JP2017153355A - Power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zigzag connection transformer in which a winding number is increased in about 15% in comparison with Y connection or Δ connection.SOLUTION: A power conversion device comprises: at least three coils of first coils 105RS, ST, and TR, second coils 106RP, SP, and TP, and third coils 106RN, SN, and TN; and first arms 107RP, SP, and TP and second arms 107RN, SN, and TN formed from at least one two-terminal circuit element including an energy storage element or a plurality of series bodies. The second coil and the first arm form a first series body, and the third coil and the second arm form a second series body. The power conversion device is characterized in including at least one or more circuits in which the first and second series bodies are connected in series and the first, second and third coils are magnetically coupled so that magnetomotive forces of the second and third coils become reverse polarities.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a power conversion device, and more particularly to a power conversion device configured using an arm in which a plurality of unit converters configured by bidirectional chopper circuits, single-phase full bridge circuits, and the like are cascade-connected.

  Non-Patent Document 1 discloses circuit configurations of four types of power conversion devices called Modular Multilevel Cascade Converter (MMCC) and their applicability.

Of the four types of MMCC, MMCC-DSCC (Double-STAR Chopper Cells) is a circuit system applicable to motor drives and direct current power transmission systems (HVDC).

  In MMCC-DSCC, it was necessary to connect a buffer reactor in series with an arm that is a series body of bidirectional chopper circuits. For example, in a three-phase MMCC-DSCC, there are six arms, so six buffer reactors are required.

  When MMCC-DSCC is connected to an extra high voltage power transmission system, voltage matching and insulation are generally secured using a transformer.

  Patent Document 1 discloses a circuit system that makes it possible to integrate the transformer and the buffer reactor.

  According to Patent Document 1, a DC magnetomotive force caused by a DC current flowing in an arm of a certain phase is caused by a DC current flowing in an arm of another phase by making the secondary winding of the transformer a staggered connection. It became possible to cancel with the DC magnetomotive force. Since the DC magnetomotive force is canceled, a DC current can be passed through the transformer winding while the magnetic flux passing through the transformer core is only the AC component, and the transformer and the buffer reactor can be integrated.

In this specification, the power conversion device disclosed in Patent Document 1 is referred to as ZC (Zero-Sequence).
Canceling) —referred to as MMCC.

JP 2010-233411 A

H. Akagi, “Classification, terminology, and applications of the modular multilevel converter (MMCC)”, IPEC 2010, pp. 508-515.

  In ZC-MMCC, because the transformer secondary winding is staggered, the secondary winding of a phase is divided into two partial windings that are electrically connected in series. It is wound around the leg.

  The voltage generated in the two partial windings wound on the two legs has a phase difference of 60 degrees, but the voltage appearing at the terminal of the transformer secondary winding is a vector of voltages generated in the two partial windings. It is sum. Therefore, the amplitude becomes smaller by, for example, about 15% than the scalar sum of the voltage amplitudes generated in the respective partial windings.

  That is, in the staggered connection transformer, in order to obtain a predetermined voltage for the secondary winding, there is a problem that the number of turns needs to be increased by about 15%, for example, compared to the Y connection or the Δ connection.

  In ZC-MMCC, when a zero-phase component is superimposed on the output voltage command value of each arm, the zero-phase component appears at the DC terminal.

  For this reason, there has been a problem that it is not possible to perform control for improving the voltage utilization rate by superimposing, for example, the third harmonic voltage on the output voltage command value of each arm. The objective of this invention is providing the power converter device which can solve at least 1 of said problem.

  In order to achieve the above object, the present invention provides an arm formed by connecting in series one or more circuit elements having at least two terminals, each having a first, second, and third winding and an energy storage element. The first and second arms, the second winding and the first arm are connected in series, the third winding and the second arm are connected in series, The second and third windings are electrically connected in series, and the first, second, and third windings have opposite magnetomotive forces of the second and third windings. It is set as the structure which carries out magnetic coupling so that it may become.

  Further, the present invention provides a first three-phase winding, a second Y-connected three-phase winding, and a third Y-connected third three-phase winding. The second three-phase windings are magnetically coupled so that the three-phase windings have the same polarity for each phase, and the second and third three-phase windings have the opposite polarities for each phase. A neutral point of the winding is electrically connected to a neutral point of the third three-phase winding, and at least three terminals of the second three-phase winding are provided with energy storage elements. Connect one or more two-terminal circuit elements to an arm composed of a series body, Y-connect the three arms connected to the second three-phase winding, and set the neutral point to the first DC terminal. And one or more unit converters that are at least two-terminal circuit elements each having an energy storage element at each of the three terminals of the third three-phase winding. An arm composed of a row body is connected, and the three arms connected to the third three-phase winding are Y-connected, and the neutral point thereof is used as a second DC terminal, and the first three-phase winding of the first three-phase winding is connected. The three terminals are the first to third AC terminals.

  In the present invention, the first to third windings are magnetically coupled via an iron core.

  In the present invention, the number of turns of the second three-phase winding and the third three-phase winding is approximately the same.

  According to the present invention, an effect that the number of turns of the winding on the arm side of the transformer can be reduced by, for example, about 15% can be obtained.

In addition, since the AC component of the output voltage command value is almost opposite in polarity between the three arms connected to the first DC terminal and the three arms connected to the second DC terminal, the output voltage of the arm Even if the zero-phase component is superimposed on the command value, the zero-phase component does not appear at the DC terminal. Therefore, it is possible to perform voltage utilization rate improvement control by superimposing, for example, the third harmonic voltage on the output voltage command value of each arm without affecting the voltage of the DC terminal.

The power converter device based on this invention. Bidirectional chopper circuit type unit converter. Schematic waveform. Schematic waveform when voltage utilization rate improvement control is applied. Full bridge circuit unit converter. The figure which shows the other Example of this invention. The figure which shows another Example like this invention.

  EMBODIMENT OF THE INVENTION The form for implementing this invention is demonstrated as an Example using drawing below.

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

  The first embodiment is characterized in that the number of turns of the winding on the arm side of the transformer can be reduced by about 15% compared to the ZC-MMCC according to the prior art.

  In the first embodiment, the voltage utilization rate improvement control (hereinafter referred to as voltage utilization rate improvement control) is performed by superimposing, for example, the third harmonic voltage on the output voltage command value of each arm without affecting the voltage of the DC terminal. Called).

  The overall configuration of the first embodiment will be described below with reference to FIG.

  The power converter 102 is connected to the power system 101 via the transformer 103.

  A DC device 109 is connected between the point P and the point N of the power converter 102. The DC device 109 is drawn as a representative of a DC load such as a resistor, a DC power supply, another power converter 102 and the like.

  The power conversion device 102 includes a transformer 103, six arms 107RP, SP, TP, RN, SN, and TN. Hereinafter, after describing the configuration of the transformer 103, the configurations of the arms 107RP, SP, TP, RN, SN, and TN and the configuration of the unit converter 108 will be described. The operation principle of the power converter 102 and the principle that no DC magnetic flux is generated in the iron core of the transformer 103 will be described later.

  The transformer 103 includes iron cores 104R, S, T, primary windings 105R, S, T, positive side secondary windings 106RP, SP, TP, negative side secondary windings 106RN, SN, TN.

  The positive side secondary windings 106RP, SP, and TP are Y-connected, and are wound around the iron cores 104R, S, and T, respectively.

  Negative secondary windings 106RN, SN, and TN are Y-connected, and are wound around iron cores 104R, S, and T, respectively.

  The neutral points of the Y-connected positive secondary windings 106RP, SP, TP and the neutral points of the Y-connected negative secondary windings 106RN, SN, TN are electrically connected, In FIG. 1, the connection point is indicated by M point.

  Further, the positive side secondary windings 106RP, SP, TP and the negative side secondary windings 106RN, SN, TN are magnetically coupled so as to have opposite polarities for each phase.

Further, primary windings 105RS, ST, TR are wound around the iron cores 104R, S, T. Primary windings 105RS, ST, and TR are Δ-connected and connected to power system 101.

  Thus, each of the iron cores 104R, S, T of the transformer 103 has a primary winding 105RS, ST, TR, a positive secondary winding 106RP, SP, TP, a negative secondary winding 106RN, At least three windings of SN and TN are wound.

  In FIG. 1, the primary windings 105RS, ST, TR are magnetically coupled so as to have the same polarity as the positive secondary windings 106RP, SP, TP. The same effect can be obtained when the negative secondary windings 106RN, SN, and TN are magnetically coupled so as to have the same polarity.

  Hereinafter, the connection of the arms 107RP, SP, TP, RN, SN, and TN will be described.

One end of each of the arms 107RP, SP, and TP is connected to the RP point, the SP point, and the TP point on the opposite side to the M point of the positive side secondary windings 106RP, SP, and TP, respectively. Also, arm 107RP
, SP and TP are Y-connected at the other end and connected to point P of the power converter 102. Point P is one of the DC terminals of the power converter 102.

One end of each of the arms 107RN, SN, and TN is connected to an RN point, an SN point, and a TN point opposite to the M point of the negative secondary windings 106RN, SN, and TN, respectively. Also, arm 107RN
, SN and TN are Y-connected, and are connected to the N point of the power converter 102. N point is one of the DC terminals of the power converter 102.

Hereinafter, the configuration of the unit converter 108 will be described with reference to FIG. J = RP, RN, SP
, SN, TP, TN, and k = 1, 2,..., N, where n is the number of unit converters in the arm 107.

  The unit converter 108 includes a parallel body of a switching element (high side switching element) 201H and a freewheeling diode (high side freewheeling diode) 202H, and a parallel body of switching element (low side switching) 201L and a freewheeling diode (low side freewheeling diode) 202L. And a parallel body of the capacitor 203.

  A connection point between a parallel body of a switching element (high side switching element) 201H and a freewheeling diode (high side freewheeling diode) 202H, and a parallel body of switching element (low side switching element) 201L and a freewheeling diode (low side freewheeling diode) 202L, In FIG. 2, it is indicated by a point X.

  The output voltage Vjk of the unit converter 108 is a voltage between the X point and the L point of the capacitor, and Vjk is controlled by the switching state of the switching element (high side switching element) 201H and the switching element (low side switching element) 201L. it can.

Switching element (high-side switching element) 201 is on, switching element (
When the low-side switching element 201L is off, Vjk can be approximately equal to the voltage VCjk of the capacitor 203. In this specification, this state is referred to as the unit converter being on.

Switching element (high-side switching element) 201 is turned off, switching element (
When the low-side switching element 201L is on, Vjk can be approximately equal to zero. In this specification, this state is referred to as the unit converter being off.

  When the switching element (high-side switching element) 201 and the switching element (low-side switching element) 201L are both on, the capacitor 203 is short-circuited, and thus such an operation is prohibited.

  When the switching element (high-side switching element) 201 and the switching element (low-side switching element) 201L are both off, Vjk depends on the polarity of the current Ij. When Ij> 0, Vjk is approximately equal to zero. Also. When Ij <0, Vjk is approximately equal to the capacitor voltage VCjk.

  When n unit converters 108 are included in one arm 107j (j = RP, RN, SP, SN, TP, TN), the voltage VCjk (k = 1) of the capacitors 203 of all the unit converters 108 is included. 2,..., N) are all approximately equal to VC, the arm output voltage Vj can be controlled to an arbitrary waveform of n levels from zero to nVC.

  Hereinafter, the operation principle of the power conversion apparatus 102 will be described with reference to FIG. FIG. 3 is a schematic operation waveform when the power conversion device 102 is performing rectifier operation (power transmission from the power system 101 to the DC device 109).

  In FIG. 3, the turn ratio of the primary winding 105, the positive secondary winding 106, and the negative secondary winding 106 is set to a: 1: 1 as an example.

VGRS, VGST, VGTR are line voltages of the power system 101, IRS, IST, ITR are currents flowing through the primary windings 105RS, ST, TR, VDC, IDC are DC terminals (
Voltage and current at point P and point N).

  First, an output voltage waveform of each arm 107 will be described below, and thereafter, it will be described that AC-DC conversion is possible.

Arms 107RP, SP, TP voltages VRP, VSP, VTP command values VRP ^* , VS
As P and VTP ^* , the AC component is the line voltage VGRS, VGST, VGT of the power system 101
A voltage having an amplitude 1 / a times R and a phase delayed by π + φ [RPd], and DC components are VDCR ^* / 2, VDCS ^* / 2, and VDCT ^* / 2, respectively. The voltage command value is given. However, a is a turns ratio of a transformer.

Arms 107RN, SN, TN voltages VRN, VSN, VTN command values VRN ^* , VS
As N ^* and VTN ^* , the AC component has a voltage 1 / a times as large as the line voltages VGRS, VGST, and VGTR of the power system 101, and is a voltage delayed in phase by φ [RPd], and Voltage command values are provided such that the DC components are VDCR ^* / 2, VDCS ^* / 2, and VDCT ^* / 2, respectively. However, a is a turns ratio of a transformer.

In this specification, VRP, VSP, VTP, VRN, VSN, and VTN are referred to as arm voltages, and VRP ^* , VSP ^* , VTP ^* , VRN ^* , VSN ^* , and VTN ^* are referred to as arm voltage command values.

Note that VDCR ^* , VDCS ^* , and VDCT ^* are DC voltage components necessary for the power conversion apparatus 102 to supply DC power to the DC apparatus 109, and details will be described later.

Each arm 107RP, SP, TP is a serial body of n unit converters 108. Therefore, by controlling the number of unit converters 108 that are turned on, VRP ^* having the voltage VC of the capacitor 203 as a step ^. , VSP ^* , VTP ^* , the closest arm voltages VRP, VSP, V
TP can be output.

Similarly, since each arm 107RN, SN, and TN is a serial body of n unit converters 108, by controlling the number of unit converters 108 that are turned on, the voltage VC of the capacitor 203 is stepped. The arm voltages VRN, VSN, and VTN that are closest to the arm voltage command values VRN ^* , VSN ^* , and VTN ^* can be output.

  Hereinafter, it will be described that AC-DC power conversion is possible when each arm 107 outputs the above voltage.

First, the principle that the power conversion device 102 can receive active power from the power system 101 will be described.

Since the DC component included in the output voltages VRP, VSP, VTP, VRN, VSN, and VTN of each arm 107RP, SP, TP, RN, SN, and TN is almost offset with VDC, the secondary winding of the transformer on the positive side Only AC components of VRP, VSP, VTP, VRN, VSN, and VTN are applied to the wires 106RP, SP, TP, and the negative secondary windings 106RN, SN, and TN of the transformer.

  The voltage induced by the power system 101 in the positive side secondary windings 106RP, SP, TP, that is, the sum of the alternating components of VGRSP, VGSTP, VGTRP and VRP, VSP, VTP is the primary winding 105RS, ST of the transformer 103 , TR and positive side secondary windings 106RP, SP, and TP are applied to leakage inductances.

  VGRSP, VGSTP, and VGTRP and the AC components of VRP, VSP, and VTP have substantially the same amplitude and a phase difference of π + φ. In this case, the voltage applied to the leakage inductance is a voltage whose phase is approximately 90 degrees ahead of the voltages VGRS, VGST, and VGTR of the power system 101. Therefore, the current flowing through the leakage inductance, that is, the AC components of the currents IRP, ISP, and ITP flowing through the arms 107RP, SP, and TP are substantially in phase with the voltages VGRS, VGST, and VGTR of the power system 101.

  Similarly, the voltage induced in the negative secondary windings 106RN, SN, and TN by the power system 101, that is, the difference between the AC components of VGRSP, VGSTP, and VGTRP and VRN, VSN, and VTN is the primary winding of the transformer 103. 105RS, ST, TR and negative secondary windings 106RN, SN, TN are applied to leakage inductances.

VGRSP, VGSTP, and VGTRP and the AC components of VRN, VSN, and VTP have substantially the same amplitude and a phase difference of φ. In this case, the voltage applied to the leakage inductance is a voltage whose phase is approximately 90 degrees behind the voltages VGRS, VGST, and VGTR of the power system 101. Therefore, the current flowing through the leakage inductance, that is, the arm 107RN.
, SN, and TN, the alternating current components of the currents IRN, ISN, and ITN are substantially opposite in phase to the voltages VGRS, VGST, and VGTR of the power system 101.

If the exciting inductance of the transformer 103 is approximated to infinity, the primary winding 105RS, ST
, TR flowing currents IRS, IST, ITR satisfy the expressions (1) to (3).
S, IST, and ITR are substantially in phase with the voltages VGRS, VGST, and VGTR of the power system 101.
[Equation 1]
IRS = a (IRP-IRN) (1)
[Equation 2]
IST = a (ISP-ISN) (2)
[Equation 3]
ITR = a (ITP-ITN) (3)

  Therefore, the power conversion device 102 can receive active power from the power system 101.

  When increasing the effective power, for example, the voltage of each arm 107 may be controlled so as to increase the phase difference φ. Further, when the power conversion device 102 controls the power grid 101 to regenerate active power, the voltage of each arm 107 may be controlled so that φ becomes a negative value.

The currents IRP and IRN flowing through the arms 107RP and RN contain a DC component IZR, the currents ISP and ISN flowing through the arms 107SP and SN contain a DC component IZS, and the current ITP flowing through the arms 107TP and TN. , ITN contains a DC component IZT, but each DC component is canceled by the equations (1) to (3), and the primary windings 105RS, ST
, TR does not flow.

Hereinafter, the principle that the power converter 102 can supply DC power to the DC device 109 will be described. If it is approximated that the leakage inductance of the transformer is equal in each phase, the voltage VDC between the points P and N satisfies the equations (4) to (7).
[Equation 4]
VDC = (VDCR + VDCS + VDCT) / 3 (4)
[Equation 5]
VDCR = (VRP + VRN) / 2 (5)
[Equation 6]
VDCS = (VSP + VSN) / 2 (6)
[Equation 7]
VDCT = (VTP + VTN) / 2 (7)

A voltage VDC is applied to the DC device 109. When current IDC flows through DC device 109, DC device 109 receives power of PDC = VDC · IDC from power conversion device 102. That is, the power converter 102 can supply DC power to the DC device 109.

The IDC is expressed by equations (8) to (11) from IRP, IRN, ISP, ISN, ITP, and ITN from the currents flowing through the arms 107RP, RN, SP, SN, TP, and TN.
[Equation 8]
IDC = IZR + IZS + IZT (8)
[Equation 9]
IZR = (IRP + IRN) / 2 (9)
[Equation 10]
IZS = (ISP + ISN) / 2 (10)
[Equation 11]
IZT = (ITP + ITN) / 2 (11)

  If VDC is controlled so that IDC becomes negative, power converter 102 can receive DC power from DC device 109.

  In this specification, IZR, IZS, and IZT are referred to as through currents. Note that the through currents IZR, IZS, and IZT are not necessarily equal values.

  From the above, it can be seen that the power converter 102 can receive AC active power from the power system 101 and simultaneously supply DC power to the DC device 109.

  Further, for example, the active AC power exchanged with the power system 101 can be controlled by controlling the phase difference φ, and the DC power exchanged with the DC device 109 can be controlled by controlling the IDC via the VDC.

  When the active power received by the power conversion device 102 from the power system 101 and the DC power supplied to the DC device 109 by the power conversion device 102 are equal, the average power received by the power conversion device 102 itself is substantially zero. The voltage of the capacitor 203 of the unit converter 108 can be maintained at a substantially constant value.

  Hereinafter, the principle that no DC magnetic flux is generated in the iron cores 104R, S, and T of the transformer 103 will be described.

  As described above, the DC currents IZR, IZS, and IZT flow through the positive secondary windings 106RP, SP, and TP and the negative secondary windings 106RN, SN, and TN.

  However, since the positive side secondary windings 106RP, SP, TP and the negative side secondary windings 106RN, SN, TN are magnetically coupled with opposite polarities for each phase, the positive cores 104R, S, T are The DC magnetomotive force generated by the side secondary windings 106RP, SP, and TP cancels out the DC magnetomotive force generated by the negative secondary windings 106RN, SN, and TN.

  Therefore, no DC magnetic flux is generated in the iron cores 104R, S, T.

  Since the magnetic flux generated in the iron cores 104R, S, and T is only an AC component, the operating point of the magnetic flux can be designed so that the origin of the BH curve of the iron core material used for the iron cores 104R, S, and T is the center. .

In FIG. 1, the iron cores 104R, S, and T are depicted as individual iron cores.
Even if a three-phase three-legged iron core having three legs S, T, the same effects as in this embodiment are obtained. Further, the same effect can be obtained as a three-phase other leg iron core using a four-leg iron core or more obtained by adding one or more iron cores to the iron cores 104R, S, T.

  For this reason, even if a DC current flows through the positive secondary windings 106RP, SP, TP and the negative secondary windings 106RN, SN, TN, the DC current flows in the cross-sectional areas of the iron cores 104R, S, T. It can be designed almost the same as when there is no.

Hereinafter, referring to FIG. 4, arm voltage commands VRP ^* , VRN ^* , VSP ^* , VSN ^* , VTP ^*
, VTN ^* shows a waveform when voltage utilization factor improvement control is performed by superimposing a third harmonic component, for example.

^{VRP *, VRN *, VSP *} , VSN *, VTP *, if the VTN ^*, overlapped with the example third harmonic ^{component, VRP *, VRN *, VSP} *, VSN *, VTP *, VTN * exchanges It is possible to reduce the maximum value of the component.

The AC fundamental wave components of VRP ^* and VRN ^* are generally in antiphase, and the third harmonic component is also in antiphase. Therefore, the third harmonic component does not appear in VDCR = VRP + VRN.

Further, the AC fundamental wave components of VSP ^* and VSN ^* are generally in antiphase, and the third harmonic component is also in antiphase. Therefore, the third harmonic component does not appear in VDCS = VSP + VSN.

Similarly, the AC fundamental wave components of VTP ^* and VTN ^* are generally in antiphase, and the third harmonic component is also in antiphase. Therefore, the third harmonic component does not appear in VDCT = VTP + VTN.

From the above, since the third harmonic component does not appear in any of VDCR, VDCS, and VDCT, the third harmonic voltage does not appear in the VDC shown in the equation (4).

  Therefore, according to the present invention, it is possible to obtain an effect that the voltage utilization rate improvement control can be performed without affecting the VDC.

  In this embodiment, the unit converter 108 is a bidirectional chopper circuit. However, the unit converter 108 includes an energy storage element such as a capacitor or a battery, and is a circuit of at least two terminals, and a positive or zero voltage is applied between the two terminals. As long as the circuit can output, the same effect as the present embodiment can be obtained.

  Further, in this embodiment, the primary windings 105RS, ST, and TR are Δ-connected, but when this is Y-connected, the same effects as in this embodiment can be obtained.

  Further, in the present embodiment, the power system 101 is connected to the primary windings 105RS, ST, TR, but the same applies even if a power generator such as a wind power generator or a solar power generator is connected instead of the power system 101. The effect of. The same effect can be obtained by connecting a load device such as an electric motor instead of the power system 101.

  A second mode for carrying out the present invention will be described.

  In the second embodiment, instead of the bidirectional chopper circuit type unit converter 108 in the first embodiment, a full bridge circuit type unit converter 501 shown in FIG. 5 is used.

  In the second embodiment, in addition to the effects obtained in the first embodiment, the polarity of the voltage VDC applied to the DC device 109 can be reversed.

  Hereinafter, the principle of reversing the polarity of VDC will be described with reference to FIG.

When the DC component is reduced without changing the AC component of the arm voltage command values VRP ^* , VRN ^* , VSP ^* , VSN ^* , VTP ^* , VTN ^* , VRP ^* , VRN ^* , VSP ^* , VSN ^*
, VTP ^* and VTN ^* fall below zero, and a state occurs in which each arm must output a negative voltage.

As in the first embodiment, when the unit converter 108 is a bidirectional chopper circuit system (FIG. 2), the polarity of the arm voltages VRP, VRN, VSP, VSN, VTP, and VTN can be only positive or zero. . Therefore, arm voltage command values VRP ^* , VRN ^* , VSP ^* , VSN ^*
, VTP ^* and VTN ^* become negative, the power converter 102 cannot be properly controlled.

  On the other hand, by using the full bridge circuit type unit converter 501 instead of the unit converter 108 as in this embodiment, the polarities of the arm voltages VRP, VRN, VSP, VSN, VTP, and VTN are positive, negative. Or zero.

In this case, arm voltage command values VRP ^* , VRN ^* , VSP ^* , VSN ^* , VTP ^* , VTN ^*
Without changing the alternating current component, it is possible to reduce the direct current component to zero or to make it negative.

  Hereinafter, the principle of enabling the output voltage Vjk to be controlled by the configuration of the full-bridge circuit unit converter 501 and the switching states of the switching elements 201XH, XL, YH, and YL will be described.

  A full bridge circuit type unit converter 501 includes a switching element (X-phase high-side switching element) 201XH and a parallel diode (X-phase high-side switching diode) 202XH and a switching element (X-phase low-side switching element) 201XL and a reflux current. A parallel body of a diode (X phase low side freewheeling diode) 202XL and a parallel body of switching element (Y phase high side switching element) 201YH and a freewheeling diode (Y phase high side freewheeling diode) 202YH and a switching element (Y phase) A low-side switching element) 201YL and a parallel body of a free-wheeling diode (Y-phase low-side free-wheeling diode) 202XL, and a parallel body of a capacitor 203.

Switching element (X phase high side switching element) 201XH and freewheeling diode (
A series connection point of a parallel body of X-phase high-side freewheeling diode) 202XH, a switching element (X-phase low-side freewheeling diode) 201XL, and a parallel body of free-wheeling diode (X-phase low-side freewheeling diode) 202XL is referred to as X point.

Switching element (Y-phase high-side switching element) 201YH and freewheeling diode (
A series connection point of a parallel body of Y-phase high-side freewheeling diode) 202YH and a parallel body of switching element (Y-phase low-side freewheeling diode) 201YL and free-wheeling diode (Y-phase low-side freewheeling diode) 202XL will be referred to as a Y point.

Voltage Vjk between point X and point Y (j = RP, RN, SP, SN, TP, TN, k = 1, 2
,..., N) are output voltages of the unit converter 501.

  Hereinafter, the relationship between the switching states of the switching elements 201XH, XL, YH, and YL and Vjk will be described.

  Switching element (X phase high side switching element) 201XH is on, switching element (X phase low side switching element) 201XL is off, switching element (Y phase high side switching element) 201YH is on, switching element (Y phase low side switching element) When 201YL is off, Vjk is approximately zero.

  Switching element (X phase high side switching element) 201XH is on, switching element (X phase low side switching element) 201XL is off, switching element (Y phase high side switching element) 201YH is off, switching element (Y phase low side switching element) When 201YL is on, Vjk is approximately equal to the voltage VCjk of the capacitor 203.

  Switching element (X-phase high-side switching element) 201XH is off, switching element (X-phase low-side switching element) 201XL is on, switching element (Y-phase high-side switching element) 201YH is on, switching element (Y-phase low-side switching element) When 201YL is off, Vjk is approximately equal to a voltage having the opposite polarity to the voltage VCjk of the capacitor 203, that is, -VCjk.

  Switching element (X phase high side switching element) 201XH is OFF, switching element (X phase low side switching element) 201XL is ON, switching element (Y phase high side switching element) 201YH is OFF, switching element (Y phase low side switching element) When 201YL is on, Vjk is approximately zero.

  When both the switching element (X-phase high-side switching element) 201XH and the switching element (X-phase low-side switching element) 201XL are turned on, the capacitor 203 is short-circuited, and thus such an operation is prohibited.

  Similarly, when the switching element (Y-phase high-side switching element) 201YH and the switching element (Y-phase low-side switching element) 201YL are both turned on, the capacitor 203 is short-circuited, and thus such an operation is prohibited.

  As described above, Vjk can be controlled to be positive, zero, or negative by controlling the switching state of the switching elements 201XH, XL, YH, and YL.

  The arms 107RP, RN, SP, SN, TP, and TN are serial bodies of one or more unit converters 501. Therefore, the arm voltages VRP, VRN, VSP, VSN, VTP, and VTN can also be controlled to be positive, zero, or negative.

  In this embodiment, the unit converter 108 is a full bridge circuit. However, the unit converter 108 includes an energy storage element such as a capacitor or a battery, is a circuit of at least two terminals, and is positive, zero, or zero between the two terminals. As long as the circuit can output a voltage, the same effect as in this embodiment can be obtained.

  Further, in this embodiment, the primary windings 105RS, ST, and TR are Δ-connected, but when this is Y-connected, the same effects as in this embodiment can be obtained.

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

  In the first embodiment, the power conversion device 102 is connected to the three-phase power system 101. However, the third embodiment shows a configuration of a power conversion device that can be connected to a single-phase power system.

  Hereinafter, the configuration of the third embodiment will be described with reference to FIG.

  The power converter 602 is connected to the single-phase power system 601.

  The difference in the configuration of the power conversion device 602 of the third embodiment with respect to the power conversion device 102 of the first embodiment is that the iron cores 104S and 104T belonging to the S phase and the T phase, the primary windings 105ST and TR, and the positive secondary winding 106SP, SN, TP, TN, arm 107SP, SN, TP, TN are removed, and a capacitor 603P is connected between points P and M, and a capacitor 603N is connected between points M and N.

  Capacitors 603P and N function to divide voltage VDC between points P and N by half.

  Hereinafter, the operation principle of the power converter 602 will be described.

  The difference in the operating principle of the power conversion device 602 of the third embodiment with respect to the power conversion device 102 of the first embodiment is that the through current IZR included in the currents IRP and IRN is equal to the current IDC flowing in the DC device 109. However, in other respects, the power conversion device 602 can operate on the same principle as the power conversion device 102 of the first embodiment.

  In the third embodiment, a full-bridge circuit type unit converter 501 can be used instead of the bidirectional chopper circuit type unit converter 108. The effect of being able to control to zero or negative is obtained.

  Furthermore, the same effect can be obtained by connecting a power generation device such as a wind power generation device or a solar power generation device instead of the single-phase power system 601. The same effect can be obtained by connecting a load device such as an electric motor instead of the power system 601.

  A fourth mode for carrying out the present invention will be described.

  In the first embodiment, the power conversion device 102 is connected to the three-phase power system 101. However, the fourth embodiment shows a configuration of a power conversion device that can be connected to a single-phase power system. In the fourth embodiment, the capacitors 603P and N required in the third embodiment can be omitted.

  Further, instead of the single-phase power system 601, a single-phase power source, a single-phase load, a wind power generation system, a solar power generation system, or the like can be connected.

  Hereinafter, the configuration of the fourth embodiment will be described with reference to FIG.

  The power conversion device 701 is connected to a power system (single-phase power system) 601.

The difference in the configuration of the power conversion device 602 of the third embodiment with respect to the power conversion device 102 of the first embodiment is that the iron core 104T belonging to the T phase, the primary winding 105TR, the positive secondary windings TP and TN, the arm 107TP, TN is removed, and the primary windings 105RS and 105ST are connected in parallel to the single-phase power system 601 so as to have reverse polarity. Therefore, in FIG. 7, VGST = −VGRS.

  Hereinafter, the operation principle of the power conversion device 701 will be described.

The difference in the operating principle of the power conversion device 701 of the fourth embodiment with respect to the power conversion device 102 of the first embodiment is that the sum of the through current IZR included in the currents IRP and IRN and the through current IZS included in the current ISP and ISN. In other respects, the power conversion device 701 can operate on the same principle as the power conversion device 102 of the first embodiment.

  In the fourth embodiment, the full bridge circuit type unit converter 501 can be used instead of the bidirectional chopper circuit type unit converter 108. In this case, as in the second embodiment, the VDC is positively connected. The effect of being able to control to zero or negative is obtained.

  Furthermore, in Example 4, the same effect can be obtained by connecting a power generation device such as a wind power generation device or a solar power generation device instead of the single-phase power system 601. The same effect can be obtained by connecting a load device such as an electric motor instead of the power system 601.

DESCRIPTION OF SYMBOLS 101 Power system 102 Power converter (1st Embodiment of the power converter based on this invention)
103 Transformer 104R, 104S, 104T Core 105RS, 105ST, 105TR Primary winding 106RP, 106SP, 106TP Positive secondary winding 106RN, 106SN, 106TN Negative secondary winding 107RP, 107SP, 107TP, 107RN, 107SN, 107TN Arm 108 Unit converter (bidirectional chopper circuit type unit converter)
109 DC device 201H, 201L, 201XH, 201XL, 201YH, 201YL Switching element 202H, 202L, 202XH, 202XL, 202YH, 202YL Freewheeling diode 203, 603P, N Capacitor 501 Unit converter (full bridge circuit type unit converter)
601 Power system (single-phase power system)
602, 701 Power converter (a third embodiment of a power converter based on the present invention)

Claims (1)

Arms formed by connecting in series one or more circuit elements having at least two terminals each including first, second, and third windings and an energy storage element are provided as first and second arms,
The second winding and the first arm constitute a first series body, the third winding and the second arm constitute a second series body, and the first winding The first, second, and third windings are connected in series so that the magnetomotive force relating to the direct current of the second and third windings has a reverse polarity. Are magnetically coupled and have three phases of the first winding, the first arm, the second winding, the third winding, and the second arm. The DC circuit is composed of three sets each corresponding to the first windings for the three phases, the DC circuit has an individual iron core for each phase, and the first circuit in each phase The AC component of the output voltage of the first arm and the output voltage of the second arm have substantially opposite phase voltage waveforms, and the DC current component of the first arm in each phase and the previous component Direct current component of the second arm power conversion device, wherein the said first arm so as to be substantially identical second arm is controlled.

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