JP5836412B2 - Power converter - Google Patents

Description

  The present invention relates to a power converter, and more particularly to a power converter connected to a three-phase system via a transformer.

  Non-Patent Document 1 uses a switching element (Insulated-gate bipolar transistor: IGBT or the like) capable of on / off control, and a modular system as one method of a power converter that can output a high voltage exceeding the breakdown voltage of the switching element. -A multi-level converter (MMC) is proposed.

  In order to explain the circuit configuration of the MMC, first, names of the respective parts of the MMC are defined.

  In the MMC, the bidirectional chopper circuit shown in FIG. 4 is a unit converter.

  Each unit converter is connected to an external circuit through at least two terminals. In this embodiment, the two terminals are referred to as an x terminal and a y terminal, respectively. Also. The voltage up to the x terminal with respect to the y terminal will be referred to as the cell voltage.

  If the voltage of the energy storage element 405 of the bidirectional chopper circuit shown in FIG. 4 is VC, the cell voltage can take two values, VC and zero.

  In this embodiment, a circuit in which the x terminal and the y terminal of one or more unit converters are cascade-connected is referred to as a converter arm.

  Each transducer arm has at least two terminals. In this embodiment, the two terminals are referred to as a terminal and b terminal, respectively. The voltage up to the a terminal with respect to the b terminal is referred to as an arm voltage. The arm voltage is the sum of the cell voltages of the unit converters included in the converter arm.

  Since the arm voltage is the sum of the cell voltages, the arm voltage is a voltage in units of the voltage VC of the energy storage element included in each cell.

  In this embodiment, one terminal of the first reactor is connected in series to the b terminal of the first converter arm, and one terminal of the second reactor is connected in series to the other terminal of the first reactor, A circuit in which the a terminal of the second converter arm is connected in series to the other terminal of the second reactor is referred to as a leg.

  The a terminal of the first converter arm is called the P terminal of the leg, the connection point of the two reactors is called the M terminal of the leg, and the b terminal of the second converter arm is called the N terminal of the leg To. Therefore, each leg has at least three terminals of P terminal, M terminal, and N terminal. In this embodiment, the sum of the arm voltages of the two converter arms included in the leg is referred to as the leg voltage.

  Since the leg voltage is the sum of the arm voltages, it is also a voltage having the voltage VC of the energy storage element included in each unit converter as a unit.

  Next, the circuit configuration of the MMC will be described. Here we describe three-phase MMC as an example.

  Connect the P terminals of the three legs to each other and pull out one terminal from the connection point. Similarly, connect the N terminals of the three legs to each other and pull out the other terminal from the connection point. Thus, a three-phase MMC can be configured. In this embodiment, the terminals drawn from the three P terminals connected to each other are called the positive output terminals of the MMC, and the terminals drawn from the three N terminals connected to each other are called the negative output terminals of the MMC. I will decide.

  A DC load can be connected between the positive output terminal and the negative output terminal of the MMC.

  A three-phase power system can be connected to a total of three M terminals of the three legs. In the present embodiment, a total of three M terminals of the three legs are collectively referred to as a three-phase terminal.

  Hereinafter, the operation of the MMC will be described very simply. The three-phase terminal is connected to a three-phase power system via a transformer or a connected reactor.

  By controlling the arm voltage of each converter arm constituting the MMC, the voltage between the three-phase terminals can be controlled.

  For example, if the system frequency component of the voltage between the three-phase terminals is controlled to the same frequency and the same amplitude as the voltage between the system lines, and only the phase is slightly delayed from the phase of the system line voltage, Active power flows into the MMC.

  In addition, if the system frequency component of the voltage between the three-phase terminals is controlled to the same frequency and the same amplitude as the voltage between the system lines, and only the phase is slightly advanced from the phase of the system line voltage, the three-phase MMC Active power flows into the power system.

  While controlling the system frequency component of the voltage between the three-phase terminals to the same frequency and the same phase as the voltage between the system lines, if only the amplitude is slightly increased from the amplitude of the system line voltage, the power system and the three-phase MMC Phase reactive power is generated in the meantime.

  While controlling the system frequency component of the voltage between the three-phase terminals to the same frequency and the same phase as the voltage between the system lines, if only the amplitude is slightly decreased from the amplitude of the system line voltage, the power system and the three-phase MMC Slow reactive power is generated in the meantime.

  However, MMC has the following two problems.

  The first problem is that a reactor is required for each leg.

  In the three-phase MMC, when the energy storage element included in each unit converter is an ideal DC voltage source and all the ideal DC voltage sources have the same voltage, the switching timing of each unit converter is appropriately set. By controlling, the leg voltages of the three legs can be matched.

  However, in an actual MMC, an electrolytic capacitor or a storage battery is used as an energy storage element.

  Since each unit converter operates as a single-phase converter, the instantaneous power flowing into and out of each unit converter has a pulsating component that is twice the frequency of the power system connected to the three-phase terminal or the frequency of the three-phase load. Have.

  Further, since the MMC exchanges DC power with the DC load connected between the positive output terminal and the negative output terminal, the instantaneous power flowing into and out of each unit converter is exchanged with the DC load. There is also a power pulsation component associated with.

  Therefore, the voltage across the energy storage element (electrolytic capacitor, storage battery, etc.) included in each unit converter pulsates, and the instantaneous value of the pulsating component varies from leg to leg.

  As described above, the leg voltage is a voltage whose unit is the voltage VC of the energy storage element of the unit converter included in the leg.

  When the voltage VC of the energy storage element is different for each leg, it is impossible to always match the leg voltages of the three legs even if the switching timing of the unit converter is appropriately controlled.

  In a period in which the leg voltages of the three legs do not match, only the two reactors included in each leg share the difference in the leg voltages.

  When the inductances of the two reactors included in each leg are zero, the difference in the leg voltage is shared only by the wiring connecting the legs during this period. Since the impedance of the wiring is small, an overcurrent flows through the three legs.

  For this reason, a reactor is indispensable for each leg in order to control this overcurrent.

  A second problem is that when the MMC transmits DC power to a DC load, the reactor is enlarged.

  When the MMC transmits DC power to a load load, it is necessary to flow a zero-phase DC current through the converter arm and the reactor of each phase. For this reason, a current in which a zero-phase DC current and a normal phase / reverse phase current are superimposed flows in the reactor.

  In this case, the maximum current value becomes larger than when only the normal phase / reverse phase current flows through the reactor. In order not to cause magnetic saturation even at the maximum current value, it is necessary to increase the cross-sectional area of the core of the reactor, leading to an increase in the size of the reactor.

Makoto Sugawara and Yasufumi Akagi: “PWM Control Method and Operational Verification of Modular Multilevel Converter (MMC)”, IEEJ Transactions D, Vol. 957-965.

  Usually, when connecting various power converters to a special high voltage system, it is common to install a transformer for the purpose of voltage step-up / step-down and electrical insulation.

  And this invention provides the power converter device which makes a reactor unnecessary and can reduce a volume and weight in the power converter device comprised by cascading the unit converter linked to an electric power system through a transformer. To do.

  In order to achieve the above object, according to the present invention, in a power conversion device including a series circuit of a voltage source and a control current source, at least two sets of the series circuit of the voltage source and the control current source are connected in parallel. Each of the parallel connection points of the series circuit is used as an output terminal.

  In order to achieve the above-mentioned object, the present invention is a power conversion circuit configured by connecting a circuit in which three control current sources are star-connected to each phase of a three-phase voltage source obtained by extracting a neutral point of the three-phase voltage source. In the apparatus, the neutral point of the control current source and the neutral point of the three-phase voltage source are output terminals.

  Furthermore, in the power converter according to the present invention, the voltage source includes only a differential mode (or normal phase / reverse phase) component, and the control current source controls a differential mode (or normal phase / reverse phase) component. Thus, power is transferred to and from the voltage source, and the control current source transfers power to and from the load device or power source connected to the output terminal by controlling a common mode (or zero phase) component. It is characterized by this.

  In order to achieve the above object, the present invention provides a power converter including a single-phase or multi-phase transformer and a converter arm, wherein the power converter is a primary winding of the single-phase or multi-phase transformer. Each phase is an input terminal, and the secondary winding of the single-phase or multi-phase transformer has a structure in which a neutral point is drawn, and the secondary winding of the transformer and the converter arm are connected in series. The circuits are connected in parallel, and the parallel connection point and the neutral point of the secondary winding are used as output terminals, respectively.

  In order to achieve the above object, the present invention has a three-phase transformer in which a neutral point is drawn from a secondary winding, and three converter arms are star-connected to each phase of the secondary winding. In the power converter configured by connecting circuits, each phase of the primary winding of the three-phase transformer is used as an input terminal, and the neutral point of the converter arm and the neutral point of the secondary winding are output. It is characterized by being a terminal.

  In order to achieve the above object, the present invention provides a power converter that is connected to a three-phase power system via a transformer, wherein a primary winding of the transformer is connected to the three-phase power system, and the transformer Connect the first converter group consisting of a circuit in which three converter arms are star-connected to the first to third terminals of the secondary winding. Then, a second converter group consisting of a circuit in which another three converter arms are star-connected is connected to the fourth to sixth terminals, and a neutral point of the first converter group is connected. And the neutral point of the second converter group are output terminals of the power converter.

  In order to achieve the above object, the present invention provides a power converter that is connected to a three-phase power system via a transformer, wherein a primary winding of the transformer is connected to the three-phase power system, and the transformer The neutral point of the secondary winding of the transformer is pulled out to 4 terminals, and a circuit in which three converter arms are star-connected to each phase other than the neutral point of the secondary winding is connected. The neutral point of the converter arm and the neutral point of the secondary winding are used as output terminals of the power converter.

  Furthermore, the present invention provides a power converter, wherein the converter arm controls a differential mode (normal phase / reverse phase) current to connect a single-phase or multi-phase power system connected to a primary winding of the transformer. By transferring power and controlling the common mode (zero phase) component, power is transferred to and from the load device or power source connected to the output terminal.

  Furthermore, the present invention provides the power converter, wherein the transformer includes means for making the magnetomotive force caused by the common mode (zero phase) current flowing through the secondary winding substantially zero. is there.

  Furthermore, the present invention is characterized in that in the power converter, the primary winding and the secondary winding are interchanged.

According to the power conversion device of the present invention, the exciting inductance and the leakage inductance of the transformer also serve as the reactor in the MMC of Non-Patent Document 1, so that the reactor is unnecessary. Weight can be reduced.
Moreover, in the power converter connected to the three-phase power system through the transformer, the primary winding of the transformer is connected to the three-phase power system, and the secondary winding of the transformer is an open winding. The first converter group consisting of a circuit in which three converter arms are star-connected is connected to the first to third terminals of the secondary winding, and is divided into the fourth to sixth terminals. A second converter group consisting of a circuit in which three converter arms are star-connected is connected to a star-connected circuit, and the neutral point of the first converter group and the neutral point of the second converter group are connected. May be used as the output terminal of the power converter.

  ADVANTAGE OF THE INVENTION According to this invention, it can come out to provide the power converter device which made the reactor unnecessary and reduced the volume and weight.

  In addition, when the power converter of the present invention transfers active power to and from the power system, a zero-phase DC current flows through the secondary winding of the transformer. No effect is obtained.

1 is a circuit diagram showing a first embodiment of the present invention. The transformer in the 1st Embodiment of the present invention. Full bridge type unit converter. Bidirectional chopper type unit converter. The example which applied the 1st Embodiment of this invention as a reactive power compensation apparatus. The circuit diagram which shows the 2nd Embodiment of this invention. The transformer in the 2nd Embodiment of this invention. The circuit diagram which shows the 3rd Embodiment of this invention. The transformer in the 3rd Embodiment of this invention. The circuit diagram which shows the 4th Embodiment of this invention. The transformer in the 4th Embodiment of this invention. The circuit diagram which shows the 5th Embodiment of this invention. The transformer in the 5th Embodiment of this invention. The voltage phasor figure in the 5th Embodiment of this invention. The schematic operation | movement waveform in the 5th Embodiment of this invention. The example which applied the 5th Embodiment of this invention to the direct-current power transmission system. The circuit diagram which shows the 6th Embodiment of this invention. The transformer in the 6th Embodiment of this invention. The circuit diagram which shows the 7th Embodiment of this invention. The transformer in the 7th Embodiment of this invention. The circuit diagram which shows the 8th Embodiment of this invention. The transformer in the 8th Embodiment of this invention. The circuit diagram which shows the 9th Embodiment of this invention. The transformer in the ninth embodiment of the present invention. The circuit diagram which shows the 10th Embodiment of this invention. The transformer in the 10th embodiment of the present invention. The circuit diagram which shows the 11th Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  A first embodiment for carrying out the present invention will be described.

  The structure of the power converter device 101 of this invention is demonstrated using FIG.

  The power conversion apparatus 101 includes a transformer 105, a positive side converter group 112, and a negative side converter group 116.

  In the present embodiment, each phase of the three-phase power system 100 is referred to as an R phase, an S phase, and a T phase. The line voltage is expressed as VRS, VST, VTR. Furthermore, a current flowing through each phase of the three-phase power system 100 is called a system current and is expressed as IR, IS, IT.

  Next, the configuration of the transformer 105 will be described with reference to FIGS. 1 and 2.

  The transformer 105 includes an R-phase terminal 102, an S-phase terminal 103, a T-phase terminal 104, a u-phase positive terminal 106, a v-phase positive terminal 107, a w-phase positive terminal 108, a u-phase negative terminal 109, and a v-phase. A total of nine terminals including a negative terminal 110 and a w-phase negative terminal 111 are provided.

  FIG. 2 shows the polarity of the magnetomotive force generated in each iron core by each winding of the transformer 105 and the connection of each winding. The transformer 105 has iron cores 202 to 204, and these iron cores constitute a tripod iron core. The primary winding 200 is delta-connected, and the windings 205, 206, and 207 between the R phase and the S phase, between the S phase and the T phase, and between the T phase and the R phase are wound around the iron cores 202, 203, and 204, respectively. . The number of turns of the windings 205 to 207 is substantially equal.

  The secondary winding 201 includes a u-phase winding 208, a v-phase winding 209, and a w-phase winding 210. The number of turns of the windings 208 to 210 is substantially equal.

  In the first embodiment, the voltage across the u-phase winding 208 is denoted as Vu, the voltage across the v-phase winding 209 is denoted as Vv, and the voltage across the w-phase winding 210 is denoted as Vw.

  A load device 123 is connected between the positive output terminal 121 and the negative output terminal 122 of the power converter. In this specification, the voltage applied to the load device 123 is denoted as VD, and the current flowing through the load device 123 is denoted as ID.

  Next, the configuration of the positive side converter group 112 and the negative side converter group 116 will be described.

  The positive-side converter group 112 includes a u-phase positive-side converter arm 113, a v-phase positive-side converter arm 114, and a w-phase positive-side converter arm 115. The negative-side converter group 116 includes a u-phase negative-side converter arm 117, a v-phase negative-side converter arm 118, and a w-phase negative-side converter arm 119.

  Each converter arm 113-115, 117-118 is provided with a terminal and b terminal. In this embodiment, the voltage up to the a terminal with the b terminal as a reference is referred to as an arm voltage. Each converter arm 113 to 115 and 117 to 118 is a circuit in which one or a plurality of unit converters 120 are cascade-connected.

  The a terminal of the u-phase positive converter arm 113 is connected to the positive output terminal 121, and the b terminal is connected to the u-phase positive terminal 106 of the transformer 105. In this embodiment, the arm voltage of the u-phase positive side converter arm 113 is expressed as VarmuH.

  The a terminal of the v-phase positive converter arm 114 is connected to the positive output terminal 121, and the b terminal is connected to the v-phase positive terminal 107 of the transformer 105. In this embodiment, the arm voltage of the v-phase positive side converter arm 114 is expressed as VarmvH.

  The a terminal of the w-phase positive converter arm 115 is connected to the positive output terminal 121, and the b terminal is connected to the w-phase positive terminal 108 of the transformer 105. In the present embodiment, the arm voltage of the w-phase positive converter arm 115 is expressed as VarmwH.

  The a terminal of the u phase negative converter arm 117 is connected to the u phase negative terminal 109 of the transformer 105, and the b terminal is connected to the negative output terminal 122. In this embodiment, the arm voltage of the u-phase negative side converter arm 117 is expressed as VarmuL.

  The a terminal of the v phase negative converter arm 118 is connected to the v phase negative terminal 110 of the transformer 105, and the b terminal is connected to the negative output terminal 122. In this embodiment, the arm voltage of the v-phase negative converter arm 118 is denoted as VarmvL.

  The a terminal of the v-phase negative side converter arm 119 is connected to the w-phase negative side terminal 111 of the transformer 105, and the b terminal is connected to the negative side output terminal 122. In this embodiment, the arm voltage of the w-phase negative converter arm 119 is denoted as VarmwL.

  In the first embodiment, the sum of VarmuH and VarmuL is expressed as u-phase arm voltage Varmu. Also, the sum of VarmvH and VarmvL will be expressed as v-phase arm voltage Varmu. Similarly, the sum of VarmwH and VarmwL will be expressed as w-phase arm voltage Varmu.

  In the first embodiment, the current flowing through the u-phase positive converter arm 113 and the u-phase negative converter arm 117 is the u-phase arm current Iu, the v-phase positive converter arm 114 and the v-phase negative converter arm. The current flowing through 118 is denoted as v-phase arm current Iv, and the current flowing through w-phase positive side converter arm 115 and w-phase negative side converter arm 119 is denoted as w-phase arm current Iw.

  Next, the configuration of the unit converter 120 will be described with reference to FIGS. 3 and 4.

  FIG. 3 shows an example of the internal configuration of the unit converter 120. The unit converter of FIG. 3 is a full bridge circuit. The unit converter 120 is a two-terminal circuit having an x terminal 300 and a y terminal 301, and includes an x-phase high-side switching element 302, an x-phase low-side switching element 303, a y-phase high-side switching element 304, and a y-phase low-side. A switching element 305 and an energy storage element 306 are included. The switching elements 302 to 305 are on / off control type power semiconductor elements represented by IGBT. The energy storage element 306 is a capacitor, a storage battery, or the like. In the present embodiment, the voltage up to the x terminal with respect to the y terminal is referred to as a cell voltage Vcell of the unit converter.

  On the other hand, the unit converter 120 may be a bidirectional chopper as shown in FIG.

  The bidirectional chopper shown in FIG. 4 includes a high side switching element 403, a low side switching element 404, and an energy storage element 405. The switching elements 403 and 404 are on / off control type power semiconductor elements represented by IGBT. The energy storage element 405 is a capacitor, a storage battery, or the like. In this embodiment, the voltage in FIG. 4 is also expressed as a cell voltage Vcell.

Next, the operation of the power conversion apparatus 101 will be described for the following three cases.
(1) When receiving active power from the three-phase power system 100 and supplying single-phase AC power or DC power to the load device 123 (2) receiving single-phase AC power or DC power from the load device 123 and receiving three-phase power When active power is supplied to the power grid 100 (3) When reactive power is exchanged with the three-phase power grid 100

  Hereinafter, an operation when the power conversion device 101 receives active power from the three-phase power system 100 and supplies single-phase AC power or DC power to the load device 123 will be described. Here, the load device 123 is a DC power transmission line, and the power conversion device 101 is a power conversion device on the power transmission side as viewed from the DC power transmission line, or the load device 123 is a motor drive inverter, and the motor drive -It is assumed that the inverter is in a power running operation or the load device 123 is a single-phase AC load.

  In this embodiment, the voltages obtained by converting the line voltages VRS, VST, VTR of the three-phase power system 100 to the transformer secondary side are expressed as aVRS, aVST, aVTR. Here, a is the turn ratio of the secondary winding to the transformer primary winding.

  Here, the relationship between the voltage Vu, Vv, Vw of the secondary winding of the transformer, the arm voltage Varmu, Varmv, Varmw, and the voltage VD of the load device 123 will be described.

  The relationship between Vu, Varmu, and VD is expressed by the following equation.

(Equation 1)
Vu = VD-Varmu

  The relationship between Vv, Varmv, and VD is expressed by the following equation.

(Equation 2)
Vv = VD-Varmv

  The relationship between Vw, Varmw, and VD is expressed by the following equation.

(Equation 3)
Vw = VD-Varmw

  As described above, the voltages Vu, Vv, and Vw of the secondary winding of the transformer can be controlled by controlling the u-phase arm voltage Varmu, the v-phase arm voltage Varmv, and the w-phase arm voltage Varmw from Equations 1 to 3.

  Here, the reason why the reactor is unnecessary in the first embodiment will be described.

  The voltage aVRS obtained by converting the line voltage VRS between the R phase and the S phase of the three-phase power system 100 to the transformer secondary side and the sum aVRS + Varmu of the u-phase arm voltage Varmu, and between the S phase and the T phase of the three-phase power system 100 The voltage aVST obtained by converting the line voltage VST to the transformer secondary side and the sum aVST + Varmv of the v-phase arm voltage Varmv and the line voltage VTR between the T phase and the R phase of the three-phase power system 100 are converted to the transformer secondary side. The sum of the voltage aVTR and the w-phase arm voltage Varmw aVTR + Varmw may be different from each other.

  The difference between aVRS + Varmu, aVST + Varmv, and aVTR + Varmw is shared by the leakage inductance of the transformer 105.

  Therefore, no reactor is required in the first embodiment.

  If the frequencies and amplitudes of Vu, Vv, and Vw are matched with the frequencies and amplitudes of aVRS, aVST, and aVTR, and only the phases of Vu, Vv, and Vw are slightly delayed from the phases of aVRS, aVST, and aVTR, three phases are obtained. Active power can be caused to flow from the power system 100 to the power converter 101.

  Next, it will be described that the arm voltage can be controlled by the switching state of the switching elements constituting the unit converter 120.

  First, the case where the unit converter 120 is a full bridge circuit (FIG. 3) will be described.

  The x-phase high-side switching element 302 and the x-phase low-side switching element 303 are alternately turned on / off. Further, the y-phase high-side switching element 304 and the y-phase low-side switching element 305 are alternately turned on / off.

  When the x-phase high-side switching element 302 is on, the x-phase low-side switching element 303 is off, the y-phase high-side switching element 304 is off, and the y-phase low-side switching element 305 is on, it depends on the current Icell The cell voltage Vcell is substantially equal to the voltage VC of the energy storage element 306.

  When the x-phase high-side switching element 302 is on, the x-phase low-side switching element 303 is off, the y-phase high-side switching element 304 is on, and the y-phase low-side switching element 305 is off, it depends on the current Icell The cell voltage Vcell is almost zero.

  When x-phase high-side switching element 302 is off, x-phase low-side switching element 503 is on, y-phase high-side switching element 304 is off, and y-phase low-side switching element 305 is on, it depends on current Icell. The cell voltage Vcell is almost zero.

  When the x-phase high-side switching element 302 is off, the x-phase low-side switching element 303 is on, the y-phase high-side switching element 304 is on, and the y-phase low-side switching element 305 is off, it depends on the current Icell In other words, the cell voltage Vcell is approximately equal to a voltage obtained by inverting the polarity of the voltage VC of the energy storage element 306.

  When the x-phase high-side switching element 302, the x-phase low-side switching element 303, the y-phase high-side switching element 304, and the y-phase low-side switching element 305 are all off, the cell voltage Vcell depends on the polarity of the current Icell. Determined. When Icell is positive, the cell voltage Vcell is approximately equal to the voltage VC of the energy storage element 306. When Icell is negative, the cell voltage Vcell is approximately equal to the voltage obtained by inverting the polarity of the voltage VC of the energy storage element 306.

  Next, the case where the unit converter 120 is a bidirectional chopper (FIG. 4) will be described.

  When the high-side switching element 403 is on and the low-side switching element 604 is off, the cell voltage Vcell is approximately equal to the voltage VC of the DC capacitor 604 without depending on the current Icell.

  When the high-side switching element 403 is off and the low-side switching element 404 is on, the cell voltage Vcell is almost zero without depending on the current Icell.

  When both the high side switching element 403 and the low side switching element 604 are off, the cell voltage Vcell is determined depending on the polarity of the current Icell. When Icell is positive, the cell voltage Vcell is approximately equal to the voltage VC of the energy storage element 306. When Icell is negative, the cell voltage Vcell is approximately equal to zero.

  Next, a method for supplying power to the load device 123 will be described.

  The current ID flowing through the load device 123 is the sum (Iu + Iv + Iw) of the arm currents Iu, Iv, Iw. When the arm voltages Varmu, Varmv, and Varmw do not include a zero phase component, the arm currents Iu, Iv, and Iw also do not include a zero phase component. When the arm currents Iu, Iv, and Iw do not include a zero-phase component, Iu + Iv + Iw = ID = 0, and power cannot be transmitted to the load device 123.

  In this case, the active power flowing into the power conversion device 101 from the three-phase power system 100 is stored in an energy storage element (such as an electrolytic capacitor) inside each unit converter 120.

  In order to supply electric power to the load device 123, the zero-phase components of the arm voltages Varmu, Varmv, and Varmv are adjusted to control the zero-phase components of the arm currents Iu, Iv, and Iw. From Kirchhoff's current law, since ID = Iu + Iv + Iw, the current ID can be supplied by adjusting the zero-phase components of Iu, Iv, and Iw.

  In addition, when the active power flowing into the power conversion device 101 from the three-phase power system 100 is equal to the active power consumed by the load device 123, the energy flowing into and out of each unit converter 120 is one cycle of the three-phase power system. It becomes almost zero on average.

  Further, as the current ID, a direct current, an alternating current, or a current in which both are superimposed can be passed.

  When the power converter 101 and the load device 123 exchange only single-phase reactive power, control is performed so that the active power flowing from the three-phase power system 100 to the power converter 101 is zero.

  Hereinafter, an operation when the power conversion device 101 receives active power from the load device 123 and supplies active power to the three-phase power system 100 will be described. Here, the load device 123 is a DC power transmission line, and the power conversion device 101 is a power conversion device on the power receiving side as viewed from the DC power transmission line, or the load device 123 is a motor drive / inverter. The case where the inverter is performing regenerative braking or the case where the load device 123 is a single-phase AC power source is assumed.

  When the frequencies and amplitudes of Vu, Vv, and Vw are made to coincide with the frequencies and amplitudes of aVRS, aVST, and aVTR, and only the phases of Vu, Vv, and Vw are slightly advanced from the phases of aVRS, aVST, and aVTR, the power Active power can be supplied from the converter 101 to the three-phase power system 100.

  Next, a method for receiving power from the load device 123 will be described.

  The current ID flowing from the load device 123 is the sum (Iu + Iv + Iw) of the arm currents Iu, Iv, Iw. When the arm voltages Varmu, Varmv, and Varmw do not include a zero phase component, the arm currents Iu, Iv, and Iw also do not include a zero phase component. When the arm currents Iu, Iv, and Iw do not include a zero-phase component, Iu + Iv + Iw = ID = 0, and power cannot be supplied from the load device 123.

  In this case, active power flowing out from the power conversion device 101 to the three-phase power system 100 is supplied from an energy storage element (such as an electrolytic capacitor) inside each unit converter 120.

  In order to allow electric power to flow from the load device 123 to the power conversion device 100, the zero phase components of the arm voltages Varmu, Varmv, and Varmv are adjusted to control the zero phase components of the arm currents Iu, Iv, and Iw. From Kirchhoff's current law, since ID = Iu + Iv + Iw, the current ID can be supplied by adjusting the zero-phase components of Iu, Iv, and Iw.

  In addition, when the active power flowing out from the power converter 101 to the three-phase power system 100 is equal to the active power flowing into the power converter from the load device 123, the energy flowing into each unit converter 120 is the three-phase power. The average of one cycle of the system is almost zero.

  Hereinafter, a case will be described in which the power conversion device 101 receives and receives reactive power from the three-phase power system 100 and the load device 123 is open (ID = 0). Here, the case where the power converter device 101 is operating as a reactive power compensator is assumed.

  When the frequency and phase of Vu, Vv, and Vw are made to coincide with the frequency and phase of aVRS, aVST, and aVTR, and only the amplitude of Vu, Vv, and Vw is slightly increased from the amplitude of aVRS, aVST, and aVTR, the power The phase advance reactive power can be supplied from the converter 101 to the three-phase power system 100.

  In addition, when only the amplitudes of Vu, Vv, and Vw are slightly decreased from the amplitudes of aVRS, aVST, and aVTR while matching the frequencies and phases of Vu, Vv, and Vw with the frequencies and phases of aVRS, aVST, and aVTR. The phase reactive power can be supplied from the power converter 101 to the three-phase power system 100.

  Next, it will be described that in this embodiment, the series circuit of the transformer secondary winding and the converter arm can be regarded as a voltage source and a control current source.

  A three-phase power system 100 is connected to the primary winding of the transformer. Since the electric power system 100 can be regarded as a voltage source, the voltage induced in the secondary winding by the electric power system 100 can also be regarded as a voltage source.

  Also, the converter arm can adjust the voltage applied to the leakage inductance and the excitation inductance of the secondary winding of the transformer by appropriately adjusting the arm voltage of the converter arm.

  The current flowing through the leakage inductance and the excitation inductance is proportional to the time integral of the voltage applied to the leakage inductance and the excitation inductance. Therefore, the converter arm can control the current flowing through the leakage inductance and the excitation inductance via the arm voltage of the converter arm.

  For this reason, the series circuit of the converter arm, the exciting inductance, and the leakage inductance can be regarded as a control current source.

  In the present embodiment, the power converter connected to the three-phase power system has been described. In the three-phase circuit, the normal phase / reverse phase current corresponds to the differential mode current, and the zero phase current corresponds to the common mode current.

  In addition, this embodiment can be applied not only to a three-phase power system but also to a power conversion device linked to a single-phase or multi-phase system by increasing or decreasing the number of converter arms.

  As an application example of the present embodiment, an example in which the power converter 100 is applied as a reactive power compensator will be described. FIG. 5 is an example of a substation in which the power converter 101 is installed. The substation 501 is connected to the three-phase power system 500. The substation bus 502 is connected with a load 503 and the power converter 101 according to the present embodiment. By appropriately adjusting the reactive power Q between the power converter 101 and the three-phase power system 500 by the above-described method, the amplitude of the voltage V of the substation bus 502 is controlled to be kept constant.

  A second mode for carrying out the present invention will be described. In the first embodiment, the primary winding of the transformer is a delta connection, but in the second embodiment, the primary winding of the transformer is a star connection.

  Hereinafter, only the parts of the configuration of the second embodiment that are different from the configuration of the first embodiment will be described.

  FIG. 6 is a circuit diagram showing a second embodiment of the present invention. The power converter 600 is connected to the three-phase power system 100 via the three-phase AC terminals 102 to 104, and exchanges active / reactive power with the three-phase power system 100. The power converter 600 includes a transformer 601, a positive converter group 112, and a negative converter group 113.

  In the present embodiment, the phase voltages of the R phase, the S phase, and the T phase of the three-phase power system 100 are expressed as VR, VS, and VT.

  The positive-side converter group 112 and the negative-side converter group 113 in FIG. 6 are the same as the positive-side converter group 112 and the negative-side converter group 113 in the first embodiment (FIG. 1), respectively.

  FIG. 7 shows the polarity of the magnetomotive force generated in each iron core by each winding of the transformer 601 and the connection of each winding. The transformer 601 has iron cores 202 to 204, and these iron cores constitute a tripod iron core. The primary winding 700 is star-connected, and the R-phase, S-phase, and T-phase windings 701, 702, and 703 are wound around the iron cores 202, 203, and 204, respectively.

  The secondary winding 201 of FIG. 7 is the same as the secondary winding 201 of FIG. In the second embodiment, the same effect as in the first embodiment can be obtained.

  A third embodiment for carrying out the present invention will be described. The third embodiment is a modification of the first embodiment. In the first embodiment, two converter groups on the positive side and the negative side are used, but in the third embodiment, only one converter group is used.

  In the third embodiment, the same effect as in the first embodiment can be obtained, and the number of terminals of the transformer can be reduced from 9 terminals to 7 terminals.

  In the following, only the parts of the configuration of the third embodiment that are different from the configuration of the first embodiment will be described.

  FIG. 8 is a circuit diagram showing a third embodiment of the present invention. The power conversion device 800 is linked to the three-phase power system 100 via the three-phase AC terminals 102 to 104 and exchanges active / reactive power with the three-phase power system 100. The power conversion device 800 includes a transformer 801 and a converter group 806.

  The transformer 801 includes a total of seven terminals: an R phase terminal 102, an S phase terminal 103, a T phase terminal 104, a u phase terminal 802, a v phase terminal 803, a w phase terminal 804, and a neutral point terminal 805.

  Therefore, the number of terminals of the transformer can be reduced from 9 terminals to 7 terminals as compared with the first and second embodiments.

  FIG. 9 shows the polarity of the magnetomotive force generated in each iron core by each winding of the transformer 801 and the connection of each winding. The transformer 801 has iron cores 202 to 204, and these iron cores constitute a tripod iron core. The primary winding 200 has the same configuration as that of the first embodiment (FIG. 2).

  The secondary winding 900 includes a u-phase winding 901, a v-phase winding 902, and a w-phase winding 903. The number of turns of the windings 901 to 903 is approximately equal. The u-phase winding 901, the v-phase winding 903, and the w-phase winding 903 are star-connected, and the neutral point n is drawn to the neutral point terminal 805.

  The converter group 806 includes a u-phase converter arm 807, a v-phase positive side converter arm 808, and a w-phase positive side converter arm 809.

  The a terminal of the u-phase converter arm 806 is connected to the positive output terminal 121, and the b terminal is connected to the u-phase terminal 802 of the transformer 801. In the third embodiment, the arm voltage of the u-phase converter arm 113 is expressed as Varmu.

  The a terminal of the v-phase converter arm 807 is connected to the positive output terminal 121, and the b terminal is connected to the v-phase terminal 803 of the transformer 801. In the third embodiment, the arm voltage of the v-phase converter arm 807 is expressed as Varmv.

  The a terminal of the v-phase converter arm 808 is connected to the positive output terminal 121, and the b terminal is connected to the w-phase terminal 804 of the transformer 801. In the third embodiment, the arm voltage of the w-phase converter arm 807 is denoted as Varmw.

  The converter arms 806 to 808 in the third embodiment (FIG. 8) are substantially the same as the converter arms 113 to 115 and 117 to 119 in FIG. 1 of the first embodiment and FIG. The difference is that the number of unit converters 120 is approximately doubled.

  A fourth mode for carrying out the present invention will be described. The fourth embodiment is a modification of the second embodiment. In the second embodiment, two converter groups of the positive side and the negative side are used. In the fourth embodiment, the same effect as that of the third embodiment is obtained by using only one converter group. In the third embodiment, the primary winding of the transformer is a delta connection, but in the fourth embodiment, the primary winding of the transformer is a star connection.

  In the following, only the parts of the configuration of the fourth embodiment that are different from the configuration of the third embodiment will be described.

  FIG. 10 is a circuit diagram showing a fourth embodiment of the present invention. The power conversion apparatus 1000 is linked to the three-phase power system 100 via the three-phase AC terminals 102 to 104, and exchanges active / reactive power with the three-phase power system 100. The power conversion apparatus 1000 includes a transformer 1001 and a converter group 805.

  The transformer 1001 includes a total of seven terminals including an R-phase terminal 102, an S-phase terminal 103, a T-phase terminal 104, a u-phase terminal 110, a v-phase terminal 111, a w-phase terminal 112, and a neutral point terminal 705.

  FIG. 11 shows the polarity of the magnetomotive force generated in each iron core by each winding of the transformer 1001 and the connection of each winding. The transformer 1001 has iron cores 202 to 204, and these iron cores constitute a tripod iron core. The primary winding 700 in FIG. 10 is the same as the primary winding 700 in FIG. 7 of the second embodiment.

  Further, the secondary winding 900 is the same as the secondary winding 900 in FIG. 9 of the third embodiment, and the converter group 706 in FIG. 9 is the same as the converter group 706 in FIG. 7 of the third embodiment.

  A fifth mode for carrying out the present invention will be described. The fifth embodiment is a modification of the first embodiment. It is characterized in that the secondary winding of the transformer is divided into two parts for each phase and the connection is made so that the magnetomotive force caused by the zero-phase current is zero.

  In the fifth embodiment, the same effect as in the first embodiment can be obtained. In addition to this, when the current ID is passed through the load device 123, the iron core cross-sectional area of the transformer can be reduced as compared with the first to fourth embodiments. This is because the magnetomotive force resulting from the zero-phase current is zero as described above.

  FIG. 12 is a circuit diagram showing a fifth embodiment of the present invention. The configuration of FIG. 12 of the fifth embodiment is a circuit configuration in which the transformer 105 of FIG.

  The transformer 1201 includes an R-phase terminal 102, an S-phase terminal 103, a T-phase terminal 104, a u-phase positive terminal 1202, a v-phase positive terminal 1203, a w-phase positive terminal 1204, a u-phase negative terminal 1206, and a v-phase. A total of nine terminals including a negative terminal 1207 and a w-phase negative terminal 1208 are provided.

  FIG. 13 shows the polarity of magnetomotive force generated in each iron core by each winding of the transformer 1201 and the connection of each winding. The transformer 1201 has iron cores 202 to 204, and these iron cores constitute a tripod iron core. The primary winding 200 in FIG. 13 is the same as the primary winding 200 in FIG.

  The secondary winding 1300 includes a u-phase positive winding 1301, a v-phase positive winding 1302, a w-phase positive winding 1303, a u-phase negative winding 1304, a v-phase negative winding 1305, and a w-phase negative winding 1305. A side winding 1306 is provided. The number of turns of the windings 1301 to 1306 is substantially equal.

  The u-phase positive winding 1301 and the u-phase negative winding 1304 are electrically connected in series. The u-phase positive side winding 1301 is wound around the iron core 202, and the u-phase negative side winding 1304 is wound around the iron core 204. Note that the magnetomotive force generated in the iron core 202 by the u-phase positive winding 1301 and the magnetomotive force generated in the iron core 204 by the u-phase negative winding 1304 are connected so as to have approximately the same size and opposite polarity. .

  The v-phase positive winding 1302 and the v-phase negative winding 1305 are electrically connected in series. The v-phase positive side winding 1302 is wound around the iron core 203, and the v-phase negative side winding 1305 is wound around the iron core 202. Note that the magnetomotive force generated in the iron core 203 by the v-phase positive side winding 1302 and the magnetomotive force generated in the iron core 202 by the v-phase negative side winding 1305 are connected so as to have approximately the same size and opposite polarity. .

  The w-phase positive winding 1303 and the w-phase negative winding 1306 are electrically connected in series. The w-phase positive side winding 1303 is wound around the iron core 204, and the w-phase negative side winding 1306 is wound around the iron core 203. Note that the magnetomotive force generated in the iron core 204 by the w-phase positive winding 1303 and the magnetomotive force generated in the iron core 203 by the w-phase negative winding 1306 are connected so as to have approximately the same size and opposite polarity. .

  In this embodiment, the u-phase positive side winding 1301 and the u-phase negative side winding 1304 are collectively referred to as a u-phase winding. Further, the v-phase positive side winding 1302 and the v-phase negative side winding 1305 are collectively referred to as a v-phase winding. Similarly, the w-phase positive side winding 1304 and the w-phase negative side winding 1306 are collectively referred to as a w-phase winding.

  In this embodiment, the voltage across the u-phase positive winding 1301 is VuH, the voltage across the v-phase positive winding 1302 is VvH, the voltage across the w-phase positive winding 1303 is VwH, and the u-phase negative winding 1302. The voltage between both ends of 1304 is expressed as VuL, the voltage between both ends of the v-phase negative side winding 1305 is expressed as VvL, and the voltage between both ends of the w-phase negative side winding 1306 is expressed as VwL.

  Also, the sum of VuH and VuL is called u-phase voltage Vu, the sum of VvH and VvL is called v-phase voltage Vv, and the sum of VwH and VwL is called w-phase voltage Vw.

  FIG. 14 shows the voltage of the primary winding 200 of the transformer 1201 (that is, the line voltages VRS, VST, VTR of the three-phase power system 100) and the voltages VuH, VvH, VwH, VuL, VvL of the secondary winding 1300. , VwL, Vu, Vv, Vw phasor diagrams.

  The positive side converter group 112 in FIG. 12 is the same as the converter group 112 in FIG. Further, the negative side converter group 116 in FIG. 12 is the same as the converter group 116 in FIG.

  Differences between the first embodiment and the fifth embodiment will be described below. As described in the first embodiment, when the power conversion apparatus 101 exchanges active power with the three-phase power system 100, a current ID flows. The current ID also flows when the power conversion device 101 supplies single-phase reactive power to the load device 123. The current ID is divided approximately equally into the converter arms of each phase and becomes a zero phase component (zero phase current) of each arm current Iu, Iv, Iw. Therefore, when the current ID flows, a zero-phase current flows through the secondary winding 201. In this embodiment, the zero-phase current is expressed as Iz.

  When the current ID is a direct current, a zero-phase direct current flows through the secondary winding, which may cause a direct current magnetic bias or magnetic saturation of the iron core.

  On the other hand, consider a case where the power conversion device 1200 according to the fifth embodiment passes a current ID through the load device 123. As in the case of the first embodiment, a zero-phase current flows through the secondary winding 1300 of the transformer 1201.

  In the iron core 202, the magnetomotive force generated by Iz flowing through the u-phase positive side winding 1301 and the magnetomotive force generated by Iz flowing through the v-phase negative side winding 1305 are approximately the same magnitude and opposite in polarity and substantially cancel each other.

  In the iron core 203, the magnetomotive force generated by Iz flowing through the v-phase positive side winding 1302 and the magnetomotive force generated by Iz flowing through the w-phase negative side winding 1306 are substantially the same magnitude and opposite in polarity and substantially cancel each other.

  In the iron core 204, the magnetomotive force generated by Iz flowing through the w-phase positive winding 1303 and the magnetomotive force generated by Iz flowing through the u-phase negative winding 1304 are approximately the same magnitude and opposite in polarity and substantially cancel each other.

  Therefore, even when the ID is DC, the DC magnetomotive force is almost zero, so that almost no DC bias is generated in the iron core.

  Hereinafter, the operation of the power conversion device 1200 will be described with reference to FIG. However, FIG. 15 is an example of an operation waveform of the power conversion device 1200. The line voltages VRS, VST, VTR, the system currents IR, IS, IT, the arm voltages Varmu, Varmv, Varmw, and arm voltages of the three-phase power system 100 are shown. A schematic waveform of a zero phase component (Varmu + Varmv + Varmw) / 3, arm currents Iu, Iv, Iw, and output terminal current ID is depicted.

  In FIG. 15, the power converter 1200 receives active power from the system with a power factor of 1, applies a DC voltage to the load device 123, and allows a DC current to flow. That is, VD and ID are direct current.

  In the description of FIG. 15, the unit converter 120 is the bidirectional chopper circuit shown in FIG.

  The arm voltages Varmu, Varmv, and Varmw of each converter arm have a multi-level waveform having a number of levels substantially equal to the number of unit converters 120 included in the converter arm. Varmu, Varmv, and Varmw contain a three-phase AC component and a zero-phase DC component. The zero-phase DC component (Varmu + Varmv + Varmw) / 3 of Varmu, Varmv, and Varmw is approximately equal to the output terminal voltage VD.

  Since Varmu, Varmv, and Varmw include a zero-phase DC component that is substantially equal to VD, the u-phase voltage Vu, the v-phase voltage Vv, and the w-phase voltage Vw are represented by Varmu, Varmv from Equations 1, 2, and 3, respectively. , Varmw's alternating current component and has a phase opposite to that of the alternating current component.

  The voltage difference between Vu, Vv, Vw and the voltages aVRS, aVST, aVTR obtained by converting the line voltages VRS, VST, VTR of the three-phase power system 100 to the secondary side of the transformer 101 is the same as that of the primary winding 200. Supported by the leakage inductance of the transformer 101 between the secondary windings 201.

  When Vu, Vv, and Vw are controlled to the same frequency and the same amplitude as aVRS, aVST, and aVTR, and only the phase is controlled to be slightly delayed, active power is allowed to flow from the three-phase power system 100 to the power conversion device 1200. Can do.

  The differential voltage between the zero-phase component of Varmu, Varmv, and Varmw and the voltage VD of the output terminal is supported by the inductance with respect to the zero-phase component of the secondary winding 1300. The zero-phase components Iz of Iu, Iv, and Iw are proportional to the time integration of the difference voltage. Therefore, the zero-phase components Iz of Iu, Iv, and Iw can be controlled by controlling the zero-phase DC components of Varmu, Varmv, and Varmw. The sum of zero phase components of Iu, Iv, and Iw is ID.

  FIG. 16 is an example in which the power conversion device 1200 according to this embodiment is applied to a DC power transmission system. The power conversion device 1200 in the land A is linked to the three-phase power system 1600. The power conversion device 1200 in the land B is linked to the three-phase power system 1601. The output terminals 120 and 121 of the two power converters 1200 are connected by a submarine cable, and power is interchanged between the land A and the land B.

  FIG. 17 is a circuit diagram showing a sixth embodiment of the present invention. In the above-described fifth embodiment, the primary winding of the transformer is a delta connection, but in the sixth embodiment, the same effect as that of the fifth embodiment is obtained by using the primary winding of the transformer as a star connection.

  Hereinafter, only the parts of the configuration of the sixth embodiment that are different from the configuration of the fifth embodiment will be described.

  The positive converter group 112 in FIG. 17 is the same as the positive converter group 112 in the first embodiment (FIG. 1). Moreover, the negative side converter group 116 of FIG. 17 is the same as the negative side converter group 113 of the embodiment (FIG. 1).

  FIG. 18 shows the polarity of the magnetomotive force generated in each iron core by each winding of the transformer 1701 and the connection of each winding. The transformer 1701 has iron cores 202 to 204, and these iron cores constitute a tripod iron core. The primary winding 700 of FIG. 18 is the same as the primary winding 700 of FIG. Further, the secondary winding 1300 of FIG. 18 is the same as the secondary winding 1300 of FIG. 13 of the fifth embodiment.

  FIG. 19 is a circuit diagram showing a seventh embodiment of the present invention. The seventh embodiment is a modification of the fifth embodiment. In the fifth embodiment, two converter groups on the positive side and the negative side are used, but in the seventh embodiment, only one converter group is used.

  In the seventh embodiment, the same effects as in the fifth embodiment can be obtained, and similarly to the third embodiment, the number of terminals of the transformer can be reduced from nine terminals to seven terminals.

  In the following, only the parts of the configuration of the seventh embodiment that are different from the configuration of the fifth embodiment will be described.

  A converter group 806 in FIG. 19 is the same as the converter group 806 in FIG. 8 of the third embodiment.

  The transformer 1901 includes a total of seven terminals: an R-phase terminal 102, an S-phase terminal 103, a T-phase terminal 104, a u-phase terminal 1902, a v-phase terminal 1903, a w-phase terminal 1904, and a neutral point terminal 1905.

  FIG. 20 shows the polarity of the magnetomotive force generated in each iron core by each winding of the transformer 1901 and the connection of each winding. The transformer 1901 has iron cores 202 to 204, and these iron cores constitute a tripod iron core. The primary winding 200 in FIG. 20 is the same as the primary winding 200 in FIG.

  20, the u-phase positive winding 1301, the v-phase positive winding 1302, the w-phase positive winding 1303, the u-phase negative winding 1304, and the v-phase negative winding 1305 constituting the secondary winding 2000 of FIG. , W-phase negative winding 1306 are the u-phase positive winding 1301, the v-phase positive winding 1302, the w-phase positive winding 1303, and the u-phase negative winding 1304 of FIG. The v-phase negative side winding 1305 and the w-phase negative side winding 1306 are the same.

  However, one end of the u-phase negative-side winding 1304 and the v-phase negative-side winding 1305 and the w-phase negative-side winding 1306 are star-connected, and the neutral point n is the neutral point terminal 1905, and the transformer 1901 Pull out to the outside.

  An eighth embodiment for carrying out the present invention will be described. The eighth embodiment is a modification of the seventh embodiment. In the seventh embodiment, the primary winding of the transformer is a delta connection, but in the eighth embodiment, the same effect as that of the seventh embodiment is obtained by using the primary winding of the transformer as a star connection.

  Hereinafter, only the parts of the configuration of the eighth embodiment that are different from the configuration of the seventh embodiment will be described.

  FIG. 21 is a circuit diagram showing an eighth embodiment of the present invention.

  The converter group 806 in FIG. 21 is the same as the converter group 806 in FIG. 8 of the third embodiment.

  The transformer 2100 includes a total of seven terminals: an R phase terminal 102, an S phase terminal 103, a T phase terminal 104, a u phase terminal 1902, a v phase terminal 1903, a w phase terminal 1904, and a neutral point terminal 1905.

  FIG. 22 shows the polarity of magnetomotive force generated in each iron core by each winding of the transformer 2101 and the connection of each winding. The transformer 1901 has iron cores 202 to 204, and these iron cores constitute a tripod iron core. The primary winding 700 of FIG. 22 is the same as the primary winding 700 of FIG. The secondary winding 2000 of FIG. 22 is the same as the secondary winding 2000 of FIG.

  A ninth mode for carrying out the present invention will be described. In Examples 5 to 8, the secondary winding of the transformer is divided into two parts for each phase, and wiring is performed so that the magnetomotive force caused by the zero-phase current is zero. On the other hand, in the ninth embodiment, the same effect as in the seventh embodiment is obtained by using the compensation winding that compensates the magnetomotive force caused by the zero-phase current.

  Hereinafter, only the parts of the configuration of the ninth embodiment that are different from the configuration of the seventh embodiment will be described.

  FIG. 23 is a circuit diagram showing a ninth embodiment of the present invention. The power conversion device 2300 is connected to the three-phase power system 100 via the three-phase AC terminals 102 to 104, and exchanges active / reactive power with the three-phase power system 100. The power conversion device 2300 includes a transformer 2301 and a converter group 806.

  The converter group 806 in FIG. 23 is the same as the converter group 806 in FIG. 8 of the third embodiment.

  The transformer 2301 includes seven terminals of an R phase terminal 102, an S phase terminal 103, a T phase terminal 104, a u phase terminal 2302, a v phase terminal 2303, a w phase terminal 2304, and a compensation winding terminal 2305.

  FIG. 24 shows the polarity of the magnetomotive force generated in each iron core by each winding of the transformer 2301 and the connection of each winding. The transformer 2303 includes iron cores 202 to 204, a primary winding 200, a secondary winding 2400, and a compensation winding 2404. The iron cores 202 to 204 constitute a tripod iron core.

  The primary winding 200 is the same as the primary winding 200 of FIG.

  The secondary winding 2400 includes a u-phase winding 2401, a v-phase secondary winding 2402, and a w-phase secondary winding 2403. The secondary winding 2400 has substantially the same configuration as the secondary winding 900 in FIG. 9 of the third embodiment, except that the neutral point n is connected to the compensation winding 2404.

  The compensation winding 2404 includes a u-phase compensation winding 2405, a v-phase compensation winding 2406, and a w-phase compensation winding 2407. The number of turns of the compensation winding 2404 is 1/3 that of the secondary winding 2400.

  The u-phase compensation winding 2405 is wound around the iron core 202. The v-phase compensation winding 2405 is wound around the iron core 203. Further, the w-phase compensation winding 2405 is wound around the iron core 203.

  The u-phase compensation winding 2405, the v-phase compensation winding 2406, and the w-phase compensation winding 2407 are connected in series.

  One end of the compensation winding 2404 is connected to the negative output terminal 122. Therefore, the current ID flowing through the load device 123 flows through the compensation winding 2404.

  The magnetomotive force generated by the current ID flowing through the u-phase compensation winding 2405 in the iron core 202, the magnetomotive force generated by the current ID flowing through the v-phase compensation winding 2406 in the iron core 203, and the current ID flowing through the w-phase compensation winding 2407 are the iron core. The magnetomotive force generated in 204 is approximately the same size and the same polarity.

  The ID flowing through the compensation winding 2404 is shunted at the neutral point n and flows as the zero-phase component Iz of the secondary winding 2400. That is, Iz = ID / 3.

  The magnetomotive force generated in the iron core 202 by Iz flowing in the u-phase winding 2401 and the magnetomotive force generated in the iron core 202 by ID flowing in the u-phase compensation winding 2405 are approximately the same magnitude and have opposite polarities, and thus substantially cancel each other. .

  The magnetomotive force generated in the iron core 203 by Iz flowing in the v-phase winding 2402 and the magnetomotive force generated in the iron core 203 by ID flowing in the v-phase compensation winding 2406 are approximately the same size and have opposite polarities, and thus substantially cancel each other. .

  The magnetomotive force generated in the iron core 204 by Iz flowing in the w-phase winding 2403 and the magnetomotive force generated in the iron core 204 by ID flowing in the w-phase compensation winding 2407 are approximately the same size and have opposite polarities, and thus substantially cancel each other. .

  Therefore, as in Examples 5 to 8, when the ID is DC, the DC magnetomotive force is almost zero, so that almost no DC bias is generated in the iron core.

  A tenth embodiment for carrying out the present invention will be described. In the ninth embodiment, the primary winding of the transformer is a delta connection. In the tenth embodiment, the same effect as that of the ninth embodiment is obtained by using the primary winding of the transformer as a star connection.

  Hereinafter, only the parts of the configuration of the tenth embodiment that are different from the configuration of the ninth embodiment will be described.

  FIG. 25 is a circuit diagram showing a tenth embodiment of the present invention. The power conversion device 2500 is connected to the three-phase power system 100 via the three-phase AC terminals 102 to 104, and exchanges active / reactive power with the three-phase power system 100. The power conversion device 2500 includes a transformer 2501 and a converter group 806.

  The converter group 806 in FIG. 25 is the same as the converter group 806 in FIG. 8 of the third embodiment.

  FIG. 26 shows the polarity of the magnetomotive force generated in each iron core by each winding of the transformer 2501 and the connection of each winding. The transformer 2303 includes iron cores 202 to 204, a primary winding 700, a secondary winding 2400, and a compensation winding 2404. The iron cores 202 to 204 constitute a tripod iron core.

  The primary winding 700 in FIG. 26 is the same as the primary winding 700 in FIG. 7 of the second embodiment.

  The secondary winding 2400 of FIG. 26 is the same as the secondary winding 2400 of FIG.

  An eleventh embodiment for carrying out the present invention will be described. The eleventh embodiment is a modification of the fifth embodiment. In the eleventh embodiment, the same effect as that of the fifth embodiment can be obtained.

  Hereinafter, only the parts of the configuration of the eleventh embodiment that are different from the configuration of the fifth embodiment will be described.

  FIG. 27 is a circuit diagram showing a tenth embodiment of the present invention. In the eleventh embodiment, as compared with FIG. 12 of the fifth embodiment, the polarities of the u negative converter arm 117, the v negative converter arm 118, and the w negative converter arm 118 are reversed.

  Similarly in the first, second, fifth, and sixth embodiments, the polarities of the u negative side converter arm 117, the v negative side converter arm 118, and the w negative side converter arm 118 may be reversed.

  The power converter of the present invention can be used for a reactive power compensator (STATCOM), a back-to-back system (frequency converter, etc.), a direct current power transmission system (HVDC), a motor drive, and the like.

100, 500, 1600, 1601 Three-phase power systems 101, 600, 800, 1000, 1200, 1700, 1900, 2100, 2300, 2500, 2700 Power converter 102 R phase terminal 103 S phase terminal 104 T phase terminals 105, 601 , 801, 1001, 1201, 1701, 1901, 2101, 2301, 2501 Transformer 106, 1202 u-phase positive terminal 107, 1203 v-phase positive terminal 108, 1204 w-phase positive terminal 109, 1205 u-phase negative terminal 110, 1207 w-phase negative terminal 111, 1206 v-phase negative terminal 112 positive-side converter group 113 u-phase positive-side converter arm 114 v-phase positive-side converter arm 115 w-phase positive-side converter arm 116, 2701 negative Side converter group 117 u phase negative side converter arm 118 v phase negative side converter arm 119 w-phase negative converter arm 120 unit converter 121 positive output terminal 122, 402 negative output terminal 200 primary winding 201, 700, 900, 1300, 2000, 2400 secondary winding 202, 203, 204 iron core 205 R phase-S phase winding 206 S phase-T phase winding 207 T phase-R phase winding 208, 901, 2401 u phase winding 209, 902, 2402 v phase winding 210, 903, 2403 w phase winding Line 300 x terminal 301 y phase terminal 302 x phase high side switching element 303 x phase low side switching element 304 y phase high side switching element 305 y phase low side switching element 306,405 DC capacitor 400 Bidirectional chopper type unit conversion 401 x-phase output terminal 403 high-side switching element 404 low Id switching element 501 Substation 502 Substation bus 503 Load 802, 1902, 2302 u phase terminals 803, 1903, 2303 v phase terminals 804, 1904, 2304 w phase terminals 805, 1905 Neutral point terminals 1301 u phase positive side winding Line 1302 v-phase positive winding 1303 w-phase positive winding 1304 u-phase negative winding 1305 v-phase negative winding 1306 w-phase negative winding 1602 submarine cable 2404 compensation winding 2405 u-phase compensation winding 2406 v-phase compensation winding 2407 w-phase compensation winding

Claims (4)

On the other hand between the side DC terminals and the other side DC terminal has a configuration plurality of unit converters and one winding is to be three parallel-connected series circuits in series, the unit converter, a capacitor, said capacitor A switching element that outputs the voltage of the current or inputs power to the capacitor, and the current induced in the one side winding charges the capacitor of the unit converter that includes the one side winding to form a series circuit. The unit converter connected in series outputs a voltage that opposes the AC voltage of the one-side winding so that the voltage of the series circuit approaches DC. One side winding of each of two series circuits is connected to AC power supply or AC load via the other side winding, The power converter characterized by things.   2. The structure according to claim 1, wherein the one side winding and the other side winding constitute a transformer, and the one side winding of the transformer has a structure in which a neutral point is drawn and connected. Power conversion device.   2. The power conversion device according to claim 1, wherein a three-phase transformer is configured such that the one-side winding is pulled out to have a neutral point, and a star-connected circuit is configured to the one-side winding. The power converter according to claim 1, wherein the unit converter is disposed so as to sandwich the one side winding.