JP7456972B2 - power converter - Google Patents

Description

Embodiments of the present invention relate to a power conversion device.

Among AC-DC power conversion devices, there are power conversion devices that are connected to a common AC circuit on the AC side and connected to different DC circuits or connected in series on the DC side. When power converters are connected to different DC circuits, it is sometimes desirable to flexibly combine the power converters to obtain a desired DC voltage. In these cases, the DC circuits of the power converter are substantially divided and separated, and power may not be exchanged between the DC circuits.

In such a power conversion device, it is necessary to control the balance between DC voltages of each DC power converter. However, if the current flowing on the AC or DC side is zero or has a very small value, it is difficult to stably control the DC voltage of each power converter to maintain a balance. . Among the controls that maintain the balance of DC voltage, there is control that maintains the DC voltage between multiple power converters, and control that maintains the balance between multiple DC circuits that exist inside each power converter in the case of a multilevel converter. including controls to maintain the

For example, by setting a current command value to force current to flow through an AC circuit or a DC circuit to which the power converter is connected, stable operation of the power converter can be ensured. On the other hand, for example, when the AC circuit is used in a power system, there is a problem in that the power converter causes unnecessary fluctuations in active power and generation of reactive power, causing voltage fluctuations in the power system. .

Patent No. 3923756

The embodiment aims to provide a power conversion device that operates stably without affecting external circuits.

A power conversion device according to an embodiment includes: a plurality of power converters connected between an AC circuit and a DC circuit and performing power conversion between AC power of the AC circuit and DC power of the DC circuit; A plurality of windings provided between an AC circuit and the plurality of power converters, connected so that a circulating current flows within a primary winding connected to the AC circuit, and connected to each of the plurality of power converters. a transformer having a secondary winding; and a control device that generates a gate pulse for controlling the plurality of power converters and supplies the gate pulse to the plurality of power converters. The control device generates a first control amount based on the AC voltage of the AC circuit, the AC current of the AC circuit, and a preset current command value, and controls the DC circuit of each of the plurality of power converters. A second control amount is generated based on the DC voltage average value on the side and a preset DC voltage average command value, and a DC voltage command value is generated based on the first control amount and the second control amount. and generates a third control amount for each of the plurality of power converters based on the DC voltage on the DC circuit side of each of the plurality of power converters and the DC voltage average value, and generates a third control amount for each of the plurality of power converters. When the conditions are met, a fourth control amount is generated for each of the plurality of power converters based on a preset zero-sequence current command value, and the DC voltage command value, the third control amount, and The gate pulse is generated based on the fourth control amount.

In this embodiment, a power conversion device is provided that operates stably without affecting external circuits.

FIG. 1 is a schematic block diagram illustrating a power conversion device according to a first embodiment. FIG. 2 is a schematic block diagram illustrating a part of the power conversion device of the first embodiment. FIG. 2 is a schematic block diagram illustrating a part of the power conversion device of the first embodiment. FIG. 2 is a schematic block diagram illustrating a power conversion device according to a second embodiment. FIG. 2 is a schematic block diagram illustrating a part of a power conversion device according to a second embodiment.

Embodiments of the present invention will be described below with reference to the drawings.
Note that the drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc. are not necessarily the same as those in reality. Furthermore, even when the same part is shown, the dimensions and ratios may be shown differently depending on the drawing.
Note that in the present specification and each figure, the same elements as those described above with respect to the existing figures are denoted by the same reference numerals, and detailed explanations are omitted as appropriate.

(First embodiment)
FIG. 1 is a schematic block diagram illustrating a power conversion device according to an embodiment.
As shown in FIG. 1 , power conversion device 10 is connected to AC circuit 1 via transformer 2 . The AC circuit 1 can include an AC power source, an AC load, an AC power transmission line, and the like. The AC circuit 1 is, for example, an AC power system. The transformer 2 is a transformer whose primary side is Δ-connected, and is, for example, a three-phase transformer. The transformer 2 is not limited to three-phase, but may be multi-phase, as long as it is configured to form a closed circuit so that circulating current flows through the primary side. A plurality of windings are provided on the secondary side of the transformer 2, and the plurality of windings are insulated from each other.

Power conversion device 10 is connected to DC circuit 3 . The DC circuit 3 can include a DC power source, a DC load, a DC power transmission line, and the like. In this example, the power converter 20 is a three-level neutral point clamp type converter, and the DC circuit 3 is provided with a capacitor between the neutral point and the positive and negative terminals. In this example, the DC circuit 3 includes multiple DC loads. The plurality of power converters 20 are each connected to a plurality of DC loads on their respective DC sides. In the following description, it is assumed that these DC loads are electrically insulated or connected to each other through high resistance, and cannot exchange DC power with each other. Although the DC voltage values output by the power converter 20 are the same in this example, they are not limited to the same, and may be different values.

Power converter 10 includes a plurality of power converters 20 and a control device 50. The AC sides of the plurality of power converters 20 are connected to the plurality of secondary windings of the transformer 2, respectively. The DC sides of the plurality of power converters 20 are connected to the DC circuit 3. In this example, the number of the plurality of power converters 20 corresponds to the number of DC circuits 3, and more than nine power converters 20 are provided. Note that the number of power converters 20 is not limited to this example, and may be two or more.

Control device 50 is connected to multiple power converters 20. The control device 50 controls the phase voltage v1 of the AC circuit 1, the line current i1 of the AC circuit 1, the AC current i2 flowing on the AC side of the plurality of power converters 20, and the DC voltage V3 on the DC side of the plurality of power converters 20. The respective detected values are inputted, a gate pulse GP for operating the plurality of power converters 20 is generated, and the gate pulse GP is supplied to each of the plurality of power converters 20.

In the figure, the phase voltage v1 and line current i1 represent the voltage and current of each phase, and when the AC circuit 1 is a three-phase AC, the detected values of the phase voltage and line current for the three phases are It is input to the control device 50. In addition, the AC current i2 and the DC voltage V3 are respective detection values of the plurality of power converters 20, and in the case of 10 power converters 20, the detection values of the AC current i2 and the DC voltage V3 of 10 sets. is input to the control device 50.

FIG. 2 is a schematic block diagram illustrating a part of the power conversion device of this embodiment.
FIG. 2 shows a main circuit portion of the power converter 20. As shown in FIG.
As shown in FIG. 2, in this example, the power converter 20 has a three-level neutral point clamp type converter circuit as its main circuit. Power converter 20 includes switching elements 22a to 22h and diodes 24a to 24d. The switching elements 22a to 22h are self-extinguishing semiconductor elements such as IGBTs (Insulated Gate Bipolar Transistors) and MOSFETs (Metal-Oxide-Semiconductor Field Effect Transistors), and have diodes connected in antiparallel. Power converter 20 includes terminals 21a and 21b on the AC side and terminals 21c, 21d, and 21e on the DC side. A secondary winding of the transformer 2 is connected to the terminals 21a and 21b. A capacitor is connected to the terminals 21c and 21d, and a capacitor is also connected to the terminals 21d and 21e. These capacitors are circuit elements forming the DC circuit 3 in this example.

Switching elements 22a and 22b are connected in series at a connection node n1. Switching elements 22c and 22d are connected in series at a connection node n2. Switching elements 22e and 22f are connected in series at a connection node n3. The switching elements 22g and 22h are connected in series at a connection node n4. A series connection circuit of switching elements 22a, 22b, switching elements 22c, 22d, switching elements 22e, 22f, and switching elements 22g, 22h is called an arm.

The arm made up of switching elements 22a and 22b is connected in series with the arm made up of switching elements 22c and 22d. Connection nodes of the arms formed by the switching elements 22a and 22b and the arms formed by the switching elements 22c and 22d are connected to the AC side terminal 21a.

Diodes 24a and 24b connected in series are connected between connection nodes n1 and n2. A connection node of the series connection circuit of diodes 24a and 24b is connected to a terminal 21d, which is a neutral point on the DC side.

The arm made up of switching elements 22e and 22f is connected in series with the arm made up of switching elements 22g and 22h. Connection nodes of the arms formed by the switching elements 22e and 22f and the arms formed by the switching elements 22g and 22h are connected to the AC side terminal 21b.

Diodes 24c and 24d connected in series are connected between connection nodes n3 and n4. A connection node of the series connection circuit of the diodes 24c and 24d is connected to the terminal 21d.

The series circuit of switching elements 22a to 22d and the series circuit of switching elements 22e to 22h are connected in parallel between DC side terminals 21c and 21e. The arm formed by switching elements 22a and 22b, the arm formed by switching elements 22c and 22d, the arm formed by switching elements 22e and 22f, and the arm formed by switching elements 22g and 22h connect AC side terminals 21a and 21b and DC side terminals 21c and 21e. It is a full bridge circuit with This full bridge circuit is clamped to the potential of terminal 21d by diodes 24a to 24cd. The potential of the terminal 21d is the neutral point.

Power converter 20 is connected to the secondary winding of transformer 2 via terminals 21a and 21b. Power converter 20 is connected to DC circuit 3 via terminals 21c to 21e. A capacitor is connected between the terminals 21c and 21d, and a capacitor is also connected between the terminals 21d and 21e. As shown in FIG. 1, the neutral point terminals 21d of the plurality of power converters 20 may not be connected to each other or may be connected to each other. When connected to each other, the terminal 21d may be grounded, for example, to the earth.

FIG. 3 is a schematic block diagram illustrating a part of the power conversion device of this embodiment.
FIG. 3 shows a detailed configuration example of the control device 50 of the power conversion device 10 shown in FIG. 1.
As shown in FIG. 3, the control device 50 includes a dq converter 51, a current controller 53, an average value calculator 54, a DC voltage controller 55, an inverse dq converter 61, and a gate pulse generator 62. , a DC voltage balance control section 64 , a zero-phase current controller 65 , and a neutral point potential control section 66 .

The dq converter 51, the current controller 53, the average value calculator 54, and the DC voltage controller 55 are commonly used by the plurality of power converters 20. The inverse dq conversion section 61, the gate pulse generation section 62, the DC voltage balance control section 64, the zero-phase current controller 65, and the neutral point potential control section 66 are provided for each of the plurality of power converters 20. . That is, the output of the current controller 53 is added to the outputs of the DC voltage balance controller 64 and the zero-phase current controller 65 for each power converter 20, and is input to the inverse dq converter 61.

The detected value of the phase voltage v1 and the detected value of the line current i1 of the AC circuit 1 are input to the dq converter 51 by the voltage detector 4 and the current detector 5. The dq conversion unit 51 performs dq conversion on the input detected value of the phase voltage v1 and the detected value of the line current i1, and outputs a d-axis component and a q-axis component.

The current controller 53 inputs the current command value output from the current command value calculation circuit 52 and the output value of the dq converter 51, and sets a control amount (the first value) so that the output of the dq converter 51 follows the current command value. 1 control amount). The current command value calculation circuit 52 may output a current command value given from the outside, or calculates and outputs a current command value based on the given power command value. Although not shown, the dq converter 51 outputs a d-axis output value corresponding to the active current and a q-axis output value corresponding to the reactive current. Therefore, two sets of current controller 53 and current command value calculation circuit 52 are provided to correspond to the d-axis output and the q-axis output.

The average value calculation unit 54 receives the detected value of the DC voltage V3 output from each of the plurality of power converters 20. The average value calculation unit 54 calculates and outputs the average value of the plurality of input DC voltages V3. If n power converters 20 are provided and the DC voltages output by the n power converters 20 are V1, V2, ..., Vn, then the DC voltage average value Vave output by the average value calculation unit 54 is as follows. It is calculated as (V1+V2+...+Vn)/n.

The DC voltage controller 55 inputs the DC voltage average value Vave calculated by the average value calculation unit 54, and sets a control amount (second voltage value) so that the DC voltage average value Vave follows a preset DC voltage command value V3*. 2 control amount) is generated and output. The control amount output by the DC voltage controller 55 is added to the control amount output by the current controller 53 and supplied to the inverse dq converter 61 for each power converter 20.

The DC voltage average value Vave is input to the DC voltage balance control section 64 . The detected value of the DC voltage Vi (i=1 to n) detected by the voltage detector 7 provided on the DC circuit side of each power converter 20 is input to the DC voltage balance control section 64. That is, the DC voltage Vi output from the i-th power converter 20 is input to the DC voltage balance control section 64 provided corresponding to the i-th power converter 20. The DC voltage balance control unit 64 generates and outputs a control amount (third control amount) so that the detected value of the DC voltage Vi follows the DC voltage average value Vave. The output control amount is added to the control amount output by the current controller 53.

The zero-sequence current controller 65 includes a detected value of the phase voltage v1 by the voltage detector 4 provided in the AC circuit 1 and a detected value of the alternating current i2 by the current detector 6 provided on the AC side of the power converter 20. is input. In this example, the zero-phase current controller 65 has a DC voltage balance detection function. The DC voltage balance detection function receives the detected value of the DC voltage Vi by the voltage detector 7 provided on the DC side of the power converter 20, and detects the detected value of the DC voltage Vi as a preset DC voltage balance threshold. When the value exceeds the zero-phase current controller 65, a zero-phase current command value is supplied to the zero-phase current controller 65. In other words, the zero-sequence current controller 65 controls the control amount (fourth control amount) is generated and output, and when the detected values of DC voltage Vi of all power converters 20 are lower than the DC voltage balance threshold, control according to the zero-sequence current command value is not output.

Whether the zero-phase current controller 65 generates and outputs a control amount corresponding to the zero-phase current command value is not limited to the above, and the detection value of the AC current i2 detected by the AC side current detector 5 may be used. For example, the zero-phase current controller 65 has an AC current detection function, and generates and outputs a control amount corresponding to the zero-phase current command value when the detection value of the AC current i2 falls below an AC current threshold value preset in the AC current detection function. The zero-phase current controller 65 does not output a control amount corresponding to the zero-phase current command value when the detection value of the AC current i2 is greater than the AC current threshold value.

The inverse dq converter 61 is provided for each power converter 20, and adds the control amount output from the DC voltage balance controller 64 and the zero-phase current controller 65 to the control amount output from the current controller 53. Add and input. The inverse dq conversion unit 61 performs inverse dq conversion on the added value of these control amounts to generate and output a voltage command value.

The neutral point potential control unit 66 inputs the output of the inverse dq conversion unit 61 and the detected value of the AC current i2 on the AC side of the power converter 20, and determines the neutral point of the DC side of each power converter 20. A control amount for neutral point potential control to maintain the potential of the terminal 21d is generated and output. The control amount output from the neutral point potential control section 66 is added to the voltage command value output from the inverse dq conversion section 61.

The gate pulse generation section 62 has a triangular wave oscillator having a phase according to the i-th power converter 20. The gate pulse generation unit 62 compares the triangular wave generated by the triangular wave oscillator with the voltage command value generated by the inverse dq conversion unit 61 and the neutral point potential control unit 66, thereby generating the i-th power converter 20. Generates and outputs a gate pulse according to the

In the above example, the DC voltage V3 of each power converter 20 is assumed to be the same, but if the DC voltage setting value of each power converter 20 is different, the value of each DC voltage is set to the DC voltage command value V3*. It is necessary to normalize and use it. For simplicity, a case of three power converters 20 will be described.

If the DC voltage setting values of the three power converters 20 are 100V, 200V, and 300V, and the DC voltage command value V3* is 200V, the power converters whose DC voltage settings are 100V, 200V, and 300V The 20 normalization constants are "2", "1", and "2/3", respectively.

The DC voltage detected by the voltage detector 6 of each power converter 20 is multiplied by a normalization constant and input to the average value calculation unit 54, DC voltage balance control unit 64, and zero-phase current controller 65. . This allows the control device 50 to perform DC voltage balance control and operate the DC voltage balance detection function of the zero-phase current controller 65, as described above.

Although the DC voltage command value V3* is an average value of the set values of each DC voltage, it goes without saying that it can be set to any value. Furthermore, the present invention is not limited to the above, and the DC voltage detected by the voltage detector 6 may be input as is, and a value obtained by dividing the DC voltage average value Vave by a normalization constant may be used for each power converter 20. In this case, the DC voltage command value V3* is the average value of the DC voltage settings of each power converter 20.

The operation and effects of the power conversion device 10 of this embodiment will be explained.
In the power conversion device 10 of this embodiment, the control amounts corresponding to the d-axis and the q-axis, which are generated and output by the dq conversion unit 51, the current controller 53, the average value calculation unit 54, and the DC voltage controller 55, are It is output as a current command value for all n power converters 20. Then, in the power converter 10, a control amount corresponding to each power converter 20 is generated and output by a DC voltage balance control section 64 and a zero-sequence current controller 65 provided corresponding to each power converter 20. and is added to the control amounts for all power converters 20 to correct and output the current command value.

In normal operation, the zero-sequence current controller 65 does not output a control amount according to the zero-sequence current command value. Therefore, since no unnecessary zero-sequence current is caused to flow on the AC side of each power converter 20, performance such as conversion efficiency of the power converter 10 itself can be improved.

In the zero-phase current controller 65, when the DC voltage V3 outputted by any of the power converters 20 is out of balance with the DC voltage outputted by the other power converters 20, the control device 50 controls the power conversion. It is determined that the input or output current for the operation of the transformer 20 is insufficient and it is difficult to maintain stable control, and the transformer 2 operates to flow zero-sequence current as a circulating current to the primary side of the transformer 2. .

Thus, in this embodiment, the transformer 2 whose primary winding is Δ-connected is used between each power converter 20 and the AC circuit 1. Thereby, when the zero-sequence current controller 65 of the control device 50 outputs the zero-sequence current command value, the zero-sequence current can be caused to flow in the Δ connection of the transformer 2 as a circulating current. The zero-sequence current flowing in the Δ connection does not flow out from the Δ connection or flow into the Δ connection, so operation continues without affecting the AC circuit 1 even while the zero-sequence current is flowing. can do.

The zero-phase current controller 65 compares the detected value of the DC voltage Vi of the i-th power converter 20 and compares it with the DC voltage balance threshold, so that the detected value of the DC voltage Vi meets the DC voltage balance threshold. When the zero-phase current command value is greater than or equal to the zero-phase current command value, a control amount corresponding to the zero-phase current command value can be output. Therefore, it is possible to determine whether or not the current required for control is insufficient for each power converter 20, and the control amount according to the zero-sequence current command value is reliably output to realize stable control. be able to.

In the power conversion device 10 of the present embodiment, the alternating current i2 of the alternating current circuit 1 may be detected as a condition for the zero-phase current controller 65 to output a control output instead of the above. By appropriately setting the alternating current threshold for the zero-sequence current controller 65 to output a control output, stable control operation can be reliably achieved.

(Second embodiment)
FIG. 4 is a schematic block diagram illustrating the power conversion device according to this embodiment.
In this embodiment, the plurality of power converters 220 are connected in series on the DC side. The plurality of power converters 220 are two-level full bridge circuits, unlike in the other embodiments described above. Regarding the full bridge circuit, although not shown, two series circuits of switching elements are connected in parallel, and a capacitor is connected in parallel to the series circuit of switching elements. The AC circuit 1 is connected to a connection node of a series circuit of switching elements. A DC circuit 203 is connected to both ends of the capacitor. The voltage across the capacitor is a DC voltage V3.

In this embodiment, the configuration of the control device 250 is different from that of the other embodiments described above because the power converter 220 is of a two-level full bridge type. If the components are the same as those in the other embodiments described above, the same reference numerals are given, and detailed explanations will be omitted as appropriate. Note that the main circuit of the power converter may be a half-bridge circuit instead of the full-bridge circuit. As in the case of the other embodiments described above, it is of course possible to use a neutral point clamp type three-level converter.

As shown in FIG. 4, the power conversion device 210 of this embodiment includes a plurality of power converters 220 and a control device 250.
The plurality of power converters 220 are connected in series through a DC circuit 203. The plurality of power converters 220 are each connected to the secondary winding of the transformer 2. When n power converters 220 are set to the same DC voltage V3, the DC voltage that the power converter 210 supplies to the DC circuit 203 and is supplied from the DC circuit 203 is n×V3. Note that the DC voltages on the DC circuit 203 side of each power converter 220 may be the same value as described above, or may be different values.

The control device 250 includes a detected value of the phase voltage v1 of the AC circuit 1, a detected value of the line current i1 of the AC circuit 1, a detected value of the AC current i2 of the plurality of power converters 220, and a detected value of the DC current of the plurality of power converters 220. The detected value of the DC voltage V3 on the side is input. Control device 250 generates gate pulse GP based on v1, i1, i2, and V3, and supplies it to multiple power converters 220.

In this embodiment, as in the other embodiments described above, the transformer 2 is Δ-connected on the AC circuit 1 side, and a plurality of Power converter 220 circulates a zero-sequence current within the Δ connection of transformer 2, and can continue to operate stably even when the load current flowing through power converter 220 is small.

FIG. 5 is a schematic block diagram illustrating a part of the power conversion device of this embodiment.
FIG. 5 shows the configuration of a control device 250 included in the power conversion device 210 of this embodiment. In FIG. 5, detection of each of the phase voltage v1, line current i1, alternating current i2, and direct current voltage V3 input to the control device 250 is shown, and although the block on the power converter 220 side is not shown, the above-mentioned This is similar to FIG. 3 for other embodiments.

This embodiment differs from the other embodiments described above in that the power converter 220 has a two-level full-bridge circuit configuration, and therefore is not provided with a block that performs neutral point potential control. In other respects, the control device 250 has the same configuration as the control device 50 in the first embodiment. That is, the control device 250 includes a dq converter 51, a current controller 53, an average value calculator 54, a DC voltage controller 55, an inverse dq converter 61, a gate pulse generator 62, and a DC voltage balancer 55. It includes a control section 64 and a zero-phase current controller 65.

The dq conversion unit 51, the current controller 53, the average value calculation unit 54, and the DC voltage controller 55 are commonly used in the plurality of power converters 220, and the inverse dQ conversion unit 61, the gate pulse generation unit 62, and the DC voltage balance A control unit 64 and a zero-phase current controller 65 are provided for each of the plurality of power converters 220. That is, the output of the current controller 53 is added to the outputs of the DC voltage balance controller 64 and the zero-phase current controller 65 for each power converter 20, and is input to the inverse dq converter 61.

In the control device 250 of the power converter 220 of this embodiment, the control amount generated and output by the DC voltage balance control section 64 is added to the control amount output from the inverse dq conversion section 61. Further, the control amount generated and output by the zero-phase current controller 65 is also added to the control amount output by the inverse dq conversion section 61.

As a result, the gains set in the DC voltage balance control section 64 and the zero-phase current controller 65 are appropriately adjusted. Note that the configuration of the control device 50 may be the same as that of the first embodiment. Also in the case of the first embodiment, the outputs of the DC voltage balance control section 64 and the zero-phase current controller 65 of the control device 50 are subjected to inverse dq conversion instead of the control amount output from the current controller 53. It may be added to the control amount output from the section 61.

The DC voltage balance control unit 64 generates and outputs a control amount so that the detected value of the input DC voltage V3 follows the DC voltage average value Vave supplied from the average value calculation unit 54.

The zero-sequence current controller 65 controls a control amount to follow the zero-sequence current command value when the DC voltage V3 of the target power converter 220 is out of balance with the DC voltage of other power converters. Generate and output.

In this way, in the power conversion device 210 of this embodiment, the zero-sequence current controller 65 can cause a zero-sequence current to flow in the Δ connection of the transformer 2. Therefore, even if the external circuit causes the current flowing through the power converter 220 to have no load or a small value, the power converter 210 can be stably operated.

In each embodiment, the circuit configuration of the power converter may be a three-level neutral point clamp type, or a two-level full bridge type or half bridge type. Further, even in the case of a three-level neutral point clamp type, the circuit type is not limited to the above-mentioned general circuit type, and various improved types may be used. In addition to including a DC voltage balance control section 64 and a zero-sequence current controller 65, the control device has an appropriate configuration selected depending on the circuit configuration of the power converter.

In this way, it is possible to realize a power conversion device that operates stably without affecting external circuits.

Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention, as well as within the scope of the claimed invention and its equivalents. Further, each of the embodiments described above can be implemented in combination with each other.

1 AC circuit, 2 Transformer, 3 DC circuit, 10,210 Power converter, 20,220 Power converter, 50,250 Control device, 51 dq converter, 53 Current controller, 54 Average value calculation unit, 55 DC Voltage controller, 61 Inverse dq conversion unit, 62 Gate pulse generation unit, 64 DC voltage balance control unit, 65 Zero-sequence current controller, 66 Neutral point potential control unit

Claims (6)

a plurality of power converters that are connected between an AC circuit and a DC circuit and perform power conversion between AC power of the AC circuit and DC power of the DC circuit;
provided between the AC circuit and the plurality of power converters, connected so that a circulating current flows within a primary winding connected to the AC circuit, and connected to each of the plurality of power converters. a transformer having multiple secondary windings;
a control device that generates a gate pulse for controlling the plurality of power converters and supplies the gate pulse to the plurality of power converters;
Equipped with
The control device includes:
Generating a first control amount based on the AC voltage of the AC circuit, the AC current of the AC circuit, and a preset current command value;
generating a second control amount based on a DC voltage average value on the DC circuit side of each of the plurality of power converters and a preset DC voltage average command value;
generating a DC voltage command value based on the first control amount and the second control amount;
generating a third control amount for each of the plurality of power converters based on the DC voltage on the side of the DC circuit of each of the plurality of power converters and the DC voltage average value;
When a predetermined condition is satisfied, a fourth control amount is generated for each of the plurality of power converters based on a preset zero-sequence current command value,
A power conversion device that generates the gate pulse based on the DC voltage command value, the third control amount, and the fourth control amount. The power conversion device according to claim 1, wherein the predetermined condition is a case where a DC voltage on the DC circuit side of each of the plurality of power converters exceeds a preset threshold. 3. The power converter device according to claim 1, wherein the predetermined condition is a case where a current on the AC circuit side of the plurality of power converters is lower than a preset threshold. The power converter device according to claim 1, wherein the DC circuit sides of the plurality of power converters are insulated from each other. The power converter device according to claim 1, wherein the DC circuit sides of the plurality of power converters are connected in series. When the DC voltage setting value of one power converter is different from the DC voltage setting value of the other power converter among the DC voltage setting values of the plurality of power converters,
The control device according to any one of claims 1 to 5, wherein the set value of the DC voltage of the one power converter is normalized by a preset constant to generate the third control amount. power converter.

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