JP2013123330A - Electric power conversion system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized electric power conversion system capable of outputting voltage and current waveforms with small harmonic components without a harmonic suppression filter.SOLUTION: A phase unit 13 is constituted of: a switching unit 12P including a leg constituted of switching elements SuP and SxP and diodes D1 and D2 and a capacitor C1; and a switching unit 12N including a leg constituted of switching elements SuN and SxN and diodes D3 and D4 and a capacitor C2. A junction point between the switching units 12P and 12N is connected to an output terminal 10. A series circuit of two power sources Vs1 and Vs2 is connected in parallel to a series circuit of the switching units 12P and 12N. A junction point between the power sources Vs1 and Vs2 is connected to a ground point. A control section 20 controls ON/OFF of the switching elements SuP, SxP, SuN and SxN such that integrated values of charging/discharging currents of the capacitors C1 and C2 become zero throughout one cycle of an AC power source voltage.

Description

  The present invention relates to a power converter that converts power from direct current to alternating current or from alternating current to direct current.

  Conventionally, a three-phase two-level converter and a three-phase two-level inverter as shown in FIG. 14 have been applied to converters that convert AC in the power system into DC and inverters that convert DC into AC and drive the motor. It was. For example, a three-phase two-level inverter is configured with six semiconductor switching elements that are the minimum necessary for configuring a power conversion device that outputs three-phase alternating current from direct current, and thus can be reduced in size and cost.

  The output voltage waveform of the three-phase two-level inverter is such that, when the input DC voltage is Vdc, the binary switching between + Vdc / 2 and -Vdc / 2 is performed by PWM (pulse width modulation) for each phase. It is a pseudo AC waveform. In order to reduce switching harmonics, high-voltage motor drive inverters that use high-voltage switching elements and power system-connected inverters that convert direct-current power, such as long-distance submarine cables, to AC A filter composed of a reactor and a capacitor is inserted into the phase AC output. In such a power conversion device, the filter capacity is increased in order to reduce the harmonic component flowing out to the power system to a level that does not adversely affect other devices, leading to an increase in cost and weight.

  Further, in the circuit system disclosed in the literature, as shown in FIG. 15, a power converter that can be directly connected to the power system and distribution system voltage without voltage step-down by a transformer generally used conventionally. R & D is also underway. This power converter operates as, for example, a CVCF (constant voltage constant frequency) inverter.

  When this is put to practical use, transformers that are large in weight and volume and relatively costly to the entire system are not required, and the output voltage / current waveform approaches a sine wave due to multi-leveling. You can also enjoy the benefits that are no longer needed.

2009 cigre Papers Paper 401 (Multilevel Voltage-Sourced Converters for HVDC and FACTS Applications: Siemens AG

  However, in such a circuit system, in order to constantly control the voltage value of the DC capacitor, which is a component of each switching unit, it is necessary in principle to constantly flow a reflux current that circulates the DC power supply. Since the three phases are connected to the same DC power source, if the DC voltage composite value of each phase is slightly different, there is a risk that an excessive short circuit current flows between the phases and the device is destroyed. In order to prevent this, a buffer reactor is inserted in each phase to limit the short-circuit current. Such a buffer reactor increases the size and cost of the apparatus.

  The embodiment provides a small-sized power conversion device that can output a voltage-current waveform with a small harmonic component without a harmonic suppression filter and does not require a high-cost, large-sized reactor such as a buffer reactor. Objective.

  The power conversion device according to the embodiment is a power conversion device that converts power from direct current to alternating current or from alternating current to direct current, a leg in which two switching elements having self-extinguishing capability are connected in series, and a parallel connection to the leg When the constituent element including the capacitor is a switching unit, the phase unit in which two or more unit arms in which the switching units are connected in series are connected in series and the switching elements constituting the phase unit are controlled. A control unit, the uppermost end of the phase unit is connected to the positive side of the DC power supply, the lowermost end is connected to the negative side of the DC power supply, and the interconnection point of the series-connected unit arms serves as an AC terminal to the AC power supply. A power conversion device to be connected, wherein the control unit switches a period for each positive and negative half wave of the AC power supply voltage to constitute a negative unit arm. After all the switching elements of the knit are turned off, the period for controlling on / off of the switching elements of the switching unit constituting the positive unit arm and all the switching elements of the switching unit constituting the positive unit arm are turned off. The state is divided into a period for controlling on / off of the switching element of the switching unit constituting the negative unit arm, the control is switched in each divided period, and through one cycle of the AC power supply voltage, The switching timing of the control is set in one cycle of the AC power supply voltage so that the integrated value of the charge / discharge current of the capacitor of the switching unit becomes zero, and the on / off of the switching element is controlled.

It is a figure which shows the structure of 1st Embodiment of a power converter device. It is a figure which shows the structure of the power converter device with which the phase unit 13 was comprised by the series circuit of two switching units 12P and 12N. It is a figure which shows operation | movement in the case of functioning the power converter device of FIG. 2 as a CVCF inverter. It is a figure which shows the optimal switching phase angle (theta) chg with respect to modulation factor (alpha). It is a figure which shows the timing of control mode switching. It is a figure which shows the structure of 2nd Embodiment of a power converter device. It is a figure which shows the modification of 2nd Embodiment. It is a figure which shows the structure of 3rd Embodiment of a power converter device. It is a figure which shows the structure of 4th Embodiment of a power converter device. It is a figure which shows the optimal switching phase angle (theta) chg with respect to the modulation factor (alpha) in 4th Embodiment. It is a figure which shows the timing of the control mode switch in 4th Embodiment. It is a figure which shows operation | movement of 4th Embodiment. It is a figure which shows operation | movement of 5th Embodiment. It is a figure which shows the structure of the conventional 3 phase 2 level converter and 3 phase 2 level inverter. It is a figure which shows the structure of the conventional power converter device.

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

  FIG. 1 is a diagram illustrating a configuration of a first embodiment of a power converter. The power conversion device according to the first embodiment converts, for example, single-phase 50 Hz AC power into DC power via an insulating transformer, or converts DC power into single-phase 50 Hz AC power and outputs it via an insulating transformer. . AC / DC conversion and DC / AC conversion can be changed depending on the control method of the power converter. The same applies to this embodiment and other embodiments described later.

  The power converter shown in FIG. 1 is a chopper bridge unit converter in which a capacitor C1 is connected in parallel to a leg 11 in which a circuit in which a switching element Q1 having a self-extinguishing capability and a diode D1 are connected in antiparallel is connected in series. Is configured as a switching unit 12. The phase unit 13 is configured by connecting 2 × N switching units in series. In the example of FIG. 1, an example of N = 2 is shown, and two phase units 13 of U phase and V phase are connected in parallel and connected to the DC side.

  The control operation of the first embodiment will be described with reference to FIGS. In the power conversion device of FIG. 2, the phase unit 13 is configured by a series circuit of two switching units 12P and 12N. The switching unit 12P includes a leg composed of switching elements SuP and SxP and diodes D1 and D2, and a capacitor C1 connected in parallel to the leg. The switching unit 12N includes a leg composed of switching elements SuN and SxN, diodes D3 and D4, and a capacitor C2 connected in parallel to the leg. The connection point of the switching units 12P and 12N is connected to the output terminal 10.

  The phase unit 13 is connected in parallel with a series circuit of two power sources Vs1, Vs2. The output voltages of the two power sources Vs1 and Vs2 are Vdc, and the connection point between the power sources Vs1 and Vs2 is connected to the ground point. The control unit 20 generates a gate command for the switching elements constituting the switching units 12P and 12N based on the comparison between the triangular wave from the triangular wave generation unit 21 and the voltage command value.

  Let the neutral point of the DC power source be a voltage-referenced ground point (terminal 11), and let the voltage at the AC output terminal 10 seen from the ground point be Vu. The positive and negative voltages of the DC power supply are Vdc, the capacitor voltage of the switching unit is Vc, the output voltage of the switching unit 12P connected to the positive power supply is VuP, and the output voltage of the switching unit 12N connected to the negative power supply is VuN. And

  FIG. 3 shows the operation when the power conversion device of FIG. 2 is made to function as a CVCF inverter, the vertical axis shows the magnitude of voltage, current or power, and the horizontal axis shows the cycle of AC output.

  The operation of outputting a single-phase 50 Hz alternating current as an alternating current output voltage in the circuit of FIG. 2 includes the following two operation modes, mode M1 and mode M2.

  (1) Mode M1: The negative side switching unit 12N is gate-blocked, that is, the gates of the switching elements SuN and SxN are both turned off, and the output voltage VuP of the positive side switching unit 12P is controlled as follows.

VuP = Vdc−VuRef
(VuRef: AC voltage command to be output)
At this time, the output voltage Vu is output as follows.

Vu = Vdc−VuP = Vdc− (Vdc−VuRef) = VuRef
FIG. 3A shows the output voltage Vu and the output current Iu. In FIG. 3A, the magnitude of 10 on the vertical axis corresponds to the power supply voltage Vdc, the mode 1 is a mode during periods T2, T4, and T6, and the voltage VuP corresponds to the upper shaded portion. In this mode M1, the switching elements SuP and SxP of the switching unit 12P perform switching based on the gate command from the control unit 20, as shown in the upper diagram of FIG. 3B, and the output voltage VuP is generated. . The mode switching timing will be described later.

  (2) Mode M2: The positive side switching unit 12P is gate-blocked and the output voltage VuN of the negative side switching unit 12N is controlled as follows.

VuN = Vdc + VuRef
(VuRef: AC voltage command to be output)
At this time, the output voltage Vu is output as follows.

Vu = −Vdc + VuN = −Vdc + (Vdc + VuRef)
= VuRef
In FIG. 3A, mode 2 is a mode during periods T1, T3, and T5, and voltage VuN corresponds to the lower shaded portion. In this mode M2, the switching elements SuN and SxN of the switching unit 12N perform switching based on the gate command from the control unit 20, as shown in the lower diagram of FIG. 3B, and the output voltage VuN is generated.

  FIG. 3C shows the voltage VuP between the output terminals of the switching unit 12P (thick solid line) and the voltage VuN between the output terminals of the switching unit 12N (thick dotted line). The magnitudes of the voltages VuP and VuN shown in FIG. 3C are the same as the voltages VuP and VuN in the shaded area in FIG. The control unit 20 generates a gate command for the switching units 12P and 12N based on the comparison between the voltage command value as shown in FIG. 3C and the triangular wave generated by the triangular wave generator 21.

  FIG. 3D shows the input / output current IuP (solid line) of the switching unit 12P and the input / output current IuN (dotted line) of the switching unit 12N. FIG. 3E shows the charge / discharge power PowerP (solid line) of the capacitor C1 and the charge / discharge power PowerN (dotted line) of the capacitor C2, where the positive characteristic indicates the charge power and the negative characteristic indicates the discharge power.

  In the mode M1, since the negative side switching unit 12N is stopped in the gate block state, the AC load current Iu always flows through the positive side switching unit 12P. For example, during the period T2, if the switching element SuP is on and SxP is off, current is output from the output terminal 10 via the power source Vs1, the diode D1, and the capacitor C1. In the period T2, if the switching element SuP is off and SxP is on, the current is output from the output terminal 10 via the power source Vs1 and the switching element SxP.

  Further, during the period T4 or T6, if the switching element SuP is on and SxP is off, current flows from the output terminal 10 (load) into the power source Vs1 via the capacitor C1 and the switching element SuP. In the period T4 or T6, if the switching element SuP is off and SxP is on, current flows from the output terminal 10 (load) to the power source Vs1 via the diode D2.

  At this time, the capacitor C1 of the positive switching unit 12P is charged / discharged by the electric power PowerP expressed by the following equation.

PowerP = VuP × Iu = (Vdc−VuRef) × Iu
When VuRef and Iu are operated in the same phase, that is, with a power factor of 1, for example, when operated with only the switching unit 12P, the average value of PowerP (charge / discharge power of the capacitor C1) in one AC cycle is negative. . That is, if the output voltage control is performed only by the operation of the mode M1, the capacitor voltage average value of the positive side switching unit 12P cannot be kept constant, and the operation cannot be continued.

  Similarly, when the output voltage control is performed only by the operation of the mode M2, that is, when only the switching unit 12N is operated, the power N when operating at the power factor of 1 has a positive average value in one AC cycle. Thus, the capacitor voltage average value cannot be kept constant, and the operation cannot be continued.

  In the present embodiment, in order to solve this problem, as already shown in FIG. 3 (b), the operation mode of the mode M1 is performed for each positive half wave and negative half wave of one cycle of AC 50 Hz. And the operation mode of mode M2 is switched. Further, when the operation mode switching timing (phase angle) is fixed, the charging / discharging power of the capacitor of the switching unit is negative (in accordance with the increase (or decrease) of the amplitude command modulation factor (hereinafter, modulation factor α) ( Move to the plus side). The modulation rate α indicates the amplitude ratio between the input DC voltage and the output AC voltage. When the modulation rate is “1”, the amplitudes of the input DC voltage Vdc and the output AC voltage Vu are the same.

  Therefore, in the present embodiment, an optimum switching phase angle θchg as shown in FIG. 4 is previously obtained by calculation according to the modulation rate α of the output voltage with respect to the phase θ of the AC voltage (AC voltage command). The switching phase angle θchg is set to a smaller value as the modulation rate is larger. Based on the switching phase angle θchg, mode switching is performed as shown in FIG.

  Mode switching is performed as follows.

1) Mode M2 when θ <θchg
2) Mode M1 when θchg <θ <π−θchg
3) Mode M2 when π−θchg <θ <π
4) Mode M1 when π <θ <π + θchg
5) When π + θchg <θ <2π−θchg, mode M2
6) Mode M1 when 2π−θchg <θ <2π
The relationship between the modulation factor α and the switching phase angle θ can be expressed as follows. That is, when the U-phase voltage Vu and the U-phase current Iu are expressed as follows:
Vu = Vdc × (1 + α · sin θ)
Iu = I × sin θ
Θ is determined so as to satisfy the following equation.

  FIG. 4 shows the relationship between α and θ satisfying this.

  3 and 5 both show a case where 0.8 is commanded as the modulation rate and the operation is performed with the corresponding switching phase angle θchg set to 36 ° as shown by the dotted line in FIG. .

  With the above configuration, a voltage current waveform with a low harmonic level can be applied without a harmonic suppression filter, and the average value of the capacitor voltage of the switching unit can be controlled to be constant without flowing a DC circulating current. become. Therefore, it is not necessary to use a high-cost and large-sized reactor such as a buffer reactor, and it becomes possible to provide a small-sized power conversion device.

The switching between the mode M1 and the mode M2 has been described as being instantaneous. However, immediately after one of the switching units is controlled to the gate block, the current continues to flow through the unit due to the inductance component of the circuit. The switching unit may be short-circuited and overcurrent may flow. In this case, such an overcurrent can be prevented by providing a dead time for gate-blocking the two units together.
Next, a second embodiment will be described. FIG. 6 is a diagram illustrating a configuration of the second embodiment of the power conversion device.

  This power converter is a converter that inputs three-phase alternating current (R-phase, S-phase, T-phase), which is common in a power system, to converters (1) to (3) via a transformer Tr1 and converts it into direct current Indicates. The primary side of the transformer Tr1 is a three-phase star connection or a delta connection, the secondary side is divided into a total of six lines of single phase × 3, and the power conversion device shown in FIG. 1 is provided as a converter for each phase. The output terminals of the converters (1) to (3) are connected in parallel to each other and then connected to a DC power supply (capacitor C3).

  By using this configuration, the same effect as in the first embodiment can be obtained even in power conversion from three-phase alternating current to direct current.

  Further, the same control as in the above embodiment is applied to the control of each phase of the circuit as shown in FIG. 7 in which the buffer reactor is removed from the circuit of the conventional DC / 3-phase AC converter as shown in FIG. Also good.

  Next, a third embodiment will be described. FIG. 8 is a diagram showing the configuration of the third embodiment of the power converter.

  This power conversion device converts three-phase alternating current (R-phase, S-phase, T-phase) common in the power system to the converters (1) to (3) via the transformer Tr2 as in the second embodiment. The converter which inputs and converts into direct current is shown. The primary side of the transformer Tr2 is a three-phase star connection or a delta connection, the secondary side is divided into a total of six lines of single phase × 3, and the power conversion device shown in FIG. 1 is provided as a converter for each phase. The output terminals of the converters (1) to (3) are connected in series with each other and then connected to a DC power supply (capacitor C4).

  Next, a fourth embodiment will be described. FIG. 9 is a diagram illustrating a configuration of a fourth embodiment of the power conversion device.

  The power conversion device according to the fourth embodiment is a converter that converts a single-phase 50 Hz power source into direct current through an insulating transformer.

  The U-phase unit has 2 × N pieces of chopper bridge unit converters, each of which has two legs connected in series with a self-extinguishing capability and a capacitor connected in parallel. The phase unit which connected the switching unit 12 in series is comprised. In the example of FIG. 9, an example of N = 2 is shown.

  The V-phase unit has the same configuration as a conventional two-level inverter in which two legs Sv and Sy in which two switching elements having a self-extinguishing capability are connected in series are connected in series. Two phase units of U phase and V phase are connected in parallel and then connected to a DC power supply (capacitor C5).

  The operation of each U-phase switching unit is basically the same as in the first embodiment, but the mode switching timing phase θchg is different from that in the first embodiment due to the different V-phase configuration. It is operated by a function that can be shown by the graph of FIG.

  The V-phase switching operation is a so-called one-pulse operation, and switching is performed according to the following conditional branch.

(1) When VuRef> 0, upper element Sv on, lower element Sy off (2) When VuRef <0, upper element Sv off, lower element Sy on FIG. 11 and FIG. 8 is commanded, and as shown by the dotted line in FIG. 10, the corresponding switching phase angle θchg is set to 51 ° to operate.

  Even with the above configuration, a voltage current waveform having a low harmonic level can be output without using a harmonic suppression filter, and the capacitor voltage of the switching unit can be output without flowing a DC circulating current, as in the first embodiment. It becomes possible to control the average value of. As a result, it is not necessary to use a high-cost and large-sized reactor such as a buffer reactor, and it is possible to provide a small-sized power converter, and further, there are fewer components (switching elements and diodes) than the configuration of FIG. Etc.) can be realized.

  Next, a fifth embodiment will be described with reference to FIGS. The power conversion device according to the fifth embodiment is a power converter (converter) that converts a three-phase 50 Hz power source into direct current through an insulating transformer.

  As shown in FIG. 7, a switching unit 12 is a 2 × N chopper bridge unit converter having one leg connected in series with two switching elements having self-extinguishing capability and a capacitor connected in parallel. The phase unit 14 in which the switching units are connected in series is configured. The three phase units 14 of U phase, V phase, and W phase are connected in parallel at the DC section and then connected to the DC side.

  A control operation in the fifth embodiment will be described. For simplicity, the case where the phase unit is composed of two switching units 12P and 12N as in FIG. 2 will be described.

  Let the neutral point of the DC power supply be the ground point and use the voltage as a reference, and let the voltage at the AC output point viewed from the ground point be Vu. The positive and negative voltages of the DC power supply are Vdc, the capacitor voltage of the switching unit is Vc, the output voltage of the switching unit connected to the positive side of the power supply is VuP, and the output voltage of the switching unit connected to the negative side of the power supply is VuN. .

  To output a single-phase 50 Hz alternating current as an alternating current output voltage in the circuit of FIG. 2, there are the following three operation modes.

  (1) Mode M1: The negative side switching unit 12N is gate-blocked and the output voltage VuP of the positive side switching unit 12P is controlled as follows.

Positive side switching unit VuP = Vdc−VuRef
(VuRef is the AC voltage command you want to output)
At this time, the output voltage Vu is output as follows.

Vu = Vdc−VuP = Vdc− (Vdc−VuRef) = VuRef
(2) Mode M2: The positive side switching unit 12P is gate-blocked and the output voltage VuN of the negative side switching unit 12N is controlled as follows.

Negative switching unit VuN = Vdc + VuRef
(VuRef is the AC voltage command you want to output)
At this time, the output voltage Vu is output as follows.

Vu = −Vdc + VuN = −Vdc + (Vdc + VuRef) = VuRef
(3) Mode M3: The output voltages VuP and VuN of the positive side switching unit 12P and the negative side switching unit 12N are controlled as follows.

Positive side switching unit VuP = Vdc−VuRef
Negative switching unit VuN = Vdc + VuRef
(VuRef is the AC voltage command you want to output)
At this time, the output voltage Vu is output as follows.

Vu = −Vdc + VuN = −Vdc + (Vdc + VuRef) = VuRef
= Vdc-VuP = Vdc- (Vdc-VuRef) = VuRef
In this mode M3, since both the positive and negative switching units perform the switching operation, a path for allowing a direct current to flow from the DC power source through both the positive switching unit and the negative switching unit is established. Using this path, when the capacitor voltage of the switching unit decreases, the current Icharge flows in the charging direction, and when the voltage increases, the current Icharge flows in the discharging direction, thereby making the average value of the capacitor voltage constant. I can keep it.

  In the operation mode M1, since the negative side switching unit is stopped by the gate block, the AC load current Iu always passes through the positive side switching unit.

  At this time, the capacitor of the positive side switching unit is charged / discharged by electric power PowerP expressed by the following equation.

PowerP = VuP × Iu = (Vdc−VuRef) × Iu
When calculating for the case where VuRef and Iu are operating in the same phase, that is, a power factor of 1, the average value of PowerP in one AC cycle is negative. That is, when the output voltage control is performed only in the operation mode M1, the capacitor voltage average value of the positive side switching unit cannot be kept constant, and the operation cannot be continued.

  Similarly, when the output voltage control is performed only in the operation mode M2, PowerN with a power factor of 1 has a positive average value in one AC cycle, and the capacitor voltage average value cannot be kept constant. The operation cannot be continued.

  Therefore, in the present embodiment, in order to solve this problem, as shown in the graphs of FIGS. 13A and 13B, the operation mode for each positive half-wave and negative half-wave of AC 50 Hz is as described above. In addition to M1 and operation mode M2, operation mode M3 is inserted and switched. The mode is switched for the phase θ synchronized with the power supply AC.

1) Mode M3 when 0 <θ <π / 6
2) Mode M1 when π / 6 <θ <π−π / 6
3) Mode M3 when π-π / 6 <θ <π + π / 6
4) Mode M2 when π + π / 6 <θ <2π−π / 6
5) Mode M3 when 2π−π / 6 <θ <2π
Since the mode M3 forms a current path that connects the positive and negative of the DC power supply, if the U phase, V phase, and W phase are operated simultaneously in the mode M3, a short circuit path is formed between the phases, and overcurrent protection operation and overcurrent Although element destruction due to current occurs, the timing of switching to mode M3 is shifted between the U phase, V phase, and W phase by switching the mode every π / 6 as described above, so that a short circuit path is formed between the phases. Can be prevented.

  The currents IuP and IuN that flow through the positive unit 12P and the negative unit 12N are controlled to values represented by the following equations.

1) When 0 <θ <π / 6,
IuP = Iu-Icharge
IuN = Icharge
2) When π / 6 <θ <π−π / 6,
IuP = Iu
IuN = 0
3) -1 When π-π / 6 <θ <π,
IuP = Iu-Icharge
IuN = Icharge
3) -2 When π <θ <π + π / 6,
IuP = -Icharge
IuN = Iu + Icharge
4) When π + π / 6 <θ <2π−π / 6 IuP = 0
IuN = Iu
5) Mode M3 when 2π−π / 6 <θ <2π
IuP = -Icharge
IuN = Iu + Icharge
With the above configuration, it is possible to output a low-harmonic voltage current waveform without a harmonic suppression filter, and to control the average value of the capacitor voltage of the switching unit to a constant level without passing a DC circulating current. Thus, it is possible to provide a small power converter without the need for a high-cost and large-sized reactor such as a buffer reactor.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 11 ... Leg, 12 ... Switching unit, 13 ... Phase unit, Vs1, Vs2 ... DC power supply, Q1, SuP, SxP, SuN, SxN ... Switching element, Tr1, Tr2 ... Transformer, C1-C3 ... Capacitor, D1-D4 ... diode.

Claims (11)

A component including a leg in which two switching elements having a self-extinguishing capability are connected in series and a capacitor connected in parallel to the leg is configured as a switching unit,
A phase unit in which two or more unit arms in which one or more of the switching units are connected in series are connected in series;
A control unit for controlling each switching element constituting the phase unit,
A power conversion device in which the uppermost end of the phase unit is connected to the positive side of the DC power supply, the lowermost end is connected to the negative side of the DC power supply, and the interconnection point of the series-connected unit arms is connected to the AC power supply as an AC terminal. There,
The controller is
During the period of each positive and negative half wave of the AC power supply voltage, all switching elements of the switching unit that constitutes the negative unit arm are turned off, and then the switching elements of the switching unit that constitutes the positive unit arm are controlled on / off. And the period to
The switching elements of the switching units constituting the positive unit arm are all turned off and then divided into periods for controlling on / off of the switching elements of the switching units constituting the negative unit arm. Switch control in each period,
The switching timing of the control is set in one cycle of the AC power supply voltage so that the integrated value of the charge / discharge current of the capacitor of the switching unit becomes zero throughout the cycle of the AC power supply voltage, and the switching element is turned on / off. The power converter device characterized by controlling.   The power converter according to claim 1, wherein a transformer that divides the three-phase alternating current output from the phase unit into three single-phase alternating currents is connected to the alternating-current side of the plurality of phase units.   The power converter according to claim 1, wherein six of the phase units are connected in parallel. The phase unit includes a phase bridge in which two units are connected in parallel;
A series connection circuit in which the DC sides of the three phase bridges are connected in series;
The power converter according to claim 1 or 2, wherein a transformer for dividing a three-phase alternating current into three single-phase alternating currents is connected to the alternating current side of the series connection circuit.   Six of the phase units are connected in parallel to a DC power source, and the AC terminal is connected to the single-phase AC side of a transformer that divides the three-phase AC into three single-phase ACs. The power conversion device according to claim 1, wherein conversion is performed. Two phase units connected in parallel are configured as a phase bridge, three phase bridges are connected in series, and both ends of the series circuit are connected to a DC power source,
The AC terminal of each phase bridge is connected to the single-phase AC of the transformer that divides the 3-phase AC into three single-phase AC, so that power conversion between DC and 3-phase AC can be performed. The power conversion device according to claim 1. A component including a leg in which two switching elements having a self-extinguishing capability are connected in series and a capacitor connected in parallel to the leg is configured as a switching unit,
A first phase unit having two or more unit arms connected in series with one or more switching units connected in series and having an interconnection point as an AC terminal;
A second phase unit including at least two switching elements connected in series between positive and negative terminals of a DC power source, and having a connection point of the at least two switching elements as an AC terminal;
A control unit that controls each switching element constituting the first and second phase units, wherein one of the single-phase AC power supplies is connected to the AC terminal of the first phase unit, and the other is the second phase. A power converter connected to the AC terminal of the unit,
The controller is
The switching element constituting the second phase unit is operated in a one-pulse operation that is turned on and off once per cycle in synchronization with the positive and negative of the AC power supply voltage,
With respect to the switching elements constituting the first phase unit, the positive and negative half-wave periods of the AC power supply voltage are set to the positive state after all switching elements of the switching units constituting the negative unit arm are turned off. A period for controlling on / off of the switching element of the switching unit constituting the side unit arm;
The switching elements of the switching units constituting the positive unit arm are all turned off and then divided into periods for controlling on / off of the switching elements of the switching units constituting the negative unit arm. Switch control in each period,
The switching timing of the control is set in one cycle of the AC power supply voltage so that the integrated value of the charge / discharge current of the capacitor of the switching unit becomes zero throughout one cycle of the AC power supply voltage, and the switching element is turned on / off. The power converter characterized by controlling.   The power converter according to claim 7, wherein three sets of the first and second phase units are connected in parallel to perform power conversion between direct current and three-phase alternating current.   The power converter according to claim 7, wherein three sets of parallel circuits of the first and second phase units are connected in series to perform power conversion between direct current and three-phase alternating current. A component including a leg in which two switching elements having a self-extinguishing capability are connected in series and a capacitor connected in parallel to the leg is configured as a switching unit.
At least two units connected in series between a first phase unit having two or more unit arms connected in series with one or more switching units connected in series and having an interconnection point as an AC terminal, and a positive / negative terminal of a DC power supply A second phase unit including a switching element and having the connection point of the at least two switching elements as an AC terminal; and a control unit that controls each switching element constituting the first and second phase units; One of the single-phase AC power supplies is a power converter connected to the AC terminal of the first phase unit, and the other is connected to the AC terminal of the second phase unit,
The controller is
The switching elements constituting the second phase unit are operated in a one-pulse operation that is turned on and off once per cycle in synchronization with the positive and negative of the AC power supply voltage,
With respect to the switching elements constituting the first phase unit, the switching elements of the switching unit constituting the negative unit arm are all turned off in accordance with the positive / negative of the AC power supply voltage, and then the positive unit arm A period for controlling on / off of the switching element of the switching unit constituting
The switching elements of the switching units constituting the positive unit arm are all turned off and then divided into periods for controlling on / off of the switching elements of the switching units constituting the negative unit arm. Switch control in each period,
The switching timing of the control is set in a half cycle of the AC power supply voltage so that the integrated value of the charging / discharging current of the capacitor of the switching unit becomes zero through one cycle of the AC power supply voltage. A power converter characterized by controlling on / off. A component including a leg in which two switching elements having a self-extinguishing capability are connected in series and a capacitor connected in parallel to the leg is configured as a switching unit.
A phase unit in which two or more unit arms in which one or more of the switching units are connected in series are connected in series;
A control unit for controlling each switching element constituting the phase unit,
A power conversion device in which the uppermost end of the phase unit is connected to the positive side of the DC power supply, the lowermost end is connected to the negative side of the DC power supply, and the interconnection point of the series-connected unit arms is connected to the AC power supply as an AC terminal. There,
The controller is
During the period of each positive and negative half wave of the AC power supply voltage, all switching elements of the switching unit that constitutes the negative unit arm are turned off, and then the switching elements of the switching unit that constitutes the positive unit arm are controlled on / off. And the period to
A period for controlling on / off of the switching elements of the switching unit constituting the negative unit arm, after all the switching elements of the switching unit constituting the positive unit arm are turned off,
Control is performed in one cycle of the AC power supply voltage by dividing the switching unit that constitutes the positive unit arm and the switching element of the switching unit that constitutes the negative unit arm into a period during which the on / off operation is performed. Switch operation,
During the period in which both the unit unit constituting the positive unit arm and the switching element of the switching unit constituting the negative unit arm are turned on / off, the voltage of the capacitor constituting the switching unit is averaged. A power converter that controls a current from a DC power supply so as to be constant.

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