Power conversion device

Patent metadata

Field	Value
Publication number	US-9960709-B2
Application number	US-201615549330-A
Country	US
Kind code	B2
Filing date	Mar 7, 2016
Priority date	Mar 17, 2015
Publication date	May 1, 2018
Grant date	May 1, 2018

Abstract

A power conversion device includes: a positive arm and a negative arm each of which is formed by connecting a plurality of converter cells in series, the converter cells each being composed of a plurality of semiconductor switching elements and a DC capacitor; and a control circuit. An arm balance control unit in the control circuit calculates a first voltage adjustment value for balancing voltage of the DC capacitors in the positive arm and voltage of the DC capacitors in the negative arm. The control circuit adjusts an AC control command using the first voltage adjustment value, thereby calculating an AC voltage command for AC voltage to be outputted to an AC line for each phase.

First claim

The invention claimed is:

1. A power conversion device comprising:
a power converter for performing power conversion between three-phase AC and DC, the power converter including a plurality of leg circuits each having a positive arm and a negative arm which are connected in series and are connected to an AC line for each phase, the plurality of leg circuits being connected in parallel between positive and negative DC buses; and
a control device for controlling the power converter, wherein
each of the positive arm and the negative arm of each leg circuit includes a converter cell composed of: a series unit including a plurality of semiconductor switching elements connected in series to each other; and a DC capacitor connected in parallel to the series unit,
the control device includes a voltage command generation unit for generating a positive arm voltage command for the positive arm and a negative arm voltage command for the negative arm, and performs output control of each converter cell in the positive arm and the negative arm by PWM control,
the voltage command generation unit includes:
an AC current control unit for calculating an AC control command for controlling an AC current component flowing through the AC line for each phase;
an arm balance control unit for, on the basis of positive capacitor voltage which is voltage of the DC capacitor in the positive arm and negative capacitor voltage which is voltage of the DC capacitor in the negative arm, calculating a first voltage adjustment value for balancing the positive capacitor voltage and the negative capacitor voltage;
an AC-side command calculation unit for outputting an AC voltage command for AC voltage to be outputted to the AC line for each phase; and
a command distributing unit for determining the positive arm voltage command and the negative arm voltage command on the basis of the AC voltage command and a DC voltage command for DC voltage between the DC buses, and

the AC-side command calculation unit calculates the AC voltage command by adjusting the AC control command using the first voltage adjustment value.

2. The power conversion device according to claim 1 , wherein
each of the positive arm and the negative arm includes a plurality of the converter cells connected in series.

3. The power conversion device according to claim 1 , wherein
the voltage command generation unit includes a neutral point command calculation unit for outputting a neutral point voltage command for controlling neutral point voltage,
the arm balance control unit calculates a second voltage adjustment value for adjusting the neutral point voltage, on the basis of the positive capacitor voltage and the negative capacitor voltage,
the neutral point command calculation unit calculates the neutral point voltage command on the basis of the second voltage adjustment value and the neutral point voltage that is detected, and
the command distributing unit determines the positive arm voltage command and the negative arm voltage command on the basis of the AC voltage command, the DC voltage command, and further, the neutral point voltage command.

4. The power conversion device according to claim 1 , wherein
the first voltage adjustment value is a value calculated by removing a zero sequence component.

5. The power conversion device according to claim 1 , wherein
the arm balance control unit calculates a zero sequence component from a calculation result of performing such calculation as to reduce a voltage difference between the positive capacitor voltage and the negative capacitor voltage, and subtracts the zero sequence component from the calculation result, thereby calculating the first voltage adjustment value.

6. The power conversion device according to claim 3 , wherein
the arm balance control unit calculates the second voltage adjustment value on the basis of the positive capacitor voltage, the negative capacitor voltage, and further, polarity information about zero sequence current in the positive arm and the negative arm.

7. The power conversion device according to claim 6 , wherein
the arm balance control unit determines, as the polarity information, a polarity of at least one of active power and DC current flowing through the power converter, calculates a zero sequence component from a calculation result of performing such calculation as to reduce a voltage difference between the positive capacitor voltage and the negative capacitor voltage, and multiplies the zero sequence component by the polarity information, thereby calculating the second voltage adjustment value.

8. The power conversion device according to claim 3 , wherein
the neutral point command calculation unit calculates the neutral point voltage command on the basis of only the neutral point voltage that is detected, without using the second voltage adjustment value, when a magnitude of at least one of active power and DC current flowing through the power converter is equal to or smaller than a corresponding one of threshold values respectively set for the active power and DC current.

9. The power conversion device according to claim 3 , wherein
the AC-side command calculation unit calculates the AC voltage command without adjusting the AC control command using the first voltage adjustment value, when a magnitude of at least one of active power and DC current flowing through the power converter is greater than a corresponding one of threshold values respectively set for the active power and DC current.

10. The power conversion device according to claim 1 , wherein
the arm balance control unit calculates the first voltage adjustment value for each phase.

11. The power conversion device according to claim 1 , wherein
the voltage command generation unit includes a circulating current control unit for generating a circulation control command for controlling a circulating current component for each phase which circulates among the leg circuits, and
the command distributing unit determines the positive arm voltage command and the negative arm voltage command on the basis of the AC voltage command, the DC voltage command, and further, the circulation control command.

12. The power conversion device according to claim 1 , wherein
a reactor is connected in series to one of the positive arm and the negative arm in each leg circuit.

13. The power conversion device according to claim 1 , wherein
reactors that are different in reactance are respectively connected in series to the positive arm and the negative arm in each leg circuit.

14. The power conversion device according to claim 1 , wherein
the positive capacitor voltage and the negative capacitor voltage are an average value of voltages of the DC capacitors in the positive arm and an average value of voltages of the DC capacitors in the negative arm, respectively.

15. The power conversion device according to claim 2 , wherein
the voltage command generation unit includes a neutral point command calculation unit for outputting a neutral point voltage command for controlling neutral point voltage,
the arm balance control unit calculates a second voltage adjustment value for adjusting the neutral point voltage, on the basis of the positive capacitor voltage and the negative capacitor voltage,
the neutral point command calculation unit calculates the neutral point voltage command on the basis of the second voltage adjustment value and the neutral point voltage that is detected, and
the command distributing unit determines the positive arm voltage command and the negative arm voltage command on the basis of the AC voltage command, the

Assignees

• Mitsubishi Electric Corp
• Toshiba Mitsubishi Elec Ind

Inventors

• MUKUNOKI Kaho
• Fujii Toshiyuki
• Uda Ryosuke
• Tsuchiya Taichiro
• Matsuda Akihiro
• Taguchi Hisanori

Classifications

• H02M7/48

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

• H02M7/49

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

• H02M2007/4835

  Electricity · mapped topic

• H02M7/487 Primary

  Neutral point clamped inverters · CPC title

• H02M7/483 Primary

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