Uninterruptible power supply and method for controlling the uninterruptible power supply

Abstract

To suppress fluctuations in an output voltage when switching from commercial power supply to inverter power supply due to the occurrence of an overvoltage in a commercial AC power supply in an uninterruptible power supply.SOLUTION: When a commercial AC power supply 1 is normal, an uninterruptible power supply 100 executes commercial power supply in which an AC input voltage is supplied to a load 2 via a switch 10, and when a power outage or overvoltage occurs in the commercial AC power supply 1, the switch 10 is turned off and the uninterruptible power supply 100 transitions to inverter power supply in which a bidirectional converter 12 converts the DC voltage of a power storage device 3 into an AC output voltage and supplies the AC output voltage to the load 2. When a power outage or overvoltage occurs in the commercial AC power supply 1, a control device 16 generates a control command for the bidirectional converter 12 by control calculation for compensating for deviation of the AC output voltage from the output voltage command value. When an overvoltage occurs in the commercial AC power supply 1, the control device 16 reduces change in the control command relative to a change in the AC output voltage compared to when a power outage occurs in the commercial AC power supply 1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an uninterruptible power supply and a method for controlling the uninterruptible power supply. [Background technology]

[0002] For example, Japanese Patent Laid-Open Publication No. 2006-187089 (Patent Document 1) discloses an uninterruptible power supply using a parallel processing system. This uninterruptible power supply is configured to supply AC power from the commercial AC power supply to a load via a high-speed switch when the commercial AC power supply is normal, and to control a bidirectional converter to convert the AC power supplied from the commercial AC power supply into DC power and charge the storage battery. If a power outage occurs in this state, the high-speed switch is turned off to instantly disconnect the commercial AC power supply, and the bidirectional converter switches to inverter power supply, which converts the power stored in the storage battery into AC power and supplies it to the load, thereby continuing to supply power to the load. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-187089 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-described parallel processing type uninterruptible power supply, in order to compensate for a power outage of the commercial AC power supply, the deviation between the output voltage of the bidirectional converter and a predetermined voltage command value is determined, and the bidirectional converter is controlled to eliminate this deviation.

[0005] Therefore, even if an overvoltage occurs in the commercial AC power supply, the overvoltage can be compensated for by controlling the bidirectional converter to eliminate the deviation between the voltage command value and the output voltage, just as in the case of a power outage.

[0006] However, when output voltage control for compensating for power outages is applied to output voltage control for compensating for overvoltages, the amount of control relative to the deviation may become excessive, and undershoot may occur in the output voltage when switching to inverter power supply. In this case, there is a concern that fluctuations in the output voltage may cause unstable operation of the load.

[0007] The present disclosure has been made to solve such problems, and an object of the present disclosure is to suppress fluctuations in output voltage when switching from commercial power supply to inverter power supply due to the occurrence of an overvoltage in the commercial AC power supply in an uninterruptible power supply configured to be able to switch between commercial power supply and inverter power supply. [Means for solving the problem]

[0008] An uninterruptible power supply according to an aspect of the present disclosure is connected between a commercial AC power supply and a load. The uninterruptible power supply includes an input terminal receiving an AC input voltage from the commercial AC power supply, an output terminal connected to the load, a switch connected between the input terminal and the output terminal, a bidirectional converter connected between the output terminal and a power storage device, and a control device controlling the switch and the bidirectional converter. When the commercial AC power supply is normal, the uninterruptible power supply turns on the switch and performs commercial power supply, supplying the AC input voltage to the load via the switch. In response to a power outage or overvoltage of the commercial AC power supply, the uninterruptible power supply turns off the switch and transitions to inverter power supply, in which the bidirectional converter converts a DC voltage of the power storage device into an AC output voltage and supplies the AC output voltage to the load. When a power outage or overvoltage of the commercial AC power supply occurs, the control device is configured to generate a control command for the bidirectional converter by performing a control calculation to compensate for a deviation of the AC output voltage from an output voltage command value. When an overvoltage of the commercial AC power supply occurs, the control device reduces a change in the control command relative to a change in the AC output voltage compared to when a power outage of the commercial AC power supply occurs.

[0009] A control method for an uninterruptible power supply according to another aspect of the present disclosure is a control method for an uninterruptible power supply connected between a commercial AC power supply and a load. The uninterruptible power supply includes an input terminal receiving an AC input voltage from the commercial AC power supply, an output terminal connected to the load, a switch connected between the input terminal and the output terminal, and a bidirectional converter connected between the output terminal and a power storage device. The control method includes the steps of: when the commercial AC power supply is normal, turning on the switch to perform commercial power supplying, in which the AC input voltage is supplied to the load via the switch; and, in response to a power outage or overvoltage of the commercial AC power supply, turning off the switch and transitioning to inverter power supplying, in which the bidirectional converter converts a DC voltage of the power storage device into an AC output voltage and supplies the AC output voltage to the load. The step of transitioning to inverter power supplying includes the step of generating a control command for the bidirectional converter by performing a control calculation to compensate for a deviation of the AC output voltage from an output voltage command value. In the step of generating the control command, when an overvoltage of the commercial AC power supply occurs, a change in the control command relative to a change in the AC output voltage is made smaller than when a power outage of the commercial AC power supply occurs. [Effects of the Invention]

[0010] According to the present disclosure, it is possible to suppress fluctuations in the output voltage of an uninterruptible power supply when switching from commercial power supply to inverter power supply due to the occurrence of an overvoltage in the commercial AC power supply. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a circuit block diagram showing the configuration of an uninterruptible power supply device that forms the basis of the present disclosure. [Figure 2] FIG. 2 is a diagram illustrating the operation of the uninterruptible power supply during normal operation. [Figure 3] FIG. 10 is a block diagram showing the configuration of a converter control unit according to a comparative example. [Figure 4] FIG. 3 is a waveform diagram showing a change over time in AC output voltage when a power outage occurs in the commercial AC power supply. [Figure 5] 4 is a waveform diagram showing a change in AC output voltage over time when an overvoltage occurs in a commercial AC power supply. FIG. [Figure 6] 2 is a block diagram showing a configuration of a converter control unit included in a control device of the uninterruptible power supply according to the first embodiment. FIG. [Figure 7] 5A and 5B are diagrams for explaining a process for generating an output voltage command value in an output voltage command generating unit. [Figure 8] 10 is a flowchart illustrating an example of a procedure for generating an output voltage command value executed by an output voltage command generating unit. [Figure 9] 4 is a waveform diagram showing a change over time in the AC output voltage supplied from the uninterruptible power supply according to the first embodiment to a load. FIG. [Figure 10] 10A and 10B are diagrams for explaining a modified example of the process of generating an output voltage command value in the output voltage command generating unit. [Figure 11] FIG. 11 is a block diagram showing a configuration of a converter control unit included in a control device of an uninterruptible power supply according to a second embodiment. [Figure 12] 12 is a flowchart showing an example of a procedure of a process executed in a voltage control unit shown in FIG. [Figure 13] FIG. 11 is a block diagram showing a configuration of a converter control unit included in a control device of an uninterruptible power supply according to a modification of the second embodiment. [Figure 14] 10 is a flowchart illustrating an example of a procedure of a process executed in a voltage control unit. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0013] [Uninterruptible power supply configuration] First, an uninterruptible power supply (UPS) on which this disclosure is based will be described. Fig. 1 is a circuit block diagram showing the configuration of the uninterruptible power supply (UPS) on which this disclosure is based. The uninterruptible power supply (UPS) 100 supplies a three-phase AC voltage supplied from a commercial AC power supply 1 or a bidirectional converter 12 to a load 2, but for the sake of simplicity of the drawings and explanation, Fig. 1 only shows the parts related to one phase.

[0014] As shown in FIG. 1, the uninterruptible power supply 100 includes an input terminal T1, an output terminal T2, a DC terminal T3, VCBs (Vacuum Circuit Breakers) 4, 6, and 8, a high-speed switch (HSS) 10, a bidirectional converter 12, a bidirectional chopper 14, a reactor L1, capacitors C1 and C2, current detectors CD1 and CD2, and a control device 16.

[0015] The input terminal T1 receives an AC input voltage VI of a commercial frequency supplied from a commercial AC power supply 1. The instantaneous value of the AC input voltage VI is detected by a control device 16. The control device 16 determines that a power outage has occurred in the commercial AC power supply 1 when the AC input voltage VI falls below a predetermined lower limit value VL. The control device 16 also determines that an overvoltage has occurred in the commercial AC power supply 1 when the AC input voltage VI exceeds a predetermined upper limit value VH.

[0016] The output terminal T2 is connected to a load 2. The load 2 is driven by an AC output voltage VO supplied from the output terminal T2. The instantaneous value of the AC output voltage VO is detected by the control device 16.

[0017] The DC terminal T3 is connected to the battery 3. The battery 3 stores DC power. The battery 3 corresponds to one example of a "power storage device." The power storage device may be a capacitor instead of the battery 3. The DC voltage VB at the DC terminal T3 (corresponding to the terminal voltage of the battery 3) is detected by the control device 16.

[0018] VCB4, HSS10, and VCB6 are connected in series between input terminal T1 and output terminal T2. VCB4 and VCB6 are turned on during normal operation of uninterruptible power supply 100, and are turned off, for example, during maintenance of HSS10 (during maintenance bypass power supply).

[0019] The HSS 10 is configured by, for example, a semiconductor switching element, and is controlled by the control device 16. The HSS 10 is turned on when the commercial AC power supply 1 is normal, and is turned off when the commercial AC power supply 1 is abnormal (due to a power outage or overvoltage). The HSS 10 corresponds to one embodiment of a "switch."

[0020] The VCB 8 is connected between the input terminal T1 and the output terminal T2. The VCB 8 is turned off during normal operation of the uninterruptible power supply 100 and turned on, for example, during maintenance bypass power supply. When the VCB 8 is turned on, an AC input voltage VI is supplied from the commercial AC power supply 1 to the load 2 via the VCB 8, and the load 2 operates.

[0021] An AC terminal 12a of the bidirectional converter 12 is connected to a node N1 between the HSS 10 and the VCB 6 via a reactor L1. A DC terminal 12b of the bidirectional converter 12 is connected to a DC line 13. The bidirectional converter 12 is a well-known device including a plurality of semiconductor switching elements and a plurality of diodes, and is controlled by a control device 16 using, for example, PWM (Pulse Width Modulation). By turning on and off each semiconductor switching element included in the bidirectional converter 12 at a predetermined switching frequency, it is possible to convert AC power to DC power, and conversely, to convert DC power to AC power.

[0022] The reactor L1 and capacitor C1 constitute an AC filter. The AC filter is a low-pass filter that passes commercial frequency current and blocks switching frequency current generated by the bidirectional converter 12. In other words, the AC filter converts the output voltage of the bidirectional converter 12 into a sinusoidal AC voltage.

[0023] The capacitor C2 is connected to the DC line 13 and smooths and stabilizes the DC voltage VD of the DC line 13. The instantaneous value of the DC voltage VD of the DC line 13 is detected by the control device 16.

[0024] The bidirectional chopper 14 is connected between the DC line 13 and the DC terminal T3. The bidirectional chopper 14 is controlled by a control device 16, and supplies DC power between the DC line 13 and the battery 3. The bidirectional chopper 14 is a well-known device that includes a plurality of semiconductor switching elements and a plurality of diodes.

[0025] The current detector CD1 detects the AC current Ii flowing through the HSS 10 and provides a signal Iif indicating the detected value to the control device 16. The current detector CD2 detects the AC current IL flowing through the reactor L1 and provides a signal ILf indicating the detected value to the control device 16.

[0026] The control device 16 controls the entire uninterruptible power supply 100 based on the AC voltages VI and VO, the DC voltages VD and VB, the output signal Iif of the current detector CD1, and the output signal ILf of the current detector CD2. The control device 16 can typically be configured with a microcomputer in which a predetermined program is pre-stored. For example, the control device 16 is configured to include a CPU (Central Processing Unit), memory, and input / output circuits. A program is pre-stored in a portion of the memory, and the mechanism shown in FIG. 1 can be realized by the CPU executing the program. Note that at least a portion of the control device 16 may be configured using circuits such as an FPGA (Field Programmable Gate Array) and an ASIC (Application Specific Integrated Circuit).

[0027] The control device 16 includes a power outage / overvoltage detection unit 20, a switch control unit 22, a converter control unit 24, and a chopper control unit .

[0028] The power failure / overvoltage detection unit 20 detects whether a power failure or overvoltage has occurred in the commercial AC power supply 1 based on the AC input voltage VI supplied from the commercial AC power supply 1, and outputs a power failure detection signal DU and an overvoltage detection signal DO indicating the detection results to the switch control unit 22, the converter control unit 24, and the chopper control unit 26.

[0029] Specifically, when the AC input voltage VI is higher than the lower limit VL and lower than the upper limit VH, the power outage / overvoltage detection unit 20 determines that the commercial AC power supply 1 is normal and sets the power outage detection signal DU and the overvoltage detection signal DO to the inactive H (logical high) level. On the other hand, when the AC input voltage VI is lower than the lower limit VL, the power outage / overvoltage detection unit 20 determines that a power outage has occurred in the commercial AC power supply 1 and sets the power outage detection signal DU to the active L (logical low) level. Furthermore, when the AC input voltage VI is higher than the upper limit VH, the power outage / overvoltage detection unit 20 determines that an overvoltage has occurred in the commercial AC power supply 1 and sets the overvoltage detection signal DO to the active L level.

[0030] The switch control unit 22 controls the on / off of the HSS 10 based on the power failure detection signal DU and the overvoltage detection signal DO. Specifically, when the commercial AC power supply 1 is normal (DU=DO=H), the switch control unit 22 turns on the HSS 10 to perform commercial power supply. In commercial power supply, AC power is supplied from the commercial AC power supply 1 to the load 2 via the VCB 4, HSS 10, and VCB 6, and the load 2 is operated.

[0031] Furthermore, when a power outage occurs in the commercial AC power supply 1 (DU=L) or when an overvoltage occurs in the commercial AC power supply 1 (DO=L), the switch control unit 22 turns off the HSS 10 to electrically disconnect the commercial AC power supply 1 from the load 2. In this case, inverter power supply is performed. During inverter power supply, AC power is supplied to the load 2 from the battery 3 via the bidirectional chopper 14 and the bidirectional converter 12. Therefore, as long as DC power is stored in the battery 3, the load 2 can continue to operate.

[0032] The converter control unit 24 controls the bidirectional converter 12 based on the power failure detection signal DU, the overvoltage detection signal DO, the AC output voltage VO, the DC voltage VD, and the output signals Iif and ILf of the current detectors CD1 and CD2. Specifically, during commercial power supply, AC power from the commercial AC power supply 1 is supplied to the bidirectional converter 12 via the VCB 4, the HSS 10, and the VCB 6. The bidirectional converter 12 converts the AC output voltage VO into a DC voltage VD and outputs it to the DC line 13. The converter control unit 24 controls the bidirectional converter 12 in synchronization with the AC output voltage VO so that the DC voltage VD of the DC line 13 becomes equal to the DC voltage command value VDR.

[0033] During inverter power supply, the bidirectional converter 12 converts the DC voltage VD supplied from the battery 3 via the bidirectional chopper 14 and the DC line 13 into an AC output voltage VO and supplies the AC output voltage VO to the load 2. The converter control unit 24 controls the bidirectional converter 12 so that the AC output voltage VO becomes equal to the output voltage command value VREF.

[0034] The chopper control unit 26 controls the bidirectional chopper 14 based on the power failure detection signal DU, the overvoltage detection signal DO, the DC voltages VD and VB, etc. Specifically, during commercial power supply, the bidirectional chopper 14 stores the DC power supplied from the bidirectional converter 12 via the DC line 13 in the battery 3. The chopper control unit 26 controls the bidirectional chopper 14 so that the DC voltage VB at the DC terminal T3 becomes the battery voltage command value VBR.

[0035] Furthermore, during inverter power supply, the bidirectional chopper 14 converts the DC voltage VB of the battery 3 into a DC voltage VD and outputs it to the DC line 13. The chopper control unit 26 controls the bidirectional chopper 14 so that the DC voltage VD of the DC line 13 becomes equal to the DC voltage command value VDR.

[0036] [Uninterruptible power supply operation] Next, the operation of the uninterruptible power supply 100 during normal operation will be described with reference to Figure 2. During normal operation, VCBs 4 and 6 are turned on, and VCB 8 is turned off. In Figure 2, the flow of power supplied from the uninterruptible power supply 100 to the load 2 is indicated by arrows.

[0037] When the commercial AC power supply 1 is normal (DU=DO=H), commercial power supply is executed. During commercial power supply, as shown in Fig. 2(A), the HSS 10 is turned on, and AC power is supplied from the commercial AC power supply 1 to the load 2 via the VCB 4, the HSS 10, and the VCB 6, and the load 2 is operated.

[0038] Furthermore, AC power is supplied from the commercial AC power supply 1 to the bidirectional converter 12 via the VCB 4 and the HSS 10, and the AC power is converted into DC power by the bidirectional converter 12 and supplied to the DC line 13. This DC power is stored in the battery 3 by the bidirectional chopper 14. At this time, the DC voltage VD of the DC line 13 is maintained at the DC voltage command value VDR.

[0039] If a power outage or overvoltage occurs in the commercial AC power supply 1 during commercial power supply (DU or DO = L), the system switches to inverter power supply. During inverter power supply, the HSS 10 is instantly turned off, and the commercial AC power supply 1 and the load 2 are electrically disconnected, as shown in Figure 2(B).

[0040] At the same time, DC power from the battery 3 is supplied to the DC line 13 by the bidirectional chopper 14. Then, the DC power is converted to AC power by the bidirectional converter 12 and supplied to the load 2, thereby continuing the operation of the load 2. At this time, the AC output voltage VO at the output terminal T2 is maintained at the output voltage command value VREF of the commercial frequency.

[0041] If the commercial AC power supply 1 is restored during inverter power supply, the HSS 10 is turned on again and commercial power supply is performed. In this case, the control device 16 controls the bidirectional converter 12 to match the phase and frequency of the AC output voltage VO with the phase and frequency of the AC input voltage VI, and then turns on the HSS 10. This makes it possible to prevent the AC output voltage VO from fluctuating and causing the operation of the load 2 to become unstable.

[0042] Furthermore, AC power from the commercial AC power supply 1 is converted to DC power by the bidirectional converter 12 and the bidirectional chopper 14 and stored in the battery 3. Therefore, according to the uninterruptible power supply 100, even if a power outage or overvoltage occurs in the commercial AC power supply 1, the operation of the load 2 can be continued.

[0043] [Problems with uninterruptible power supplies] Next, problems with the uninterruptible power supply 100 will be described.

[0044] As described above, when a power outage or overvoltage occurs in the commercial AC power supply 1, the HSS 10 is instantly turned off and the bidirectional chopper 14 and the bidirectional converter 12 are controlled to convert the DC power of the battery 3 into AC power, thereby causing the uninterruptible power supply 100 to switch from commercial power supply to inverter power supply.

[0045] At this time, the converter control unit 24 controls the bidirectional converter 12 so that the AC output voltage VO becomes equal to the output voltage command value VREF. This output voltage command value VREF corresponds to a target voltage of the AC output voltage VO that is set in advance based on the rated voltage VR of the commercial AC power supply 1. Note that the upper limit value VH and lower limit value VL in the power outage / overvoltage detection unit 20 correspond to the upper limit value and lower limit value, respectively, of an allowable voltage range that is set to be approximately ±10% of the rated voltage VR (target voltage).

[0046] Specifically, the converter control unit 24 calculates the deviation ΔVO=VREF-VO of the AC output voltage VO from the output voltage command value VREF, and performs a control calculation (for example, a proportional-plus-integral calculation) on the calculated deviation ΔVO to generate a voltage command value that is a control command for the bidirectional converter 12. Then, the converter control unit 24 controls the bidirectional converter 12 using the generated voltage command value.

[0047] Fig. 3 is a block diagram showing the configuration of converter control unit 24 according to the comparative example. As shown in Fig. 3, converter control unit 24 according to the comparative example includes a DC voltage control unit 240 for controlling DC voltage VD of DC line 13, and an AC voltage control unit 242 for controlling AC output voltage VO.

[0048] The DC voltage control unit 240 includes a DC voltage command generation unit 30, subtractors 32 and 36, a voltage control unit 34, and a current control unit 38. The DC voltage command generation unit 30 generates a DC voltage command value VDR that is a target voltage for the DC voltage VD. The subtractor 32 calculates the deviation ΔVD=VDR-VD between the DC voltage command value VDR and the DC voltage VD.

[0049] Voltage control unit 34 generates a current command value Ic1 so as to eliminate the deviation ΔVD calculated by subtractor 32. Subtractor 36 calculates the deviation ΔIL=Ic1-ILf between the current command value Ic1 and the AC current IL indicated by the output signal ILf of current detector CD2. Current control unit 38 generates a voltage command value Vc1 so as to eliminate the deviation ΔIL calculated by subtractor 36.

[0050] The AC voltage control unit 242 includes an output voltage command generating unit 40 , subtractors 42 and 46 , a voltage control unit 44 , and a current control unit 48 .

[0051] An output voltage command generating unit 40 generates an output voltage command value VREF, which is a target value for the AC output voltage VO. The output voltage command value VREF is set based on the rated voltage VR of the commercial AC power supply 1. A subtractor 42 calculates the deviation ΔVO=VREF-VO between the output voltage command value VREF and the AC output voltage VO.

[0052] The voltage control unit 44 generates a current command value Ic2 so that the deviation ΔVO calculated by the subtractor 42 disappears. The voltage control unit 44 can be configured as a PI controller that performs proportional and integral calculations on the deviation ΔO. Specifically, the voltage control unit 44 includes a proportional calculation unit 50, an integral calculation unit 52, and an adder 54. The proportional calculation unit 50 performs proportional calculations on the deviation ΔVO. The integral calculation unit 52 performs integral calculations on the deviation ΔVO. The adder 54 generates the current command value Ic2 by adding the results of the proportional calculation and the integral calculations. Note that the voltage control unit 44 may also be configured as a PID controller that further performs differential calculations. As a result, the AC output voltage VO is feedback-controlled so that it is equal to the output voltage command value VREF.

[0053] The subtractor 46 calculates the deviation ΔIL=Ic2-ILf between the current command value Ic2 and the AC current IL indicated by the output signal ILf of the current detector CD2. The current control unit 48 generates the voltage command value Vc2 so that the deviation ΔIL calculated by the subtractor 46 is eliminated.

[0054] The selector 244 selects either the voltage command value Vc1 or the voltage command value Vc2 based on the power outage detection signal DU and the overvoltage detection signal DO output from the power outage / overvoltage detection unit 20. Specifically, when the power outage detection signal DU and the overvoltage detection signal DO are both at H level, that is, when the commercial AC power supply 1 is normal, the selector 244 selects the voltage command value Vc1 and provides the selected voltage command value Vc1 to the PWM control unit 246. On the other hand, when the power outage detection signal DU or the overvoltage detection signal DO is at L level, that is, when a power outage or an overvoltage has occurred in the commercial AC power supply 1, the selector 244 selects the voltage command value Vc2 and provides the selected voltage command value Vc2 to the PWM control unit 246.

[0055] The PWM control unit 246 compares the voltage command value Vc1 or Vc2 provided by the selector 244 with a carrier signal (e.g., a triangular wave signal) of a predetermined frequency, and generates a gate signal for the bidirectional converter 12 based on the comparison result. The gate signal turns on and off multiple semiconductor switching elements constituting the bidirectional converter 12.

[0056] That is, when the commercial AC power supply 1 is normal, the bidirectional converter 12 is controlled based on the voltage command value Vc1, and is thereby able to output a DC voltage VD equal to the DC voltage command value VDR to the DC line 13.

[0057] Furthermore, when a power outage or overvoltage occurs in the commercial AC power supply 1, the bidirectional converter 12 is controlled based on the voltage command value Vc2, thereby being able to supply the AC output voltage V0 equal to the output voltage command value V0 to the load 2.

[0058] Fig. 4 is a waveform diagram showing the change over time in the AC output voltage VO when a power outage occurs in the commercial AC power supply 1. Fig. 4 collectively shows the instantaneous values ​​of the three-phase line voltages supplied from the commercial AC power supply 1 or the bidirectional converter 12.

[0059] In Fig. 4, the commercial AC power supply 1 is normal at time t0, and a power outage occurs in the commercial AC power supply 1 at time t1, which is later than time t0. During the period from time t0 to time t1, commercial power supply (see Fig. 2(A)) is performed. Therefore, the AC output voltage VO becomes equal to the AC input voltage VI supplied from the commercial AC power supply 1.

[0060] At time t1, when it is detected that the AC input voltage VI has dropped below the lower limit value VL, causing a power outage in the commercial AC power supply 1, the control device 16 turns off the HSS 10 and switches the uninterruptible power supply 100 from commercial power supply to inverter power supply (see FIG. 2(B)).

[0061] At this time, a switching time occurs, which is the time from when an OFF command is given to the HSS 10 until the HSS 10 is turned off. This switching time is the time from time t1 to time t2 in Figure 4, and typically has a length of several ms to several tens of ms. During the switching time, commercial power supply and inverter power supply are performed in parallel, so that AC voltage is supplied to the load 2 from both the commercial AC power supply 1 and the bidirectional converter 12.

[0062] As described above, the bidirectional converter 12 is controlled in accordance with the voltage command value Vu2 generated by proportional-plus-integral calculation of the deviation ΔVO=VREF-VO between the AC output voltage VO and the output voltage command value VREF set based on the rated voltage VR of the commercial AC power supply 1. Since the deviation ΔVO is a positive value immediately after the start of control, the amount of change in the voltage command value Vu2 also becomes a positive value.

[0063] Therefore, the AC output voltage VO, which has fallen below the lower limit VL, rises above the output voltage command value VREF and then fluctuates while converging toward the rated voltage VR. As shown in FIG. 4, by controlling the bidirectional converter 12 so that the AC output voltage VO falls within the allowable voltage range at time t2 when the switching time ends, it is possible to suppress a decrease in the AC output voltage VO after the HSS 10 is turned off. This can be achieved by determining the response speed of the proportional-integral control in the voltage control unit 44 of the AC voltage control unit 242 (see FIG. 3) according to the length of the switching period. As an example, the AC output voltage VO can be quickly brought closer to the rated voltage VR by increasing the proportional gain Kp of the proportional calculation unit 50 and the integral gain Ki of the integral calculation unit 52.

[0064] Fig. 5 is a waveform diagram showing the change over time in the AC output voltage VO when an overvoltage occurs in the commercial AC power supply 1. As in Fig. 4, Fig. 5 collectively shows the instantaneous values ​​of the three-phase line voltages supplied from the commercial AC power supply 1 or the bidirectional converter 12.

[0065] 5, the commercial AC power supply 1 is normal at time t0, and an overvoltage occurs in the commercial AC power supply 1 at time t1, which is later than time t0. During the period from time t0 to time t1, commercial power supply (see FIG. 2(A)) is performed, so the AC output voltage VO is equal to the AC input voltage VI supplied from the commercial AC power supply 1.

[0066] At time t1, when an overvoltage of the commercial AC power supply 1 is detected due to the AC input voltage VI exceeding the upper limit value VH, the control device 16 turns off the HSS 10 and switches the uninterruptible power supply 100 from commercial power supply to inverter power supply (see FIG. 2(B)).

[0067] As in Fig. 4, during the switching period from time t1 to time t2, commercial power supply and inverter power supply are executed in parallel. The bidirectional converter 12 is controlled in accordance with a voltage command value Vu2 generated by proportional-integral calculation of the deviation ΔVO=VREF-VO between the output voltage command value VREF and the AC output voltage VO. In contrast to Fig. 4, the deviation ΔVO is a negative value immediately after the start of control, and therefore the amount of change in the voltage command value Vu2 is a negative value.

[0068] During the switching time, the AC input voltage VI supplied from the commercial AC power supply 1 is higher than the AC voltage output from the bidirectional converter 12, so the AC output voltage VO becomes equal to the AC input voltage VI. Then, when the HSS 10 is turned off at time t2, the AC output voltage VO becomes equal to the AC voltage output from the bidirectional converter 12. In other words, the AC output voltage VO instantaneously switches from the AC input voltage VI to the output voltage of the bidirectional converter 12.

[0069] In FIG. 5, after time t2 when the switching time ends, the AC output voltage VO undershoots the output voltage command value VREF. The magnitude of this undershoot increases as the amount of change in the voltage command value Vu2 relative to the deviation ΔVO increases. This undershoot may cause the AC output voltage VO to fall outside the allowable voltage range immediately after the switching time ends. As a result, there is a concern that the operation of the load 2 may become unstable.

[0070] One possible cause of such undershoot of the AC output voltage VO is that the response speed of the proportional-integral control in the AC voltage control unit 242 is determined from the viewpoint of compensating for a power outage of the commercial AC power supply 1. That is, because the response speed of the proportional-integral control in the voltage control unit 44 is determined in order to quickly restore the reduced AC output voltage VO to the rated voltage VR within the switching time, when compensating for an overvoltage of the commercial AC power supply 1, the manipulated variable of the voltage command value Vu2 becomes excessive, which is thought to cause an undershoot of the AC output voltage VO.

[0071] An object of the present disclosure is to suppress undershoot of the AC output voltage VO that occurs when compensating for such an overvoltage of the commercial AC power supply 1. In the following first and second embodiments, means for solving this object will be described in detail.

[0072] [Embodiment 1] Figure 6 is a block diagram showing the configuration of converter control unit 24A included in control device 16 of uninterruptible power supply 100 according to embodiment 1. Uninterruptible power supply 100 according to embodiment 1 has the same configuration as uninterruptible power supply 100 shown in Figures 1 and 3 except for the configuration of converter control unit 24A in control device 16, and therefore will not be shown or described again.

[0073] 6, converter control unit 24A includes a DC voltage control unit 240, an AC voltage control unit 242A, a selector 244, and a PWM control unit 246. Converter control unit 24A is obtained by replacing AC voltage control unit 242 included in converter control unit 24 shown in FIG. 3 with AC voltage control unit 242A.

[0074] AC voltage control unit 242A is configured to include output voltage command generation unit 40A, subtractors 42 and 46, voltage control unit 44, and current control unit 48. AC voltage control unit 242A differs from AC voltage control unit 242 shown in FIG. 3 in that AC voltage control unit 242A includes output voltage command generation unit 40A instead of output voltage command generation unit 40.

[0075] The output voltage command generating unit 40A receives the AC input voltage VI, the output signal Iif of the current detector CD1, and the overvoltage detection signal DO. The output voltage command generating unit 40A generates an output voltage command value VREF based on these signals.

[0076] Fig. 7 is a diagram for explaining the generation process of the output voltage command value VREF in the output voltage command generating unit 40A. Fig. 7 shows the time waveform (corresponding to the dashed line in the figure) of the AC input voltage VI supplied from the commercial AC power supply 1 and the time waveform (corresponding to the solid line in the figure) of the output voltage command value VREF. Both VI and VREF collectively show the instantaneous values ​​of the three-phase line voltages.

[0077] 7, the AC input voltage VI from the commercial AC power supply 1 is lower than the upper limit value VH during the period from time ta to time tc, and exceeds the upper limit value VH after time tc. During the period from time ta to time tc, the HSS 10 in the uninterruptible power supply 100 is turned on, and commercial power supply (see FIG. 2(A)) is performed. Therefore, the AC output voltage VO becomes equal to the AC input voltage VI.

[0078] At time tc, when the AC input voltage VI exceeds the upper limit value VH and an overvoltage is detected in the commercial AC power supply 1, the HSS 10 is turned off and the uninterruptible power supply 100 switches from commercial power supply to inverter power supply (see FIG. 2(B)). At time td, which is a switching time after time tc, the HSS 10 is turned off.

[0079] The output voltage command generating unit 40A is configured to variably set the output voltage command value VREF in accordance with the AC input voltage VI. Specifically, the output voltage command generating unit 40A compares the AC input voltage VI with the rated voltage VR (target voltage) of the commercial AC power supply 1. When the AC input voltage VI is lower than the rated voltage VR, the output voltage command generating unit 40A sets the output voltage command value VREF to the rated voltage VR.

[0080] On the one hand, when the AC input voltage VI is greater than or equal to the rated voltage VR and less than or equal to the upper limit value VH, the output voltage command generation unit 40A sets the output voltage command value VREF to a voltage equal to the AC input voltage VI. Further, when the AC input voltage VI exceeds the upper limit value VH, that is, when an overvoltage of the commercial AC power supply 1 occurs, the output voltage command generation unit 40A sets the output voltage command value VREF to the upper limit value VH.

[0081] In the example of FIG. 7, during the period from time ta to time tb, since VI < VR, the output voltage command value VREF is set to the rated voltage VR. During the period from time tb to time tc, since VR ≦ VI ≦ VH, the output voltage command value VREF coincides with the AC input voltage VI. Therefore, the output voltage command value VREF also rises following the AC input voltage VI. However, after time tc, since VI > VH, the output voltage command value VREF is set to the upper limit value VH.

[0082] Note that when the AC input voltage VI pulsates after time tb, the output voltage command value VREF will also pulsate following the AC input voltage VI, and there is a possibility that the voltage control in the AC voltage control unit 242A becomes unstable. Therefore, the output voltage command generation unit 40A can be configured to perform an averaging process (for example, a moving average process) on the AC input voltage VI and generate the output voltage command value VREF based on the AC input voltage VI after the averaging process. According to this, the stability of voltage control can be improved.

[0083] As shown in FIG. 7, when HSS10 is turned off at time td, the output voltage command generation unit 40A gradually decreases the output voltage command value VREF to the rated voltage VR. The speed at which the output voltage command value VREF is decreased at this time can be set to satisfy the voltage setting time defined in advance in the uninterruptible power supply device 100. The voltage setting time refers to the time from when the AC output voltage VO exceeds the allowable voltage range until it stabilizes within the allowable voltage range again.

[0084] With such a configuration, the output voltage command value VREF becomes a voltage higher than the rated voltage VR and lower than or equal to the upper limit value VH according to the AC input voltage VI during the period from the time tb when the AC input voltage VI becomes equal to or higher than the rated voltage VR to the time td when HSS10 is turned off.

[0085] The subtractor 42 calculates the deviation ΔVO = VREF - VO between the output voltage command value VREF and the AC output voltage VO. Since the output voltage command value VREF is set to be higher than the rated voltage VR and lower than or equal to the upper limit value VH according to the AC input voltage VI, the deviation ΔVO at the switching time becomes smaller compared to the comparative example shown in FIG. 3.

[0086] The voltage control unit 44 performs a proportional-integral operation on the deviation ΔVO obtained by the subtractor 42 to generate the current command value Ic2. The subtractor 46 calculates the deviation ΔIL = Ic2 - ILf between the current command value Ic2 and the AC current IL indicated by the output signal ILf of the current detector CD2. The current control unit 48 generates the voltage command value Vc2 so that the deviation ΔIL obtained by the subtractor 46 becomes zero.

[0087] FIG. 8 is a flowchart showing an example of the procedure of the generation process of the output voltage command value VREF executed in the output voltage command generation unit 40A. As shown in FIG. 8, in step (hereinafter simply referred to as "S") 01, the output voltage command generation unit 40A detects the instantaneous value of the AC input voltage VI. In S02, the output voltage command generation unit 40A determines whether the AC input voltage VI is equal to or higher than the rated voltage VR of the commercial AC power supply 1. When VI < VR (when the determination in S02 is NO), the output voltage command generation unit 40A sets the output voltage command value VREF to the rated voltage VR in S08.

[0088] On the other hand, if VI≧VR (YES in S02), then in S03 output voltage command generation unit 40A sets output voltage command value VREF to AC input voltage VI. Next, in S04 output voltage command generation unit 40A detects whether or not an overvoltage has occurred in commercial AC power supply 1 based on overvoltage detection signal DO from power failure / overvoltage detection unit 20. If an overvoltage has not occurred in commercial AC power supply 1 (NO in S04), that is, if AC input voltage VI of commercial AC power supply 1 does not exceed upper limit value VH, output voltage command generation unit 40A returns to S02 and sets output voltage command value VREF to AC input voltage VI or rated voltage VR according to the comparison result between AC input voltage VI and rated voltage VR.

[0089] On the other hand, if an overvoltage occurs in the commercial AC power supply 1 (YES determination in S04), that is, if the AC input voltage VI of the commercial AC power supply 1 exceeds the upper limit value VH, the output voltage command generation unit 40A sets the output voltage command value VREF to the upper limit value VH in S05. Next, the output voltage command generation unit 40A determines in S06 whether the switch control unit 22 has turned off the HSS 10. In S06, for example, it is determined based on the output signal Iif of the current detector CD1 whether the AC current Ii is flowing. If the AC current Ii is flowing, the determination in S06 is NO, and if the AC current Ii is not flowing, the determination in S06 is YES.

[0090] If it is determined that the HSS 10 is not turned off (NO in S06), the output voltage command generating unit 40A returns to S02 and sets the output voltage command value VREF to the AC input voltage VI or the rated voltage VR. On the other hand, if it is determined that the HSS 10 is turned off (YES in S06), the output voltage command generating unit 40A reduces the output voltage command value VREF in S07. As shown in FIG. 7, the rate at which the output voltage command value VREF is reduced is set in accordance with the voltage settling time of the uninterruptible power supply 100.

[0091] By S08, the output voltage command generation unit 40A determines whether the output voltage command value VREF matches the rated voltage VR. When VREF > VR (when the NO determination is made in S08), the output voltage command generation unit 40A returns to S07. In response to VREF = VR (when the YES determination is made in S08), the output voltage command generation unit 40A stops the processing of S07.

[0092] FIG. 9 is a waveform diagram showing the temporal change of the AC output voltage VO supplied from the uninterruptible power supply device 100 according to Embodiment 1 to the load 2, and is a figure for comparison with FIG. 5. Similar to FIG. 5, in FIG. 9, the instantaneous values of the three-phase line-to-line voltages supplied from the commercial AC power supply 1 or the bidirectional converter 12 are collectively shown.

[0093] Comparing FIG. 9 and FIG. 5, in Embodiment 1, it can be seen that after the time t2 when the switching time ends, the AC output voltage VO gradually decreases toward the rated voltage VR, and the occurrence of undershoot is suppressed. This is because during the switching time, the output voltage command value VREF is changed following the AC input voltage VI within a range not exceeding the upper limit value VH, and the output voltage command value VREF is gradually decreased in response to the turn-off of HSS10. According to this, compared with the comparative example in which the output voltage command value VREF is fixed to the rated voltage VR, the deviation ΔVO between the output voltage command value VREF and the AC output voltage VO during the switching time becomes smaller, so that the change amount of the voltage command value Vu1 can also be reduced. As a result, the fluctuation of the AC output voltage VO can be suppressed and it can be gently returned to the rated voltage VR.

[0094] According to Embodiment 1, when a power failure of the commercial AC power supply 1 occurs, since VI < VR, the output voltage command generation unit 40A sets the output voltage command value VREF to the rated voltage VR. Therefore, as shown in FIG. 4, the AC output voltage VO can be controlled so that the AC output voltage VO falls within the allowable voltage range at the time t2 when the switching time ends.

[0095] (Modification example) In the above-described Embodiment 1, the configuration in which the output voltage command value VREF is decreased to the rated voltage VR in response to the HSS10 being turned off has been described. However, the output voltage command value VREF may be decreased in response to an overvoltage occurring in the commercial AC power supply 1.

[0096] FIG. 10 is a diagram for explaining a modification example of the generation process of the output voltage command value VREF in the output voltage command generation unit 40A. In FIG. 10, similar to FIG. 7, the time waveform of the AC input voltage VI (corresponding to the broken line in the figure) supplied from the commercial AC power supply 1 and the time waveform of the output voltage command value VREF (corresponding to the solid line in the figure) are shown.

[0097] In FIG. 10, since VI < VR during the period from time ta to time tb, the output voltage command value VREF is set to the rated voltage VR. After time tb, since VI ≧ VR, the output voltage command value VREF matches the AC input voltage VI.

[0098] When an overvoltage occurs in the commercial AC power supply 1 at time tc, the output voltage command generation unit 40A gradually decreases the output voltage command value VREF to the rated voltage VR. In the example of FIG. 10, the output voltage command value VREF is decreased from time tc, but the decrease of the output voltage command value VREF may be started during the switching time. However, as shown in FIG. 10, it is preferable to decrease the output voltage command value VREF so that the output voltage command value VREF reaches the rated voltage VR after the end of the switching time. The speed at which the output voltage command value VREF is decreased can be set to satisfy the voltage regulation time of the uninterruptible power supply device 100.

[0099] In this modification example, although the deviation ΔVO between the output voltage command value VREF and the AC output voltage VO during the switching time becomes larger compared to Embodiment 1, the deviation ΔVO can be made smaller than in the comparative example in which the output voltage command value VREF is the rated voltage VR. Therefore, the same effect as in Embodiment 1 can be obtained in this modification example.

[0100] Furthermore, in this modification, the deviation ΔVO at the time td when the HSS 10 is turned off can be made smaller than in the first embodiment. Therefore, the AC output voltage VO can be returned to the rated voltage VR more quickly.

[0101] [Embodiment 2] Figure 11 is a block diagram showing the configuration of converter control unit 24B included in control device 16 of uninterruptible power supply 100 according to embodiment 2. Uninterruptible power supply 100 according to embodiment 2 has the same configuration as uninterruptible power supply 100 shown in Figures 1 and 3 except for the configuration of converter control unit 24B in control device 16, and therefore will not be shown or described again.

[0102] 11, converter control unit 24B includes DC voltage control unit 240, AC voltage control unit 242B, selector 244, and PWM control unit 246. Converter control unit 24B is obtained by replacing AC voltage control unit 242 included in converter control unit 24 shown in FIG. 3 with AC voltage control unit 242B.

[0103] AC voltage control unit 242B is configured to include output voltage command generation unit 40, subtractors 42 and 46, voltage control unit 44B, and current control unit 48. AC voltage control unit 242B differs from AC voltage control unit 242 shown in FIG. 3 in that it includes voltage control unit 44B instead of voltage control unit 44.

[0104] The voltage control unit 44B includes a proportional calculation unit 50L, a proportional calculation unit 50H, an integral calculation unit 52, an adder 54, and a switching circuit 56. The proportional calculation units 50L and 50H perform proportional calculations on the deviation ΔVO=VREF−VO. However, the proportional gain KpL in the proportional calculation unit 50L is smaller than the proportional gain KpH in the proportional calculation unit 50H (KpL <KpH)。

[0105] The integral calculation unit 52 performs integral calculation on the deviation ΔVO. The adder 54 generates a current command value Ic2 by adding the proportional calculation result and the integral calculation result.

[0106] The switching circuit 56 is provided between the subtractor 42 and the proportional calculation units 50L, 50H. The switching circuit 56 is configured to selectively input the deviation ΔVO calculated by the subtractor 42 to either one of the proportional calculation units 50L, 50H based on the overvoltage detection signal DO from the power failure / overvoltage detection unit 20. Specifically, when the overvoltage detection signal DO is at H level, i.e., when no overvoltage is occurring in the commercial AC power supply 1, the switching circuit 56 inputs the deviation ΔVO to the proportional calculation unit 50H. When the overvoltage detection signal DO is at L level, i.e., when an overvoltage is occurring in the commercial AC power supply 1, the switching circuit 56 inputs the deviation ΔVO to the proportional calculation unit 50L.

[0107] According to this, when the commercial AC power supply 1 is normal or when a power outage of the commercial AC power supply 1 occurs, the proportional calculation unit 50H performs proportional calculation on the deviation ΔVO, and the current command value Ic2 is generated based on the result of this proportional calculation and the result of integral calculation by the integral calculation unit 52. The proportional gain KpH can be set so that the AC output voltage VO falls within the allowable voltage range within the switching period.

[0108] On the other hand, when an overvoltage occurs in the commercial AC power supply 1, the proportional calculation unit 50L performs proportional calculation on the deviation ΔVO, and generates a current command value Ic2 based on the result of this proportional calculation and the result of integral calculation by the integral calculation unit 52. The proportional gain KpL can be set to, for example, about 1 / 2 to 1 / 4 of the proportional gain KpH.

[0109] As described above, in the second embodiment, the AC voltage control unit 242B is configured to fix the output voltage command value VREF to the rated voltage VR, while temporarily reducing the proportional gain Kp used in the proportional calculation of the deviation ΔVO from KpH to KpL when the commercial AC power supply 1 is in an overvoltage state.

[0110] According to this, when an overvoltage occurs in the commercial AC power supply 1, the amount of change in the voltage command value Vu2 with respect to the deviation ΔVO is smaller than when an overvoltage occurs, making it possible to suppress undershoot of the AC output voltage VO immediately after the end of the switching time. Also, when a power outage occurs in the commercial AC power supply 1, proportional calculation is performed using a high proportional gain KpH, making it possible to increase the amount of change in the voltage command value Vu2 with respect to the deviation ΔVO and quickly restore the AC output voltage VO to the rated voltage VR.

[0111] Fig. 12 is a flowchart showing an example of a procedure of processing executed by the voltage control unit 44B shown in Fig. 11. As shown in Fig. 12, in S11, the voltage control unit 44B detects whether an overvoltage is occurring in the commercial AC power supply 1 based on the overvoltage detection signal DU from the power failure / overvoltage detection unit 20. If an overvoltage is not occurring in the commercial AC power supply 1 (NO determination in S11), that is, if the AC input voltage VI of the commercial AC power supply 1 does not exceed the upper limit value VH, the voltage control unit 44B selects a proportional gain KpH in S14. The voltage control unit 44B performs proportional calculation using the selected proportional gain KpH, and generates a current command value Ic2 based on the result of this proportional calculation and the result of an integral calculation.

[0112] On the other hand, when an overvoltage occurs in the commercial AC power supply 1 (YES determination in S11), that is, when the AC input voltage VI of the commercial AC power supply 1 exceeds the upper limit value VH, the voltage control unit 44B selects a proportional gain KpL lower than the proportional gain KpH in S12. The voltage control unit 44B performs proportional calculation using the selected proportional gain KpL, and generates a current command value Ic2 based on the proportional calculation result and the integral calculation result.

[0113] In step S13, the voltage control unit 44B determines whether the commercial AC power supply 1 has recovered (restored) from an overvoltage state to a normal state. If the overvoltage detection signal DU has transitioned from an L level to an H level, the determination in step S13 is YES.

[0114] If the commercial AC power supply 1 is in an overvoltage state (determined as NO in S13), the voltage control unit 44B returns to S12 and selects the proportional gain KpL. If the commercial AC power supply 1 is restored (determined as YES in S13), the voltage control unit 44B selects the proportional gain KpH in S14. The voltage control unit 44B performs proportional calculation using the selected proportional gain KpH, and generates the current command value Ic2 based on the result of this proportional calculation and the result of the integral calculation.

[0115] (Variation) In the above-described second embodiment, the configuration has been described in which, when the commercial AC power supply 1 is in an overvoltage state, the proportional gain Kp used in the proportional calculation for the deviation ΔVO between the output voltage command value VREF and the AC output voltage VO is temporarily reduced. However, the configuration may also be such that the integral gain Ki used in the integral calculation is reduced in accordance with the reduction in the proportional gain Kp.

[0116] Fig. 13 is a block diagram showing the configuration of converter control unit 24C included in control device 16 of uninterruptible power supply 100 according to a modification of embodiment 2. As shown in Fig. 13, converter control unit 24C includes DC voltage control unit 240, AC voltage control unit 242C, selector 244, and PWM control unit 246. Converter control unit 24C is obtained by replacing AC voltage control unit 242B included in converter control unit 24B shown in Fig. 11 with AC voltage control unit 242C.

[0117] AC voltage control unit 242C includes output voltage command generation unit 40, subtractors 42 and 46, voltage control unit 44C, and current control unit 48. AC voltage control unit 242C differs from AC voltage control unit 242B shown in FIG. 11 in that it includes voltage control unit 44C instead of voltage control unit 44B.

[0118] Voltage control unit 44C includes proportional calculation unit 50L, proportional calculation unit 50H, integral calculation unit 52L, integral calculation unit 52H, adder 54, and switching circuits 56 and 58. Voltage control unit 44C differs from voltage control unit 44B in that it has integral calculation units 52L and 52H and switching circuit 58 instead of integral calculation unit 52.

[0119] The integral calculation units 52L and 52H perform integral calculations on the deviation ΔVO=VREF−VO. However, the gain KiL in the integral calculation unit 52L is smaller than the gain KiH in the integral calculation unit 52H (KiL <KiH)。

[0120] The switching circuit 58 is provided between the subtractor 42 and the integration calculation units 52L and 52H. The switching circuit 58 selectively inputs the deviation ΔVO calculated by the subtractor 42 to one of the integration calculation units 52L and 52H based on the overvoltage detection signal DO from the power failure / overvoltage detection unit 20. Specifically, when the overvoltage detection signal DO is at H level, i.e., when no overvoltage occurs in the commercial AC power supply 1, the switching circuit 58 inputs the deviation ΔVO to the integration calculation unit 52H. When the overvoltage detection signal DO is at L level, i.e., when an overvoltage occurs in the commercial AC power supply 1, the switching circuit 58 inputs the deviation ΔVO to the integration calculation unit 52L.

[0121] According to this, when the commercial AC power supply 1 is normal or when a power outage occurs in the commercial AC power supply 1, the proportional calculation unit 50H executes proportional calculation on the deviation ΔVO, and the integral calculation unit 52H executes integral calculation on the deviation ΔVO. Then, based on the results of the proportional calculation and the integral calculation, the current command value Ic2 is generated.

[0122] On the other hand, when an overvoltage occurs in the commercial AC power supply 1, the proportional calculation unit 50L performs a proportional calculation on the deviation ΔVO, and the integral calculation unit 52L performs an integral calculation on the deviation ΔVO. Then, based on the results of the proportional calculation and the integral calculation, a current command value Ic2 is generated.

[0123] As described above, in this modification, the AC voltage control unit 242C is configured to fix the output voltage command value VREF to the rated voltage VR, while temporarily reducing the proportional gain Kp used in the proportional calculation of the deviation ΔVO and the integral gain Ki used in the integral calculation when the commercial AC power supply 1 is in an overvoltage state.

[0124] 11, as the integral gain Ki in the integral calculation unit 52 is increased, the AC output voltage VO can be made to coincide with the output voltage command value VREF in a short time, but this may increase the oscillation of the AC output voltage VO. Therefore, there is a concern that the effect of suppressing overshoot achieved by lowering the proportional gain Kp may be weakened. In this modification, by lowering the integral gain Ki in accordance with the decrease in the proportional gain Kp, oscillation of the AC output voltage VO can be suppressed, and overshoot can be more reliably suppressed.

[0125] Fig. 14 is a flowchart showing an example of the procedure of the process executed in voltage control unit 44 C. The flowchart in Fig. 14 is obtained by adding the processes of S121 and S141 to the flowchart in Fig. 12.

[0126] 14, if no overvoltage is occurring in the commercial AC power supply 1 (NO determination in S11), which is the same as in Fig. 12, the voltage control unit 44C selects a proportional gain KpH in S14 and selects an integral gain KiH in S141. The voltage control unit 44C performs a proportional-integral calculation using the selected gains KpH and KiH, and generates a current command value Ic2 based on the result of this proportional-integral calculation.

[0127] On the other hand, when an overvoltage occurs in the commercial AC power supply 1 (YES determination in S11), the voltage control unit 44C selects a proportional gain KpL lower than the proportional gain KpH in S12, and also selects an integral gain KiL lower than the integral gain KiH in S121. The voltage control unit 44C performs a proportional-integral calculation using the selected gains KpL and KiL, and generates a current command value Ic2 based on the result of this proportional-integral calculation.

[0128] 12, if the commercial AC power supply 1 is in an overvoltage state (NO determination in S13), the voltage control unit 44C returns to S12 and S121 and selects gains KpL and KiL. Then, if the commercial AC power supply 1 is restored (YES determination in S13), the voltage control unit 44C selects gains KpH and KiH in S14 and S141. The voltage control unit 44C performs proportional integral calculation using the selected gains KpH and KiH, and generates a current command value Ic2 based on the result of this proportional integral calculation.

[0129] As described above, in the uninterruptible power supply 100 according to the first and second embodiments, when a power outage occurs in the commercial AC power supply 1, a control command (voltage command value Vu2) for the bidirectional converter 12 is generated by controlling and calculating the deviation of the AC output voltage VO from the output voltage command value VREF so that the AC output voltage VO falls within the allowable voltage range within the switching time of the HSS 10. This makes it possible to suppress a decrease in the AC output voltage VO immediately after the switching time. On the other hand, when an overvoltage occurs in the commercial AC power supply 1, the change in the control command (voltage command value Vu2) relative to a change in the AC output voltage VO is made smaller than when a power outage occurs in the commercial AC power supply 1. This makes it possible to suppress fluctuations (undershoot) in the AC output voltage VO and converge it to the rated voltage VR.

[0130] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The technical scope of the present disclosure is defined by the claims, not by the description of the above embodiments, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0131] 1 Commercial AC power supply, 2 Load, 3 Battery, 10 HSS, 12 Bidirectional converter, 13 DC line, 14 Bidirectional chopper, 16 Control device, 20 Power outage / overvoltage detection unit, 22 Switch control unit, 24, 24A to 24C Converter control unit, 26 Chopper control unit, 30 DC voltage command generation unit, 32, 36, 42, 46 Subtractor, 34, 44, 44B, 44C Voltage control unit, 38, 48 Current control unit, 40, 40A Output voltage command generation unit, 50, 50L, 50H Proportional calculation unit, 52, 52L, 52H Integral calculation unit, 54 Adder, 56, 58 Switching circuit, 100 Uninterruptible power supply, 240 DC voltage control unit, 242, 242A to 242C AC voltage control unit, 244 Selector, 246 PWM control unit, T1 Input terminal, T2 output terminal, T3 DC terminal, C1, C2 capacitor, CD1, CD2 current detector, L1 reactor, Kp, KpH, KpL proportional gain, Ki, KiH, KiL integral gain, VREF output voltage command value, VI AC input voltage, VO AC output voltage, DU power failure detection signal, DO overvoltage detection signal.

Claims

1. An uninterruptible power supply connected between a commercial AC power source and a load, an input terminal for receiving an AC input voltage from the commercial AC power supply; an output terminal connected to the load; a switch connected between the input terminal and the output terminal; a bidirectional converter connected between the output terminal and a power storage device; a control device that controls the switch and the bidirectional converter, the uninterruptible power supply is configured to, when the commercial AC power supply is normal, turn on the switch and perform commercial power supply in which the AC input voltage is supplied to the load via the switch, and, in response to the occurrence of a power outage or an overvoltage of the commercial AC power supply, turn off the switch and transition to inverter power supply in which the bidirectional converter converts the DC voltage of the power storage device into an AC output voltage and supplies the AC output voltage to the load; when a power outage or an overvoltage occurs in the commercial AC power supply, the control device is configured to generate a control command for the bidirectional converter by executing a control calculation to compensate for a deviation of the AC output voltage with respect to an output voltage command value; The control device reduces the change in the control command relative to the change in the AC output voltage when an overvoltage occurs in the commercial AC power supply compared to when a power outage occurs in the commercial AC power supply.

2. The control device When the AC input voltage is lower than a target voltage based on a rated voltage of the commercial AC power supply, the output voltage command value is set to the target voltage; when the AC input voltage exceeds the target voltage, the output voltage command value is set to the AC input voltage, and in response to an occurrence of an overvoltage of the commercial AC power supply causing the AC input voltage to exceed an upper limit value, the output voltage command value is set to the upper limit value; 2. The uninterruptible power supply according to claim 1, wherein when the switch is turned off in response to an occurrence of an overvoltage in the commercial AC power supply, the output voltage command value is reduced to the target voltage.

3. The control device When the AC input voltage is lower than a target voltage based on a rated voltage of the commercial AC power supply, the output voltage command value is set to the target voltage; When the AC input voltage exceeds the target voltage, the output voltage command value is set to the AC input voltage; 2. The uninterruptible power supply according to claim 1, wherein, when an overvoltage occurs in the commercial AC power supply, the output voltage command value is reduced so that the output voltage reaches the target voltage after a switching time until the switch is turned off has elapsed.

4. the control device is configured to perform averaging processing on the AC input voltage; 4. The uninterruptible power supply according to claim 2, wherein when the AC input voltage exceeds the target voltage, the AC input voltage after the averaging process is set as the AC input voltage.

5. 4. The uninterruptible power supply according to claim 2, wherein the control device reduces the output voltage command value so that the AC output voltage falls within an allowable voltage range of the commercial AC power supply within a voltage settling time of the uninterruptible power supply.

6. the control device is configured to generate the control command by performing a proportional-integral operation on the deviation; when a power outage occurs in the commercial AC power supply, the control device executes the proportional-integral calculation using a first proportional gain; 2. The uninterruptible power supply according to claim 1, wherein when an overvoltage occurs in the commercial AC power supply, the proportional-plus-integral calculation is performed using a second proportional gain that is lower than the first proportional gain.

7. 7. The uninterruptible power supply according to claim 6, wherein the control device changes the second proportional gain to the first proportional gain when the commercial AC power supply recovers from an overvoltage state.

8. the control device is configured to generate the control command by performing a proportional-integral operation on the deviation; when a power outage occurs in the commercial AC power supply, the proportional-plus-integral calculation is performed using a first proportional gain and a first integral gain; 2. The uninterruptible power supply according to claim 1, wherein, when an overvoltage occurs in the commercial AC power supply, the proportional-plus-integral calculation is performed using a second proportional gain lower than the first proportional gain and a second integral gain lower than the first integral gain.

9. 9. The uninterruptible power supply according to claim 8, wherein the control device changes the second proportional gain to the first proportional gain and changes the second integral gain to the first integral gain when the commercial AC power supply recovers from an overvoltage state.

10. A method for controlling an uninterruptible power supply connected between a commercial AC power supply and a load, comprising: The uninterruptible power supply is an input terminal for receiving an AC input voltage from the commercial AC power supply; an output terminal connected to the load; a switch connected between the input terminal and the output terminal; a bidirectional converter connected between the output terminal and a power storage device, The control method includes: a step of turning on the switch and supplying the AC input voltage to the load via the switch when the commercial AC power supply is normal; in response to an occurrence of a power outage or an overvoltage of the commercial AC power supply, turning off the switch and transitioning to inverter power supply in which the bidirectional converter converts the DC voltage of the power storage device into an AC output voltage and supplies the AC output voltage to the load, the step of transitioning to inverter power supply includes a step of generating a control command for the bidirectional converter by executing a control calculation for compensating for a deviation of the AC output voltage with respect to an output voltage command value; A control method for an uninterruptible power supply, wherein in the step of generating a control command, when an overvoltage occurs in the commercial AC power supply, a change in the control command with respect to a change in the AC output voltage is made smaller than when a power outage occurs in the commercial AC power supply.

11. The step of generating a control command includes: when the AC input voltage is lower than a target voltage based on a rated voltage of the commercial AC power supply, setting the output voltage command value to the target voltage; when the AC input voltage exceeds the target voltage, setting the output voltage command value to the AC input voltage, and in response to an occurrence of an overvoltage of the commercial AC power supply causing the AC input voltage to exceed an upper limit value, setting the output voltage command value to the upper limit value; 11. The control method for an uninterruptible power supply according to claim 10, further comprising the step of: when the switch is turned off in response to an occurrence of an overvoltage in the commercial AC power supply, reducing the output voltage command value to the target voltage.

12. The step of generating a control command includes: when the AC input voltage is lower than a target voltage based on a rated voltage of the commercial AC power supply, setting the output voltage command value to the target voltage; when the AC input voltage exceeds the target voltage, setting the output voltage command value to the AC input voltage; 11. The control method for an uninterruptible power supply according to claim 10, further comprising: when an overvoltage occurs in the commercial AC power supply, reducing the output voltage command value so that the output voltage reaches the target voltage after a switching time until the switch is turned off has elapsed.

13. the step of generating the control command includes a step of performing a proportional-plus-integral operation on the deviation; 11. The control method for an uninterruptible power supply according to claim 10, wherein the step of performing the proportional-integral calculation executes the proportional-integral calculation using a first proportional gain when a power outage occurs in the commercial AC power supply, and executes the proportional-integral calculation using a second proportional gain lower than the first proportional gain when an overvoltage occurs in the commercial AC power supply.

14. the step of generating the control command includes a step of performing a proportional-plus-integral operation on the deviation; 11. The control method for an uninterruptible power supply according to claim 10, wherein the step of performing the proportional-plus-integral calculation, when a power outage occurs in the commercial AC power supply, performs the proportional-plus-integral calculation using a first proportional gain and a first integral gain, and, when an overvoltage occurs in the commercial AC power supply, performs the proportional-plus-integral calculation using a second proportional gain lower than the first proportional gain and a second integral gain lower than the first integral gain.

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