JP2016010240A - Power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that, in the case where a voltage type converter is used for a power conversion device in which unit converters are multiplexed in series to a transformer, there is the risk that a little direct current may flow to the transformer and in order to enlarge a bias magnetism tolerance, countermeasures such as enlarging a transformer core or using a transformer including a gap are required.SOLUTION: In the power conversion device, the unit converters each including a switching element and at least one capacitor are multiplexed in series to the transformer. The power conversion device is characterized in that a current that flows to the unit converter flows through any one of the capacitors without fail.

Description

  The present invention relates to a power converter.

  In general, power converters that convert power to and from an AC such as an AC system usually have a transformer installed between the AC and the AC in order to ensure step-up / down of the AC voltage and electrical insulation. . In a power converter using such a transformer, it is necessary to ensure power quality such as suppressing the outflow of harmonic currents to the AC system.

  Therefore, by providing multiple converters and adding the voltage waveforms of each stage output from the multiple converters, it is close to a sine wave and exceeds the breakdown voltage of the semiconductor switching element used inside the converter. A serial multiple conversion device, which is a voltage-type power converter capable of outputting a high voltage, is widely used. In the present specification, a power conversion device in which a converter is serially multiplexed in a transformer is referred to as a serial multiple conversion device.

On the other hand, when a DC component is included in the output obtained by adding the voltage waveforms of the respective stages output from the converter, a problem of so-called DC demagnetization in which a DC current flows through the winding of the transformer occurs. In order to solve this DC bias problem, the current between the converter and the transformer is detected, the average value of the detected current is calculated, and the average value obtained by the calculation is used to calculate the current of the converter. A technique for correcting a control command is known. That is, a technique for correcting an output control command of a converter using an average value of a current flowing between each converter and each transformer is known. Such a technique is described in, for example, JP-A-7-194141.

JP 7-194141 A

  As described above, the voltage source power converter may output a DC voltage due to, for example, an offset error of a current sensor used to control the current flowing through the voltage source power converter.

  In the transformer, the magnetic flux changes due to the time integration of the voltage applied to the winding. Therefore, when a DC voltage is applied to the transformer winding, a DC component is generated in the magnetic flux.

  The magnetic flux and the magnetic flux density are in a proportional relationship, and when a direct current component is generated in the magnetic flux, the direct current component is also superimposed on the magnetic flux density of the transformer core.

  In this specification, the superposition of a DC component on the magnetic flux density of the transformer core is referred to as DC magnetization.

  Since the transformer core has a saturation magnetic flux density determined by the material and shape, if excessive DC bias is generated, the magnetic flux density of the transformer core approaches or exceeds the saturation magnetic flux density. The normal operation as a container is hindered.

  Inhibition of normal operation as a transformer includes generation of overcurrent due to a decrease in excitation inductance of the transformer.

  In addition, if DC bias magnetism occurs in a part of the transformer that constitutes the serial multiple converter, the voltage sharing ratio output by each unit converter collapses and overvoltage is generated between the other transformer windings. There is a possibility that the magnetism further proceeds.

  Here, in order to prevent the above-mentioned DC bias, several suppression methods have been proposed so far, and the current flowing between the power converter and the transformer is detected as in the above prior art. When performing feedback control so that it does not contain a DC component, excessive DC bias may occur if there is an offset error in the current sensor detection value or the means for performing feedback control. .

  Next, it is conceivable to control the DC current to zero using a high-precision DC current sensor with a small offset error. However, the addition of a device such as a DC current sensor causes an increase in installation area and a decrease in reliability.

  Furthermore, it is conceivable to use a transformer that has been preliminarily assumed to have the offset error and has an increased withstand bias. However, there is a problem that increasing the cross-sectional area of the iron core is unavoidable in order to increase the withstand bias.

An object of the present invention is to solve at least one of the above-described problems, and to provide a power conversion device capable of preventing DC bias magnetism with high accuracy without increasing the size of the device. .

  To achieve the above object, the present invention connects a plurality of one-side windings in series, connects the one-side windings connected in series to an alternating current, and each of the plurality of one-side windings. Corresponding to the other side winding, and a power converter is connected to each of the other side windings. The power converter includes a capacitor, a terminal, an output from the capacitor to the terminal, and the terminal. And at least one of the circuits including the other-side winding is formed with a demagnetization suppression circuit that passes through the capacitor in any state of conduction / cut-off operation of the switching element. Configured to be.

Alternatively, a plurality of one-side windings are connected in series, the one-side windings connected in series are connected to an alternating current, and a corresponding other-side winding is provided for each of the plurality of one-side windings. , Connecting a power converter to each of the other windings, wherein at least one of the power converters operates a capacitor, a terminal, an output from the capacitor to the terminal, and a charge from the terminal to the capacitor A first capacitor, a second capacitor connected in series with the first capacitor, and a first switching element capable of outputting the voltage of the first capacitor to the circuit And a second switching element capable of outputting the voltage of the second capacitor to the circuit, and when a DC component current flows through the circuit passing through the other winding of the transformer, Reduce ingredients Said first switching element so as to have configured to operate the second switching element.

In the present invention, by adopting the above-described configuration, it is possible to prevent the DC bias magnetism with high accuracy without increasing the size of the device.

1st form of the power converter device by this invention Half-bridge type unit converter Schematic waveform of half-bridge type unit converter 1 Schematic waveform of half-bridge unit converter 2 Schematic waveform of half-bridge unit converter 3 Control block diagram that reflects capacitor voltage imbalance in output voltage command value (single phase) 2nd form of the power converter device by this invention Double half bridge type unit converter 3rd form of the power converter device by this invention Example of main unit converter (full bridge converter) 4th form of the power converter device by this invention Three-phase half-bridge type unit converter Control block diagram that reflects capacitor voltage imbalance in output voltage command value (three-phase)

  A first embodiment of the present invention will be described.

  The first embodiment is a serial multiple conversion device using a plurality of unit converters configured by a half-bridge circuit.

  According to the present embodiment, it is possible to obtain an effect that excessive DC bias can be suppressed even when a transformer having a small bias tolerance is used.

  Hereinafter, the overall circuit configuration of the first embodiment, the circuit configuration of the unit converter, the principle of suppressing DC bias, and the converter control means will be described.

  First, the overall circuit configuration of the first embodiment will be described with reference to FIG.

  The serial multiple conversion apparatus 103 of the present invention is connected to a single-phase bus 102 connected to a single-phase AC system 101.

  Hereinafter, the internal configuration of the serial multiple conversion apparatus 103 of the present invention will be described.

  The serial multiple conversion apparatus 103 according to the present invention includes a transformer 104 and a unit converter 105, and the unit converter 105 includes a half bridge circuit.

  Hereinafter, the voltage and current of each part depicted in FIG. 1 are defined.

  The phases of the single-phase AC system 101 and the single-phase bus 102 are referred to as U-phase and V-phase, the voltage of the single-phase AC system 101 is expressed as VS, and the voltage output from the serial multiple converter 103 of the present invention is expressed as VCON. write.

  The current flowing from the single-phase bus 102 to the serial multiple conversion device 103 of the present invention is denoted as ICON.

  When it is not particularly necessary to distinguish, the half-bridge unit converter 105, a double half-bridge unit converter 702, which will be described later with reference to FIG. 7, and a full-bridge unit converter 902, which will be described later with reference to FIG. , And a three-phase half-bridge type unit converter 1105, which will be described later with reference to FIG. 11, are simply referred to as “unit converters”, and the total number of unit converters is expressed as N.

  Hereinafter, the internal configuration of the half-bridge unit converter 105 of the present invention will be described with reference to FIG.

  The anti-parallel circuit of the X-phase upper switching element 201XP and the X-phase upper free-wheeling diode 202XP and the anti-parallel circuit of the X-phase lower switching element 201XN and the X-phase lower-side circulating diode 202XN are connected in series at the point x. Is a first series circuit.

  The half-bridge unit converter 105 of the present invention includes two capacitors, an upper capacitor 203P and a lower capacitor 203N, as energy storage elements.

  The upper capacitor 203P and the lower capacitor 203N are connected in series at m points, and this is a second series circuit.

The half-bridge type unit converter 105 of the present invention has a configuration in which the first and second series circuits are connected in parallel at the p point and the n point. A transmission communication line 107, a reception communication line 108, a gate drive means 204, and a capacitor balance control means 205 are provided for communicating with the central control means 106.

  Hereinafter, the voltage / current in the half-bridge type unit converter 105 of the present invention will be defined.

  The voltage at point x with reference to point m is referred to as the output voltage of unit converter 105 and is denoted as Vk.

  Each unit converter controls the output voltage Vk of the unit converter based on the gate pulse command gk transmitted to the unit converter by the central control means 106.

  Further, the current flowing toward the point x is expressed as Ik.

  Here, k represents the connection number of the unit converter, and k = 1, 2,.

  Hereinafter, k added to each voltage of the unit converter 105 of the present invention has the same meaning.

  The voltage of the upper capacitor 203P is expressed as VCPk, and the voltage of the lower capacitor 203N is expressed as VCNk.

  In the present specification, unless it is particularly necessary to distinguish, the X-phase upper switching element 201XP, the X-phase lower switching element 201XN in FIG. 2 and other unit converters described later (see FIGS. 8, 10, and 12). The switching elements 201XP, 201XN, 201YP, 201YN, 201ZP, and 201ZN used for reference) are also collectively referred to simply as “switching elements”.

  2, 8, 10, and 12, the symbol of IGBT (insulated-gate bipolar transistor) is drawn as a switching element. However, the present invention is not limited to the IGBT, and is an on / off control type switching. If it is an element, other switching elements such as BJT (bipolar junction transistor), MOSFET (metal-oxide-semiconductor field-effect transistor), GTO (gate turn-off) thyristor, IGCT (integrated gate-commutated thyristor) are used. Even in such a case, the effects of the present invention can be obtained.

  Hereinafter, the relationship between the on / off state of the switching element and the output voltage Vk will be described. A path through which the current Ik flows will also be described.

  When the X-phase upper switching element 201XP is on and the X-phase lower switching element 201XN is off, the voltage at the point x with respect to the point m is substantially equal to the voltage VCPk of the upper capacitor 203P. That is, Vk = VCPk.

  In this case, the current Ik flowing through the unit converter passes through the upper capacitor 203P.

  When the X-phase upper switching element 201XP is off and the X-phase lower switching element 201XN is on, the voltage at the x point with respect to the m point is approximately equal to the voltage VCNk of the lower capacitor 203N, and The voltage has a reverse polarity. That is, Vk = −VCNk.

  In this case, the current Ik flowing through the unit converter passes through the lower capacitor 203N.

  From the above, it can be seen that the output voltage Vk of the unit converter 105 can be controlled by controlling on / off of the switching element. In the half-bridge type unit converter 105, regardless of the on / off state of the switching element, The current Ik has a feature that it always passes through one of the capacitors 203P and N.

  Next, the principle that the half-bridge type unit converter can eliminate the DC bias when a DC current flows through the unit converter will be described.

  First, a schematic waveform of the output voltage Vk of the half-bridge type unit converter 105 when the voltage VCPk of the upper capacitor 203P is equal to the voltage VCNk of the lower capacitor 203N (VCPk = VCNk) will be described with reference to FIG. To do.

  FIG. 3 shows a case where a pulse train is generated so that the fundamental wave component of the unit converter output voltage Vk becomes Vkfund by, for example, PWM (Pulse Width Modulation) control.

  When VCPk = VCNk as shown in FIG. 3, Vk contains the fundamental wave component Vkfund, but does not contain a DC component.

  Next, with reference to FIG. 4, considering the case of Ikdc> 0, Ikdc passes through either the upper capacitor 203P or the lower capacitor 203N.

  In other words, VCPk rises and VCNk falls due to the positive current DC component Ikdc, so that VCPk> VCNk.

  When VCPk> VCNk is satisfied by the positive current DC component Ikdc, the schematic waveform shown in FIG. 3 changes as shown in FIG. 4, and the voltage pulse of Vk includes the positive voltage DC component Vkdc in addition to the fundamental wave component Vkfund. contains.

  Since the positive voltage direct current component Vkdc generated in the unit converter works in a direction to reduce the positive current direct current component Ikdc flowing in the unit converter, it works in a direction in which the direct current magnetic demagnetization of the transformer is eliminated.

  Next, referring to FIG. 5 and considering the case of Ikdc <0, Ikdc passes through either the upper capacitor 203P or the lower capacitor 203N.

  In other words, VCPk decreases and VCNk increases due to the negative current DC component Ikdc, so that VCPk <VCNk.

  When VCPk <VCNk is satisfied by the negative current DC component Ikdc, the schematic waveform shown in FIG. 3 changes as shown in FIG. 5, and the voltage pulse of Vk includes the negative voltage DC component Vkdc in addition to the fundamental wave component Vkfund. contains.

  Since the negative voltage direct current component Vkdc generated in the unit converter works in a direction to reduce the negative current direct current component Ikdc flowing in the unit converter, it works in a direction in which the direct current magnetism of the transformer is eliminated.

  4 and 5, when the current DC component Ikdc flows, the voltage DC component Vkdc is included in the voltage pulse of Vkfund. Therefore, the generated current DC component Ikdc can be reduced.

  Next, the central control means 106 for controlling the output voltage VCON of the serial multiple conversion apparatus 103 of the present invention and the capacitor balance control means 205 having a function capable of preventing excessive DC bias of the transformer 104 will be described. .

  First, each control block of the central control means 106 will be described with reference to FIG.

  The total capacitor voltage constant control means 601 in the central control means 106 receives the upper capacitor voltage VCPk and the lower capacitor voltage VCNk from all unit converters via the receiving communication line 108, and the average value thereof is the total capacitor voltage. Control is performed so as to follow the command value VC *.

  The power control means 602 receives the active power command P * and PC * and the reactive power command Q * and interchanges the active power and reactive power with the single-phase AC system 101.

  The current control unit 603 performs control so that the current ICON flowing in the power converter follows the current command ICON * output from the power control unit 602.

  The current control means 603 detects the system voltage VS and performs voltage feedforward control.

  Unit converter control means 604 includes control means for dividing voltage command VCON * output from current control means 603 into unit converter commands, and control means for equalizing the capacitor voltage of each unit converter. .

  An output voltage command VUNIK before the capacitor voltage correction of each unit converter output from the unit converter control unit 604 and a capacitor voltage correction command VCORk output from the capacitor balance control unit 205 described later are added using an adder 607. These are added to generate a fundamental wave command Vkfund * for the output voltage Vk of the unit converter.

  Then, the gate pulse generating means 608 compares the fundamental voltage command Vkfund * of the output voltage with the carrier wave Vcarry of a constant frequency, and generates the gate pulse command gk according to the magnitude thereof, so that it can be transmitted via the transmission communication line 107. The gate pulse command gk is transmitted to each unit converter.

  For example, a triangular wave is used as the carrier wave Vcarrier. However, if the control method is to match the fundamental voltage command Vkfund * of the output voltage with the fundamental wave component Vkfund of the actual unit converter output voltage Vk, a space is used. It is also possible to apply other modulation methods such as a vector method, and this embodiment includes such a case.

  Next, the capacitor balance control means 205 which is one of the features of the present invention will be described.

  The capacitor balance control means 205 of the present invention obtains the capacitor voltage from the voltage sensors 206P and 206N of the unit converter, and calculates the difference voltage between the two using the adder 605, whereby the polarity and magnitude of the voltage DC component Vkdc are calculated. Judging.

  Then, the calculated difference voltage is multiplied by the control gain 606, and a correction voltage command VCORk that can cancel the DC component Vkdc generated in the unit converter is output.

  Therefore, the correction voltage command VCORk has a value opposite in sign to the voltage direct current component Vkdc.

  As a result, the correction voltage command VCORk for canceling the voltage DC component Vkdc contained in Vk can be output, so that an effect of preventing excessive DC bias of the transformer 105 can be obtained.

  2 shows a circuit configuration in which the capacitor balance control means 205 is incorporated in the unit converter 105, the same effect can be obtained even if the capacitor balance control means 205 is incorporated in the central control means 106.

  Moreover, it has been described above that the half-bridge type unit converter 105 has a function of suppressing direct current magnetization in the half-bridge type unit converter 105 itself.

  Therefore, the first embodiment is not necessarily a serial multiple conversion device including the capacitor balance control means 205.

In the above, the principle which can prevent the excessive direct current | flow magnetism of the transformer 104 by providing the half-bridge type | mold unit converter 105 was demonstrated.

  A second embodiment of the present invention will be described.

  The second embodiment is a power conversion device in which capacitor midpoints in a half-bridge type unit converter having different capacitor voltage values are connected to each other.

  According to the present embodiment, it is possible to output the same voltage as in the first embodiment while reducing the number of transformers, and to suppress excessive DC bias.

  Hereinafter, the overall configuration of the second embodiment and the internal configuration of the unit converter will be described. However, only differences from the first embodiment will be described.

  First, the overall configuration of the second embodiment and the configuration of the unit converter will be described with reference to FIG.

  The serial multiple conversion device 701 of the present invention is connected to a single-phase bus 102 connected to the single-phase AC system 101, and the serial multiple conversion device 701 is composed of a transformer 104 and a unit converter 702.

  Hereinafter, the voltage and current of each part depicted in FIG. 7 will be defined.

  The phases of the single-phase AC system 101 and the single-phase bus 102 are referred to as U-phase and V-phase, the voltage of the single-phase AC system 101 is expressed as VS, and the voltage output by the serial multiple conversion device 701 of the present invention is expressed as VCON. write.

  The current flowing from the single-phase bus 102 to the serial multiple conversion device 701 of the present invention is denoted as ICON.

  Hereinafter, the internal configuration of the unit converter 702 of the present invention will be described with reference to FIG.

  The unit converter 702 of the present invention has a configuration in which the capacitor midpoint m1 of the half-bridge unit converter 105x is connected to the capacitor midpoint m2 of the half-bridge unit converter 105y.

  Further, the point x of the half-bridge type unit converter 105x and the point y of the Y-phase unit converter 105y are connected to the transformer 104, respectively.

  In this specification, the circuit configuration of the unit converter 702 is referred to as a “double half-bridge type unit converter”.

  Hereinafter, the voltage / current in the double half bridge type unit converter 702 of the present invention will be defined.

  The voltage at the point x with respect to the point y is referred to as the output voltage of the double half bridge unit converter 702 and is denoted as Vk.

  Further, the current flowing toward the point x is expressed as Ik.

  The voltage of the upper capacitor 203P of the X-phase unit converter 105x is expressed as VCXPk, and the voltage of the lower capacitor 203N is expressed as VCXNk.

  The voltage of the upper capacitor 203P of the Y-phase unit converter 105y is expressed as VCYPk, and the voltage of the lower capacitor 203N is expressed as VCYNk.

  Hereinafter, the relationship between the on / off state of the switching element and the output voltage Vk will be described.

  When the X-phase upper switching element 201XP is on, the X-phase lower switching element 201XN is off, the Y-phase upper switching element 201YP is off, and the Y-phase lower switching element 201YN is on, The voltage is Vk = VCXPk + VCYNk. In this case, the current Ik flowing through the unit converter passes through the capacitors 203XP and 203YN.

  When the X-phase upper switching element 201XP is on, the X-phase lower switching element 201XN is off, the Y-phase upper switching element 201YP is on, and the Y-phase lower switching element 201YN is off, The voltage Vk = VCXPk−VCYPk. In this case, the current Ik flowing through the unit converter passes through the capacitors 203XP and 203YP.

  When the X-phase upper switching element 201XP is off, the X-phase lower switching element 201XN is on, the Y-phase upper switching element 201YP is off, and the Y-phase lower switching element 201YN is on, The voltage Vk = −VCXNk + VCYNk. In this case, the current Ik flowing through the unit converter passes through the capacitors 203XN and 203YN.

  When the X-phase upper switching element 201XP is off, the X-phase lower switching element 201XN is on, the Y-phase upper switching element 201YP is on, and the Y-phase lower switching element 201YN is off, The voltage Vk = −VCXNk−VCYPk. In this case, the current Ik flowing through the unit converter passes through the capacitors 203XN and 203YP.

  From the above, it can be seen that the output voltage Vk of the double half-bridge unit converter 702 of the present invention can be controlled by controlling on / off of the switching element.

  Further, as compared with the serial multiple conversion device 103 according to the first embodiment, the serial multiple conversion device 702 according to the present embodiment is characterized in that it can output the same number of voltages while reducing the number of transformers 104.

  In the double half bridge type unit converter 702 of the present invention, the current Ik passes through any of the capacitors 203XP, 203XN, 203YP, and 203YN regardless of the on / off state of the switching element.

  Therefore, for the same reason as the half-bridge type unit converter 105 of the present invention, it is possible to obtain the effect that the DC bias can be eliminated.

  Further, the capacitor balance control means 205x and 205y of the present invention can be applied to each of the half bridge type unit converters 105x and 105y.

The principle that the half-bridge type unit converter can eliminate the DC bias, the control method of the central control means 106, and the control method of the capacitor balance control means 205x and 205y of the present invention are the same as in the first embodiment, and are omitted. To do.
FIG. 8 shows a circuit configuration in which the capacitor balance control means 205x and 205y are incorporated in the unit converter 702, but the same effect can be obtained even if the capacitor balance control means 205x and 205y are incorporated in the central control means 106.

  The double half bridge type unit converter 702 has been described above that the conversion circuit itself has a function of suppressing direct current bias.

Therefore, the second embodiment does not necessarily need to be a serial multiple conversion device including the capacitor balance control means 205x and 205y.

  A third embodiment of the present invention will be described.

  Embodiment 3 is a power conversion apparatus in which a half-bridge type unit converter is connected between a transformer and a main unit converter.

  According to the present embodiment, it is possible to suppress the direct current magnetization regardless of the circuit configuration of the main unit converter, and it is possible to suppress excessive direct current magnetization without using a highly accurate current sensor. can get.

  Hereinafter, the overall configuration of the third embodiment and the configuration of the unit converter will be described. However, only differences from the first embodiment will be described.

  First, the overall configuration of the third embodiment and the configuration of the unit converter will be described with reference to FIG.

  901 of the present invention is connected to a single-phase bus 102 connected to a single-phase AC system 101, and the serial multiple converter 901 of the present invention includes a transformer 104 and a half-bridge type unit converter 105. , Main unit converter 902.

  Compared with the serial multiple conversion apparatus 103 of the present invention shown in FIG. 1 according to the first embodiment, the serial multiple conversion apparatus 901 of the present invention includes a half-bridge type unit converter 105, a transformer 104 and a main unit converter 902. It is characterized by being connected between them.

  The main unit converter 902 is a unit converter that does not include a control unit for suppressing DC bias, and a full-bridge type unit converter described later is an example.

  In this specification, the full bridge type unit converter is treated as the main unit converter. However, the present invention is not limited to the full bridge type unit converter, and other control means for suppressing the DC bias magnetism. The effect of the present invention can also be obtained when using a unit converter that does not include.

  Hereinafter, the voltage and current of each part depicted in FIG. 9 are defined.

  The phases of the single-phase AC system 101 and the single-phase bus 102 are referred to as U-phase and V-phase, the voltage of the single-phase AC system 101 is expressed as VS, and the voltage output from the serial multiple converter 103 of the present invention is expressed as VCON. write.

  The current flowing from the single-phase bus 102 to the serial multiple conversion device 901 of the present invention is denoted as ICON.

  Hereinafter, the internal configuration of the main unit converter 902 will be described with reference to FIG.

  The anti-parallel circuit of the X-phase upper switching element 201XP and the X-phase upper free-wheeling diode 202XP and the anti-parallel circuit of the X-phase lower switching element 201XN and the X-phase lower free-wheeling diode 202XN are connected in series at the point x. This is the first series circuit.

  The anti-parallel circuit of the Y-phase upper switching element 201YP and the X-phase upper free-wheeling diode 202YP and the anti-parallel circuit of the Y-phase lower switching element 201YN and the Y-phase lower free-wheeling diode 202YN are connected in series at the point y. This is the second series circuit.

  The main unit converter 902 includes a capacitor 203 as an energy storage element.

  The main unit converter 902 has a configuration in which the first and second series circuits are connected in parallel at the p point and the n point of the capacitor 203.

  Hereinafter, the voltage / current in the main unit converter 902 is defined.

  The voltage at point x with reference to point y is referred to as the output voltage of full-bridge unit converter 902 and is denoted as Vk.

  Further, the current flowing toward the point x is expressed as Ik.

  The voltage of the capacitor 203 of the main unit converter 902 is expressed as VCk.

  Hereinafter, the relationship between the on / off state of the switching element and the output voltage Vk will be described.

  When the X-phase upper switching element 201XP is on, the X-phase lower switching element 201XN is off, the Y-phase upper switching element 201YP is on, and the Y-phase lower switching element 201YN is off, The voltage is almost zero. That is, Vk = 0. In this case, the current Ik flowing through the unit converter does not pass through the capacitor 203.

  When the X-phase upper switching element 201XP is on, the X-phase lower switching element 201XN is off, the Y-phase upper switching element 201YP is off, and the Y-phase lower switching element 201YN is on, The voltage is approximately equal to the voltage VCk of the capacitor 203. That is, Vk = VCk. In this case, the current Ik flowing through the unit converter passes through the capacitor 203.

  When the X-phase upper switching element 201XP is off, the X-phase lower switching element 201XN is on, the Y-phase upper switching element 201YP is on, and the Y-phase lower switching element 201YN is off, The voltage is approximately equal in magnitude to the voltage VCk of the capacitor 203 and has a reverse polarity. That is, Vk = −VCk. In this case, the current Ik flowing through the unit converter passes through the capacitor 203.

  When the X-phase upper switching element 201XP is off, the X-phase lower switching element 201XN is on, the Y-phase upper switching element 201YP is off, and the Y-phase lower switching element 201YN is on, The voltage is almost zero. That is, Vk = 0. In this case, the current Ik flowing through the unit converter does not pass through the capacitor 203.

  As described above, in the full-bridge type unit converter 902, there are cases where the current Ik flows through the capacitor 203 and cases where it does not flow depending on the on / off state of the switching element.

  In other words, since there is a period in which the current direct current component Ikdc does not flow to the capacitor 203, it is not possible to suppress excessive direct current magnetization of the transformer core.

  In this embodiment, a half-bridge type unit converter 105 is connected in series between the transformer 104 and the main unit converter 902. The half-bridge type unit converter 105 is in an on / off state of a switching element. It has been described in the first embodiment that the current Ik passes through one of the capacitors 203P and N regardless of the current.

  Therefore, by adding the half-bridge type unit converter 105 to the main unit converter 902 using the full bridge circuit, it is possible to obtain an effect of suppressing DC bias without using a high-accuracy current sensor.

The principle that the half-bridge type unit converter 105 can eliminate DC bias, the control method of the central control means 106, and the control method of the capacitor balance control means 205 of the present invention are the same as those in the first embodiment, and will be omitted. .

  A fourth embodiment of the present invention will be described.

  The fourth embodiment is a power conversion apparatus in which half-bridge unit converters are serially multiplexed and connected to a three-phase AC system via a transformer.

  According to the present embodiment, it is possible to obtain an effect that DC bias can be suppressed with a simple circuit configuration even in a three-phase power device such as a STATCOM (Static Synchronous Compensator).

  Hereinafter, the overall configuration of the fourth embodiment and the configuration of the unit converter will be described. However, only differences from the first embodiment will be described.

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

  The serial multiple conversion device 1103 of the present invention is linked to a three-phase bus 1102 connected to a three-phase AC system 1101, and the serial multiple conversion device 1103 of the present invention includes a three-phase transformer 1104 and a unit converter 1105. It is configured.

  Hereinafter, the voltage and current of each part depicted in FIG. 11 are defined.

  The phases of the three-phase AC system 1101 and the three-phase bus 1102 are referred to as A phase, B phase, and C phase, the voltage of the AC system 1101 is expressed as VSab, VSbc, and VSca. VabCON, VbcCON, VcaCON are written.

  Further, currents flowing from the single-phase bus 102 to the serial multiple converter 103 of the present invention are denoted as IaCON, IbCON, and IcCON.

  Hereinafter, the internal configuration of the unit converter 1105 of the present invention will be described with reference to FIG.

  The unit converter 1105 of the present invention is composed of three half-bridge type unit converters, an X-phase unit converter 105x, a Y-phase unit converter 105y, and a Z-phase unit converter 105w. The capacitor midpoint m1 is connected to the capacitor midpoint m2 of the half-bridge unit converter 105y and the capacitor midpoint m3 of the half-bridge unit converter 105z.

  Further, the x point of the half-bridge type unit converter 105 x, the y point of the Y-phase unit converter 105 y, and the z point of the half-bridge type unit converter 105 z are connected to the three-phase transformer 1104.

  In this specification, the circuit configuration of the unit converter 1105 is referred to as a “three-phase half-bridge type unit converter”.

  Hereinafter, the voltage / current in the three-phase half-bridge type unit converter 1105 of the present invention will be defined.

  The voltage at the x point relative to the y point is the xy phase line voltage Vxyk, the voltage at the y point relative to the z point is the yz phase line voltage Vyzk, and the voltage at the z point relative to the x point is the zx phase line. This is expressed as an inter-voltage Vzxk.

  A current flowing toward the point x is denoted as Ixk, a current flowing toward the point y is denoted as Iyk, and a current flowing toward the point z is denoted as Izk.

  The voltage of the upper capacitor 203P of the X-phase unit converter 105x is expressed as VCPxk, and the voltage of the lower capacitor 203N is expressed as VCNxk.

  Further, the voltage of the upper capacitor 203P of the Y-phase unit converter 105y is expressed as VCPyk, and the voltage of the lower capacitor 203N is expressed as VCNyk.

  The voltage of the upper capacitor 203P of the Z-phase unit converter 105z is expressed as VCPzk, and the voltage of the lower capacitor 203N is expressed as VCNzk.

  The relationship between the on / off state of the switching element and the output voltage Vk is omitted because it is a configuration in which three single-phase unit converters are connected. In the three-phase half-bridge unit converter 1105 of the present invention, Regardless of the on / off state of the switching element, the currents Ixk, Iyk, Izk pass through any of the capacitors 203XP, 203XN, 203YP, 203YN, 203ZP, 203ZN.

Accordingly, the capacitor balance control means 205x, 205y, 205z of the present invention is provided for each of the half-bridge type unit converters 105x, 105y, 105z in the same manner as the single-phase converter described in the first embodiment, the second embodiment, and the third embodiment. Application can suppress excessive direct current bias.
FIG. 12 shows a circuit configuration in which the capacitor balance control means 205x, 205y, and 205z are incorporated in the unit converter 1105, but the same effect can be obtained even if the capacitor balance control means 205x, 205y, and 205z are incorporated in the central control means 1309. Can be obtained.

  FIG. 13 illustrates control blocks of the central control unit 1309 of the three-phase serial multiple conversion device 1103 and the capacitor balance control units 205x, 205y, and 205z of the present invention.

  In FIG. 13, j represents the phase of the unit converter 1105, and j = x, y, z.

  The central control means 1309 and capacitor balance control means 205x, 205y, 205z shown in FIG. 13 are equivalent to the single-phase serial multiple converters 103, 701, 901 described in the first, second, and third embodiments. The explanation is omitted because the control means is used.

  As described above, the three-phase half-bridge type unit converter 1105 has a function of suppressing the direct-current bias in the conversion circuit itself.

  Therefore, the present invention does not necessarily have to be a serial multiple conversion device provided with the capacitor balance control means 205x, 205y, 205z.

  From the above, the three-phase serial multiple conversion device 1103 can eliminate the DC bias for the same reason as the single-phase serial multiple conversion device described so far.

DESCRIPTION OF SYMBOLS 101 ... Single phase alternating current system 102 ... Single phase bus 103 ... Serial multiple conversion apparatus 104 ... Transformer 105 ... Half bridge type unit converter 106 ... Central control means 203 ... Capacitor 205: Capacitor voltage balance control means 206 ... Voltage sensor 701 ... Series multiple converter 702 ... Double half bridge type converter 901 ... Serial multiple converter 902 ... Main unit conversion 1101 ... Three-phase AC system 1102 ... Three-phase bus 1103 ... Series multiple converter 1104 ... Three-phase transformer 1105 ... Three-phase half-bridge type unit converter 1309 ... Central control means

Claims (9)

Connecting a plurality of one-side windings in series, connecting the one-side windings connected in series to an alternating current, and providing a corresponding other-side winding for each of the plurality of one-side windings; A power converter is connected to each other winding, and the power converter includes a capacitor, a terminal, an output from the capacitor to the terminal, and a switching element for operating charging from the terminal to the capacitor. And at least 1 of the circuit containing the said other side coil | winding forms the demagnetization suppression circuit which passes a capacitor | condenser in any state of the conduction | electrical_connection of a switching element, or the interruption | blocking operation | movement.
The power converter according to claim 1, wherein the demagnetization suppression circuit is a half-bridge circuit.
2. The power conversion device according to claim 1, wherein the demagnetization suppression circuit is configured by a two-terminal full bridge circuit, and a half bridge circuit is connected in series to one of the terminals.
3. The power converter according to claim 2, wherein a midpoint of two capacitors constituting one half-bridge circuit and a midpoint of two capacitors constituting the other half-bridge circuit are connected. Conversion device.
5. The power converter according to claim 2, wherein a voltage of two capacitors included in the half-bridge circuit is detected, and an output of the unit converter is determined based on a difference between the two capacitor voltages. A power conversion device comprising control means having a function of correcting a voltage command value.
The three-phase half-bridge type according to claim 1, wherein three-phase unit converters comprising three half-bridge circuits and three-phase unit converters in which three midpoints of two capacitors constituting the half-bridge circuit are connected in series are transformer-multiplexed. A power conversion device characterized in that a current flowing through a unit converter flows through one of the capacitors in any state of conduction / cut-off operation of an switching element.
The power conversion device according to claim 6, wherein two capacitor voltages of each phase included in the three-phase unit converter are detected, and an output of the three-phase unit converter is determined based on a difference between the two capacitor voltages. A power conversion device comprising control means having a function of correcting a voltage command value.
The power converter according to claim 1, wherein the power converter can be operated as a STATCOM.
  Connecting a plurality of one-side windings in series, connecting the one-side windings connected in series to an alternating current, and providing a corresponding other-side winding for each of the plurality of one-side windings; A power converter is connected to each other winding, and at least one of the power converters operates to operate a capacitor, a terminal, an output from the capacitor to the terminal, and a charge from the terminal to the capacitor. A first capacitor having a device, a second capacitor connected in series with the first capacitor, a first switching device capable of outputting the voltage of the first capacitor to the circuit, A second switching element capable of outputting the voltage of the second capacitor to the circuit, and when a DC component current flows through the circuit passing through the other winding of the transformer, the DC component is I'll attenuate Power conversion apparatus characterized by operating the first switching element and second switching element.