Power conversion device

Patent metadata

Field	Value
Publication number	US-2025274054-A1
Application number	US-202218858380-A
Country	US
Kind code	A1
Filing date	May 6, 2022
Priority date	May 6, 2022
Publication date	Aug 28, 2025
Grant date	—

Abstract

A power conversion device includes: a power converter which includes a plurality of arms for each phase of an alternating-current system; and a control device. Each arm, among the plurality of arms, has a plurality of converter cells that are cascade-connected. The plurality of converter cells each have a plurality of switching elements, and a power storage element. The control device includes: a balance control unit to control a balance of voltages of power storage elements between predetermined groups, based on a balance command value; a circulating-current control unit to control a circulating current circulating through the power converter, based on a circulating-current command value; and an oscillation control unit to cause the balance command value to oscillate at a first frequency lower than a fundamental frequency of the alternating-current system, based on the voltages of the power storage elements included in the arm.

First claim

1 . A power conversion device connected to an alternating-current system, the power conversion device comprising:
a power converter which includes a plurality of arms for each phase of the alternating-current system; and a control device to control the power converter, wherein each arm, among the plurality of arms, has a plurality of converter cells that are cascade-connected, the plurality of converter cells each have a plurality of switching elements, and a power storage element connected to the plurality of switching elements, and the control device includes: processing circuitry
to control a balance of voltages of power storage elements between predetermined groups, based on a balance command value;
to control a circulating current circulating through the power converter, based on a circulating-current command value; and
to cause the balance command value to oscillate at a first frequency lower than a fundamental frequency of the alternating-current system, based on the voltages of the power storage elements included in the arm.

2 . The power conversion device according to claim 1 , wherein
the processing circuitry generates the circulating-current command value for balancing the voltages of the power storage elements between the predetermined groups.

3 . The power conversion device according to claim 1 , wherein
the processing circuitry
extracts a maximum voltage value and a minimum voltage value of the power storage elements included in the arm, and
performs an oscillating control that superimposes an oscillating component of the first frequency onto the balance command value, based on a first difference between the maximum voltage value and the minimum voltage value.

4 . The power conversion device according to claim 3 , wherein
when the first difference is greater than or equal to a first threshold, the processing circuitry starts the oscillating control.

5 . The power conversion device according to claim 4 , wherein
after the oscillating control is started, when the first difference is less than or equal to a second threshold less than the first threshold, the processing circuitry stops the oscillating control.

6 . The power conversion device according to claim 1 , wherein
the processing circuity
extracts a maximum voltage value and a minimum voltage value of the power storage elements included in the arm, and
performs an oscillating control that superimposes an oscillating component of the first frequency onto the balance command value, based on a second difference between a minimum value of the maximum voltage values during a first period and a maximum value of the minimum voltage values during the first period.

7 . The power conversion device according to claim 6 , wherein
when the second difference is greater than or equal to a third threshold, the processing circuitry starts the oscillating control.

8 . The power conversion device according to claim 7 , wherein
a rate of change in the minimum value and the maximum value is restricted by a rate-of-change limiter, the second difference is a value obtained by subtracting the maximum value, whose rate of change is restricted, from the minimum value whose rate of change is restricted.

9 . The power conversion device according to claim 7 8 , wherein
after the oscillating control is started, when the second difference is less than or equal to a fourth threshold less than the third threshold, the processing circuitry stops the oscillating control.

10 . The power conversion device according to claim 6 , wherein
the first period is greater than or equal to a fundamental period of the alternating-current system.

11 . The power conversion device according to claim 1 , wherein
when an amplitude of a fundamental frequency component of an average voltage value of the power storage elements included in the arm is less than or equal to a fifth threshold, the processing circuitry starts an oscillating control that superimposes an oscillating component of the first frequency onto the balance command value.

12 . The power conversion device according to claim 11 , wherein
when the fundamental frequency component is greater than or equal to a sixth threshold greater than the fifth threshold, the processing circuitry stops the oscillating control.

13 . The power conversion device according to claim 11 , wherein
when the fundamental frequency component is greater than or equal to the fifth threshold, the processing circuitry intermittently performs the oscillating control.

14 . The power conversion device according to claim 1 , wherein
the plurality of arms include a positive-side arm and a negative-side arm, and the balance command value includes a first average voltage value of the power storage elements included in the power converter and a second average voltage value of the power storage elements included in the positive-side arm, wherein the processing circuitry
causes the average voltage value of the power storage elements included in a phase to follow the first average voltage value to control the balance of the voltages of the power storage elements between phases;
causes the average voltage value of the power storage elements included in the negative-side arm to follow the second average voltage value to control the balance of the voltages of the power storage elements between the plurality of arms; and
adds up a result of operation for controlling the balance of the voltages of the power storage elements between the phases and a result of operation for controlling the balance of the voltages of the power storage elements between the plurality of arm to generate the circulating-current command value.

15 . The power conversion device according to claim 14 , wherein
the processing circuitry superimposes the oscillating component of the first frequency onto one of the first average voltage value and the second average voltage value.

16 . A power conversion device connected to an alternating-current system, the power conversion device comprising:
a power converter which includes a plurality of arms for each phase of the alternating-current system; and a control device to control the power converter, wherein each arm, among the plurality of arms, has a plurality of converter cells that are cascade-connected, the plurality of converter cells each have a plurality of switching elements, and a power storage element connected to the plurality of switching elements, wherein the control device performs an oscillating control that causes a balance command value to oscillate, depending on a balance of power storage elements within the arm, the balance command value being a value for use in a balance control of voltages of the power storage elements between predetermined groups, and when a variation in the voltages of the power storage elements within the arm falls within a set range, the control device stops the oscillating control.

17 . The power conversion device according to claim 16 , wherein
when the variation in the voltages of the power storage elements within the arm falls within the set range, the control device stops the oscillating control to stop the oscillating control before the power storage elements within a same arm provides a same voltage.

18 . The power conversion device according to claim 16 , wherein
the variation in the voltages of the power storage elements within the arm is a difference between a maximum voltage value and a minimum voltage value of the power storage elements included in the arm.

Assignees

• Mitsubishi Electric Corp

Inventors

• KAJIYAMA Takuya
• Uda Ryosuke
• Tanaka Miwako
• Nakayama Akito

Classifications

• H02M7/4833

  Capacitor voltage balancing · CPC title

• H02M1/0025

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

• H02M1/32

  Means for protecting converters other than automatic disconnection · CPC title

• H02M7/4835 Primary

  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

• H02M1/007

  Plural converter units in cascade (push-pull DC/DC converters with pre-regulator H02M3/3374; DC-AC converters following a DC-DC stage including a high frequency transformer H02M7/4807; DC-AC converters following a DC-DC conversion stage generating periodically varying voltages H02M7/4826) · CPC title