Uninterruptible power supply device and short-circuit failure detection method

Abstract

To provide an uninterruptible power supply device and a short-circuit failure detection method capable of detecting short-circuit failures of switches provided on two lines of an AC electric path, respectively.SOLUTION: A switching control part 31 turns on a switch 4 and a bypass switch 6a in a bypass power supply via a bypass line 20, and turns off the switch 4 and the bypass switch 6a in an inverter power supply. An uninterruptible power supply device 1 includes a short-circuit failure detection part 32. The short-circuit failure detection part 32 detects a short-circuit failure of the switch 4 on the basis of an input voltage after the inverter power supply is started and a bypass voltage Vbps, and detects a short-circuit failure of the bypass switch 6a on the basis of a load voltage VLoad after the inverter power supply is started and the bypass voltage Vbps.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an uninterruptible power supply and a method for detecting a short-circuit fault. [Background technology]

[0002] Patent Document 1 discloses a method for detecting relay welding that can quickly determine whether a relay has welded or not without requiring an auxiliary contact or a dedicated circuit. Patent Document 1 determines whether a relay has welded or not based on whether the frequency deviates from a predetermined range during the synchronization process between the first and second electric circuits that sandwich the relay when a voltage is detected in the first electric circuit (commercial power system) during power supply from an independent output. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-171161 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventional technology can detect relay welding when the relay is welded on both two wires of an AC circuit, but cannot detect relay welding when the relay is welded on only one of the two wires of an AC circuit.

[0005] An aspect of the present invention is to provide an uninterruptible power supply and a short-circuit fault detection method that can detect short-circuit faults in switches provided on two wires of an AC power line, respectively. [Means for solving the problem]

[0006] An uninterruptible power supply according to one aspect of the present invention includes a bypass line consisting of two lines connecting an input end connected to an AC power source and an output end connected to a load. The uninterruptible power supply includes an input-side bypass switch provided on one line of the bypass line. The uninterruptible power supply includes a first branch line branching from the bypass line downstream of the input-side bypass switch, and a second branch line branching from the bypass line downstream of a branch point of the first branch line. The uninterruptible power supply includes a unit that performs inverter power supply. The unit is connected between the first branch line and the second branch line, and converts AC voltage input via the first branch line into DC voltage to charge a power storage device, and converts DC voltage stored in the power storage device into AC voltage to output via the second branch line. The uninterruptible power supply includes an output-side bypass switch provided on the other line of the bypass line, on which the input-side bypass switch is not provided, between a branch point of the first branch line and a branch point of the second branch line. The uninterruptible power supply includes an input voltage detector, a load voltage detector, and a bypass voltage detector. The input voltage detector detects the input voltage at the input terminal. The load voltage detector detects the load voltage at the output terminal. The bypass voltage detector detects the bypass voltage of the bypass line between the input-side bypass switch and the output-side bypass switch. The uninterruptible power supply includes a switching control unit. The switching control unit turns on the input-side bypass switch and the output-side bypass switch in bypass power feeding via the bypass line, and turns off the input-side bypass switch and the output-side bypass switch in inverter power feeding. The uninterruptible power supply includes a short-circuit fault detection unit. The short-circuit fault detection unit detects a short-circuit fault of the input-side bypass switch based on the input voltage and the bypass voltage after the inverter power feeding has started, and detects a short-circuit fault of the output-side bypass switch based on the load voltage and the bypass voltage after the inverter power feeding has started. A short-circuit fault detection method according to one aspect of the present invention includes an input-side bypass switch provided on one line of a bypass line connecting an input end connected to an AC power source and an output end connected to a load. The short-circuit fault detection method detects a short-circuit fault between the input-side bypass switch and an output-side bypass switch provided on the other line of the bypass line on which the input-side bypass switch is not provided. The short-circuit fault detection method detects an input voltage at the input end, a load voltage at the output end, and a bypass voltage of the bypass line between the input-side bypass switch and the output-side bypass switch. The short-circuit fault detection method detects a short-circuit fault of the input-side bypass switch based on the input voltage and the bypass voltage when the input-side bypass switch is off, and detects a short-circuit fault of the output-side bypass switch based on the load voltage and the bypass voltage when the output-side bypass switch is off. [Effects of the Invention]

[0007] According to one aspect of the present invention, it is possible to detect short-circuit faults in the switches provided on each of the two wires of an AC electric circuit. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of an uninterruptible power supply. [Figure 2] 2 is a diagram showing an inverter power supply state of the uninterruptible power supply device shown in FIG. 1. FIG. [Figure 3] 2 is a diagram illustrating a configuration of a short-circuit failure detection unit illustrated in FIG. 1. FIG. [Figure 4] 4 is a flowchart illustrating the operation of the comparison unit shown in FIG. 3. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following embodiments, components having similar functions will be given the same reference numerals and descriptions thereof will be omitted as appropriate.

[0010] An uninterruptible power supply 1 (hereinafter referred to as UPS 1) of this embodiment is of a continuous commercial power supply type, and with reference to FIG. 1, includes a plurality of units 10a, 10b and a power storage device 100 that supplies backup power in the event of a power outage.

[0011] The power storage device 100 includes, for example, a battery pack in which a plurality of battery cells (secondary batteries such as lithium ion batteries and lead-acid batteries) are connected in series and / or parallel, and a battery management system (BMS) that manages the plurality of battery cells. The power storage device 100 may be configured using a flywheel or a capacitor. There is no limit to the number of power storage devices 100, and the number can be increased or decreased depending on the required backup time.

[0012] The multiple units 10a, 10b may operate independently as a continuous commercial power supply type uninterruptible power supply. By connecting multiple units 10a, 10b in parallel, the output capacity of the UPS 1 is increased. There is no limit to the number of units 10a, 10b, and they can be increased or decreased depending on the required output capacity.

[0013] The UPS 1 includes a two-line bypass line 20. The bypass line 20 connects an input end 2 (terminal block or inlet) from the AC power source to the UPS 1 and an output end 3 (terminal block or outlet) from the UPS 1 to a load.

[0014] The UPS 1 includes a switch 4 that opens and closes the connection between the AC power source and the bypass line 20 on the upstream side of the bypass line 20. The switch 4 is an input-side bypass switch, and is provided on one of the lines of the two-line bypass line 20. The switch 4 is made up of a relay, which is a mechanical switch that is two lines of the AC circuit, and is turned off in the event of a power outage to prevent voltage from occurring at the input terminal 2 of the UPS 1.

[0015] The UPS 1 includes a rectifier circuit 5, one end of which is connected to the bypass line 20 upstream of the switch 4. The UPS 1 includes a master control unit 30, the other end of which is connected to the rectifier circuit 5. When there is no power outage, the rectifier circuit 5 half-wave rectifies the AC voltage input from one end and supplies the rectified DC voltage (control power) to the master control unit 30. The master control unit 30 is an arithmetic processing circuit such as a microcomputer including a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), etc. A control program for controlling the operation of the UPS 1 is stored in the ROM. The master control unit 30 reads the control program stored in the ROM and loads it into the RAM, thereby functioning as a switching control unit 31 and a short-circuit fault detection unit 32.

[0016] The UPS 1 includes a branch line 21 branching off from the bypass line 20 downstream of the switch 4, and a branch line 22 branching off from the bypass line 20 downstream of the branch point of the branch line 21. Each of the units 10a and 10b has an input terminal T in and a battery connection terminal T connected to the power storage device 100. Batt and the output terminal T connected to the branch line 22. out That is, the plurality of units 10a and 10b are connected in parallel to the bypass line 20.

[0017] Each unit has input terminal T in The input noise filter 11 is provided downstream of the in and output terminal T out An output noise filter 11 provided upstream of the out Each unit includes a charger (CHG) 12, a converter 13, an inverter 14, a control power supply 15, and a slave control unit 16.

[0018] Charger (CHG) 12 is connected to input terminal T in Input noise filter 11 inThe charger (CHG) 12 converts the AC voltage input via the charger 12 into a DC voltage and outputs it to the DC power line DC.

[0019] The converter 13 is configured, for example, by an insulated DC-DC converter, and is connected to the downstream side of the charger CHG via a DC power line DC. The DC power line DC is connected to the battery connection terminal T via wiring (not shown) in each of the units 10a and 10b. Batt The converter 13 converts the voltage of the direct current power line DC into a predetermined voltage and supplies it to the inverter 14.

[0020] The inverter 14 converts the DC voltage supplied from the converter 13 into an AC voltage. The AC voltage converted by the inverter 14 is passed through the output-side noise filter 11. out via output terminal T out is output from

[0021] The unit 10a is connected to the input terminal T in and output terminal T out The unit 10a is provided with an individual bypass line 23 that connects the power storage device 100 and the power storage device 100. The unit 10a is provided with a switch 17 that switches between power supply from the individual bypass line 23 and power supply from the power storage device 100 via the inverter 14. The unit 10a can also operate independently as an uninterruptible power supply of a continuous commercial power supply type.

[0022] The UPS 1 may be constructed by using units 10a or 10b with the same configuration for each unit, which can further enhance mass production efficiencies such as improved parts procurement and reduced production costs.

[0023] The UPS 1 includes a bypass switch 6a provided on the bypass line 20 and an inverter switch 6b provided on the branch line 22. The bypass switch 6a is an output-side bypass switch and is provided on a line of the two-wire bypass line 20 where no switch 4 is provided. The bypass switch 6a is provided on the bypass line 20 between the branch point of the branch line 21 and the branch point of the branch line 22. The bypass switch 6a and the inverter switch 6b include a mechanical switch such as a relay, and a semiconductor switch such as a triac thyristor connected in parallel with the mechanical switch. Connecting the semiconductor switch in parallel with the mechanical switch enables the bypass switch 6a and the inverter switch 6b to perform switching at high speed.

[0024] UPS1 is connected to the output terminal T of unit 10a. out and the output side switch 7a provided on the AC power line connecting the branch line 22, and the output terminal T out and an output-side switch 7b provided on the AC power line connecting the branch line 22. The output-side switches 7a and 7b are configured by relays, which are mechanical switches.

[0025] The UPS 1 is connected to the inverter switch 6b and the output terminals T of the units 10a and 10b. out The other ends of the rectifier circuits 8a and 8b are connected to the master control unit 30.

[0026] UPS1 is connected to the branch line 21 and the input terminal T of the unit 10a. in and an input side switch 9a provided on the AC power line connecting the branch line 21 and the input terminal T of the unit 10b. in and an input-side switch 9b provided on an AC power line connecting the two. The input-side switches 9a and 9b are configured by relays, which are mechanical switches.

[0027] The slave control unit 16 is an arithmetic processing circuit such as a microcomputer equipped with a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc. The ROM stores a control program for controlling the operation of each of the units 10a and 10b. The slave control unit 16 reads the control program stored in the ROM and loads the control program into the RAM, thereby controlling the operation of each part in each of the units 10a and 10b.

[0028] The UPS 1 includes an input voltage detector 41, a bypass voltage detector 42, a load voltage detector 43, and a bus voltage detector 44. The input voltage detector 41 converts the AC voltage at the input terminal 2 into an input voltage V in The bypass voltage detector 42 detects the AC voltage of the bypass line 20 between the switch 4 and the bypass switch 6a as a bypass voltage V bps The load voltage detector 43 detects the AC voltage at the output terminal 3 as a load voltage V Load The bus voltage detector 44 detects the AC voltage of the branch line 22 upstream of the inverter switch 6b as the bus voltage V bus Detect as.

[0029] When the power supply to the UPS 1 is turned on, the master control unit 30 (switching control unit 31) turns on the input side switches 9a, 9b and the output side switches 7a, 7b during the startup sequence. Also, during the startup sequence of the UPS 1, the slave control units 16 of the units 10a, 10b switch the switches 17 to connect the inverter 14 and the output terminal T out Connect with.

[0030] During non-power outages (normal times), the master control unit 30 (switching control unit 31) turns on the switch 4 and the bypass switch 6a and turns off the inverter switch 6b, as shown in FIG. 1, to supply AC voltage from the AC power source to the load via the bypass line 20.

[0031] When the master control unit 30 (switching control unit 31) detects a power outage, it transmits an inverter start-up signal and phase information to the slave control units 16 of each of the units 10a and 10b, and turns off the input-side switches 9a and 9b, as shown in FIG. 2. The slave control units 16 of each of the units 10a and 10b that have received the inverter start-up signal and phase information start up the inverter 14. Next, as shown in FIG. 2, the master control unit 30 (switching control unit 31) turns off the switch 4 and the bypass switch 6a and turns on the inverter switch 6b. This switches the bypass power supply, which supplies power from the bypass line 20 to the load, to the inverter power supply, which supplies power from the power storage device 100 to the load via the inverter 14. The switch 17 switches off the inverter 14 and the output terminal T before the power outage is detected. out By connecting these, it is possible to shorten the time required to switch from bypass power supply via the bypass line 20 to inverter power supply. In the event of a power outage (emergency), the rectifier circuits 8a and 8b half-wave rectify the AC voltage input from one end and supply the rectified DC voltage (control power supply) to the master control unit 30.

[0032] The short circuit fault detection unit 32 of the master control unit 30 detects the input voltage V in and bypass voltage V bps The short circuit fault detection unit 32 detects a short circuit fault (welding) of the switch 4 based on the load voltage V Load and bus voltage V bus The short circuit fault detection unit 32 detects a short circuit fault of the inverter switch 6b (welding of the mechanical switch, short circuit of the semiconductor switch) based on the load voltage V Load and bypass voltage V bps 3, the short-circuit failure detection unit 32 includes rectifiers 51a to 51d, low-pass filters 52a to 52d (hereinafter referred to as LPFs 52a to 52d), and a comparison unit 53.

[0033] The rectifier 51a converts the input voltage V detected by the input voltage detector 41 into in The LPF52a full-wave rectifies the input voltage V in to input voltage Vin It generates the average value of the absolute value of the input voltage V in The average absolute value of is the average input voltage V * in is input to the comparison unit 53.

[0034] The rectifier 51b is connected to the bypass voltage V bps The LPF52b full-wave rectifies the bypass voltage V bps to bypass voltage V bps Generate the average value of the absolute value of the bypass voltage V bps The average absolute value of the bypass voltage V * bps is input to the comparison unit 53.

[0035] The rectifier 51c is connected to the load voltage V Load The LPF52c full-wave rectifies the load voltage V Load to load voltage V Load The average value of the absolute value of the load voltage V Load The average absolute value of is the load voltage average value V * Load is input to the comparison unit 53.

[0036] The rectifier 51d is connected to the bus voltage V bus The LPF52d full-wave rectifies the full-wave rectified bus voltage V bus to bus voltage V bus The average value of the absolute value of the bus voltage V is calculated. bus The average value of the absolute value of is the average bus voltage V * bus is input to the comparison unit 53.

[0037] 4, the comparison unit 53 monitors the start of bypass power supply (step S101) and also monitors the start of inverter power supply (step S102). The start of bypass power supply in step S101 is detected by detecting the timing at which the inverter switch 6b is turned off by the switching control unit 31. The start of inverter power supply in step S102 is detected by detecting the timing at which the switch 4 and the bypass switch 6a are turned off by the switching control unit 31.

[0038] When the bypass power supply is started in step S101, the comparison unit 53 waits for a preset mask time to elapse (step S103). * Load (LPF52c) and bus voltage average value V * bus If the time constant of the LPF 52c and the LPF 52d is 2 seconds, it takes about 8 seconds to settle into a steady state, so the mask time is set to, for example, 10 seconds.

[0039] When the mask time has elapsed in step S103, the comparison unit 53 calculates the load voltage average value V * Load and the average bus voltage V * bus It is determined whether the load voltage average value V * Load and the average bus voltage V * bus If the load voltage average value V is equal to the load voltage average value V, the comparison unit 53 detects a short-circuit fault in the inverter switch 6b (step S105) and ends the short-circuit fault detection operation. * Load and the average bus voltage V * bus If they are not the same, the comparison unit 53 returns to steps S101 and S102 to monitor the start of bypass power feeding and inverter power feeding.

[0040] When inverter power supply is started in step S102, the comparison unit 53 waits for a preset mask time to elapse (step S106). * in (LPF52a), bypass voltage average value V * bps (LPF52b) and average load voltage V * Load If the time constants of the LPFs 52a, 52b, and 52c are 2 seconds, it takes about 8 seconds to settle to a steady state, so the mask time is set to, for example, 10 seconds.

[0041] When the mask time has elapsed in step S106, the comparison unit 53 calculates the input voltage average value V * in and the average bypass voltage V * bps It is determined whether the input voltage average value V * in and the average bypass voltage V * bps If it can be considered that the two are the same, the comparison unit 53 detects a short-circuit fault in the switch 4 (step S108) and ends the short-circuit fault detection operation.

[0042] Average input voltage V * in and the average bypass voltage V * bps and are not the same, the comparison unit 53 determines whether the load voltage average value V * Load and the average bypass voltage V * bps It is determined whether the load voltage average value V * Load and the average bypass voltage V * bps If the load voltage average value V is equal to the load voltage average value V, the comparison unit 53 detects a short-circuit fault in the bypass switch 6a (step S110) and ends the short-circuit fault detection operation. * Load and the average bypass voltage V *bps If they are not the same, the comparison unit 53 returns to steps S101 and S102 to monitor the start of bypass power feeding and inverter power feeding.

[0043] In the above-described embodiment, the short-circuit fault detection unit 32 of the master control unit 30 detects the input voltage V in , bypass voltage V bps , load voltage V Load and bypass voltage V bps The average load voltage V * Load , bus voltage average value V * bus , average load voltage V * Load and the average bypass voltage V * bps is generated and compared by the comparator 53, thereby performing the short circuit fault detection operation.

[0044] However, the short circuit fault detection operation performed by the short circuit fault detection unit 32 is not limited to this. For example, the short circuit fault detection unit 32 of the master control unit 30 may perform the short circuit fault detection operation by calculating the difference between each voltage, calculating the average value of the calculated differences, and comparing the calculated average value with a threshold value. Specifically, when the input voltage V in and the bypass voltage V bps The comparison unit 53 may then compare the average value of the differences with a threshold value to detect a short-circuit fault in the switch 4. The same applies to the detection of a short-circuit fault in the inverter switch 6b and the bypass switch 6a.

[0045] (summary) (1) A UPS 1 (uninterruptible power supply) according to each embodiment of the present invention includes a bypass line 20 consisting of two lines connecting an input terminal 2 connected to an AC power source and an output terminal 3 connected to a load. The uninterruptible power supply 1 includes a switch 4 (input-side bypass switch) provided on one line of the bypass line 20. The uninterruptible power supply 1 includes a branch line 21 (first branch line) branching off from the bypass line 20 downstream of the switch 4, and a branch line 22 (second branch line) branching off from the bypass line 20 downstream of the branch point of the branch line 21. The uninterruptible power supply 1 includes units 10a and 10b. The units 10a and 10b are connected between the branch line 21 and the branch line 22, and perform inverter power supply, converting an AC voltage input via the branch line 21 into a DC voltage to charge the power storage device 100, and converting a DC voltage stored in the power storage device 100 into an AC voltage to output the AC voltage via the branch line 22. The uninterruptible power supply 1 includes a bypass switch 6a (output side bypass switch) provided between a branch point of a branch line 21 of the other line where the switch 4 is not provided in the bypass line 20 and a branch point of a branch line 22. The uninterruptible power supply 1 includes an input voltage detector 41, a load voltage detector 43, and a bypass voltage detector 42. The input voltage detector 41 detects an input voltage V in The load voltage detector 43 detects the load voltage V Load The bypass voltage detector 42 detects the bypass voltage V of the bypass line 20 between the switch 4 and the bypass switch 6a. bps The uninterruptible power supply 1 includes a switching control unit 31. The switching control unit 31 turns on the switch 4 and the bypass switch 6a in the case of bypass power supply via the bypass line 20, and turns off the switch 4 and the bypass switch 6a in the case of inverter power supply. The uninterruptible power supply 1 includes a short-circuit fault detection unit 32. The short-circuit fault detection unit 32 detects the difference between the input voltage and the bypass voltage V after the inverter power supply has started. bps and detects a short circuit fault in the switch 4 based on the load voltage V after the inverter power supply is started. Load and bypass voltage V bps Based on this, a short circuit fault of the bypass switch 6a is detected.

[0046] According to the UPS 1 described in (1) above, it is possible to detect short-circuit faults in the switches 4 and the bypass switches 6a provided on the two lines of the bypass line 20, which is an AC electric circuit.

[0047] (2) The short-circuit fault detection unit 32 described above in (1) uses LPFs 52a to 52d (low-pass filters) to detect the input voltage V in The average input voltage V * in and the bypass voltage V bps The average bypass voltage V * bps and the load voltage V Load The average load voltage V * Load The short-circuit fault detection unit 32 calculates the average input voltage V after the inverter power supply is started and the mask time set based on the time constants of the LPFs 52a to 52d has elapsed. * in and the average bypass voltage V * bps Based on this, a short circuit fault of switch 4 is detected, and the load voltage average value V * Load and the average bypass voltage V * bps and detect a short-circuit fault in the bypass switch 6a based on the above.

[0048] The UPS 1 described in (2) above can easily detect short-circuit faults in the switch 4 and the bypass switch 6a by using the voltage average value. In addition, the UPS 1 can use the voltage average value at the timing when each voltage settles to a steady state after the start of inverter power supply, so it can accurately detect short-circuit faults in the switch 4 and the bypass switch 6a.

[0049] (3) The UPS 1 described in (1) or (2) above is configured by an inverter switch 6b provided on the branch line 22 and a bus voltage V bus The short-circuit fault detection unit 32 detects the load voltage V after the bypass power supply is started. Load and bus voltage Vbus Based on this, a short circuit fault of the inverter switch 6b is detected.

[0050] The UPS 1 described in (3) above can also detect a short-circuit fault in the inverter switch 6 b provided on the branch line 22.

[0051] (4) The short-circuit fault detection method according to each embodiment of the present invention detects a short-circuit fault between a switch 4 provided on one line of a bypass line 20 connecting an input terminal 2 connected to an AC power supply and an output terminal 3 connected to a load, and a bypass switch 6a provided on the other line of the bypass line 20 where the switch 4 is not provided. The short-circuit fault detection method detects a short-circuit fault between an input voltage V in and the load voltage V at output terminal 3 Load and the bypass voltage V of the bypass line 20 between the switch 4 and the bypass switch 6a. bps The short circuit fault detection method is to detect the input voltage V in and bypass voltage V bps and detects a short circuit fault in the switch 4 based on the load voltage V Load and bypass voltage V bps Based on this, a short circuit fault of the bypass switch 6a is detected.

[0052] According to the short-circuit fault detection method described in (4) above, it is possible to detect short-circuit faults in the switches 4 and the bypass switches 6a provided on the two lines of the bypass line 20, which is an AC electric circuit.

[0053] Although the present invention has been described above with reference to specific embodiments, it goes without saying that the above embodiments are merely examples and can be modified and implemented without departing from the spirit of the present invention. [Explanation of symbols]

[0054] 1 Uninterruptible power supply (UPS) 2 input terminals 3 Output terminal 4 Switches 5 Rectifier circuit 6a Bypass switch 6b Inverter switch 7a, 7b Output side switch 8a, 8b rectifier circuit 9a, 9b Input side switches 10a, 10b units 11in input noise filter 11out Output noise filter 12 Charger (CHG) 13 Converter 14 Inverter 15 Control power supply 16 Slave control unit 17 Switch 20 Bypass Line 21, 22 Branch lines 23 Individual bypass line 30 Master control unit 31 Switching control section 32 Short circuit fault detection section 41 Input voltage detector 42 Bypass voltage detector 43 Load voltage detector 44 Bus voltage detector 51a~51d Rectifier 52a~52d Low-pass filters (LPF) 53 Comparison section 100 Electricity storage device

Claims

1. a bypass line consisting of two lines connecting an input end connected to an AC power source and an output end connected to a load; an input side bypass switch provided on one line of the bypass line; a first branch line branching off from the bypass line downstream of the input-side bypass switch; a second branch line branching off from the bypass line downstream of a branch point of the first branch line; a unit that performs inverter power supply, the unit being connected between the first branch line and the second branch line, and that converts AC voltage input via the first branch line into DC voltage to charge a power storage device, and also converts DC voltage stored in the power storage device into AC voltage to output the AC voltage via the second branch line; an output-side bypass switch provided between a branch point of the first branch line and a branch point of the second branch line of the other line on which the input-side bypass switch is not provided in the bypass line; an input voltage detector for detecting an input voltage at the input terminal; a load voltage detector for detecting a load voltage at the output terminal; a bypass voltage detector that detects a bypass voltage of the bypass line between the input side bypass switch and the output side bypass switch; a switching control unit that turns on the input side bypass switch and the output side bypass switch in the bypass power supply via the bypass line, and turns off the input side bypass switch and the output side bypass switch in the inverter power supply; an uninterruptible power supply comprising: a short-circuit failure detection unit that detects a short-circuit failure of the input-side bypass switch based on the input voltage and the bypass voltage after the inverter power supply has started, and that detects a short-circuit failure of the output-side bypass switch based on the load voltage and the bypass voltage after the inverter power supply has started.

2. 2. The uninterruptible power supply according to claim 1, wherein the short-circuit fault detection unit uses a low-pass filter to obtain an input voltage average value of the input voltage, a bypass voltage average value of the bypass voltage, and a load voltage average value of the load voltage, and detects a short-circuit fault of the input-side bypass switch based on the input voltage average value and the bypass voltage average value after the inverter power supply has started and a mask time set based on the time constant of the low-pass filter has elapsed, and detects a short-circuit fault of the input-side bypass switch based on the load voltage average value and the bypass voltage average value.

3. an inverter switch provided on the second branch line; a bus voltage detector that detects a bus voltage of the second branch line upstream of the inverter switch, 3. The uninterruptible power supply according to claim 1, wherein the short-circuit failure detection unit detects a short-circuit failure of the inverter switch based on the load voltage and the bus voltage after the bypass power supply is started.

4. 1. A short-circuit fault detection method for detecting a short-circuit fault between an input-side bypass switch provided on one line of a bypass line connecting an input end connected to an AC power supply and an output end connected to a load, and an output-side bypass switch provided on the other line of the bypass line on which the input-side bypass switch is not provided, comprising: detecting an input voltage at the input terminal, a load voltage at the output terminal, and a bypass voltage of the bypass line between the input side bypass switch and the output side bypass switch; A short-circuit fault detection method for detecting a short-circuit fault of the input-side bypass switch based on the input voltage and the bypass voltage when the input-side bypass switch is turned off, and detecting a short-circuit fault of the output-side bypass switch based on the load voltage and the bypass voltage when the output-side bypass switch is turned off.

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