Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
  • H02M1/00—Details of apparatus for conversion
  • H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J9/00—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting
  • H02J9/04—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source
  • H02J9/06—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source with automatic change-over, e.g. UPS systems
  • H02J9/062—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source with automatic change-over, e.g. UPS systems for AC powered loads
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J9/00—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting
  • H02J9/04—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source
  • H02J9/06—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source with automatic change-over, e.g. UPS systems
  • H02J9/068—Electronic means for switching from one power supply to another power supply, e.g. to avoid parallel connection
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
  • H02M7/00—Conversion of AC power input into DC power output; Conversion of DC power input into AC power output
  • H02M7/02—Conversion of AC power input into DC power output without possibility of reversal
  • H02M7/04—Conversion of AC power input into DC power output without possibility of reversal by static converters
  • H02M7/12—Conversion of AC power input into DC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
  • H02M7/00—Conversion of AC power input into DC power output; Conversion of DC power input into AC power output
  • H02M7/42—Conversion of DC power input into AC power output without possibility of reversal
  • H02M7/44—Conversion of DC power input into AC power output without possibility of reversal by static converters
  • H02M7/48—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode

Definitions

• Patent Document 1 discloses an uninterruptible power supply system including a converter, a DC voltage converter, and an inverter.
• the converter converts the AC voltage from the AC power supply into first to third DC voltages and outputs them to the first to third DC lines.
• the DC voltage converter converts the fourth DC voltage from the power storage device into first to third DC voltages and supplies them to the first to third DC lines.
• the inverter converts the first to third DC voltages from the first to third DC lines into AC voltages and supplies them to the load.
• This uninterruptible power supply further includes a first capacitor connected between the first and second DC lines, a second capacitor connected between the second and third DC lines, and a control device.
• a control device controls the converter so that the first voltage, which is the sum of the terminal voltages of the first and second capacitors, becomes the reference voltage and the second voltage, which is the difference between the terminal voltages of the first and second capacitors, disappears.
• the control device stops operation of the converter and controls the DC voltage converter so that the first voltage becomes the reference voltage and the second voltage disappears.
• Patent Document 2 discloses an uninterruptible power supply in which the AC power supply and load are three-phase, four-wire.
• the control device controls the converter so that the first voltage becomes the reference voltage and the second voltage, which is the difference between the terminal voltages of the first and second capacitors, disappears.
• the control device controls the DC voltage converter so that the first voltage becomes the reference voltage and the second voltage disappears. If the absolute value of the second voltage exceeds a predetermined threshold voltage during a power outage in the AC power supply, the control device further controls the converter to reduce the second voltage.
• the uninterruptible power supply does not have a detector for detecting the terminal voltage of the filter capacitor, it is unable to determine the difference between the terminal voltages of the first and second capacitors and the terminal voltage of the filter capacitor, which raises concerns that balance control by the converter may become difficult.
• Patent Document 2 when the difference between the terminal voltage of the first and second capacitors and the terminal voltage of the filter capacitor disappears, the first and second capacitors cannot be discharged or charged even when the converter is operating, and an operation to discharge the filter capacitor is required. Therefore, Patent Document 2 reduces the second voltage by alternately repeating the operation of discharging or charging the first and second capacitors and the operation of discharging the filter capacitor. This raises concerns that it may become difficult to quickly resolve the imbalance between the first and second capacitors in the event of a power outage in the AC power supply.
• An uninterruptible power supply comprises first to third DC lines, a first capacitor, a second capacitor, a switch, an AC input filter, a converter, an inverter, first and second voltage detectors, and a control device.
• the first capacitor is connected between the first and second DC lines.
• the second capacitor is connected between the second and third DC lines.
• the switch has a first terminal that receives AC voltage supplied from the AC power source, and is turned on when the AC power source is healthy and turned off when there is an AC power outage.
• the AC input filter has a first terminal that is connected to the second terminal of the switch.
• the converter is connected between the second terminal of the AC input filter and the first to third DC lines.
• the converter When the AC power source is healthy, the converter converts AC power from the AC power source into DC power and supplies it to the first to third DC lines.
• the inverter is connected between the first to third DC lines and the load, converts DC power from the first to third DC lines into AC power, and supplies it to the load.
• the first and second voltage detectors detect the voltages across the terminals of the first and second capacitors, respectively.
• the control device controls the converter based on the detected values of the first and second voltage detectors.
• the AC input filter includes a first reactor having a first terminal connected to the second terminal of the switch, and a second reactor having a first terminal connected to the second terminal of the switch.
• the converter includes a first multilevel circuit and a second multilevel circuit.
• the first multilevel circuit is connected between the second terminal of the first reactor and the first to third DC lines, and is configured to be able to convert between AC voltage and the first to third DC voltages.
• the second multilevel circuit is connected between the second terminal of the second reactor and the first to third DC lines, and is configured to be able to convert between AC voltage and the first to third DC voltages.
• the control device calculates a first voltage, which is the sum of the terminal voltages of the first and second capacitors, and a second voltage, which is the difference between the terminal voltages of the first and second capacitors, based on the detection values of the first and second voltage detectors.
• the control device controls the first and second multilevel circuits so that the first voltage becomes the first reference voltage and the second voltage disappears.
• the control device controls the first and second multilevel circuits so that the second voltage disappears.
• This disclosure provides an uninterruptible power supply that can easily and quickly eliminate the imbalance in the voltage between the terminals of the first and second capacitors during an AC power outage.
• FIG. 8 is a time chart showing waveforms of a voltage command value, a triangular wave signal, and a PWM signal shown in FIG. 7 .
• 10A and 10B are diagrams showing switching patterns of four IGBTs included in each bridge circuit. 6 is a time chart showing the operation of the second control circuit shown in FIG. 5 .
• FIG. 10 is an equivalent circuit diagram showing the operation of one phase of the converter when Ep>En.
• FIG. 10 is an equivalent circuit diagram showing the operation of one phase of the converter when Ep>En.
• 6 is a time chart showing the operation of the second control circuit shown in FIG. 5 .
• FIG. 10 is an equivalent circuit diagram showing the operation of one phase of the converter when Ep ⁇ En.
• FIG. 10 is an equivalent circuit diagram showing the operation of one phase of the converter when Ep ⁇ En.
• FIG. 6 is a block diagram showing the configuration of a control circuit shown in FIG. 5 .
• 10 is a flowchart showing an example of balance control by a converter during a power outage of a commercial AC power supply.
• FIG. 11 is a circuit diagram showing a main part of an uninterruptible power supply according to a third embodiment.
• 10A and 10B are diagrams showing switching patterns of four IGBTs included in each bridge circuit.
• 6 is a time chart showing the operation of the second control circuit.
• FIG. 10 is an equivalent circuit diagram showing the operation of one phase of the converter when Ep>En.
• FIG. 10 is an equivalent circuit diagram showing the operation of one phase of the converter when Ep>En.
• 6 is a time chart showing the operation of the second control circuit.
• FIG. 10 is an equivalent circuit diagram showing the operation of one phase of the converter when Ep ⁇ En.
• FIG. 10 is an equivalent circuit diagram showing the operation of one phase of the converter when Ep ⁇ En.
• Fig. 1 is a block diagram showing the overall configuration of an uninterruptible power supply 100 according to embodiment 1.
• the uninterruptible power supply 100 includes a switch 1, an AC input filter 2, a converter 3, an inverter 4, an AC output filter 5, a DC voltage converter (hereinafter referred to as "DC/DC") 6, a control device 10, DC lines L1 to L3, a neutral point line L4, capacitors C1 and C2, voltage detectors 31, 34, and 35, current detectors 32 and 37, and a power outage detector 33.
• DC/DC DC voltage converter
• Switch 1 includes switches 1R, 1S, and 1T. First terminals of switches 1R, 1S, and 1T are connected to the R-phase terminal TR, S-phase terminal TS, and T-phase terminal TT of the commercial AC power supply 41, respectively, and receive the R-phase voltage VR, S-phase voltage VS, and T-phase voltage VT supplied from the commercial AC power supply 41, respectively.
• the neutral terminal TN of the commercial AC power supply 41 is connected to one end of the neutral line L4.
• Switches 1R, 1S, and 1T are controlled by control device 10 and are turned on when three-phase AC power is being supplied normally from commercial AC power supply 41 (when commercial AC power supply 41 is operating normally), and are turned off when the supply of three-phase AC power from commercial AC power supply 41 is stopped (when commercial AC power supply 41 experiences a power outage). Switches 1R, 1S, and 1T are turned off when the commercial AC power supply 41 experiences a power outage, electrically disconnecting commercial AC power supply 41 from AC input filter 2.
• AC input filter 2 is a three-phase LC filter circuit composed of capacitor 11 (capacitors 11R, 11S, 11T) and reactor 12 (reactors 12R, 12S, 12T).
• the positive electrodes of capacitors 11R, 11S, 11T are connected to the second terminals of switches 1R, 1S, 1T, respectively, and their negative electrodes are both connected to neutral line L4.
• the first terminals of reactors 12R, 12S, 12T are connected to the second terminals of switches 1R, 1S, 1T, respectively, and the second terminals of reactors 12R, 12S, 12T are connected to the three input nodes of converter 3, respectively.
• the AC input filter 2 is a low-pass filter that allows commercial frequency AC power supplied from the commercial AC power supply 41 to pass to the converter 3, while preventing the switching frequency signal generated by the converter 3 from passing to the commercial AC power supply 41.
• DC lines L1 to L3 are connected to the three output nodes of converter 3, and their second ends are connected to the three input nodes of inverter 4.
• DC line L2 is connected to neutral line L4.
• DC lines L1 to L3 are also connected to three high-voltage nodes of DC voltage converter 6.
• DC lines L1 to L3 are set to a positive voltage, neutral voltage, and negative voltage, respectively, by converter 3 and DC voltage converter 6.
• Capacitor C1 is connected between DC lines L1 and L2 and smooths and stabilizes the DC voltage Ep between DC lines L1 and L2.
• Capacitor C2 is connected between DC lines L2 and L3 and smooths and stabilizes the DC voltage En between DC lines L2 and L3.
• the converter 3 is controlled by the control device 10, and when the commercial AC power supply 41 is operating normally, it converts the three-phase AC power supplied from the commercial AC power supply 41 via the AC input filter 2 into DC power, which is then supplied to the inverter 4 and DC voltage converter 6 via DC lines L1 to L3.
• the control device 10 stops operation of the converter 3.
• the inverter 4 is controlled by the control device 10 and converts the DC power from the converter 3 and the DC voltage converter 6 into three-phase AC power at commercial frequencies.
• the three-phase AC power generated by the inverter 4 is supplied to the load 42 via the AC output filter 5.
• the AC output filter 5 is a three-phase LC filter circuit composed of reactors 18 (reactors 18U, 18V, 18W) and capacitors 19 (capacitors 19U, 19V, 19W).
• reactors 18 reactors 18U, 18V, 18W
• capacitors 19 capacitors 19U, 19V, 19W.
• the first terminals of reactors 18U, 18V, 18W are connected to the three output nodes of inverter 4, respectively, and their second terminals are connected to the U-phase terminal TU, V-phase terminal TV, and W-phase terminal TW of load 42.
• Battery B1 (power storage device) is connected between the two low-voltage nodes of DC voltage converter 6.
• DC voltage converter 6 is controlled by control device 10, and when commercial AC power supply 41 is healthy, DC power generated by converter 3 is stored in battery B1. At that time, control device 10 controls DC voltage converter 6 so that the inter-terminal voltage VB of battery B1 becomes equal to reference battery voltage VBR.
• the DC voltage converter 6 supplies DC power from battery B1 to inverter 4 via DC lines L1 to L3.
• the voltage detector 31 detects the instantaneous values of the AC voltages VR, VS, and VT at the second terminals of the switches 1R, 1S, and 1T, and outputs three-phase voltage signals indicating the three-phase AC voltages VR, VS, and VT to the control device 10 and the power outage detector 33.
• the current detector 32 detects the instantaneous values of the AC currents IR, IS, and IT flowing into the three input nodes of the converter 3, and outputs three-phase current signals indicating the three-phase AC currents IR, IS, and IT to the control device 10.
• the power outage detector 33 determines whether a power outage has occurred in the commercial AC power supply 41 based on the three-phase voltage signal from the voltage detector 31, and outputs a power outage signal PC indicating the result of the determination.
• the power outage signal PC is at the inactive "L” level.
• the power outage signal PC is at the active "H” level.
• the power outage signal PC is provided to the control device 10.
• Voltage detector 34 detects the terminal voltage Ep of capacitor C1 and outputs a signal indicating the detected voltage Ep to control device 10.
• Voltage detector 35 detects the terminal voltage En of capacitor C2 and outputs a signal indicating the detected voltage En to control device 10.
• Voltage detector 36 detects the terminal voltage VB of battery B1 and outputs a signal indicating the detected voltage VB to control device 10.
• Current detector 37 detects the current IB output from battery B1 and outputs a signal indicating the detected current IB to control device 10.
• the control device 10 receives a three-phase voltage signal from the voltage detector 31, a three-phase current signal from the current detector 32, signals from the voltage detectors 34 to 36, a signal from the current detector 37, and a power outage signal PC from the power outage detector 33, and controls the entire uninterruptible power supply 100.
• the converter 3, inverter 4, and DC voltage converter 6 are composed of semiconductor switches including semiconductor switching elements.
• IGBTs Insulated Gate Bipolar Transistors
• PWM Pulse Width Modulation
• FIG. 2 is a block diagram showing an example of the hardware configuration of the control device 10.
• the control device 10 is composed of a CPU (Central Processing Unit) 102, memory 104, and input/output (I/O) circuit 106.
• the CPU 102, memory 104, and I/O circuit 106 can exchange data with each other via a bus 108. Programs are stored in a portion of the memory 104, and the CPU 102 can execute these programs to realize various functions described below.
• the I/O circuit 106 inputs and outputs signals and data to and from the outside of the control device 10.
• control device 10 can be configured using circuits such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). Also, at least a portion of the control device 10 can be configured using analog circuits.
• FPGA Field Programmable Gate Array
• ASIC Application Specific Integrated Circuit
• FIG. 3 is a circuit diagram showing an example of the configuration of the converter 3 shown in Fig. 1.
• the converter 3 includes an R-phase arm 3R, an S-phase arm 3S, and a T-phase arm 3T. Since the phase arms 3R, 3S, and 3T of the converter 3 have the same circuit configuration, the circuit configuration of the R-phase arm 3R will be described as a representative example.
• reactor 12R includes reactors 12RA and 12RB.
• R-phase arm 3R includes three-level circuits 3A and 3B.
• a first terminal of reactor 12RA is connected to a second terminal of switch 1R, and a second terminal of reactor 12RA is connected to an input node 3a of three-level circuit 3A.
• a first terminal of reactor 12RB is connected to a second terminal of switch 1R, and a second terminal of reactor 12RB is connected to an input node 3b of three-level circuit 3B.
• Reactor 12RA corresponds to an example of a "first reactor”
• reactor 12RB corresponds to an example of a "second reactor.”
• Three-level circuit 3A corresponds to one embodiment of the "first multi-level circuit.”
• IGBT Q1A and diode D1A form the "first switch”
• IGBTs Q2A and Q4A and diodes D2A and D4A form the "second switch”
• IGBT Q3A and diode D3A form the "third switch.”
• Three-level circuit 3B corresponds to one embodiment of the "second multi-level circuit.”
• IGBT Q1B and diode D1B form the "fourth switch
• IGBTs Q2B and Q4B and diodes D2B and D4B form the "fifth switch”
• IGBT Q3B and diode D3B form the "sixth switch.”
• Reactor 22 includes reactors 22P and 22N.
• Reactor 22P is connected between the connection point of IGBTs Q1D and Q2D and the positive electrode of battery B1.
• Reactor 22N is connected between the connection point of IGBTs Q3D and Q4D and the negative electrode of battery B1. Note that reactor 22 may include either reactor 22P or 22N.
• FIG. 5 is a block diagram showing the portion of the control device 10 that is related to the control of the converter 3 and the DC voltage converter 6.
• the control device 10 includes an adder 51, a subtractor 52, a first control circuit 53, a second control circuit 54, a switching circuit 55, and a control circuit 80.
• the first control circuit 53 controls the converter 3 based on the three-phase voltage signal from the voltage detector 31, the three-phase current signal from the current detector 32, the signal indicating the DC voltage VDC from the adder 51, and the signal indicating the DC voltage ⁇ E from the subtractor 52. Specifically, the first control circuit 53 controls the converter 3 so that the phases of the three-phase AC voltages VR, VS, and VT match the phases of the three-phase AC currents IR, IS, and IT, the DC voltage VDC becomes the reference DC voltage VDCR, and the DC voltage ⁇ E becomes zero.
• the switching circuit 55 is provided between the control circuits 53, 54 and the converter 3.
• the switching circuit 55 connects one of the control circuits 53, 54 to the converter 3 based on the power outage signal PC from the power outage detector 33. Specifically, when the power outage signal PC is at the inactive "L" level (when the commercial AC power supply 41 is operating normally), the switching circuit 55 connects the first control circuit 53 to the converter 3. When the power outage signal PC is at the active "H" level (when the commercial AC power supply 41 is experiencing a power outage), the switching circuit 55 connects the second control circuit 54 to the converter 3.
• Adder 68A adds the voltage command value VRa* and the R-phase voltage VR detected by the voltage detector 31 to generate a voltage command value VR0*.
• Adder 71B adds the voltage command value VSa* and the S-phase voltage VS detected by the voltage detector 31 to generate a voltage command value VS0*.
• Adder 68C adds the voltage command value VTa* and the T-phase voltage VT detected by the voltage detector 31 to generate a voltage command value VT0*.
• Adder 71A adds voltage command values VR0* and V1* to generate voltage command value VR*.
• Adder 71B adds voltage command values VS0* and V1* to generate voltage command value VS*.
• Adder 71C adds voltage command values VT0* and V1* to generate voltage command value VT*.
• the voltage command values VR*, VS*, and VT* are sinusoidal signals at commercial frequency.
• Triangular wave signals Cu1a and Cu1b are in-phase signals. Triangular wave signals Cu2a and Cu2b are in-phase signals. Triangular wave signals Cu1a and Cu2a are out of phase. In the example of Figure 7, triangular wave signal Cu2a is 180° out of phase with triangular wave signal Cu1a.
• Comparator 95 compares the voltage command value VR* with the triangular wave signal Cu1a from triangular wave generator 91, and outputs a PWM signal ⁇ 1A indicating the comparison result.
• Buffer 110 provides PWM signal ⁇ 1A to three-level circuit 3A.
• NOT circuit 111 inverts PWM signal ⁇ 1A to generate PWM signal ⁇ 2A, which is provided to three-level circuit 3A.
• IGBTs Q1A and Q2A are turned on when PWM signals ⁇ 1A and ⁇ 2A are at "H” level, and turned off when PWM signals ⁇ 1A and ⁇ 2A are at "L" level.
• Comparator 96 compares the voltage command value VR* with the triangular wave signal Cu1b from triangular wave generator 92, and outputs a PWM signal ⁇ 3A indicating the comparison result.
• Buffer 112 provides PWM signal ⁇ 3A to three-level circuit 3A.
• NOT circuit 113 inverts PWM signal ⁇ 3A to generate PWM signal ⁇ 4A, which is provided to three-level circuit 3A.
• IGBTs Q3A and Q4A are turned on when PWM signals ⁇ 3A and ⁇ 4A are at "H” level, and turned off when PWM signals ⁇ 3A and ⁇ 4A are at "L" level.
• Comparator 98 compares the voltage command value VR* with the triangular wave signal Cu2b from triangular wave generator 94, and outputs a PWM signal ⁇ 3B indicating the comparison result.
• Buffer 116 provides PWM signal ⁇ 3b to three-level circuit 3B.
• NOT circuit 117 inverts PWM signal ⁇ 3B to generate PWM signal ⁇ 4B, which is provided to three-level circuit 3B.
• IGBTs Q3B and Q4B are turned on when PWM signals ⁇ 3B and ⁇ 4B are at "H” level, and turned off when PWM signals ⁇ 3B and ⁇ 4B are at "L” level.
• Figure 8 is a time chart showing the waveforms of the voltage command value VR*, triangular wave signals Cu1a, Cu1b, Cu2a, and Cu2b, and PWM signals ⁇ 1A to ⁇ 4A and ⁇ 1B to ⁇ 4B shown in Figure 7.
• (A) shows the waveforms of the voltage command value VR* and triangular wave signals Cu1a, Cu1b, Cu2a, and Cu2b
• (B) to (E) show the waveforms of the PWM signals ⁇ 1A, ⁇ 3A, ⁇ 4A, and ⁇ 2A, respectively.
• (F) to (I) show the waveforms of the PWM signals ⁇ 1B, ⁇ 3B, ⁇ 4B, and ⁇ 2B, respectively.
• the voltage command value VR* is a sine wave signal at commercial frequency.
• Triangular wave signals Cu1a and Cu2a are in-phase signals.
• Triangular wave signals Cu2a and Cu2b are in-phase signals.
• Triangular wave signal Cu2a is 180° out of phase with triangular wave signal Cu1a.
• Triangular wave signal Cu2b is 180° out of phase with triangular wave signal Cu1b.
• Figures 8(A) to 8(I) show the voltage command value VR* and the waveforms of signals Cu1a, Cu1b, Cu2a, Cu2b, ⁇ 1A to ⁇ 4A, and ⁇ 1B to ⁇ 4B corresponding to the R phase
• the voltage command values and signal waveforms corresponding to the S phase and T phase are similar.
• the voltage command values and signal waveforms corresponding to the R phase, S phase, and T phase are shifted by 120°.
• each phase arm two parallel-connected 3-bell circuits 3A, 3B are interleaved.
• triangular wave signals Cu1a, Cu1b and triangular wave signals Cu2a, Cu2b that are phase-shifted relative to the triangular wave signals Cu1a, Cu1b are prepared.
• the results of comparing the voltage command value VR* with the triangular wave signals Cu1a, Cu1b are defined as PWM signals ⁇ 1A to ⁇ 4A
• the results of comparing the voltage command value VR* with the triangular wave signals Cu2a, Cu2b are defined as PWM signals ⁇ 1B to ⁇ 4B.
• the ripple component contained in the sum of the output currents of the three-level circuits 3A and 3B is reduced, and the effective frequency of the ripple component is doubled, making it possible to reduce the size of the AC input filter 2. Furthermore, because the current is divided between the three-level circuits 3A and 3B in each phase arm, power loss per IGBT is reduced, resulting in easier thermal design of the IGBT.
• the switching pattern of the IGBTs in each bridge circuit is composed of three modes.
• Figure 9 shows the switching patterns of the four IGBTs included in each bridge circuit.
• Figure 9 also shows the operation of bridge circuit 3A in each mode.
• Figure 9 (A) shows mode 1. In mode 1, IGBTs Q1A and Q4A are turned on, IGBTs Q2A and Q3A are turned off, and positive-side capacitor C1 is charged or discharged.
• Figure 9 (B) shows mode 2. In mode 2, IGBTs Q2A and Q4A are turned on, IGBTs Q1A and Q3A are turned off, and the charge states of positive-side capacitor C1 and negative-side capacitor C2 do not change much.
• Figure 9 (C) shows mode 3. In mode 3, IGBTs Q2A and Q3A are turned on, IGBTs Q1A and Q4A are turned off, and negative-side capacitor C2 is charged or discharged. Note that the arrows in Figures 9 (A) and (C) indicate the direction of current flow during charging. During discharging, current flows in the opposite direction to the arrows.
• the voltage command value VR* is the voltage command value VR0* plus the voltage command value V1*.
• the voltage command value V1* is positive when Ep ⁇ En.
• the switching pattern of the four IGBTs included in each bridge circuit is determined by comparing the voltage command value VR* with the triangular wave signals Cu1a, Cu1b, Cu2a, and Cu2b.
• the voltage command value VR* is the voltage command value VR0* plus the voltage command value V1*.
• the voltage command value V1* becomes negative.
• the switching pattern of the four IGBTs included in each bridge circuit is determined by comparing the voltage command value VR* with the triangular wave signals Cu1a, Cu1b, Cu2a, and Cu2b.
• the first control circuit 53 generates PWM signals ⁇ 1A to ⁇ 4A and ⁇ 1B to ⁇ 4B so that the phases of the three-phase AC voltages VR, VS, and VT match the phases of the three-phase AC currents IR, IS, and IT, the DC voltage VDC becomes the reference DC voltage VDCR, and the DC voltage ⁇ E becomes 0.
• the power outage signal PC is at the inactivation level "L" (when the commercial AC power supply 41 is functioning normally)
• the first control circuit 53 and converter 3 are connected by the switching circuit 55.
• the PWM signals ⁇ 1A to ⁇ 4A and ⁇ 1B to ⁇ 4B are provided via the switching circuit 55 to the gates of the IGBTs Q1A to Q4A and Q1B to Q4B of the R-phase arm 3R, respectively.
• FIG. 10 is a time chart showing the operation of the second control circuit 54 shown in FIG. 10 illustrates the control of one phase (e.g., the R-phase arm 3R) of the converter 3 when Ep>En.
• FIG. 10A illustrates the waveforms of Ep and En.
• FIG. 10B to FIG. 10E illustrate the waveforms of the PWM signals ⁇ 1A to ⁇ 4 and ⁇ 1B to ⁇ 4B generated by the second control circuit 54.
• PWM signal ⁇ 1A is set to "H” level and "L” level at a predetermined frequency fc.
• PWM signals ⁇ 2A to ⁇ 4A, ⁇ 1B, and ⁇ 3B are fixed to "L” level, and PWM signals ⁇ 2B and ⁇ 4B are fixed to "H” level.
• FIGS. 11 and 12 are equivalent circuit diagrams showing the operation of one phase of converter 3 when Ep > En.
• PWM signal ⁇ 1A is set to "H” level and PWM signals ⁇ 2B and ⁇ 4B are set to "H” level
• IGBT Q1A first switch
• IGBTs Q2B and Q4B fifth switch
• electromagnetic energy is stored in reactors 12RA and 12RB.
• FIG. 13 is a time chart showing the operation of the second control circuit 54 shown in FIG. 5.
• FIG. 13 shows the control of one phase of the converter 3 (for example, the R-phase arm 3R) when Ep ⁇ En.
• FIG. 13(A) shows the waveforms of Ep and En.
• FIGS. 13(B) to (E) show the waveforms of the PWM signals ⁇ 1A to ⁇ 4 and ⁇ 1B to ⁇ 4B generated by the second control circuit 54.
• FIGS. 14 and 15 are equivalent circuit diagrams showing the operation of one phase of converter 3 when Ep ⁇ En.
• PWM signal ⁇ 3A is set to "H” level and PWM signals ⁇ 2B and ⁇ 4B are set to "H” level
• IGBT Q3A third switch
• IGBTs Q2B and Q4B fifth switch
• electromagnetic energy is stored in reactors 12RA and 12RB.
• the switching circuit 55 connects the second control circuit 54 to the converter 3.
• the PWM signals ⁇ 1A to ⁇ 4A and ⁇ 1B to ⁇ 4B are applied via the switching circuit 55 to the gates of the IGBTs Q1A to Q4A and Q1B to Q4B of the R-phase arm 3R, respectively.
• balance control by converter Next, a description will be given of balance control by the converter 3 when the commercial AC power supply 41 is normal.
• the first control circuit 53 and the converter 3 are connected by the switching circuit 55.
• the first control circuit 53 When Ep ⁇ En, in order to balance the voltages of capacitors C1 and C2, the first control circuit 53 adds a positive voltage command value V1* to the voltage command values VR0*, VS0*, and VT0* to generate voltage command values VR*, VS*, and VT*.
• the first control circuit 53 adds a negative voltage command value V1* to the voltage command values VR0*, VS0*, and VT0* to generate voltage command values VR*, VS*, and VT*.
• the voltage command values VR*, VS*, VT* are compared with the triangular wave signals Cu1a, Cu1b, Cu2a, Cu2b to generate PWM signals ⁇ 1A to ⁇ 4A and ⁇ 1B to ⁇ 4B.
• Capacitor C1 is charged during periods when the voltage command values VR*, VS*, VT* are positive.
• Capacitor C2 is charged during periods when the voltage command values VR*, VS*, VT* are negative.
• the second control circuit 54 turns on IGBTs Q2B and Q4B (fifth switches) of three-level circuit 3B, and turns on and off IGBT Q1A (first switch) of three-level circuit 3A at a predetermined frequency fc, as shown in FIG. 10.
• IGBT Q1A When IGBT Q1A is turned on, as shown in Figure 11, current flows out of capacitor C1, reducing the terminal voltage Ep of capacitor C1 and storing electromagnetic energy in reactors 12RA and 12RB.
• IGBT Q1A When IGBT Q1A is turned off, as shown in Figure 12, the electromagnetic energy stored in reactors 12RA and 12RB is released, charging capacitor C2 and increasing the terminal voltage En of capacitor C2.
• ⁇ E Ep - En gradually decreases.
• IGBTs Q1A to Q4A and Q1B to Q4B are turned off, and operation of converter 3 is stopped.
• the second control circuit 54 turns on IGBTs Q2B and Q4B (fifth switches) of three-level circuit 3B, and turns on and off IGBT Q3A (third switch) of three-level circuit 3A at a predetermined frequency fc, as shown in FIG. 13.
• control circuit 80 controls the DC voltage converter 6 based on the power failure signal PC from the power failure detector 33, the signal indicating the battery voltage VB from the voltage detector 36, the signal indicating the battery current IB from the current detector 37, and the signal indicating the DC voltage VDC from the adder 51.
• the control circuit 80 controls the DC voltage converter 6 so that battery current IB at a level corresponding to the DC voltage VDC flows from capacitors C1 and C2 to battery B1, and battery voltage VB becomes reference battery voltage VBR.
• control circuit 80 controls DC voltage converter 6 so that battery current IB at a level corresponding to battery voltage VB flows from battery B1 to capacitors C1 and C2, and DC voltage VDC becomes reference DC voltage VDCR. In other words, this differs from the balance control described in Patent Documents 1 and 2 in that balance control by DC voltage converter 6 is not performed when the commercial AC power supply 41 is out of service.
• the control unit 82 is activated when the power outage signal PC is at the "H" activation level (when the commercial AC power supply 41 is powered down), and controls the DC voltage converter 6 so that a current IB of a level corresponding to the inter-terminal voltage VB of battery B1 flows from battery B1 to capacitors C1 and C2, and the DC voltage VDC becomes the reference DC voltage VDCR.
• the control unit 82 includes a reference voltage generation circuit 83, subtractors 84 and 86, a voltage control circuit 85, a current control circuit 87, and a PWM circuit 88.
• the voltage control circuit 85 calculates a current command value IB* at a level corresponding to the voltage ⁇ VDC based on the terminal voltage VB of battery B1 detected by the voltage detector 36.
• the voltage control circuit 85 calculates the current command value IB* by, for example, performing a proportional or proportional-integral operation on ⁇ VDC.
• Current control circuit 87 generates a voltage command value V* based on the deviation ⁇ IB between the current command value IB* and the current value IB.
• the PWM circuit 88 When the power outage signal PC is at the "H" level, which is the activation level (when the commercial AC power supply 41 is powered down), the PWM circuit 88 is activated and outputs a signal to drive the four IGBTs included in the semiconductor switch 21 based on the voltage command value V*.
• the DC voltage converter 6 is controlled by a signal from the PWM circuit 88, and supplies DC power from the battery B1 to the inverter 4.
• the PWM circuit 88 When the power outage signal PC is at the inactivation level "L" (when the commercial AC power supply 41 is operating normally), the PWM circuit 88 is deactivated and does not perform PWM control of the DC voltage converter 6. Note that when the commercial AC power supply 41 is operating normally, the DC voltage converter 6 is controlled by the control unit 81, and DC power is stored in the battery B1.
• switch 1 When the commercial AC power supply 41 is operating normally, switch 1 is turned on and three-phase AC power from the commercial AC power supply 41 is supplied to converter 3 via switch 1 and AC input filter 2, where it is converted to DC power.
• This DC power is stored in battery B1 by DC voltage converter 6 and converted to three-phase AC power by inverter 4.
• the three-phase AC power generated by inverter 4 is supplied to load 42 via AC output filter 5, driving load 42.
• switch 1 In the event of a power outage in the commercial AC power supply 41, switch 1 is basically turned off, converter 3 is stopped, and DC power from battery B1 is supplied to inverter 4 via DC voltage converter 6, where it is converted into three-phase AC power at the commercial frequency.
• the three-phase AC power generated by inverter 4 is supplied to load 42 via AC output filter 5.
• FIG. 17 is a flowchart showing a modified example of balance control by the converter 3 during a power outage of the commercial AC power supply 41.
• the flowchart shown in FIG. 17 is executed by the second control circuit 54 shown in FIG. 5.
• the first threshold voltage V1 is a positive voltage.
• the second control circuit 54 operates the R-phase arm 3R, the S-phase arm 3S, and the T-phase arm 3T in step S04.
• the three-level circuits 3A and 3B of each of the three-phase arms 3R, 3T, and 3S are controlled so that the DC voltage ⁇ E is eliminated.
• the second control circuit 54 compares the absolute value of ⁇ E with 0 in step S03. If the absolute value of ⁇ E is less than or equal to the second threshold voltage V2 and greater than 0 (YES in S02), the second control circuit 54 operates one of the three-phase arms (e.g., R-phase arm 3R) and stops the operation of the remaining two-phase arms (e.g., S-phase arm 3S and T-phase arm 3T) in step S06. In S06, the three-level circuits 3A and 3B of the R-phase arm 3R are controlled so that the DC voltage ⁇ E disappears.
• the three-phase arms e.g., R-phase arm 3R
• stops the operation of the remaining two-phase arms e.g., S-phase arm 3S and T-phase arm 3T
• the second control circuit 54 stops the operation of the three-phase arms 3R, 3S, and 3T in step S07.
• Third Embodiment Figure 18 is a circuit diagram showing the main parts of an uninterruptible power supply according to a third embodiment, and is a diagram to be compared with Figure 3.
• the third embodiment differs from the first embodiment in that each phase arm 3R, 3S, 3T of the converter 3 is configured with a three-level circuit 3Ax, 3Bx. Since each phase arm 3R, 3S, 3T of the converter 3 has the same circuit configuration, the circuit configuration of the R-phase arm 3R will be described as a representative example.
• the three-level circuit 3Ax includes IGBTs Q1A to Q4A and diodes D1A to D6A.
• the IGBTs Q1A to Q4A are connected in series between DC lines L1 and L3.
• the diodes D1A to D4A are connected in anti-parallel to the IGBTs Q1A to Q4A, respectively.
• the diode D5A is connected to the connection point between the IGBTs Q1A and Q2A and the DC line L2.
• the diode D6A is connected to the connection point between the IGBTs Q3A and Q4A and the DC line L.
• Diodes D1A to D4A function as freewheeling diodes, and diodes D5A and D6A function as clamp diodes.
• the input node 3a of the three-level circuit 3Ax is connected to the second terminal of the reactor 12RA and to the connection point of the IGBTs Q2A and Q3A.
• Three-level circuit 3Ax corresponds to one embodiment of a "first multi-level circuit.”
• IGBTs Q1A and Q2A and diodes D1A and D2A form a "first switch”
• IGBTs Q2A and Q3A and diodes D2A, D3A, D5A, and D6A form a "second switch”
• IGBTs Q3A and Q4A and diodes D3A and D4A form a "third switch.”

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