Circulating current injection control

• US 10,153,712 B2
• Filed: 05/15/2017
• Issued: 12/11/2018
• Est. Priority Date: 05/15/2017
• Status: Active Grant

• Current Assignee: Virginia Tech Intellectual Properties, Inc.
• Original Assignee: Virginia Tech Intellectual Properties, Inc.
• Inventors: Wang, Jun, Burgos, Rolando, Boroyevich, Dushan
• Primary Examiner(s): Berhane, Adolf
• Assistant Examiner(s): Quddus, Nusrat
• Application Number:
  US15/595,109
• Publication Number:
  US 20180331632A1
• Time in Patent Office: 575 Days
• Field of Search: 363 37, 363 39- 41, 363 55- 5602, 363 97- 98, 363131, 363132
• CPC Class Codes: H02J 5/00 Circuit arrangements for transfer of electric power between ac networks and dc networks H02J3/36 takes precedence
• CPC Class Codes: H02M 1/143 using compensating arrangements for reducing noise from the supply in transmission systems H04B15/005
• CPC Class Codes: H02M 7/483 Converters with outputs that each can have more than two voltages levels
• CPC Class Codes: H02M 7/4835 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 Class Codes: H02M 7/539 with automatic control of output wave form or frequency H02M7/5375 - H02M7/5387 take precedence

Abstract

In one example, a power converter includes a modular multilevel converter (MMC) electrically coupled between a first power system and a second power system. The MMC includes an arrangement of switching submodules, and the switching submodules include an arrangement of switching power transistors and capacitors. The MMC also includes a controller configured to inject a common mode frequency signal into a circulating current control loop. The circulating current control loop is relied upon to reduce at least one low frequency component in power used for charging the capacitors in the switching submodules. By injecting the common mode frequency signal into the circulating current control loop, the switching submodules can be switched at higher frequencies, the capacitances of the capacitors in the MMC can be reduced, and the power density of the MMC can be increased.

Claims

1. A power converter, comprising:

a modular multilevel converter (MMC) electrically coupled between a first power system and a second power system, the MMC comprising;

an arrangement of switching submodules, at least one of the switching submodules comprising an arrangement of switching power transistors and capacitors, the switching power transistors comprising high-current, high-frequency medium-voltage semiconductor switches; and

a controller comprising a proportional-integral control loop and a proportional-resonant control loop, the controller being configured to inject a high frequency common mode signal into a circulating current control loop of the MMC, wherein;

based on the high frequency common mode signal injected into the circulating current control loop, the controller is configured to switch the switching power transistors at a higher frequency to reduce at least one low frequency component in power used for charging the capacitors and increase a power density of the MMC; and

the controller is configured to inject the high frequency common mode signal into the circulating current control loop of the controller to reduce a magnitude of voltage ripple in the capacitors.

2. The power converter according to claim 1, wherein a size of the capacitors can be reduced based on a reduction of the magnitude of voltage ripple in the capacitors.

3. The power converter according to claim 1, wherein the high frequency common mode signal is injected into a circulating current reference used by the proportional-resonant control loop.

4. The power converter according to claim 1, wherein the proportional-resonant control loop is configured to increase a gain associated with at least one of a direct current (DC) component, a harmonic line frequency component, or a common mode frequency component of a circulating current in the MMC.

5. The power converter according to claim 1, wherein:

the first power system comprises a direct current (DC) power system; and

the second power system comprises an alternating current (AC) power system.

6. The power converter according to claim 1, wherein the switching power transistors comprise silicon carbide (SiC) metal oxide semiconductor field effect transistors (MOSFETs).

7. A power converter, comprising:

a modular multilevel converter (MMC) electrically coupled between a first power system and a second power system, the MMC comprising;

a leg comprising a cascade arrangement of switching submodules, at least one of the switching submodules comprising an arrangement of switching power transistors and capacitors, the switching power transistors comprising high-current, high-frequency medium-voltage semiconductor switches; and

a controller comprising a proportional-integral control loop and a proportional-resonant control loop, the controller being configured to inject a high frequency common mode signal into a circulating current control loop of the MMC, wherein;

based on the high frequency common mode signal injected into the circulating current control loop, the controller is configured to reduce at least one low frequency component in power used for charging the capacitors; and

the controller is configured to inject the high frequency common mode signal into the circulating current control loop of the controller to reduce a magnitude of voltage ripple in the capacitors.

8. The power converter according to claim 7, wherein a size of the capacitors can be reduced based on a reduction of the magnitude of voltage ripple in the capacitors.

9. The power converter according to claim 7, wherein, based on the high frequency common mode signal injected into the circulating current control loop, the controller is configured to switch the switching power transistors at a higher frequency to reduce the at least one low frequency component in power used for charging the capacitors.

10. The power converter according to claim 7, wherein the high frequency common mode signal is injected into a circulating current reference used by the proportional-resonant control loop.

11. The power converter according to claim 7, wherein the proportional-resonant control loop is configured to increase a gain associated with at least one of a direct current (DC) component, a harmonic line frequency component, or a common mode frequency component of a circulating current in the MMC.

12. The power converter according to claim 7, wherein:

the first power system comprises a direct current (DC) power system; and

the second power system comprises an alternating current (AC) power system.

13. The power converter according to claim 7, wherein the switching power transistors comprise silicon carbide (SiC) metal oxide semiconductor field effect transistors (MOSFETs).