Positive and negative bipolar modular multilevel alternating current-alternating current frequency converter

Patent metadata

Field	Value
Publication number	US-12445060-B2
Application number	US-202519224792-A
Country	US
Kind code	B2
Filing date	May 31, 2025
Priority date	Mar 8, 2023
Publication date	Oct 14, 2025
Grant date	Oct 14, 2025

Abstract

The present disclosure provides a positive and negative bipolar modular multilevel alternating current (AC)-AC frequency converter, including a modular multilevel frequency converter and a three-phase three-winding bipolar transformer. The modular multilevel frequency converter has an ABC three-phase structure, each phase includes the same upper bridge arm and lower bridge arm, and the upper and lower bridge arms include n full-bridge sub-modules (FBSMs) and a bridge arm inductor connected in series. The positive and negative bipolar modular multilevel AC-AC frequency converter can be further expanded and enable bidirectional energy flow. In the present disclosure, by introducing a positive and negative bipolar three-winding transformer, an AC-AC frequency converter topology with simple structure, high efficiency, flexibility and reliability is realized, which has high practical value.

First claim

The invention claimed is:

1. A positive and negative bipolar modular multilevel alternating current (AC)-AC frequency converter, comprising a modular multilevel frequency converter and a three-phase three-winding bipolar transformer, wherein
the modular multilevel frequency converter has an ABC three-phase structure, a power frequency side is connected to a power frequency power grid, and a low frequency side is connected to a low frequency power grid through the three-phase three-winding bipolar transformer;
the three-phase three-winding bipolar transformer comprises two Y-connected secondary transformers T 1 and T 2 , T 1 is a positive transformer, and T 2 is a negative transformer; and three-phase ports of the Y-connected secondary transformer T 1 are connected to upper ends of three-phase upper bridge arms of the modular multilevel frequency converter, and three-phase ports of the Y-connected secondary transformer T 2 are connected to lower ends of three-phase lower bridge arms of the modular multilevel frequency converter; and
in the three-phase three-winding bipolar transformer, a neutral point o of T 1 and a neutral point o′ of T 2 are connected with each other, a voltage relationship between T 1 and T 2 transformer ports is that a phase difference between X and x ports is 180°, a phase difference between Y and y ports is 180°, and a phase difference between Z and z ports is 180°.

2. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 1 , wherein each phase of the modular multilevel frequency converter comprises the same upper bridge arm and the same lower bridge arm, and the upper and lower bridge arms respectively comprise n full-bridge sub-modules (FBSMs) and a bridge arm inductor connected in series.

3. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 2 , wherein the FBSM comprises first to fourth insulated gate bipolar transistors (IGBTs) and a first electrolytic capacitor, an emitter of the first IGBT is connected to a collector of the second IGBT, and a connection point is used as a positive terminal of the FBSM; an emitter of the third IGBT is connected to a collector of the fourth IGBT, and a connection point is used as a negative end of the FBSM; a collector of the first IGBT, a collector of the third IGBT and a positive electrode of the first electrolytic capacitor are connected; an emitter of the second IGBT, an emitter of the fourth IGBT and a negative electrode of the first electrolytic capacitor are connected; and the first to fourth IGBTs are all connected to anti-parallel diodes.

4. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 1 , wherein a number of modular multilevel frequency converters is M, all of which are on the power frequency side, Mis a positive integer greater than or equal to 1, the upper ends of the upper bridge arms of the M modular multilevel frequency converters are connected to the three-phase ports of the three-phase three-winding bipolar transformer T 1 , and the lower ends of the lower bridge arms of the M modular multilevel frequency converters are connected to the three-phase ports of the three-phase three-winding bipolar transformer T 2 .

5. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 1 , wherein the positive and negative bipolar modular multilevel AC-AC frequency converter has power flowing from the power frequency side to the low frequency side or from the low frequency side to the power frequency side.

6. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 2 , wherein the positive and negative bipolar modular multilevel AC-AC frequency converter has power flowing from the power frequency side to the low frequency side or from the low frequency side to the power frequency side.

7. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 3 , wherein the positive and negative bipolar modular multilevel AC-AC frequency converter has power flowing from the power frequency side to the low frequency side or from the low frequency side to the power frequency side.

8. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 4 , wherein the positive and negative bipolar modular multilevel AC-AC frequency converter has power flowing from the power frequency side to the low frequency side or from the low frequency side to the power frequency side.

9. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 1 , wherein the positive and negative bipolar modular multilevel AC-AC frequency converter has an upper bridge arm modulation wave y ju and a lower bridge arm modulation wave y jt of j phase calculated by using the following formulas:

{

y

j
⁢
u

=

y
j_l

-

y
j_g

y

j
⁢
l

=

y
j_l

+

y
j_g

where y j_1 is a low frequency modulated wave component, y j_g is a power frequency modulated wave component, and j=a, b, c.

10. The positive and negative bipolar modular multilevel AC-AC frequency converter according to claim 2 , wherein the positive and negative bipolar modular multilevel AC-AC frequency converter has an upper bridge arm modulation wave y ju and a lower bridge arm modulation wave y jt of j phase calculated by using the following formulas:

{

y

j
⁢
u

=

y
j_l

-

y
j_g

y

Assignees

• Univ Southeast

Inventors

• Deng Fujin
• Yi Haoran

Classifications

• H02M5/297

  for conversion of frequency · CPC title

• H02M5/16 Primary

  for conversion of frequency · CPC title

• H02M7/49

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