Power conversion device that limits voltage variation among energy storage devices

Patent metadata

Field	Value
Publication number	US-10790764-B2
Application number	US-201816605577-A
Country	US
Kind code	B2
Filing date	May 29, 2018
Priority date	Jun 13, 2017
Publication date	Sep 29, 2020
Grant date	Sep 29, 2020

Abstract

A power conversion device includes an MMC-type power conversion circuit and a central controller. The central controller limits an active power command value and a reactive power command value to a value corresponding to an active power limit value and a value corresponding to a reactive power limit value, respectively, and controls an operation of the power conversion circuit according to the limited active power command value and the limited reactive power command value. The central controller includes: an index value calculation unit configured to calculate an index value that shows an extent of a variation among voltages of energy storage devices included in a plurality of converter cells; and a limiter controller configured to change the active power limit value to a value smaller than the active power limit value when the index value exceeds a threshold value.

First claim

The invention claimed is:

1. A power conversion device comprising:
a power conversion circuit configured to perform power conversion between an AC power system and a DC power system, the power conversion circuit including a plurality of converter cells that are cascade-connected to each other, each of the plurality of converter cells including an energy storage device; and
a central controller configured to:
limit an active power command value and a reactive power command value to a value corresponding to an active power limit value and a value corresponding to a reactive power limit value, respectively; and
control an operation of the power conversion circuit according to the limited active power command value and the limited reactive power command value,

the central controller including:
an index value calculation unit configured to calculate an index value that shows an extent of a variation among voltages of the energy storage devices included in the plurality of converter cells; and
a limiter controller configured to change the active power limit value to a value smaller than the active power limit value when the index value exceeds a threshold value.

2. The power conversion device according to claim 1 , wherein
the power conversion circuit includes, in each phase of the AC power system:
an upper arm circuit connected to a positive-side terminal of the DC power system; and
a lower arm circuit connected to a negative-side terminal of the DC power system, and

each of the upper arm circuit and the lower arm circuit includes the plurality of converter cells that are cascade-connected to each other.

3. The power conversion device according to claim 2 , wherein the index value calculation unit is configured to, in said each phase of the AC power system: calculate a variance of voltages of the energy storage devices in the plurality of converter cells constituting the upper arm circuit, and calculate a variance of voltages of the energy storage devices in the plurality of converter cells constituting the lower arm circuit, and the index value calculation unit is configured to use a maximum value of the calculated variances as the index value.

4. The power conversion device according to claim 2 , wherein
the index value calculation unit is configured to calculate a variance of voltages of the energy storage devices in all of the plurality of converter cells constituting the power conversion circuit, and
the index value calculation unit is configured to use the calculated variance as the index value.

5. The power conversion device according to claim 2 , wherein the index value calculation unit is configured to, in said each phase of the AC power system: calculate an average value of voltages of the energy storage devices in the plurality of converter cells constituting the upper arm circuit, and calculate an average value of voltages of the energy storage devices in the plurality of converter cells constituting the lower arm circuit, and the index value calculation unit is configured to use a variance of the calculated average values as the index value.

6. The power conversion device according to claim 1 , wherein
the limiter controller is configured to set the active power limit value back to an original value when the index value exceeding the threshold value returns to the index value equal to or less than the threshold value, and when a state where the index value is equal to or less than the threshold value continues for a predetermined time period.

7. The power conversion device according to claim 1 , wherein
the central controller operates in operation modes including a first operation mode and a second operation mode,
in the second operation mode, the limiter controller is configured to set the reactive power limit value at a prescribed value, and
in the first operation mode, the limiter controller is configured to set the reactive power limit value at a smaller value among:
a value calculated based on the active power command value; and
the prescribed value.

8. The power conversion device according to claim 7 , wherein
the power conversion device is connected to another power conversion device through the DC power system, and
in the first operation mode, the limiter controller is configured to set the active power limit value as a final value at a smaller value among:
the active power limit value that is set based on the index value; and
an active power limit value that is used in the another power conversion device.

9. The power conversion device according to claim 8 , wherein
in the second operation mode, the limiter controller is configured to set the active power limit value as a final value at a smallest value among:
a value that is calculated based on the reactive power command value;
the active power limit value that is set based on the index value; and
the active power limit value that is used in the another power conversion device.

Assignees

• Mitsubishi Electric Corp

Inventors

• Adachi Tomohiro
• Hario Masahiro
• Imada Noriyuki

Classifications

• 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

• H02M7/797 Primary

  using semiconductor devices only · CPC title

• H02M7/49

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

• H02M7/48

  using discharge tubes with control electrode or semiconductor devices with control electrode · CPC title

• H02J3/36

  Arrangements for transfer of electric power between AC networks via high-voltage DC [HVDC] links; Arrangements for transfer of electric power between generators and networks via HVDC links · CPC title