Power conversion device for converting power between a DC circuit and an AC circuit by performing a non-linear operation

Patent metadata

Field	Value
Publication number	US-10205402-B2
Application number	US-201515759151-A
Country	US
Kind code	B2
Filing date	Sep 17, 2015
Priority date	Sep 17, 2015
Publication date	Feb 12, 2019
Grant date	Feb 12, 2019

Abstract

In a control device of a power conversion device, an AC control portion generates a first voltage command value representing an AC voltage component to be output from a plurality of chopper cells of each leg circuit. A DC control portion generates a second voltage command value representing a DC voltage component to be output from the plurality of chopper cells of each leg circuit. A circulating current control portion generates a third voltage command value to be output from the plurality of chopper cells of each leg circuit in order to suppress a circulating current. The circulating current control portion performs a non-linear operation with the first, second, and third voltage command values. The plurality of chopper cells of each leg circuit operate in accordance with a result of the non-linear operation.

First claim

The invention claimed is:

1. A power conversion device which converts power between a DC circuit and an AC circuit, the power conversion device comprising:
a plurality of leg circuits which correspond to respective phases of the AC circuit and are connected in parallel between common first and second DC terminals, each leg circuit including:
a plurality of converter cells cascaded to one another and each including an energy storage; and
at least one inductor connected in series to the plurality of converter cells; and

a control device which controls operations of the plurality of converter cells,
the control device including:
an AC control portion which generates a first voltage command value representing an AC voltage component to be output from the plurality of converter cells for each leg circuit based on an AC current and an AC voltage of the AC circuit;
a DC control portion which generates a second voltage command value representing a DC voltage component to be output from the plurality of converter cells for each leg circuit based on a DC current and a DC voltage of the DC circuit; and
a circulating current control portion which generates a third voltage command value representing a voltage to be output from the plurality of converter cells in order to suppress a circulating current for each leg circuit based on the circulating current which circulates through each leg circuit,

the circulating current control portion performing a non-linear operation with the first, second, and third voltage command values,
the plurality of converter cells of each leg circuit operating in accordance with a result of the non-linear operation.

2. The power conversion device according to claim 1 , wherein:
each leg circuit is divided into a first arm on a high potential side and a second arm on a low potential side with a connection portion electrically connected to a corresponding phase of the AC circuit being interposed;
the circulating current control portion generates a second value by multiplying a first value by a value calculated by adding a fixed value to the third voltage command value, the first value being obtained by subtracting the first voltage command value from the second voltage command value;
the plurality of converter cells constituting the first arm operate in accordance with the second value;
the circulating current control portion generates a fourth value by multiplying a third value by a value calculated by adding a fixed value to the third voltage command value, the third value being obtained by adding the first voltage command value to the second voltage command value; and
the plurality of converter cells constituting the second arm operate in accordance with the fourth value.

3. The power conversion device according to claim 2 , wherein:
the energy storage is a capacitor;
the control device further includes a first capacitor voltage control portion which generates a first voltage correction value based on a difference between a representative value of a capacitor voltage of the plurality of converter cells constituting the first arm and a command value of the capacitor voltage through feedback control to decrease the difference;
the circulating current control portion generates the second value with the first value corrected by linear combination with the first voltage correction value;
the control device further includes a second capacitor voltage control portion which generates a second voltage correction value based on a difference between a representative value of a capacitor voltage of the plurality of converter cells constituting the second arm and a command value of the capacitor voltage through feedback control to decrease the difference; and
the circulating current control portion generates the fourth value using the third value corrected by linear combination with the second voltage correction value.

4. The power conversion device according to claim 3 , wherein:
the first capacitor voltage control portion generates the first voltage correction value by multiplying the difference between the representative value of the capacitor voltage of the plurality of converter cells constituting the first arm and the command value of the capacitor voltage by a DC current value of the DC circuit or a polarity of the DC current value; and
the second capacitor voltage control portion generates the second voltage correction value by multiplying the difference between the representative value of the capacitor voltage of the plurality of converter cells constituting the second arm and the command value of the capacitor voltage by the DC current value of the DC circuit or the polarity of the DC current value.

5. The power conversion device according to claim 3 , wherein:
the first capacitor voltage control portion generates the first voltage correction value by multiplying the difference between the representative value of the capacitor voltage of the plurality of converter cells constituting the first arm and the command value of the capacitor voltage by an AC current value of the AC circuit or a polarity of the AC current value; and
the second capacitor voltage control portion generates the second voltage correction value by multiplying the difference between the representative value of the capacitor voltage of the plurality of converter cells constituting the second arm and the command value of the capacitor voltage by an AC current value obtained by inverting a polarity of the AC current value of the AC circuit or a polarity reverse to the polarity of the AC current value.

6. The power conversion device according to claim 1 , wherein:
each leg circuit is divided into a first arm on a high potential side and a second arm on a low potential side with a connection portion electrically connected to a corresponding phase of the AC circuit being interposed;
the circulating current control portion generates a second value by adding a first value to a value calculated by applying a non-linear transfer function to the third voltage command value, the first value being obtained by subtracting the first voltage command value from the second voltage command value;
the plurality of converter cells constituting the first arm operate in accordance with the second value;
the circulating current control portion generates a fourth value by adding a third value to a value calculated by applying a non-linear transfer function to the third voltage command value, the third value being obtained by adding the first voltage command value to the second voltage command value;
the plurality of converter cells constituting the second arm operate in accordance with the fourth value; and
the non-linear transfer function is configured such that a ratio of an output to an input increases when the input exceeds a threshold value.

7. The power conversion device according to claim 1 , wherein:
each leg circuit is divided into a first arm on a high potential side and a second arm on a low potential side with a connection portion electrically connected to a corresponding phase of the AC circuit being interposed;
the circulating current control portion generates a second value by adding a first value to a value obtained by applying a non-linear mathematical function to the third voltage command value, the first value being obtained by subtracting the first voltage command value from the second voltage command value;
the plurality of converter cells constituting the first arm operate in accordance with the second value;
the circulating current control portion generates a fourth value by adding a third value to a value obtained by applying a non-linear mathematical function to the third voltage command value, the third value being obtained by adding the first voltage com

Assignees

• Mitsubishi Electric Corp

Inventors

• Fujii Toshiyuki
• Jimichi Takushi
• Uda Ryosuke

Classifications

• H02M7/5387

  in a bridge configuration · CPC title

• H02M7/483 Primary

  Converters with outputs that each can have more than two voltages levels · CPC title

• 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

• H02M1/12 Primary

  Arrangements for reducing harmonics from AC input or output · CPC title

• H02M7/4833

  Capacitor voltage balancing · CPC title