JP5423147B2 - Three-phase power converter - Google Patents

Description

  The present invention relates to a three-phase power conversion device including a three-phase uninterruptible power supply device that inputs a three-phase alternating current and outputs a three-phase alternating current, and particularly relates to a technique for suppressing voltage pulsation even when a system abnormality occurs.

  An uninterruptible power supply is a device that continues to supply stable power to the load even when an abnormality such as a power failure, voltage drop, or frequency fluctuation occurs in the AC system. Used as supply means. The uninterruptible power supply includes, as main components, a PWM converter that receives current at a power factor of 1, a PWM inverter that outputs a sine wave voltage with less waveform distortion, and a storage battery that stores backup energy during a power failure. Have.

  FIG. 4 is a configuration diagram of an example of a conventional V-connection uninterruptible power supply. 4 includes an AC input terminals 101 to 103, an input filter reactor 104, an AC output terminals 201 to 203, an output filter reactor 204, an output filter capacitor 205, and an insulated gate bipolar transistor (IGBT) constituting a PWM converter. ) 111, 112, 131, 132, IGBTs 211, 212, 231, 232, and DC capacitors 300, 301 constituting a PWM inverter, and these constitute the main circuit.

  A storage battery (or storage battery via a D / D converter) (not shown) is connected in parallel to the DC capacitors 300 and 301.

  The voltage detector 401 detects the AC input voltage of the AC input terminals 101 to 103 and outputs the AC input voltage detection signals vR and vT to the PWM converter control device 501. The current detector 402 detects the AC input current of the AC input terminals 101 and 103 and outputs the AC input current detection signals iR and iT to the PWM converter control device 501.

  The voltage detector 403 detects the DC terminal voltage at both ends of the DC capacitors 300 and 301 and outputs a DC voltage detection signal vD to the PWM converter control device 501. The voltage detector 404 detects the AC output voltage of the AC output terminals 201 to 203 and outputs the AC output voltage detection signals vUV and vWV to the PWM inverter control device 502.

  The PWM converter control device 501 generates on / off signals g111, g112, g131, and g132 based on the AC input voltage detection signals vR and vT, the AC input current detection signals iR and iT, and the DC voltage detection signal vD, and generates the IGBT 111, 112, 131, and 132. Note that the gate drive circuit (not shown) turns on the corresponding IGBT when the on / off signal is 1, and turns off the corresponding IGBT when the on / off signal is 0.

  The PWM inverter control device 502 generates on / off signals g211, g212, g231, g232 based on the AC output voltage detection signals vUV, vWV, and outputs them to the IGBTs 211, 212, 231, 232. Note that the gate drive circuit (not shown) turns on the corresponding IGBT when the on / off signal is 1, and turns off the corresponding IGBT when the on / off signal is 0.

  FIG. 5 is a block diagram of the PWM converter control device in the uninterruptible power supply shown in FIG. In FIG. 5, an adder 513 obtains a difference signal between the DC voltage detection signal vD and the DC voltage command vD *, and a PI (proportional integration calculator) 512 performs a proportional integration operation on the difference signal to obtain a current amplitude reference signal. Is output to the multipliers 514a and 514c.

  The phase detector 510 detects the phase θ of the AC input voltage detection signals vR and vT, and the sine wave reference generator 511 has a sine wave reference signal a and c in phase with the phase θ of the AC input voltage detection signals vR and vT. Is output. The multipliers 514a and 514c multiply the sine wave reference signals a and c and the current amplitude reference signal to obtain current reference signals iR * and iT *.

  The adders 515a and 515c obtain a difference signal between the current reference signals iR * and iT * and the AC input current detection signals iR and iT, and the PIs 516a and 516c perform a proportional-integral operation on the difference signal to obtain a PWM comparison signal R. *, T *.

  The comparison wave generator 519a outputs a comparison wave signal C0 having a sufficiently high frequency (for example, 20 kHz) with respect to the AC system to the comparators 517a and 517c. The comparators 517a and 517c compare the PWM comparison signals R * and T * with the comparison wave signal C0, thereby comparing the on / off signals g111 and g131 with the on / off signals g112 and 518c obtained by inverting the on / off signals. g132 is generated. FIG. 6 shows an example in which the on / off signal g111 is generated by comparing the magnitudes of the PWM comparison signal R * and the comparison wave signal C0.

  FIG. 7 is a block diagram of the PWM inverter control device in the uninterruptible power supply shown in FIG. The PWM inverter control device 502 shown in FIG. 7 includes adders 515d, 515f, PI 516d, 516f, comparison wave generator 519b, comparators 517d, 517f, knot circuits 518d, 518f, and AC voltage commands vUV *, vWV * and Except for the point that the PWM comparison signal is generated based on the AC output voltage detection signals vUV and vWV, the control is the same as the control of the PWM converter control device 501, and the description thereof is omitted. Note that control is performed on the line voltages vUV = vU−vV and vWV = vW−vV.

  The uninterruptible power supply also divides the DC output voltage of the IGBTs 111, 112, 131, and 132 by the DC capacitor 300 and the DC capacitor 301 to create a neutral point. The neutral point, the input terminal 102, and the output terminal 202 is directly connected. In order to stabilize the neutral point voltage to an intermediate potential, a voltage equalization circuit including an IGBT 311, an IGBT 312, a reactor 302, and a voltage equalization circuit control device 503 is provided.

  The maximum AC output voltage of the PWM inverter is limited by the terminal voltage of the DC capacitors 300 and 301. If these terminal voltages are pulsated or unbalanced, a desired AC output voltage cannot be output and distortion occurs in the output waveform. Therefore, the balance of the terminal voltages of the DC capacitors 300 and 301 is compensated using a voltage equalization circuit.

  FIG. 8 is a block diagram of a voltage equalization circuit control device in the conventional V-connection uninterruptible power supply shown in FIG. The voltage equalization circuit control device 503 includes a comparison wave generator 519c, a PI 516g, a comparator 517g, and a knot circuit 518g. The PI 516g amplifies the detected voltage difference ΔvD between the both-ends voltage of the DC capacitor 300 and the both-ends voltage of the DC capacitor 301, that is, the DC voltage imbalance amount ΔVD, and outputs the manipulated variable V *. The comparator 517g compares the comparison wave signal C0 from the comparison wave generator 519c with the manipulated variable V * from the PI 516g to generate the on / off signals g311 and g312 of the IGBTs 311 and 312.

  As a conventional technique, for example, a power conversion device described in Patent Document 1 is known.

JP-A-9-224376

  When the V-connection uninterruptible power supply shown in FIG. 4 is operating in the same phase for input and output, charging from the PWM converter and discharging to the PWM inverter are balanced with respect to the DC capacitors 300 and 301. Therefore, the terminal voltages of the DC capacitors 300 and 301 are unlikely to be unbalanced. For this reason, the amount compensated by the voltage equalization circuit is small, and the loss of the voltage equalization circuit is small.

  However, when a system abnormality (AC input abnormality) occurs and the PWM converter is stopped, the terminal voltage of the DC capacitors 300 and 301 is likely to pulsate, and the voltage equalization circuit is required to compensate for this voltage pulsation. Becomes larger.

  Since the conversion capacity of the voltage equalization circuit needs to be determined by the maximum compensation amount, the voltage equalization circuit becomes large, and at the same time, the circuit utilization factor (average conversion power / rated conversion capacity) is low.

  An object of the present invention is to provide a three-phase power converter capable of obtaining a balance of the terminal voltages of the DC capacitors 300 and 301 without increasing the burden of the voltage equalization circuit when the system is abnormal.

In order to solve the above-mentioned problem, the invention of claim 1 includes a first switch connected between the anode terminal and the first relay terminal, and a second switch connected between the first relay terminal and the cathode terminal. A switch, a first conversion arm having a first AC filter reactor connected between the first relay terminal and the first AC input terminal, and a third connected between the anode terminal and the second relay terminal. A second converter having a switch, a fourth switch connected between the second relay terminal and the cathode terminal, and a second AC filter reactor connected between the second relay terminal and a third AC input terminal. An arm, a fifth switch connected between the anode terminal and the third relay terminal, a sixth switch connected between the third relay terminal and the cathode terminal, the third relay terminal and the first A third AC channel connected between the AC output terminals A third conversion arm having a rutar reactor, a seventh switch connected between the anode terminal and the fourth relay terminal, an eighth switch connected between the fourth relay terminal and the cathode terminal, A fourth conversion arm having a fourth AC filter reactor connected between the fourth relay terminal and the third AC output terminal; and between the anode terminal and the neutral point terminal or between the neutral point terminal and the cathode Storage means connected to at least one of the terminals or between the anode terminal and the cathode terminal, connection between the first AC input terminal and the first AC filter reactor, and the third AC input terminal A first AC switch that connects the second AC filter reactor, a connection between the first AC input terminal and the second AC input terminal, and a connection between the second AC input terminal and the third AC input terminal. I do 2 AC switch, and the second AC input terminal, the neutral point terminal and the second AC output terminal are connected, and when the AC input is normal, the first AC switch is turned on to supply power from the AC system. When the AC input is abnormal, the first AC switch is turned off and the second AC switch is turned on, and at least one of the first conversion arm and the second conversion arm is connected from the storage means to the anode terminal. And the first conversion arm and the second conversion arm are used as power conversion means between the neutral point terminals or between the neutral point terminals and the cathode terminals or between the anode terminals and the cathode terminals. Input current control means for controlling a three-phase AC input current by controlling on / off of each switch; voltage between the anode terminal and the neutral point terminal; and between the neutral point terminal and the cathode terminal A voltage control means for controlling a balance with the voltage of the input current; and a changeover switch for outputting a control signal of the input current control means to each switch of the first conversion arm and the second conversion arm when the AC input is normal. And the input current control means turns off the first AC switch and turns on the second AC switch when it detects an abnormality in the AC input based on the AC input, and outputs a switching signal to the switching switch. The changeover switch outputs a control signal of the voltage control means to each switch of the first conversion arm and the second conversion arm based on the changeover signal, and between the anode terminal and the fifth relay terminal. A ninth switch connected; a tenth switch connected between the fifth relay terminal and the cathode terminal; a fifth AC connected between the neutral point terminal and the fifth relay terminal; A fifth conversion arm having a filter reactor, and the voltage control means controls the on / off of each switch constituting the fifth conversion arm, thereby controlling the voltage between the anode terminal and the neutral point terminal. The balance with the voltage between the neutral point terminal and the cathode terminal is controlled.

  According to the present invention, when the AC input is abnormal, the first AC switch is turned off and the second AC switch is turned on, and at least one of the first conversion arm and the second conversion arm is connected from the storage means to the anode terminal and neutral. Since it is used as power conversion means between the point terminals or between the neutral point terminal and the cathode terminal or between the anode terminal and the cathode terminal, voltage pulsation of the storage means can be suppressed even when the system is abnormal. Further, by using at least one of the first conversion arm and the second conversion arm when the system is abnormal, the burden on the voltage equalization circuit is not increased, and the utilization factor of the circuit is improved. Since the voltage equalization circuit can be reduced in size, the apparatus can be reduced in size.

It is a block diagram of the three-phase power converter device of Example 1. It is a block diagram of the changeover switch in the three-phase power converter of Example 1. It is a block diagram of the PWM inverter control apparatus in the three-phase power converter of Example 2. It is a block diagram of the conventional V connection type uninterruptible power supply. It is a block diagram of the PWM converter control apparatus in the conventional uninterruptible power supply of a V connection system shown in FIG. It is a wave form diagram explaining operation | movement of the PWM converter control apparatus in the uninterruptible power supply device shown in FIG. It is a block diagram of the PWM inverter control apparatus in the conventional V-connection type uninterruptible power supply apparatus shown in FIG. It is a block diagram of the voltage equalization circuit control apparatus in the uninterruptible power supply of the conventional V connection system shown in FIG.

  Hereinafter, embodiments of the three-phase power converter of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a configuration diagram of the three-phase power conversion device according to the first embodiment. The three-phase power converter shown in FIG. 1 includes AC input terminals 101 to 103, input filter reactor 104, AC output terminals 201 to 203, output filter reactor 204, output filter capacitor 205, first AC switch 105, and second AC switch. 106, IGBTs 111, 112, 131, and 132 constituting a PWM converter, IGBTs 211, 212, 231 and 232 constituting a PWM inverter, DC capacitors 300 and 301, IGBTs 311 and 312 constituting a voltage equalization circuit, and a reactor 302, These constitute the main circuit.

  The first AC switch 105 includes AC switches SW1 and SW2, and the second AC switch 106 includes AC switches SW3 and SW4.

  The PWM converter controls the input current in a sine wave shape with a power factor of 1 and outputs a DC voltage between the anode terminal P and the cathode terminal N. The PWM inverter controls the DC voltage between the anode terminal P and the cathode terminal N to a sinusoidal AC voltage.

  An IGBT 111 (first switch) is connected between the anode terminal P and the first relay terminal M1. An IGBT 112 (second switch) is connected between the first relay terminal M1 and the cathode terminal N. An input filter reactor 1041 (first AC filter reactor) is connected between the first relay terminal M1 and the first AC input terminal 101 via the AC switch SW1. These constitute the first conversion arm.

  An IGBT 131 (third switch) is connected between the anode terminal P and the second relay terminal M2. An IGBT 132 (fourth switch) is connected between the second relay terminal M2 and the cathode terminal N. An input filter reactor 1042 (second AC filter reactor) is connected between the second relay terminal M2 and the third AC input terminal 103 via the AC switch SW2. These constitute the second conversion arm.

  An IGBT 211 (fifth switch) is connected between the anode terminal P and the third relay terminal M3. An IGBT 212 (sixth switch) is connected between the third relay terminal M3 and the cathode terminal N. An output filter reactor 2041 (third AC filter reactor) is connected between the third relay terminal M3 and the first AC output terminal 201. These constitute the third conversion arm.

  An IGBT 231 (seventh switch) is connected between the anode terminal P and the fourth relay terminal M4. An IGBT 232 (eighth switch) is connected between the fourth relay terminal M4 and the cathode terminal N. An output filter reactor 2042 (fourth AC filter reactor) is connected between the fourth relay terminal M4 and the third AC output terminal 203. These constitute the fourth conversion arm.

  An IGBT 311 (9th switch) is connected between the cathode terminal P and the fifth relay terminal M5. An IGBT 312 (tenth switch) is connected between the fifth relay terminal M5 and the cathode terminal N. A reactor 302 (fifth AC filter reactor) is connected between the neutral point terminal O and the fifth relay terminal M5. These constitute the fifth conversion arm.

  Second AC input terminal 102, neutral point terminal O, and second AC output terminal 202 are connected. A DC capacitor 301 is connected between the anode terminal P and the neutral point terminal O. A DC capacitor 300 is connected between the neutral point terminal O and the cathode terminal N.

  The voltage detector 401 detects the AC input voltage of the AC input terminals 101 to 103 and outputs the AC input voltage detection signals vR and vT to the PWM converter control device 501a. The current detector 402 detects the AC input current of the AC input terminals 101 and 103 and outputs the AC input current detection signals iR and iT to the PWM converter control device 501a.

  Voltage detector 403 detects the DC terminal voltage of DC capacitor 300 and the DC terminal voltage of DC capacitor 301 and outputs DC voltage detection signal vD to PWM converter control device 501a. The voltage detector 404 detects the AC output voltage of the AC output terminals 201 to 203 and outputs the AC output voltage detection signals vUV and vWV to the PWM inverter control device 502.

  The PWM converter control device 501a generates on / off signals g111, g112, g131, and g132 based on the AC input voltage detection signals vR and vT, the AC input current detection signals iR and iT, and the DC voltage detection signal vD, and generates the IGBT 111, 112, 131, and 132. Note that the gate drive circuit (not shown) turns on the corresponding IGBT when the on / off signal is 1, and turns off the corresponding IGBT when the on / off signal is 0.

  The PWM inverter control device 502 generates on / off signals g211, g212, g231, g232 based on the AC output voltage detection signals vUV, vWV, and outputs them to the IGBTs 211, 212, 231, 232. Note that the gate drive circuit (not shown) turns on the corresponding IGBT when the on / off signal is 1, and turns off the corresponding IGBT when the on / off signal is 0.

  The voltage equalization circuit control device 503a controls on / off of the switches 311 and 312 constituting the fifth conversion arm to thereby control the voltage between the anode terminal P and the neutral point terminal O and the neutral point terminal O and the cathode terminal. The balance with the voltage between N is controlled.

  The AC switch SW1 connects the first AC input terminal 101 and the input filter reactor 1041, and the AC switch SW2 connects the third AC input terminal 103 and the input filter reactor 1042. The AC switch SW3 connects the first AC input terminal 101 and the second AC input terminal 102, and the AC switch SW4 connects the second AC input terminal 102 and the third AC input terminal 103.

  When the AC input is normal, the AC switches SW1 and SW2 are turned on to supply AC power from the AC system. When the AC input is abnormal, the AC switches SW1 and SW2 are turned off and the AC switches SW3 and SW4 are turned on. The first conversion arm 110 and the second conversion arm 130 are connected from the DC capacitors 300 and 301 between the anode terminal P and the neutral point terminal O, between the neutral point terminal O and the cathode terminal N, or between the anode terminal P and the cathode terminal N. It is used as a power conversion means. Note that one of the first conversion arm 110 and the second conversion arm 130 may be used as a power conversion unit.

  More specifically, a changeover switch 406 is provided that outputs a control signal of the PWM converter control device 501a to the respective switches 111, 112, 131, 132 of the first conversion arm 110 and the second conversion arm 130 when the AC input is normal. It has been.

  The PWM converter control device 501a turns off the AC switches SW1 and SW2 and detects the AC switch SW3 when the AC input abnormality is detected based on the AC input detection voltage of the voltage detector 401 and the AC input detection current of the current detector 402. SW4 is turned on, and the switching signal S3 is output to the changeover switch 406.

  The changeover switch 406 sends the control signal of the voltage equalization circuit control device 503a to the respective switches 111, 112, 131, 132 of the first conversion arm 110 and the second conversion arm 130 based on the switching signal S3 from the PWM converter control device 501a. Output.

  FIG. 2 is a configuration diagram of the changeover switch 406 in the three-phase power converter according to the first embodiment. As shown in FIG. 2, the changeover switch 406 has four switch parts 406a to 406d. The switch parts 406a to 406d are changeover terminals a1 to a4, changeover terminals b1 to b4, common terminals c1 to c4, and contact pieces. SP1 to SP4. When the AC input is normal, the contacts SP1 to SP4 are connected to the switching terminals a1 to a4, and a control signal from the PWM converter control device 501a is output to the switches 111, 112, 131, and 132.

  When the AC input is abnormal, the contacts SP1 to SP4 are connected to the switching terminals b1 to b4 by the switching signal S3 from the PWM converter control device 501a, and the control signals g311 and g312 of the voltage equalization circuit control device 503a are connected to the switches 111. , 112, 131, 132.

  According to the three-phase power conversion device of the first embodiment configured as described above, when the AC input is normal, the AC switches SW1 and SW2 are turned on to supply power from the AC system, and the PWM converter control device 501a When an AC input abnormality is detected based on the AC input detection voltage of the detector 401 and the AC input detection current of the current detector 402, the AC switches SW1 and SW2 are turned off, the AC switches SW3 and SW4 are turned on, and the switching signal S3 Is output to the changeover switch 406.

  The changeover switch 406 sends the control signal of the voltage equalization circuit control device 503a to the respective switches 111, 112, 131, 132 of the first conversion arm 110 and the second conversion arm 130 based on the switching signal S3 from the PWM converter control device 501a. Output. That is, the voltage equalization circuit control device 503a simultaneously drives on / off the IGBTs 111, 112, 131, and 132 for the PWM converter and the IGBTs 311 and 312 for the voltage equalization circuit.

  In other words, when the AC input is abnormal, the IGBTs 111, 112, 131, 132 for the PWM converter and the reactor 104 act as a voltage equalization circuit, so that the capacity of the voltage equalization circuit is equivalently increased. For this reason, the voltage pulsation of the DC capacitors 300 and 301 can be suppressed even when the system is abnormal, and the circuit utilization rate is improved. In addition, the burden on the IGBTs 311 and 312 for the voltage equalization circuit can be reduced, and thus the size of the device can be reduced.

  FIG. 3 is a configuration diagram of the three-phase power converter according to the second embodiment. The three-phase power converter shown in FIG. 3 uses large-capacity DC capacitors 300 and 301, and stabilizes the neutral point potential only with the DC capacitors 300 and 301, thereby providing IGBTs 311 and 312 for voltage equalization circuits. The feature is omitted.

  Although not shown, a storage battery (or a storage battery via a DC-DC converter) can be provided in parallel with the DC capacitor 300 or in parallel with the DC capacitor 301 or from the anode terminal P to the cathode terminal N.

  According to the three-phase power conversion device of the second embodiment configured as described above, when the AC input is normal, the AC switches SW1 and SW2 are turned on to supply power from the AC system, and the PWM converter control device 501a When an AC input abnormality is detected based on the AC input detection voltage of the detector 401 and the AC input detection current of the current detector 402, the AC switches SW1 and SW2 are turned off, the AC switches SW3 and SW4 are turned on, and the switching signal S3 Is output to the changeover switch 406.

  The changeover switch 406 sends the control signal of the voltage equalization circuit control device 503b to the switches 111, 112, 131, 132 of the first conversion arm 110 and the second conversion arm 130 based on the switching signal S3 from the PWM converter control device 501a. Output. That is, the voltage equalization circuit control device 503b drives the IGBTs 111, 112, 131, and 132 for the PWM converter to be turned on / off, the voltage between the anode terminal P and the neutral point terminal O, the neutral point terminal O, and the cathode terminal. The balance with the voltage between N is controlled. Therefore, also in the three-phase power converter of the second embodiment, the same effect as that of the three-phase power converter of the first embodiment can be obtained, and the IGBTs 311 and 312 for the voltage equalization circuit can be reduced.

  The present invention is applicable to a three-phase uninterruptible power supply.

101-103 AC input terminal 104 Input filter reactor 105 First AC switch 106 Second AC switch 201-203 AC output terminal 204 Output filter reactor 111, 112, 131, 132, 211, 212, 231, 232, 311, 312 IGBT
300, 301 DC capacitors 401, 403, 404, 405 Voltage detector 402 Current detector 406 Changeover switch 501a PWM converter control device 502 PWM inverter control devices 503a, 503b Voltage equalization circuit control device P Anode terminal 0 Neutral point terminal N Cathode Terminal

Claims (1)

A first switch connected between the anode terminal and the first relay terminal; a second switch connected between the first relay terminal and the cathode terminal; and the first relay terminal and the first AC input terminal. A first conversion arm having a first AC filter reactor connected therebetween;
A third switch connected between the anode terminal and the second relay terminal; a fourth switch connected between the second relay terminal and the cathode terminal; the second relay terminal and a third AC input terminal. A second conversion arm having a second AC filter reactor connected between and
A fifth switch connected between the anode terminal and the third relay terminal, a sixth switch connected between the third relay terminal and the cathode terminal, the third relay terminal and the first AC output terminal A third conversion arm having a third AC filter reactor connected between and
A seventh switch connected between the anode terminal and the fourth relay terminal; an eighth switch connected between the fourth relay terminal and the cathode terminal; the fourth relay terminal and a third AC output terminal. A fourth conversion arm having a fourth AC filter reactor connected between and
Storage means connected between at least one of the anode terminal and the neutral point terminal or between the neutral point terminal and the cathode terminal or between the anode terminal and the cathode terminal;
A first AC switch for connecting the first AC input terminal and the first AC filter reactor and for connecting the third AC input terminal and the second AC filter reactor;
A second AC switch for connecting the first AC input terminal and the second AC input terminal and connecting the second AC input terminal and the third AC input terminal; and the second AC input terminal. And the neutral point terminal and the second AC output terminal,
When the AC input is normal, the first AC switch is turned on to supply power from the AC system, and when the AC input is abnormal, the first AC switch is turned off and the second AC switch is turned on. Power conversion means for converting at least one of the second conversion arms from the storage means to the anode terminal and the neutral point terminal or between the neutral point terminal and the cathode terminal or between the anode terminal and the cathode terminal. Used as
Input current control means for controlling a three-phase AC input current by controlling on / off of each switch constituting the first conversion arm and the second conversion arm;
Voltage control means for controlling the balance between the voltage between the anode terminal and the neutral point terminal and the voltage between the neutral point terminal and the cathode terminal;
A changeover switch that outputs a control signal of the input current control means to each switch of the first conversion arm and the second conversion arm when the AC input is normal;
The input current control means turns off the first AC switch and turns on the second AC switch when detecting an abnormality of the AC input based on the AC input, and outputs a switching signal to the switching switch.
The changeover switch outputs a control signal of the voltage control means to each switch of the first conversion arm and the second conversion arm based on the changeover signal,
A ninth switch connected between the anode terminal and the fifth relay terminal; a tenth switch connected between the fifth relay terminal and the cathode terminal; the neutral point terminal and the fifth relay terminal. A fifth conversion arm having a fifth AC filter reactor connected between and
The voltage control means controls on / off of each switch constituting the fifth conversion arm to thereby control the voltage between the anode terminal and the neutral point terminal and the voltage between the neutral point terminal and the cathode terminal. The three-phase power converter characterized by controlling the balance.

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