JP6085243B2 - Uninterruptible power supply system - Google Patents

Description

  The present invention relates to an uninterruptible power supply system, and more particularly to an uninterruptible power supply system that outputs a high voltage.

  2. Description of the Related Art Conventionally, an uninterruptible power supply system that boosts an output voltage of an uninterruptible power supply device with a transformer and supplies the boosted voltage to a load is known (see, for example, Patent Document 1).

  An uninterruptible power supply system is also known in which a generator is activated by an energy storage device including a flywheel device when a main AC power supply fails (see, for example, Patent Document 2).

JP-A-5-38055 JP-T-2001-502519

  However, the conventional uninterruptible power supply has a problem that the power loss in the transformer is large and the efficiency is low.

  Therefore, a main object of the present invention is to provide an uninterruptible power supply system capable of outputting a high voltage and having high efficiency.

  An uninterruptible power supply system according to the present invention includes a transformer including a primary winding that receives AC power supplied from a commercial AC power supply, a plurality of secondary windings insulated from each other, and a plurality of secondary windings. A plurality of inverters each including a converter that converts a voltage between terminals of a corresponding secondary winding into a DC voltage, and an inverter that converts a DC voltage generated by the converter into an AC voltage. It is equipped with a power failure power supply device. Multiple inverters are connected in series to the load, each stage's inverter adds its output voltage to the previous stage's output voltage and outputs it to the next stage, and the final stage's inverter is the sum of the output voltages of the multiple inverters. Apply AC voltage to the load. This uninterruptible power supply system is further connected in parallel with the load, and when AC power is normally supplied from a plurality of inverters, the AC power supplied from the plurality of inverters is converted into rotational energy of the flywheel device. When the supply of AC power from a plurality of inverters is stopped, an energy storage device is provided that converts rotational energy stored in the flywheel device into AC power and applies it to the load.

  In the uninterruptible power supply system according to the present invention, a high voltage is supplied to the load by connecting a plurality of inverters in series with the load. Therefore, since no output transformer is used, high efficiency can be obtained.

It is a circuit block diagram which shows the structure of the uninterruptible power supply system by Embodiment 1 of this invention. It is a circuit diagram which shows the structure of the input transformer shown in FIG. It is a circuit diagram which shows the structure of the high voltage uninterruptible power supply shown in FIG. It is a circuit diagram which shows the structure of the uninterruptible power supply device shown in FIG. It is a circuit diagram which shows the structure of the power converter shown in FIG. FIG. 6 is a circuit diagram showing a modification of the first embodiment. FIG. 10 is a circuit diagram showing another modification of the first embodiment. It is a circuit block diagram which shows the structure of the uninterruptible power supply system by Embodiment 2 of this invention. It is a circuit diagram which shows the structure of the high voltage uninterruptible power supply shown in FIG. It is a circuit diagram which shows the structure of the uninterruptible power supply shown in FIG. 10 is a time chart showing an operation of a portion related to the U phase in the high voltage uninterruptible power supply shown in FIG. 9. FIG. 10 is a circuit diagram showing a modification of the second embodiment. FIG. 10 is a circuit diagram showing another modification of the second embodiment. It is a circuit block diagram which shows the structure of the uninterruptible power supply system by Embodiment 3 of this invention.

[Embodiment 1]
As shown in FIG. 1, the uninterruptible power supply system according to Embodiment 1 of the present invention includes an input terminal T1, a bypass terminal T2, an output terminal T3, switches S1 to S8, an input transformer 1, a high-voltage uninterruptible power supply device 2, A non-instantaneous switch 3 and an energy storage device 4 are provided. The uninterruptible power supply system receives a three-phase three-wire commercial AC power from the commercial AC power supply 10 and the bypass AC power supply 11 and outputs a three-phase three-wire commercial frequency AC power to the load 12. For example, the line voltage of commercial AC power is 3300V, and the phase voltage is 1905V. However, for simplification of the drawings and description, FIG. 1 shows a circuit for one phase and one line.

  Input terminal T <b> 1 receives commercial AC power from commercial AC power supply 10. The bypass terminal T <b> 2 receives commercial AC power from the bypass AC power supply 11. The output terminal T3 is connected to the load 12. The switch S1 is a breaker, for example, and is connected between the input terminal T1 and the primary winding of the input transformer 1, and is normally turned on and turned off during maintenance of the uninterruptible power supply system.

  FIG. 2 is a circuit diagram showing the configuration of the input transformer 1. In FIG. 2, the input transformer 1 includes three primary windings CR, CS, and CT, and nine secondary windings CU1 to CU3, CV1 to CV3, and CW1 to CW3 that are insulated from each other. One terminals of the primary windings CR, CS, and CT receive R-phase, S-phase, and T-phase AC voltages VR, VS, and VT, respectively, and the other terminals are connected to each other. AC voltages VR, VS, and VT are all 1905 V, and their phases are shifted by 120 degrees.

  Secondary windings CU1-CU3 are electromagnetically coupled to primary winding CR. The secondary windings CV1 to CV3 are electromagnetically coupled to the primary winding CS. The secondary windings CW1 to CW3 are electromagnetically coupled to the primary winding CT. U-phase AC voltages VU1 to VU3 are output between terminals of secondary windings CU1 to CU3, respectively. Between the terminals of the secondary windings CV1 to CV3, V-phase AC voltages VV1 to VV3 are output, respectively. Between the terminals of the secondary windings CW1 to CW3, W-phase AC voltages VW1 to VW3 are output, respectively. AC voltages VU1 to VU3, VV1 to VV3, and VW1 to VW3 are all 635V. The phases of the U-phase AC voltages VU1 to VU3, the V-phase AC voltages VV1 to VV3, and the W-phase AC voltages VW1 to VW3 are shifted by 120 degrees.

  FIG. 3 is a circuit block diagram showing the configuration of the high-voltage uninterruptible power supply 2. In FIG. 3, the high voltage uninterruptible power supply 2 includes a control circuit 15, nine uninterruptible power supplies UU1 to UU3, UV1 to UV3, UW1 to UW3, and three output terminals TU, TV, and TW. The control circuit 15 controls the entire high voltage uninterruptible power supply 2. For example, the control circuit 15 controls the uninterruptible power supply devices UU1 to UU3, UV1 to UV3, UW1 to UW3 so that the output voltages VU, VV, and VW of the high-voltage uninterruptible power supply device 2 become target voltages.

  Input terminals Ta and Tb of uninterruptible power supply devices UU1 to UU3, UV1 to UV3, UW1 to UW3 are connected to one terminal and the other terminal of secondary windings CU1 to CU3, CV1 to CV3 and CW1 to CW3, respectively. Uninterruptible power supply units UU1 to UU3 convert AC power received from secondary windings CU1 to CU3, respectively, into DC power, and reconvert the DC power into commercial frequency AC power.

  Between the output terminals Tc and Td of the uninterruptible power supply devices UU1 to UU3, AC voltages VU11 to VU13 having a constant voltage (635 V) are output at commercial frequencies, respectively. The output terminal Td of the uninterruptible power supply UU1 is connected to the neutral point NP, and the output terminals Tc of the uninterruptible power supply UU1 and UU2 are connected to the output terminals Td of the uninterruptible power supply UU2 and UU3, respectively. The output terminal Tc of UU3 is connected to the output terminal TU.

  That is, uninterruptible power supply devices UU1 to UU3 are connected in series between output terminal TU and neutral point NP. The uninterruptible power supply UU2 adds its own output voltage VU12 to the output voltage VU11 of the previous uninterruptible power supply UU1, and outputs it to the next stage. The uninterruptible power supply UU3 adds its own output voltage VU13 to the output voltage VU11 + VU12 of the previous uninterruptible power supply UU2, and outputs it to the output terminal TU. Eventually, the total AC voltage VU = VU11 + VU12 + VU13 of the output voltages VU11 to VU13 of the uninterruptible power supply devices UU1 to UU3 is output to the output terminal TU. The AC voltage VU, that is, the U-phase voltage VU is 635 × 3 = 1905V.

  Similarly, uninterruptible power supply devices UV1 to UV3 convert AC power received from secondary windings CV1 to CV3 into DC power, respectively, and reconvert the DC power into commercial frequency AC power. Between the output terminals Tc and Td of the uninterruptible power supply devices UV1 to UV3, constant voltages (635V) AC voltages VV11 to VV13 are output at commercial frequencies, respectively. The output terminal Td of the uninterruptible power supply UV1 is connected to the neutral point NP, and the output terminals Tc of the uninterruptible power supply UV1 and UV2 are connected to the output terminals Td of the uninterruptible power supply UV2 and UV3, respectively. The UV3 output terminal Tc is connected to the output terminal TV.

  That is, uninterruptible power supply devices UV1 to UV3 are connected in series between output terminal TV and neutral point NP. The uninterruptible power supply UV2 adds its own output voltage VV12 to the output voltage VV11 of the previous uninterruptible power supply UV1 and outputs it to the next stage. The uninterruptible power supply UV3 adds its own output voltage VV13 to the output voltage VV11 + VV12 of the previous uninterruptible power supply UV2 and outputs it to the output terminal TV. Eventually, the AC voltage VV = VV11 + VV12 + VV13, which is the sum of the output voltages VV11 to VV13 of the uninterruptible power supply devices UV1 to UV3, is output to the output terminal TV. The AC voltage VV, that is, the V-phase voltage VV is 635 × 3 = 1905V.

  Similarly, uninterruptible power supply devices UW1 to UW3 convert AC power received from secondary windings CW1 to CW3 to DC power, respectively, and reconvert the DC power to AC power of commercial frequency. Between the output terminals Tc and Td of the uninterruptible power supply devices UW1 to UW3, AC voltages VW11 to VW13 having a constant voltage (635 V) are output at commercial frequencies, respectively. The output terminal Td of the uninterruptible power supply UW1 is connected to the neutral point NP, and the output terminals Tc of the uninterruptible power supply UW1 and UW2 are connected to the output terminals Td of the uninterruptible power supply UW2 and UW3, respectively. The output terminal Tc of UW3 is connected to the output terminal TW.

  That is, uninterruptible power supply devices UW1 to UW3 are connected in series between output terminal TW and neutral point NP. The uninterruptible power supply UW2 adds its own output voltage VW12 to the output voltage VW11 of the previous uninterruptible power supply UW1, and outputs it to the next stage. The uninterruptible power supply UW3 adds its own output voltage VW13 to the output voltage VW11 + VW12 of the previous uninterruptible power supply UW2, and outputs it to the output terminal TW. Eventually, the total AC voltage VW = VW11 + VW12 + VW13 of the output voltages VW11 to VW13 of the uninterruptible power supply devices UW1 to UW3 is output to the output terminal TW. The AC voltage VW, that is, the W-phase voltage VW is 635 × 3 = 1905V.

  The voltage VU−VV between the terminals TU and TV, that is, the line voltage VUV is 1905 × √3≈3300V. The voltage VV−VW between the terminals TV and TW, that is, the line voltage VVW is 1905 × √3≈3300V. The voltage VW−VU between the terminals TW and TU, that is, the line voltage VWU is 1905 × √3≈3300V. The phases of the line voltages VUV, VVW, VWU are shifted by 120 degrees.

  FIG. 4 is a circuit diagram showing a configuration of uninterruptible power supply UU1. In FIG. 4, uninterruptible power supply UU1 includes input terminals Ta and Tb, capacitors C1 to C4, reactors L1 and L2, transistors Q1 to Q8, Q11 to Q18, diodes D1 to D8, D11 to D18, D21 to D24, and D31. To D34, DC positive bus PL, DC neutral point bus NPL, DC negative bus NL, and output terminals Tc and Td.

  Transistors Q1, Q5, Q7, and Q3 are connected in series between buses PL and NL, and transistors Q2, Q6, Q8, and Q4 are connected in series between buses PL and NL. Diodes D1-D8 are connected in antiparallel to transistors Q1-Q8, respectively. The anodes of diodes D21 and D22 are both connected to DC neutral point bus NPL, and their cathodes are connected to the collectors of transistors Q5 and Q6, respectively. The anodes of diodes D23 and D24 are connected to the emitters of transistors Q7 and Q8, respectively, and the cathodes thereof are both connected to DC neutral point bus NPL.

  Transistors Q1-Q8 and diodes D1-D8, D21-D24 constitute a three-level converter 21. Capacitor C3 is connected between DC positive bus PL and DC neutral point bus NPL, and capacitor C4 is connected between DC neutral point bus NPL and DC negative bus NL. Capacitors C3 and C4 smooth and stabilize the DC voltage generated by converter 21.

  Reactor L1 is connected between input terminal Ta and the emitter of transistor Q5. One electrode of the capacitor C1 is connected to the input terminal Ta, and the other electrode is connected to the input terminal Tb and the emitter of the transistor Q6. Reactor L1 and capacitor C1 constitute input filter 20.

  The input filter 20 is a low-pass filter, and allows the commercial frequency AC voltage VU1 to pass through the converter 21 and prohibits the switching frequency signal generated by the converter 21 from passing to the input terminals Ta and Tb.

  Converter 21 converts AC power supplied from the corresponding secondary winding via input filter 20 to DC power. In other words, the converter 21 converts the AC voltage supplied from the corresponding secondary winding through the input filter 20 into a positive voltage, a neutral point voltage, and a negative voltage to convert the DC positive bus PL and the DC neutrality, respectively. This is applied to the point bus NLP and the DC negative bus NL.

  For example, when the voltage at the input terminal Ta is higher than the voltage at the input terminal Tb, the transistors Q5, Q1, and Q6 among the transistors Q1 to Q8 are turned on. As a result, a current flows from the input terminal Ta to the input terminal Tb through the reactor L1, the transistors Q5 and Q1, the capacitor C3, the diode D22, and the transistor Q6, and the capacitor C3 is charged. Also, transistors Q7, Q4, Q8 among transistors Q1-Q8 are turned on. As a result, a current flows from the input terminal Ta to the input terminal Tb through the reactor L1, the transistor Q7, the diode D23, the capacitor C4, and the transistors Q4 and Q8, and the capacitor C4 is charged.

  When the voltage at the input terminal Ta is lower than the voltage at the input terminal Tb, the transistors Q6, Q2, and Q5 among the transistors Q1 to Q8 are turned on. Thereby, a current flows from the input terminal Tb to the input terminal Ta through the transistors Q6 and Q2, the capacitor C3, the diode D21, the transistor Q5, and the reactor L1, and the capacitor C3 is charged. Also, transistors Q8, Q3, Q7 of transistors Q1-Q8 are turned on. As a result, a current flows from the input terminal Tb to the input terminal Ta through the transistor Q8, the diode D24, the capacitor C4, the transistors Q3 and Q7, and the reactor L1, and the capacitor C4 is charged.

  When the voltages at the input terminals Ta and Tb are substantially equal, only the transistors Q5 and Q8 or the transistors Q6 and Q7 are turned on. When only the transistors Q5 and Q8 are turned on, a current flows from the input terminal Tb to the input terminal Ta via the transistor Q8, the diodes D24 and D21, the transistor Q5, and the reactor L1. When only the transistors Q6 and Q7 are turned on, a current flows from the input terminal Ta to the input terminal Tb via the reactor L1, the transistor Q7, the diodes D23 and D22, and the transistor Q6. In this way, DC positive bus PL, DC neutral point bus NPL, and DC negative bus NL are set to a positive voltage, a neutral point voltage, and a negative voltage, respectively.

  Transistors Q11, Q15, Q17, Q13 are connected in series between buses PL, NL, and transistors Q12, Q16, Q18, Q14 are connected in series between buses PL, NL. Diodes D11-D18 are connected in antiparallel to transistors Q11-Q18, respectively. The anodes of diodes D31 and D32 are both connected to DC neutral point bus NPL, and their cathodes are connected to the collectors of transistors Q15 and Q16, respectively. The anodes of diodes D33 and D34 are connected to the emitters of transistors Q17 and Q18, respectively, and the cathodes thereof are both connected to DC neutral point bus NPL.

  Transistors Q11 to Q18 and diodes D11 to D18, D31 to D34 constitute a three-level inverter 22. Reactor L2 is connected between the emitter of transistor Q15 and output terminal Tc. One electrode of the capacitor C2 is connected to the output terminal Tc, and the other electrode is connected to the emitter of the transistor Q16 and the output terminal Td. Reactor L2 and capacitor C2 constitute output filter 23.

  Inverter 22 converts the DC power generated by converter 21 into AC power. In other words, inverter 22 has positive voltage, 0 V, and negative voltage based on the positive voltage, neutral point voltage, and negative voltage received from DC positive bus PL, DC neutral point bus NPL, and DC negative bus NL. 3 levels of alternating voltage are generated.

  For example, transistors Q11, Q15, Q18 among transistors Q11-Q18 are turned on. Thus, DC positive bus PL is connected to output terminal Tc via transistors Q11 and Q15 and reactor L2, and output terminal Td is connected to DC neutral point bus NPL via transistor Q18 and diode D34. A difference voltage (that is, a positive voltage) between the voltage and the neutral point voltage is supplied to the output filter 23.

  Further, transistors Q15, Q18, Q14 of transistors Q11-Q18 are turned on. Thereby, DC neutral point bus NPL is connected to output terminal Tc via diode D31, transistor Q15, and reactor L2, and output terminal Td is connected to DC negative bus NL via transistors Q18 and Q14. A differential voltage (that is, a positive voltage) between the neutral point voltage and the negative voltage is supplied to the output filter 23.

  In addition, transistors Q12, Q16, Q17 of transistors Q11-Q18 are turned on. Thereby, DC positive bus PL is connected to output terminal Td via transistors Q12 and Q16, and output terminal Tc is connected to DC neutral point bus NPL via reactor L2, transistor Q17, and diode D17. A voltage (that is, a negative voltage) between the neutral point voltage and the positive voltage is supplied to the output filter 23.

  Further, transistors Q16, Q17, Q13 among transistors Q11-Q18 are turned on. Thereby, DC neutral point bus NPL is supplied to output terminal Td via diode D32 and transistor Q16, and output terminal Tc is connected to DC negative bus NL via reactor L2 and transistors Q17 and Q13, and negative. A difference voltage (that is, a negative voltage) between the voltage and the neutral point voltage is supplied to the output filter 23.

  Further, only the transistors Q15 and Q18 or the transistors Q16 and Q17 are turned on. When only transistors Q15 and Q18 are turned on, DC neutral point bus NPL is connected to output terminal Tc via diode D31, transistor Q15, and reactor L2, and output terminal Td is connected to transistor Q18 and diode D34. To the DC neutral point bus NPL, and the voltage of the difference between the neutral point voltage and the neutral point voltage (that is, 0 V) is applied to the output filter 23.

  When only transistors Q16 and Q17 are turned on, DC neutral point bus NPL is connected to output terminal Td via diode D32 and transistor Q16, and output terminal Tc is connected to reactor L2, transistor Q17 and diode D33. Is connected to the DC neutral point bus NPL, and a voltage (that is, 0 V) of the difference between the neutral point voltage and the neutral point voltage is applied to the output filter 23.

  Therefore, by controlling the transistors Q11 to Q18, a desired voltage of positive voltage, 0V, and negative voltage can be supplied between the output terminals Tc and Td, and the positive voltage, 0V, and negative voltage 3 can be supplied. An alternating voltage that varies with the level can be generated.

  The output filter 23 is a low-pass filter, and passes an AC voltage having a commercial frequency to the output terminals Tc and Td, and prohibits a signal having a switching frequency generated by the inverter 22 from passing to the output terminals Tc and Td. In other words, the output filter 23 converts the waveform of the three-level AC voltage generated by the inverter 22 into a sine wave, and outputs the AC voltage of the sine wave between the output terminals Tc and Td.

  Each of the other uninterruptible power supply devices UU2, UU3, UV1 to UV3, UW1 to UW3 is the same as uninterruptible power supply device UU1, and therefore description thereof will not be repeated.

  Returning to FIG. 1, the switches S2 and S3 are connected in series between the output terminal (for example, TU) of the high-voltage uninterruptible power supply 2 and the output terminal T3. The switch S2 is a contactor, for example, and is turned on in the inverter power supply mode for supplying AC power from the inverter 22 to the load 12, and in the bypass power supply mode for supplying AC power from the bypass AC power supply 11 to the load 12 via the bypass terminal T2. Turned off.

  Switch S3 is, for example, a breaker, and is normally turned on and turned off during maintenance of the uninterruptible power supply system. The switch S4 is, for example, a breaker, and is connected between the input terminal T1 and the bypass terminal T2, normally turned off, and when it is desired to short-circuit between the terminals T1 and T2, for example, the bypass AC power supply because the commercial AC power supply 10 has failed. 11 is turned on when AC power is supplied to the input transformer 1.

  One terminal of the switch S5 is connected to the bypass terminal T2, and the other terminal is connected to the node N1 between the switches S2 and S3 via the switch S6. The switch S5 is a breaker, for example, and is normally turned on and turned off during maintenance. Switch S6 is, for example, a contactor, and is turned on in the bypass power supply mode and turned off in the inverter power supply mode.

  The uninterruptible switch 3 is connected in parallel to the switch S6, and is turned off when the high-voltage uninterruptible power supply 2 is normal, and is turned on instantaneously when the high-voltage uninterruptible power supply 2 fails. The uninterruptible switch 3 is turned off during normal times when the AC power is normally supplied from the commercial AC power supply 10 and is turned on instantaneously when the supply of AC power from the commercial AC power supply 10 is stopped. The switches S5, S6, S3 and the uninterruptible switch 3 constitute a bypass switch. The switch S7 is a breaker, for example, and is connected between the bypass terminal T2 and the output terminal T3, normally turned off, and turned on during maintenance.

  The energy storage device 4 includes a transformer 5, a power converter 6, a motor 7, and a flywheel device 8. When the AC power is normally supplied from the high-voltage uninterruptible power supply 2 or the bypass AC power supply 11, the energy storage device 4 uses the AC power supplied from the high-voltage uninterruptible power supply 2 or the bypass AC power supply 11 as a flywheel. When the supply of AC power from the high-voltage uninterruptible power supply 2 and the bypass AC power supply 11 is stopped, the rotational energy stored in the flywheel device 8 is converted into AC power. Apply to load 12.

  That is, the switch S8 is, for example, a breaker, and is connected between the output terminal T3 and the primary winding of the transformer 5, normally turned on, and turned off during maintenance. The secondary winding of the transformer 5 is connected to the power converter 6. When the AC power is normally supplied from the high-voltage uninterruptible power supply 2 or the bypass AC power supply 11, the transformer 5 converts the AC power from the high-voltage uninterruptible power supply 2 or the bypass AC power supply 11 to the power converter 6. When the supply of AC power from the high-voltage uninterruptible power supply 2 and the bypass AC power supply 11 is stopped, the AC power supplied from the power converter 6 is supplied to the load 12 via the output terminal T3. .

  FIG. 5 is a circuit diagram showing a configuration of the power converter 6 and is a diagram to be compared with FIG. As can be seen from FIG. 5, power converter 6 has the same configuration as uninterruptible power supply UU1. Reactor L1 and capacitor C1 constitute filter 30. Transistors Q1-Q8 and diodes D1-D8, D21-D24 constitute converter 31. Transistors Q11 to Q18 and diodes D11 to D18, D31 to D34 constitute a converter 32. Reactor L2 and capacitor C2 constitute filter 33.

  When the AC power is normally supplied from the high-voltage uninterruptible power supply 2 or the bypass AC power supply 11, the converter 31 is supplied from the high-voltage uninterruptible power supply 2 or the bypass AC power supply 11 via the transformer 5 and the filter 30. The supplied AC power is converted to DC power. In other words, converter 31 converts the AC voltage supplied from high-voltage uninterruptible power supply 2 or bypass AC power supply 11 through transformer 5 and filter 30 into a positive voltage, a neutral point voltage, and a negative voltage, respectively. This is applied to DC positive bus PL, DC neutral point bus NLP, and DC negative bus NL. At this time, the filter 31 prevents the noise of the switching frequency generated in the converter 31 from leaking to the transformer 5 side.

  Converter 32 operates as an inverter and converts the DC power generated by converter 31 into AC power. In other words, converter 32 has positive voltage, 0 V, and negative voltage based on the positive voltage, neutral point voltage, and negative voltage received from DC positive bus PL, DC neutral point bus NPL, and DC negative bus NL. 3 levels of alternating voltage are generated. At this time, the filter 33 converts the waveform of the three-level AC voltage generated by the converter 32 into a sine wave, and outputs the AC voltage of the sine wave between the output terminals Tc and Td.

  When AC power is not normally supplied from high-voltage uninterruptible power supply 2 and bypass AC power supply 11, converter 32 converts AC power supplied from motor 7 into DC power. In other words, the converter 32 converts the AC voltage supplied from the motor 7 into a positive voltage, a neutral point voltage, and a negative voltage to the DC positive bus PL, the DC neutral point bus NLP, and the DC negative bus NL, respectively. give. At this time, the filter 33 prevents the noise of the switching frequency generated in the converter 32 from leaking to the motor 7 side.

  Converter 31 operates as an inverter and converts the DC power generated by converter 32 into AC power. In other words, converter 31 has positive voltage, 0 V, and negative voltage based on the positive voltage, neutral point voltage, and negative voltage received from DC positive bus PL, DC neutral point bus NPL, and DC negative bus NL. 3 levels of alternating voltage are generated. At this time, the filter 30 converts the waveform of the three-level AC voltage generated by the converter 31 into a sine wave, and outputs the AC voltage of the sine wave between the input terminals Ta and Tb.

  When the AC power is normally supplied from the high-voltage uninterruptible power supply 2 or the bypass AC power supply 11, the motor 7 supplies the transformer 5 and the power converter 6 from the high-voltage uninterruptible power supply 2 or the bypass AC power supply 11. The flywheel device 8 is driven to rotate, and the flywheel device 8 is rotationally driven to store rotational energy in the flywheel device 8.

  In addition, when the supply of AC power from the high-voltage uninterruptible power supply 2 or the bypass AC power supply 11 is not normal, the motor 7 is rotationally driven by a flywheel device 8 that continues to rotate by rotational energy to generate AC power. To the power converter 6.

  The flywheel device 8 accumulates rotational energy by being rotationally driven by the motor 7, and releases rotational energy by rotationally driving the motor 7.

  Next, the operation of this uninterruptible power supply system will be described. However, for simplification of description, only the operation of the portion related to the R phase and the U phase will be described. Normally, the switches S1 to S3, S5, and S8 are turned on, and the switches S4, S6, and S7 are turned off. An AC voltage VR is supplied from the commercial AC power supply 10 to the primary winding CR of the input transformer 1 via the input terminal T1 and the switch S1. As a result, AC voltages VU1 to VU3 are output to the secondary windings CU1 to CU3 of the input transformer 1, respectively.

  Uninterruptible power supply devices UU1 to UU3 are driven by AC voltages VU1 to VU3, respectively, and output AC voltages VU11 to VU13 having sinusoidal waveforms, respectively. The AC voltages VU11 to VU13 are added to become a high-voltage AC voltage VU. The high-voltage AC voltage VU is supplied to the load 12 via the switches S2 and S3 and the output terminal T3. This state is called an inverter power supply mode because AC power is supplied from the inverter 22 of the uninterruptible power supply devices UU1 to UU3 to the load 12.

  At this time, AC power is supplied from the uninterruptible power supply devices UU1 to UU3 to the energy storage device 4 via the switches S2, S3, and S8, and the flywheel device 8 is rotationally driven by the motor 7 to store rotational energy. .

  When the output voltage of the commercial AC power supply 10 drops momentarily in the inverter power supply mode, that is, when a so-called instantaneous drop occurs, the positive voltage, the neutral point voltage, and the negative voltage are maintained by the capacitors C3 and C4. The AC voltage thus supplied is supplied to the load 12, and the load 12 is stably operated.

  In the inverter power supply mode, when the supply of AC power from the commercial AC power supply 10 is stopped (that is, when a power failure occurs), or when the high-voltage uninterruptible power supply 2 fails, the uninterruptible switch 3 is instantaneously The AC power is supplied to the load 12 from the bypass AC power supply 11 via the bypass terminal T2, the switch S5, the uninterruptible switch 3, the switch S3, and the output terminal T3, and the operation of the load 12 is continued. Note that the operation of converter 21 and inverter 22 is stopped during a power failure.

  When the switch S6 is turned on following the uninterruptible switch 3 and the switches S1 and S2 are turned off, the uninterruptible switch 3 is turned off. Thereby, AC power is supplied from the bypass AC power source 11 to the load 12 via the bypass terminal T2, the switches S5, S6, S3, and the output terminal T3, and the operation of the load 12 is continued. This is to reduce power loss in the uninterruptible switch 3. This state is called bypass power supply mode because AC power is supplied from the bypass AC power supply 11 to the load 12.

  At this time, AC power is supplied from the bypass AC power supply 11 to the energy storage device 4 via the bypass terminal T2 and the switches S5, S6, S3, and S8, and the flywheel device 8 is rotationally driven by the motor 7 to rotate energy. Is stored.

  In the bypass power supply mode, when the supply of AC power from the bypass AC power supply 11 is stopped or the output voltage of the bypass AC power supply 11 decreases momentarily, the rotational energy of the flywheel device 8 is converted into AC power by the motor 7. Is done. The AC power generated by the motor 7 is converted into AC power having the same voltage and frequency as the commercial AC power by the power converter 6 and the transformer 5 and supplied to the load 12 via the switch S8 and the output terminal T3. 12 operations are continued.

  At the time of maintenance, only the switch S7 is turned on, the other switches S1 to S6, S8 are turned off, and AC power is supplied from the bypass AC power supply 11 to the load 12 via the bypass terminal T2, the switch S7, and the output terminal T3. The load 12 is operated. When one of the AC power supplies 10 and 11 fails, the switch S4 is turned on, and the other AC power supply also functions as an AC power supply that has failed.

  In the first embodiment, a high voltage is supplied to the load 12 by connecting a plurality of uninterruptible power supply devices (for example, UU1 to UU3) in series to the load 12. Therefore, since no output transformer is used, high efficiency can be obtained.

  In addition, when the output transformer is driven by a low-voltage uninterruptible power supply, an uninterruptible power supply with a large rated current is required. It can consist of a small uninterruptible power supply.

  Further, a plurality of uninterruptible power supply devices (for example, UU1 to UU3) are connected by connecting a plurality of secondary windings (for example, CU1 to CU3) of the input transformer 1 to a plurality of uninterruptible power supply devices (for example, UU1 to UU3), respectively. Since they are insulated from each other, it is possible to use a low-breakdown-voltage transistor Q, a diode D, and the like, and to reduce the cost of the device.

  Moreover, since the energy storage device 4 is provided, the operation of the load 12 can be continued even when the power failure time is long.

  FIG. 6 is a circuit diagram showing the main part of an uninterruptible power supply system that is a modification of the first embodiment, and is a diagram contrasted with FIG. 4. Referring to FIG. 6, this uninterruptible power supply system is different from the first embodiment in that batteries 35 and 36 are provided corresponding to uninterruptible power supply devices UU1 to UU3, UV1 to UV3, UW1 to UW3, respectively. It is a point. In FIG. 6, the uninterruptible power supply UU1 and the batteries 35 and 36 are shown.

  A positive electrode and a negative electrode of battery 35 are connected to DC positive bus PL and DC neutral point bus NPL, respectively. The positive electrode and the negative electrode of battery 36 are connected to DC neutral point bus NPL and DC negative bus NL, respectively.

  When AC power is supplied from commercial AC power supply 10, converter 21 converts AC power received from corresponding secondary winding CU1 into DC power, and stores the DC power in batteries 35 and 36 and an inverter. When the supply of AC power from the commercial AC power supply 10 is stopped, it is stopped.

  When the AC power is supplied from the commercial AC power source 10, the inverter 22 converts the DC power generated by the converter 21 into AC power, and when the AC power supply from the commercial AC power source 10 is stopped. When the DC power of the batteries 35 and 36 is converted into AC power and the voltage between the terminals of the batteries 35 and 36 is reduced to the discharge end voltage, the battery 35 and 36 is stopped.

  In this modified example, even when the supply of AC power from the commercial AC power supply 10 is stopped, the high-voltage uninterruptible power supply 2 continues to supply AC power while the DC power is stored in the batteries 35 and 36. Accordingly, the uninterruptible switch 3 is not turned on when the supply of AC power from the commercial AC power supply 10 is stopped, and is turned on when the inverter 22 is stopped.

  In this modified example, the batteries 35 and 36 are provided in the uninterruptible power supply devices UU1 to UU3, UV1 to UV3, and UW1 to UW3. Therefore, when a power failure occurs, the load 12 is longer than that in the first embodiment. Can continue driving.

  FIG. 7 is a circuit diagram showing a main part of an uninterruptible power supply system which is another modification of the first embodiment, and is a diagram compared with FIG. Referring to FIG. 7, this modified example is different from the modified example of FIG. 6 in that batteries 35 and 36 are replaced by electric double layer capacitors 37 and 38, respectively. When the AC power is supplied from the commercial AC power supply 10, each uninterruptible power supply stores the generated DC power in the corresponding electric double layer capacitors 37 and 38, and the AC power is supplied from the commercial AC power supply 10. When stopped, the DC power of the electric double layer capacitors 37 and 38 is converted into AC power. In this modified example, since the electric double layer capacitors 37 and 38 are used, the life of the device can be extended and the size can be reduced as compared with the case where the batteries 35 and 36 are used.

  In the first embodiment, the AC voltage of 3.3 KV from the commercial AC power supply 10 is stepped down to an AC voltage of 635 V, a phase voltage of 1905 V is generated by a three-stage uninterruptible power supply, and 3.3 KV of Although the line voltage is regenerated, an even higher voltage uninterruptible power supply system can be constructed by increasing the number of stages of the uninterruptible power supply. For example, even if a 6.6 KV AC voltage from a commercial AC power supply is stepped down to a 635 V AC voltage, a phase voltage of 3810 V is generated by a 6-stage uninterruptible power supply, and a 6.6 KV line voltage is regenerated. Good.

[Embodiment 2]
FIG. 8 is a circuit block diagram showing a configuration of an uninterruptible power supply system according to Embodiment 2 of the present invention, and is a diagram compared with FIG. Referring to FIG. 8, this uninterruptible power supply system is different from the uninterruptible power supply system of FIG. 1 in that high voltage uninterruptible power supply 2 is replaced with high voltage uninterruptible power supply 40.

  FIG. 9 is a circuit block diagram showing the configuration of the high-voltage uninterruptible power supply 40, which is compared with FIG. Referring to FIG. 9, high-voltage uninterruptible power supply 40 is different from high-voltage uninterruptible power supply 2 in that uninterruptible power supply UU1-UU3, UV1-UV3, UW1-UW3 are uninterruptible power-supply UU1A-UU3A, It is replaced by UV1A to UV3A, UW1A to UW3A, and reactors LU, LV, and LW and capacitors CU, CV, and CW are added.

  FIG. 10 is a circuit diagram showing a configuration of uninterruptible power supply UU1A, and is a diagram contrasted with FIG. Referring to FIG. 10, uninterruptible power supply UU1A is obtained by removing reactors L1, L2 and capacitors C1, C2, that is, input filter 20 and output filter 23, from uninterruptible power supply UU1. The emitter of the transistor Q5 is directly connected to the input terminal Ta, and the emitter of the transistor Q15 is directly connected to the output terminal Tc. For this reason, the output voltage VU11A of the uninterruptible power supply UU1A is not a sine wave but a pulse signal string. Each of other uninterruptible power supply devices UU2A, UU3A, UV1A to UV3A, UW1A to UW3A has the same configuration as uninterruptible power supply UU1A.

  Returning to FIG. 9, a pulse signal sequence obtained by adding the output pulse signal sequences of the uninterruptible power supply devices UU1A to UU3A is output between the output terminal Tc of the uninterruptible power supply device UU3A and the output terminal Td of the uninterruptible power supply device UU1A. Is done. The control circuit 15 controls the inverter 22 of the uninterruptible power supply devices UU1A to UU3A by shifting the phase by a predetermined angle in order to make the waveform of the added pulse signal sequence approach a sine wave. Reactor LU is connected between output terminal Tc and output terminal TU of uninterruptible power supply UU3A, and capacitor CU is connected between output terminal Tc and neutral point NP. Reactor LU and capacitor CU constitute an output filter.

  This output filter is a low-pass filter, which passes an AC voltage of commercial frequency between the output terminal TU and the neutral point NP, and a switching frequency signal generated by the inverter 22 passes between the output terminal TU and the neutral point NP. It is prohibited to do. In other words, the output filter composed of the reactor LU and the capacitor CU converts the added output pulse signal sequence of the uninterruptible power supply units UU1A to UU3A into a sine wave, and converts the sinusoidal AC voltage VU into the output terminal TU and the neutral point. Output between NPs.

  Similarly, a pulse signal sequence obtained by adding the output pulse signal sequences of the uninterruptible power supply devices UV1A to UV3A is output between the output terminal Tc of the uninterruptible power supply device UV3A and the output terminal Td of the uninterruptible power supply device UV1A. The control circuit 15 controls the inverter 22 of the uninterruptible power supply UV1A to UV3A by shifting the phase by a predetermined angle in order to bring the waveform of the added pulse signal sequence closer to a sine wave. Reactor LV is connected between output terminal Tc and output terminal TV of uninterruptible power supply UV3A, and capacitor CV is connected between output terminal Tc and neutral point NP. Reactor LV and capacitor CV constitute an output filter.

  This output filter is a low-pass filter, and passes an AC voltage of commercial frequency between the output terminal TV and the neutral point NP, and a switching frequency signal generated by the inverter 22 passes between the output terminal TV and the neutral point NP. It is prohibited to do. In other words, the output filter composed of the reactor LV and the capacitor CV converts the added output pulse signal sequence of the uninterruptible power supply UV1A to UV3A into a sine wave, and converts the sinusoidal AC voltage VV into the output terminal TV and the neutral point. Output between NPs.

  Similarly, a pulse signal sequence obtained by adding the output pulse signal sequences of the uninterruptible power supply devices UW1A to UW3A is output between the output terminal Tc of the uninterruptible power supply device UW3A and the output terminal Td of the uninterruptible power supply device UW1A. The control circuit 15 controls the inverters 22 of the uninterruptible power supply devices UW1A to UW3A by shifting their phases by a predetermined angle in order to make the waveform of the added pulse signal sequence approach a sine wave. Reactor LW is connected between output terminal Tc and output terminal TW of uninterruptible power supply UW3A, and capacitor CW is connected between output terminal Tc and neutral point NP. Reactor LW and capacitor CW constitute an output filter.

  This output filter is a low-pass filter, which passes an AC voltage of commercial frequency between the output terminal TW and the neutral point NP, and a switching frequency signal generated by the inverter 22 passes between the output terminal TW and the neutral point NP. It is prohibited to do. In other words, the output filter consisting of the reactor LW and the capacitor CW converts the added output pulse signal sequence of the uninterruptible power supply devices UW1A to UW3A into a sine wave, and converts the AC voltage VW of the sine wave into the output terminal TW and the neutral point. Output between NPs.

  FIGS. 11A to 11D are time charts showing the operation of the portion related to the U phase in the high voltage uninterruptible power supply 40 shown in FIGS. 9 and 10. 11A shows the waveform of the output voltage VU11A of the uninterruptible power supply UU1A, and FIG. 11B shows the waveform of the U-phase voltage VU obtained by adding the output voltages VU11A to VU13A of the uninterruptible power supply UU1A to UU3A. FIG. 11 (c) shows the waveform of the U-phase and V-phase line voltage VUV, and FIG. 11 (d) shows the waveform of the U-phase current IU.

  As shown in FIG. 11A, the output voltage VU11A of the uninterruptible power supply UU1A is a positive pulse signal sequence at 0 to 180 degrees and a negative pulse signal sequence at 180 to 360 degrees. The pulse width is maximum near 90 ° and 270 °, which are the peaks of the sine wave, and the pulse width is minimum near 0 ° and 180 °, which is the zero point of the sine wave.

  Also, as shown in FIG. 11B, the waveform of the U-phase voltage VU obtained by adding the output voltages VU11A to VU13A of the uninterruptible uninterruptible power supply devices UU1A to UU3A is the waveform of the output voltage VU11A of the uninterruptible power supply UU1A. Is closer to a sine wave. Further, as shown in FIG. 11C, the waveform of the line voltage VUV is closer to a sine wave. Further, as shown in FIG. 11D, the waveform of the U-phase current IU flowing through the load 12 is substantially a sine wave. Since the operation of the portion related to the V phase and the W phase is the same as the operation of the portion related to the U phase, the description thereof will not be repeated. Other configurations and operations are the same as those in the first embodiment, and thus description thereof will not be repeated.

  In the second embodiment, the output filter is provided in common for the three uninterruptible power supply devices in each phase, and the input filter is removed, so that the circuit area can be reduced.

  FIG. 12 is a circuit diagram showing a main part of an uninterruptible power supply system which is a modified example of the second embodiment, and is a diagram compared with FIG. Referring to FIG. 12, this uninterruptible power supply system is different from the second embodiment in that batteries 35 and 36 are provided corresponding to uninterruptible power supply devices UU1A to UU3A, UV1A to UV3A, UW1A to UW3A, respectively. It is a point. In FIG. 12, uninterruptible power supply UU1A and batteries 35 and 36 are shown.

  A positive electrode and a negative electrode of battery 35 are connected to DC positive bus PL and DC neutral point bus NPL, respectively. The positive electrode and the negative electrode of battery 36 are connected to DC neutral point bus NPL and DC negative bus NL, respectively.

  When the AC power is supplied from the commercial AC power supply 10 or the energy storage device 4, the converter 21 converts the AC power received from the corresponding secondary winding CU1 into DC power, and converts the DC power into the battery 35, When the supply of AC power from the commercial AC power supply 10 is stopped, it is stopped.

  When the AC power is supplied from the commercial AC power supply 10 or the energy storage device 4, the inverter 22 converts the DC power generated by the converter 21 into AC power, and the AC power is supplied from the commercial AC power supply 10. When stopped, the DC power of the batteries 35 and 36 is converted into AC power, and when the voltage between the terminals of the batteries 35 and 36 drops to the discharge end voltage, the battery 35 and 36 stops.

  In this modified example, even when the supply of AC power from the commercial AC power supply 10 is stopped, the high voltage uninterruptible power supply 40 continues to supply AC power while the DC power is stored in the batteries 35 and 36. Accordingly, the uninterruptible switch 3 is not turned on when the supply of AC power from the commercial AC power supply 10 is stopped, and is turned on when the inverter 22 is stopped.

  In this modified example, the batteries 35 and 36 are provided in the uninterruptible power supply devices UU1A to UU3A, UV1A to UV3A, and UW1A to UW3A. Therefore, when a power failure occurs, the load 12 is longer than that in the second embodiment. Can continue driving.

  FIG. 13 is a circuit diagram showing the main part of an uninterruptible power supply system which is another modification of the second embodiment, and is a figure compared with FIG. Referring to FIG. 13, this modified example is different from the modified example of FIG. 12 in that batteries 35 and 36 are replaced with electric double layer capacitors 37 and 38, respectively. When the AC power is supplied from the commercial AC power supply 10, each uninterruptible power supply stores the generated DC power in the corresponding electric double layer capacitors 37 and 38, and the AC power is supplied from the commercial AC power supply 10. When stopped, the DC power of the electric double layer capacitors 37 and 38 is converted into AC power. In this modified example, since the electric double layer capacitors 37 and 38 are used, the life of the device can be extended and the size can be reduced as compared with the case where the batteries 35 and 36 are used.

[Embodiment 3]
FIG. 14 is a circuit block diagram showing a configuration of an uninterruptible power supply system according to Embodiment 3 of the present invention, and is compared with FIG. Referring to FIG. 14, this uninterruptible power supply system is different from the uninterruptible power supply system of FIG. 1 in that bypass AC power supply 11 is replaced with a generator 41.

  The generator 41 is a diesel generator, for example, and is connected to the bypass terminal T2. In order to operate the generator 41, it is necessary to start the generator 41 by supplying AC power for a predetermined time. The switch S4 is normally turned on and turned off during maintenance. Therefore, the commercial AC power supply 10 also serves as a bypass AC power supply. During normal times when AC power is supplied from the commercial AC power supply 10, the operation of the generator 41 is stopped, the uninterruptible power supply system operates in the same manner as in the first embodiment, and rotational energy is supplied to the flywheel device 8. Accumulated.

  When the supply of AC power from the commercial AC power supply 10 is stopped, the switch S2 is turned off and the switch S6 is turned on. The rotational energy of the flywheel device 8 is converted into AC power, and the load 12 and the generator 41 are turned on. And the operation of the load 12 is continued, and the generator 41 is started. The started generator 41 generates AC power and supplies it to the load 12 and the energy storage device 4. Therefore, the operation of the load 12 is continued.

  In the third embodiment, since the AC power is supplied from the energy storage device 4 and the generator 41 is started during a power failure, the load 12 can be operated for a long time even during a power failure.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  T1, Ta, Tb input terminal, T2 bypass terminal, T3, Tc, Td, TU, TV, TW output terminal, S1-S8 switch, 1 input transformer, 2,40 high voltage uninterruptible power supply, 3 uninterruptible switch 4, energy storage device, 5 transformer, 6 power converter, 7 motor, 8 flywheel device, 10 commercial AC power supply, 11 bypass AC power supply, 12 load, CR, CS, CT primary winding, CU1-CU3 CV1-CV3, CW1-CW3 secondary winding, UU1-UU3, UV1-UV3, UW1-UW3, UU1A-UU3A, UV1A-UV3A, UW1A-UW3A uninterruptible power supply, 15 control circuit, L1, L2, LU, LV, LW reactor, C1-C4, CU, CV, CW capacitors, Q1-Q8, Q11-Q18 transistors, D D8, D11 to D18, D21 to D24, D31 to D34 Diode, 20 input filter, 21, 31, 32 converter, 22 inverter, 23 output filter, 30, 33 filter, 35, 36 battery, 37, 38 Electric double layer Capacitor, PL DC positive bus, NPL DC neutral point bus, NL DC negative bus, 41 generator.

Claims (10)

A transformer including a primary winding that receives AC power supplied from a commercial AC power source and a plurality of secondary windings that are insulated from each other;
A converter provided corresponding to each of the plurality of secondary windings, each of which converts a voltage between terminals of the corresponding secondary winding into a DC voltage, and a capacitor that smoothes the DC voltage generated by the converter And a plurality of uninterruptible power supplies including an inverter that converts the DC voltage smoothed by the capacitor into an AC voltage,
The plurality of inverters are connected in series with the load, the inverters at each stage add their own output voltage to the output voltage of the previous stage, and output to the next stage, and the inverter at the final stage includes the plurality of inverters Apply an alternating voltage of the total output voltage to the load,
Furthermore, when the AC power is included in at least a power converter connected in parallel with the load, and AC power is normally supplied from the plurality of inverters, AC power supplied from the plurality of inverters via the power converter Is converted into rotational energy of the flywheel device, and when the supply of AC power from the plurality of inverters is stopped, the rotational energy stored in the flywheel device is converted into AC power and given to the load Uninterruptible power supply system with storage device. Furthermore, one terminal is connected to the bypass AC power supply, the other terminal is connected to the load, and the inverter power supply mode for supplying AC power from the plurality of inverters to the load is non-conductive, and the bypass AC power supply In the bypass power supply mode to supply AC power to the load
When the AC power is normally supplied from the plurality of inverters or the bypass AC power source, the energy storage device converts the AC power supplied from the plurality of inverters or the bypass AC power source to rotational energy of the flywheel device. When the supply of AC power from the plurality of inverters and the bypass AC power supply is stopped, the rotational energy stored in the flywheel device is converted into AC power and applied to the load. The uninterruptible power supply system according to 1.   Further, when the AC power is normally supplied from the commercial AC power supply, the operation is stopped, and when the supply of AC power from the commercial AC power supply is stopped, the AC generated by the energy storage device The uninterruptible power supply system according to claim 1, further comprising a generator that is started by electric power to generate AC power and that supplies the generated AC power to the load. When the AC power is supplied from the commercial AC power source, the converter converts AC power received from the corresponding secondary winding into DC power, and the supply of AC power from the commercial AC power source is stopped. If it stops,
When the AC power is supplied from the commercial AC power source, the inverter converts the DC power generated by the converter into AC power, and when the AC power supply from the commercial AC power source is stopped. The uninterruptible power supply system according to any one of claims 1 to 3, which stops. When AC power is supplied from the commercial AC power source, the converter converts AC power received from a corresponding secondary winding into DC power, stores the DC power in a power storage device, and stores it in the inverter. If the supply of AC power from the commercial AC power supply is stopped,
When the AC power is supplied from the commercial AC power source, the inverter converts the DC power generated by the converter into AC power, and when the AC power supply from the commercial AC power source is stopped. The uninterruptible power supply system according to any one of claims 1 to 3, wherein DC power of the power storage device is converted into AC power.   The uninterruptible power supply system according to claim 5, wherein the power storage device is a storage battery.   The uninterruptible power supply system according to claim 5, wherein the power storage device is an electric double layer capacitor. Each uninterruptible power supply further includes a filter circuit that converts the waveform of the output voltage of the inverter into a sine wave,
The uninterruptible power supply system according to any one of claims 1 to 7, wherein output voltages of a plurality of the filter circuits included in the plurality of uninterruptible power supply devices are added and given to the load.   The uninterruptible power supply system according to any one of claims 1 to 7, further comprising a filter circuit that converts waveforms of the added output voltages of the plurality of inverters into a sine wave and applies the sine wave to the load. .   The uninterruptible power supply system according to claim 9, wherein phases of output voltages of the plurality of inverters are sequentially shifted.

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