.

[0095] When the power consumption of the load 14 fluctuates and exceeds 100%, 100% of the power is supplied from the bypass AC power supply 11 to the load 14 via the semiconductor switch 1, and the excess power is supplied from the inverter 8 to the load 14.

[0096] 7 shows a case where the power consumption of the load 14 has increased to 200%. In this case, 100% of the power is supplied from the bypass AC power supply 11 via the semiconductor switch 1 to the load 14, and 100% of the power is supplied from the AC power supply 12 via the converter 4 to the inverter 8, and 100% of the power is supplied from the inverter 8 to the load 14. However, it is assumed that the battery 13 is already fully charged and the current flowing through the battery 13 is sufficiently small.

[0097] Fig. 8 is a circuit block diagram for explaining the operation of the uninterruptible power supply in the battery power supply mode, and is a diagram to be compared with Fig. 7. The battery power supply mode is executed when AC power supplies 11, 12 experience a power outage.

[0098] In this case, the semiconductor switch 1 is turned off to disconnect the bypass AC power supply 11 and the load 14, and the switch S1 is turned off to disconnect the AC power supply 12 and the converter 4, and the operation of the converter 4 is stopped. Also, 100% of the power is supplied from the battery 13 to the inverter 8 via the bidirectional chopper 7, and 100% of the power is supplied from the inverter 8 to the load 14.

[0099] Here, in order to clarify the effect of this embodiment, a conventional uninterruptible power supply will be described as a comparative example. Fig. 9 is a circuit block diagram for explaining the operation of the comparative example, and is a diagram to be compared with Fig. 7. Referring to Fig. 9, the comparative example differs from this embodiment in that the semiconductor switch 1 is removed.

[0100] When the AC power supply 12 is healthy, the inverter power supply mode is executed, the switches S1 to S3 are turned on, and the AC power supplied from the AC power supply 12 is converted into DC power by the converter 4. The DC power is stored in the battery 13 by the bidirectional chopper 7 and is also converted back into AC power by the inverter 8 and supplied to the load 14.

[0101] 9 shows a case where the power consumption of the load 14 is 100%. In this case, 100% of the power is supplied from the AC power source 12 via the converter 4 to the inverter 8, and 100% of the power is supplied from the inverter 8 to the load 14. However, it is assumed that the battery 13 is already fully charged, and the current flowing through the battery 13 is sufficiently small.

[0102] Fig. 10 is a circuit block diagram for explaining another operation of the comparative example, and is a diagram to be compared with Fig. 9. In Fig. 10, when the AC power supply 12 has a power failure, the battery power supply mode is executed. In this case, the switch S1 is turned off to disconnect the AC power supply 12 from the converter 4, and the operation of the converter 4 is stopped. In addition, DC power is supplied from the battery 13 to the inverter 8 via the bidirectional chopper 7, and the DC power is converted into AC power by the inverter 8 and supplied to the load 14.

[0103] 10 shows a case where the power consumption of the load 14 is 100%. In this case, 100% of the power is supplied from the battery 13 to the inverter 8 via the bidirectional chopper 7, and 100% of the power is supplied from the inverter 8 to the load 14.

[0104] Fig. 11 is a diagram for explaining the effect of this embodiment. In Fig. 11, (A) is a diagram showing the performance of a comparative example, and (B) is a diagram showing the performance of this embodiment. In the comparative example, as shown in Fig. 11(A), the inverter power supply mode is executed when the AC power supply 12 is healthy. When the power consumption of the load 14 is 100%, that is, when the load factor is 100%, the operation of the load 14 can be stably performed (circle mark).

[0105] However, if the load factor increases to 125%, the temperature of the inverter 8 rises and reaches the upper limit temperature in, for example, 10 minutes. This requires that the operation of the inverter 8 be stopped, and the load 14 can only be operated for, for example, 10 minutes (△ mark). If the load factor increases to 150%, the temperature of the inverter 8 reaches the upper limit temperature in, for example, 1 minute, and the load 14 can only be operated for, for example, 1 minute (△ mark). If the load factor increases to 200%, an overcurrent is detected, the operation of the inverter 8 is stopped, and the power supply to the load 14 is stopped (X mark).

[0106] In the comparative example, the battery power supply mode is executed when the AC power supply 12 experiences a power outage. When the power consumption of the load 14 is 100%, i.e., when the load factor is 100%, the operation of the load 14 can be continued (marked with a circle). When the load factor exceeds 125%, an overcurrent is detected, the operation of the inverter 8 is stopped, and the power supply to the load 14 is stopped (marked with an x).

[0107] 11(B), in the present embodiment, the inverter-assisted power supply mode is executed when the AC power supplies 11 and 12 are healthy. When the load factor is 100%, 100% of the power is supplied from the bypass AC power supply 11 to the load 14 via the semiconductor switch 1, so that the operation of the load 14 can be stably performed (marked with a circle).

[0108] Furthermore, when the load factor is 100 to 200%, 100% of the power is supplied from the bypass AC power supply 11 via the semiconductor switch 1 to the load 14, and the excess power of 0 to 100% is supplied from the AC power supply 12 via the converter 4 and the inverter 8 to the load 14, thereby enabling the load 14 to operate stably (marked with a circle).

[0109] In this embodiment, the battery power supply mode is executed when the AC power sources 11, 12 fail. When the load factor is 100%, the operation of the load 14 can be continued (marked with a circle). When the load factor exceeds 125%, an overcurrent is detected, the operation of the inverter 8 is stopped, and the power supply to the load 14 is stopped (marked with a cross). This is the same as in the comparative example.

[0110] As described above, in this embodiment, when the load current IL is larger than the threshold current Ith while the bypass AC power supply 11 is healthy, the assist current Ia=IL-Ith, which is the difference between the load current IL and the threshold current Ith, is supplied from the inverter 8 to the load 14. Therefore, even if the load current IL increases due to a load fluctuation, the current flowing through the semiconductor switch 1 can be maintained at or below the threshold current Ith, and overheating of the semiconductor switch 1 can be prevented. Therefore, it is possible to prevent the semiconductor switch 1 from being turned off and the operation of the load 14 from being stopped, and an uninterruptible power supply device that is resistant to load fluctuations can be realized. In addition, since it is not necessary to use a large-capacity semiconductor switch 1 in preparation for an increase in the load current IL, the device can be made smaller and less expensive.

[0111] Fig. 12 is a circuit block diagram showing a modification of the embodiment, and is a diagram to be compared with Fig. 7. Referring to Fig. 12, this modification differs from the embodiment in that converter 4 is replaced with converter 4A. The capacity (i.e., size) of converter 4A is reduced to X% of the capacity (i.e., size) of converter 4. X is a real number greater than 0 and less than 100. Fig. 12 shows a case where X=50.

[0112] 12, the inverter-assisted power supply mode is executed when the AC power sources 11 and 12 are healthy. When the load factor is 100%, 100% of the power is supplied from the bypass AC power source 11 to the load 14 via the semiconductor switch 1. When the load factor increases to 150%, 100% of the power is supplied from the bypass AC power source 11 to the load 14 via the semiconductor switch 1, and the excess 50% of the power is supplied from the AC power source 12 to the load 14 via the converter 4 and the inverter 8.

[0113] In this modification, the size of the converter can be made smaller than that of the embodiment, and the device can be made more compact.

[0114] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The present invention is defined by the claims rather than the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0115] T1 bypass input terminal, T2 input terminal, T3 DC terminal, T4 output terminal, 1 semiconductor switch, 2, 3 thyristor, S1 to S3 switches, 4 converter, CD1 to CD4 current detectors, 5 DC line, 6 capacitor, 7 bidirectional chopper, 8 inverter, 9 operation unit, 10 control device, 11 bypass AC power supply, 12 AC power supply, 13 battery, 14 load, 21 to 25 voltage detectors, 26, 27 power failure detector, 28 synchronization detector, 29 control circuit, 31 control unit, 40 phase synchronization control unit, 41 voltage command unit, 42, 53 current control unit, 43, 52 voltage control unit, 44, 54 PWM control unit, 45 selector, 50 calculation unit, 51 current command unit.

Claims

1. a semiconductor switch connected between a first AC power source and a load, the semiconductor switch being turned on when the first AC power source is healthy and turned off when a power failure occurs in the first AC power source; an inverter that converts DC power supplied from a DC power source into AC power and supplies the AC power to the load when the first AC power source is out of power, and when a load current is greater than a threshold current when the first AC power source is in a normal state, supplies an assist current that is a difference between the load current and the threshold current to the load; the inverter is placed in a standby state in which it does not supply or receive current to or from the first AC power supply and the load when the load current is smaller than the threshold current while the first AC power supply is in a normal state; The DC power supply is a converter that converts AC power supplied from the second AC power source into DC power; and a power storage device that stores DC power; when the load current is smaller than the threshold current while the first and second AC power sources are healthy, DC power generated by the rectifier is stored in the power storage device, and the inverter is placed in the standby state; when the load current is greater than the threshold current while the first and second AC power sources are healthy, the inverter generates the assist current based on the DC power generated by the forward converter; When the first and second AC power supplies fail, the DC power of the power storage device is converted into AC power by the inverter and supplied to the load.

2. 2. The uninterruptible power supply according to claim 1, wherein the threshold current is set to be equal to or lower than a rated current of the semiconductor switch.

3. 2. The uninterruptible power supply according to claim 1, wherein the capacity of the converter is set smaller than the capacity of the inverter.

Images