MODULAR CONVERTER WITH MULTILEVEL SUBMODULES

• US 20150124506A1
• Filed: 11/07/2014
• Published: 05/07/2015
• Est. Priority Date: 11/07/2013
• Status: Active Grant

• Current Assignee: Regents of The University of Minnesota (University of Minnesota)
• Original Assignee: Regents of The University of Minnesota (University of Minnesota)
• Inventors: Mohan, Ned, Sahoo, Ashish
• Granted Patent: US 10,069,430 B2
• Time in Patent Office: Days
• US Class Current: 363/126
• CPC Class Codes: H02M 1/0095 Hybrid converter topologies, e.g. NPC mixed with flying capacitor, thyristor converter mixed with MMC or charge pump mixed with buck
• CPC Class Codes: H02M 5/225 comprising two stages of AC-AC conversion, e.g. having a high frequency intermediate link
• CPC Class Codes: H02M 7/4807 having a high frequency intermediate AC stage
• CPC Class Codes: H02M 7/483 Converters with outputs that each can have more than two voltages levels
• CPC Class Codes: H02M 7/4833 Capacitor voltage balancing
• 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 7/487 Neutral point clamped inverters
• CPC Class Codes: H02P 27/08 with pulse width modulation
• CPC Class Codes: H02P 27/14 with three or more levels of voltage

Abstract

One aspect of the disclosure includes a submodule topology for a modular multilevel converter. The submodule topology includes two electronic switches connected together with a first series connection terminal connecting the electronic switches in series, the series connected switches being connected in parallel with two capacitors connected together with a second series connection terminal connecting the capacitors in series. A bidirectional electronic switch connects the first series connection terminal with the second series connected terminal. An output voltage is obtained across the first series connected terminal and a common terminal formed by the parallel connection of the series connected switches with the series connected capacitors.

Claims

1. A submodule for a modular multilevel converter, the submodule comprsing:

two electronic switches connected together with a first series connection terminal connecting the electronic switches in series;

two capacitors connected together with a second series connection terminal connecting the capacitors in series, the series connected switches being connected in parallel with the series connected capacitors; and

a bidirectional electronic switch connects the first series connection terminal with the second series connected terminal, wherein an output voltage is obtained across the first series connected terminal and a common terminal formed by the parallel connection of the series connected switches with the series connected capacitors.

2. The submodule of claim 1 wherein the bidirectional switch comprises a 4-quadrant bidirectional switch in common emitter configuration.

3. The submodule of claim 1 wherein the bidirectional switch comprises a full bridge rectifier having conventionally connected diodes and an electronic switch connected between the commonly connected anodes and the commonly connected cathodes.

4. A multi-level converter comprising:

a plurality of submodules connected in series, each submodule comprising;

two electronic switches connected together with a first series connection terminal connecting the electronic switches in series;

two capacitors connected together with a second series connection terminal connecting the capacitors in series, the series connected switches being connected in parallel with the series connected capacitors; and

a bidirectional electronic switch connects the first series connection terminal with the second series connected terminal, wherein an output voltage is obtained across the first series connected terminal and a common terminal formed by the parallel connection of the series connected switches with the series connected capacitors;

a controller operably connected to each of the electronic switches, the controller controlling each of the electronic switches in order to configure each submodule in one of at least three operating states, the operating states including a FULL ON state wherein both of the capacitors of a submodule are operably connected in series with at least one other submodule, a HALF ON state wherein one of the capacitors of a submodule are operably connected in series with at least one other submodule, and wherein a BYPASS state wherein none of the capacitors are connected in series with at least one other submodule.

5. The converter of claim 4 wherein the plurality of submodules are configured to connect to a multi-phase source of power wherein at the submodules comprise at least one upper arm of series connected submodules and at least one lower arm of series connected submodules.

6. The converter of claim 4 wherein the controller is configured to control the electronic switches based on a hybrid control scheme wherein the controller is configured to use two sets or groups of carrier waveforms wherein the carriers are phase shifted for the submodules and level shifted for the electronic switches inside each submodule.

7. The converter of claim 4 wherein the capacitors of at least one submodule do not have the same capacitance, and wherein the controller controls the electronic switches in order to configure each submodule in one of at least four operating states, the operating states including a second HALF ON state wherein one of the two capacitors of the submodule is operably connected in series with at least another submodule, the first-mentioned HALF ON state being with the other of the two capacitors of the submodule is operably connected in series with at least one other submodule.

8. The converter of claim 4 wherein the controller is configured to control each submodule based on at least a current direction and voltages across each of the capacitors.

9. The converter of claim 4 and further comprising a transformer having a first set of windings and a second set of windings, the converter being connected to the first set of windings and a multiphase component being connected to the second set windings.

10. The converter of claim 9 wherein the controller is configured to vary the voltage across the first set of windings to control an operating state of the multiphase component.

11. The converter of claim 4 wherein each bidirectional switch comprises a 4-quadrant bidirectional switch in common emitter configuration.

12. The converter of claim 4 wherein each bidirectional switch comprises a full bridge rectifier having conventionally connected diodes and an electronic switch connected between the commonly connected anodes and the commonly connected cathodes.

13. A multilevel converter assembly to operate a component, comprising:

a high frequency transformer having a first set of windings and a second set of windings, the second set of winding being configured to connect to the multiphase component;

a plurality of submodules configured to connect to a source of power wherein at the submodules comprise at least one upper arm of series connected submodules and at least one lower arm of series connected submodules, and wherein the plurality of submodules are connected to the first set of winding, each submodule comprising;

at least one capacitor; and

at least one electronic switch to selectively connect the capacitor in series with other submodule; and

a controller operably connected to each of the electronic switches, the controller controlling each of the electronic switches in order to configure each submodule in one of at least two operating states, the operating states including a FULL ON state wherein the capacitor of a submodule is operably connected in series with at least one other submodule, and a BYPASS state wherein the capacitor is not connected in series with at least one capacitor of another submodule, and wherein the controller is configured to provide at least near sinusoidal high frequency voltage across the first set of windings.

14. The converter assembly of claim 13 wherein each module comprises at least two capacitors, and wherein the controller controls each of the electronic switches in order to configure each submodule in one of at least three operating states, the operating states including a HALF ON state wherein one of the capacitors of a submodule is operably connected in series with at least one capacitor of another submodule.

15. The converter assembly of claim 14 wherein the capacitors of at least one submodule do not have the same capacitance, and wherein the controller controls the electronic switches in order to configure each submodule in one of at least four operating states, the operating states including a second HALF ON state wherein one of the two capacitors of the submodule is operably connected in series with at least one capacitor of another submodule, the first-mentioned HALF ON state being with the other of the two capacitors of the submodule is operably connected in series with at least one capacitor of another submodule.

17. The converter assembly of claim 13 wherein a second converter is operably connected between the second set of windings and the component.

18. The converter assembly of claim 13 wherein the transformer comprises a three phase transformer and the plurality of submodules are configured in at least one upper arm of series connected submodules and at least one lower arm of series connected submodules for each phase.

19. The converter assembly of claim 13 wherein the controller is configured to generate at least near sinusoidal voltage at a frequency of at least 1 kilohertz.

20. The converter assembly of claim 13 wherein the controller is configured to generate at least near sinusoidal voltage at a frequency of at least 10 kilohertz.