Power conversion device that performs power conversion between DC circuit and AC circuit

Patent metadata

Field	Value
Publication number	US-12199524-B2
Application number	US-202017759875-A
Country	US
Kind code	B2
Filing date	Mar 11, 2020
Priority date	Mar 11, 2020
Publication date	Jan 14, 2025
Grant date	Jan 14, 2025

Abstract

A power conversion device includes a plurality of leg circuits and a control device. The control device controls an output voltage at a first converter cell, which is controlled not based on the circulating current, based on a first voltage instruction value. The control device controls an output voltage at a second converter cell using a first value based on a deviation between a circulating current and a circulating current instruction value and a second value based on a deviation between a capacitor voltage and a capacitor voltage instruction value in the second converter cell. When the capacitor voltage at the second converter cell is less than a first threshold, the control device linearly combines an auxiliary voltage instruction value including at least one of a DC component and a fundamental AC component of the AC circuit with the first value and the second value.

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 being configured of two arms connected in series, a connection point between the two arms being connected to a corresponding phase of the AC circuit, opposite ends of the two arms that are connected in series being connected to the DC circuit, each of the arms including a plurality of converter cells each having a capacitor and connected in series to each other; and
a control device to control operations of the plurality of converter cells, each of the plurality of converter cells being a first converter cell controlled not based on a circulating current circulating between the plurality of leg circuits or a second converter cell controlled based on the circulating current,
wherein
the control device
controls output voltages of a plurality of the first converter cells in each of the arms based on a first voltage instruction value generated based on a DC current and a DC voltage of the DC circuit and an AC current and an AC voltage of each of the phases of the AC circuit,
controls output voltages of a plurality of the second converter cells in each of the arms using a first value based on a deviation between the circulating current and a circulating current instruction value and a second value based on a deviation between a voltage at the capacitor and an instruction value of a voltage at the capacitor in the second converter cell, and
linearly combines: an auxiliary voltage instruction value including at least one of a DC component and a fundamental AC component of the AC circuit; the first value; and the second value, and uses a result of the linear combination to control the output voltages of the plurality of the second converter cells, when the voltage at the capacitor in the second converter cell is less than a first threshold.

2. The power conversion device according to claim 1 , wherein the control device sets a sign of the DC component based on a direction of a DC current flowing into the power conversion circuit unit.

3. The power conversion device according to claim 2 , 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
sets a sign of the DC component to positive when a DC current flows from the DC circuit to the high potential-side DC terminal, and
sets a sign of the DC component to negative when a DC current flows from the DC circuit to the low potential-side DC terminal.

4. The power conversion device according to claim 1 , wherein the control device sets a phase of the fundamental AC component based on a phase of an AC current flowing into the power conversion circuit unit.

5. The power conversion device according to claim 4 , wherein the control device sets the phase of the fundamental AC component such that the phase of the fundamental AC component is in same phase with the phase of the AC current flowing into the power conversion circuit unit.

6. The power conversion device according to claim 1 , wherein
the control device
determines whether auxiliary DC power calculated from the DC current flowing into the power conversion circuit unit and a maximum value of the DC component is larger than auxiliary AC power calculated from the AC current flowing into the power conversion circuit unit and a maximum amplitude value of the fundamental AC component,
generates the auxiliary voltage instruction value including the DC component when the auxiliary DC power is larger than the auxiliary AC power, and
generates the auxiliary voltage instruction value including the fundamental AC component when the auxiliary DC power is smaller than the auxiliary AC power.

7. The power conversion device according to claim 1 , wherein the control device changes an effective value of the auxiliary voltage instruction value in a ramp shape.

8. The power conversion device according to claim 1 , wherein the second converter cell is a full-bridge type.

9. The power conversion device according to claim 1 , wherein
a first arm in the two arms includes the plurality of the first converter cells, the plurality of the second converter cells, and a first reactor, and
a second arm in the two arms includes the plurality of the first converter cells and the plurality of the second converter cells.

10. The power conversion device according to claim 9 , wherein the second arm further includes a second reactor.

11. The power conversion device according to claim 2 , wherein the control device sets a phase of the fundamental AC component based on a phase of an AC current flowing into the power conversion circuit unit.

12. The power conversion device according to claim 3 , wherein the control device sets a phase of the fundamental AC component based on a phase of an AC current flowing into the power conversion circuit unit.

13. The power conversion device according to claim 2 , wherein
the control device
determines whether auxiliary DC power calculated from the DC current flowing into the power conversion circuit unit and a maximum value of the DC component is larger than auxiliary AC power calculated from the AC current flowing into the power conversion circuit unit and a maximum amplitude value of the fundamental AC component,
generates the auxiliary voltage instruction value including the DC component when the auxiliary DC power is larger than the auxiliary AC power, and
generates the auxiliary voltage instruction value including the fundamental AC component when the auxiliary DC power is smaller than the auxiliary AC power.

14. The power conversion device according to claim 3 , wherein
the control device
determines whether auxiliary DC power calculated from the DC current flowing into the power conversion circuit unit and a maximum value of the DC component is larger than auxiliary AC power calculated from the AC current flowing into the power conversion circuit unit and a maximum amplitude value of the fundamental AC component,
generates the auxiliary voltage instruction value including the DC component when the auxiliary DC power is larger than the auxiliary AC power, and
generates the auxiliary voltage instruction value including the fundamental AC component when the auxiliary DC power is smaller than the auxiliary AC power.

15. The power conversion device according to claim 4 , wherein
the control device
determines whether auxiliary DC power calculated from the DC current flowing into the power conversion circuit unit and a maximum value of the DC component is larger than auxiliary AC power calculated from the AC current flowing into the power conversion circuit unit and a maximum amplitude value of the fundamental AC component,
generates the auxiliary voltage instruction value including the DC component when the auxiliary DC power is larger than the auxiliary AC power, and
generates the auxiliary voltage instruction value including the fundamental AC component when the auxiliary DC power is smaller than the auxiliary AC power.

16. The power conversion device according to claim 5 , wherein
the control device
determines whether auxiliary DC power calculated from the DC current flowing into the power conversion circuit unit and a maximum value of the DC component is larger than auxiliary AC power calculated from the AC current flowing int

Assignees

• Mitsubishi Electric Corp

Inventors

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

Classifications

• H02M7/4835

  comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage · CPC title

• H02M7/49 Primary

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

• H02M7/4833 Primary

  Capacitor voltage balancing · CPC title