Power conversion device

Patent metadata

Field	Value
Publication number	US-12057787-B2
Application number	US-202017793697-A
Country	US
Kind code	B2
Filing date	Mar 11, 2020
Priority date	Mar 11, 2020
Publication date	Aug 6, 2024
Grant date	Aug 6, 2024

Abstract

A power conversion device includes a power conversion circuit unit including a plurality of leg circuits, and a control device. Each of the leg circuits includes a plurality of first converter cells each having a capacitor and connected in series to each other and a plurality of second converter cells each having the capacitor and connected in series to each other. The plurality of first converter cells are controlled not based on a circulating current circulating between the plurality of leg circuits, and the plurality of second converter cells are controlled based on the circulating current. The control device stops a switching operation of at least one second converter cell in the plurality of second converter cells when a voltage at the capacitor in the second converter cell becomes less than a first threshold.

First claim

The invention claimed is:

1. A power conversion device that performs power conversion between a DC circuit and an AC circuit, the power conversion device comprising:
a power conversion circuit unit including a plurality of leg circuits corresponding to a plurality of phases of the AC circuit, each of the leg circuits including a plurality of first converter cells each having a capacitor and connected in series to each other and a plurality of second converter cells each having a capacitor and connected in series to each other; and
a control device to control operations of the plurality of first converter cells and the plurality of second converter cells,
wherein
the plurality of first converter cells are controlled not based on a circulating current circulating between the plurality of leg circuits, and the plurality of second converter cells are controlled based on the circulating current,
the control device controls at least one second converter cell in the plurality of second converter cells in a first mode or a second mode when a voltage at a capacitor in the second converter cell becomes less than a first threshold,
the first mode is a mode for stopping a switching operation of a converter cell, and
the second mode is a mode in which the converter cell is caused to perform the switching operation such that a change in an output voltage of the converter cell in the second mode becomes identical to a change in an output voltage of the converter cell in the first mode.

2. The power conversion device according to claim 1 , wherein the control device stops the switching operation of the plurality of second converter cells in the first mode, or stops the switching operation of the second converter cell including the capacitor when the voltage at the capacitor becomes less than the first threshold.

3. The power conversion device according to claim 1 , wherein the control device controls the plurality of first converter cells so as to increase an amplitude value of an AC current output from the power conversion circuit unit during the first mode or the second mode.

4. The power conversion device according to claim 3 , wherein while maintaining total power of drive power for driving an auxiliary machine including the control device and active power output from the power conversion circuit unit, the control device controls the plurality of first converter cells to change the active power so as to increase the amplitude value of the AC current.

5. The power conversion device according to claim 3 , wherein while maintaining total power of first reactive power output from the power conversion circuit unit and second reactive power output from a reactive power compensation device provided in parallel with the power conversion device, the control device controls the plurality of first converter cells to change the second reactive power so as to increase the amplitude value of the AC current.

6. The power conversion device according to claim 1 , wherein the control device controls the plurality of first converter cells so as to increase an absolute value of a DC current output from the power conversion circuit unit during the first mode or the second mode.

7. The power conversion device according to claim 6 , wherein
the plurality of leg circuits are connected in parallel to each other between a high potential-side DC terminal and a low potential-side DC terminal, and
the control device controls the plurality of first converter cells to increase the absolute value of the DC current while changing a direction of the DC current such that a difference between a time average value of first DC power output from the power conversion circuit unit to the DC circuit when a DC current flows from the DC circuit to the high potential-side DC terminal and a time average value of second DC power output from the power conversion circuit unit to the DC circuit when the DC current flows from the DC circuit to the low potential-side DC terminal becomes desired DC power.

8. The power conversion device according to claim 1 , wherein the control device controls the plurality of first converter cells such that a circulating voltage for increasing the circulating current is output from the plurality of first converter cells in the first mode or the second mode.

9. The power conversion device according to claim 8 , wherein the circulating voltage does not include a fundamental frequency component and a DC component of the AC circuit.

10. The power conversion device according to claim 1 , wherein the control device changes a transformation ratio of a transformer provided between the AC circuit and the power conversion circuit unit so as to increase an amplitude value of an AC current output from the power conversion circuit unit during the first mode or the second mode.

11. The power conversion device according to claim 1 , wherein when voltages at all the capacitors in the plurality of second converter cells become equal to or greater than a second threshold during the first mode or the second mode, the control device restarts control to cause the plurality of second converter cells to perform the switching operation based on the circulating current.

12. The power conversion device according to claim 11 , wherein
the control device sets an output voltage at a cell group including the plurality of second converter cells to an initial value of a voltage instruction value for the cell group at a time point of restarting the switching operation when the switching operation of the second converter cell is restarted, and
the control device changes the voltage instruction value in a ramp shape from the initial value.

13. The power conversion device according to claim 11 , wherein the second threshold is larger than the first threshold.

14. The power conversion device according to claim 2 , wherein the control device controls the plurality of first converter cells so as to increase an amplitude value of an AC current output from the power conversion circuit unit during the first mode or the second mode.

15. The power conversion device according to claim 2 , wherein the control device controls the plurality of first converter cells so as to increase an absolute value of a DC current output from the power conversion circuit unit during the first mode or the second mode.

16. The power conversion device according to claim 2 , wherein the control device controls the plurality of first converter cells such that a circulating voltage for increasing the circulating current is output from the plurality of first converter cells in the first mode or the second mode.

17. The power conversion device according to claim 2 , wherein the control device changes a transformation ratio of a transformer provided between the AC circuit and the power conversion circuit unit so as to increase an amplitude value of an AC current output from the power conversion circuit unit during the first mode or the second mode.

18. The power conversion device according to claim 2 , wherein when voltages at all the capacitors in the plurality of second converter cells become equal to or greater than a second threshold during the first mode or the second mode, the control device restarts control to cause the plurality of second converter cells to perform the switching operation based on the circulating current.

19. The power conversion device according to claim 3 , wherein when voltages at all the capacitors in the plurality of second converter cells become equal to or greater than a second threshold during the first mod

Assignees

• Mitsubishi Electric Corp

Inventors

• KAJIYAMA Takuya
• Fujii Toshiyuki
• Fujiwara Shuhei
• Uda Ryosuke
• Kono Yoshiyuki

Classifications

• H02M7/217

  using semiconductor devices only · CPC title

• H02M1/0009

  Devices or circuits for detecting current in a converter · CPC title

• H02M1/0025

  Arrangements for modifying reference values, feedback values or error values in the control loop of a converter · CPC title

• H02M7/4833

  Capacitor voltage balancing · CPC title

• H02M7/49 Primary

  Combination of the output voltage waveforms of a plurality of converters · CPC title