DC voltage balance control for three-level NPC power converters with even-order harmonic elimination scheme

• US 7,495,938 B2
• Filed: 02/14/2006
• Issued: 02/24/2009
• Est. Priority Date: 04/15/2005
• Status: Expired due to Fees

• Current Assignee: Rockwell Automation Technologies Incorporated (Rockwell Automation, Inc.)
• Original Assignee: Rockwell Automation Technologies Incorporated (Rockwell Automation, Inc.)
• Inventors: Liu, Congwei, Feng, Weixing, Rizzo, Steven C., Wu, Bin, Zargari, Navid R.
• Primary Examiner(s): Riley; Shawn
• Application Number:
  US11/354,597
• Publication Number:
  US 20060245216A1
• Time in Patent Office: 1,106 Days
• Field of Search: 363 15- 17, 363/34, 363/37, 363 39- 41, 363 46- 47, 363/95, 363 97- 98, 363131-134, 363/142, 363/137
• US Class Current: 363/40
• CPC Class Codes: H02M 7/4833 Capacitor voltage balancing
• CPC Class Codes: H02M 7/487 Neutral point clamped inverters
• CPC Class Codes: H02M 7/53876 based on synthesising a desired voltage vector via the selection of appropriate fundamental voltage vectors, and corresponding dwelling times

Abstract

Three-level inverter and rectifier power conversion systems and space vector modulation (SVM) controls having even-order harmonic elimination for neutral voltage balancing with a predefined vector switching sequences for half-wave symmetry in open loop system operation. The vector sequence listings for each SVM diagram segment includes switching state entries individually indicating one of three possible switching state levels positive (P), zero (0), or negative (N) for each of three or more switching groups of the power conversion system, with listings for each pair of first and second diametrically opposite diagram segments include symmetrically opposite switching states, with positive levels in the entries of the listing for the first segment corresponding to negative levels in the entries of the listing for the second segment and vice versa.

Claims

1. A three-level power conversion system, comprising:

a DC connection for receiving or supplying DC electrical power, the DC connection comprising first and second DC terminals and first and second capacitors coupled in series between the first and second DC terminals, the capacitors being coupled at a common node;

a multi-phase AC connection for receiving or supplying multi-phase electrical power, the AC connection comprising first, second, and third AC terminals, and

a three-level switching network comprising;

a first set of switching devices coupled with the DC connection and the first AC terminal, the first set operable in one of three states to selectively electrically couple the first AC terminal to one of the first DC terminal, the second DC terminal, and the common node according to a first set of switching control signals,

a second set of switching devices coupled with the DC connection and the second AC terminal, the second set operable in one of three states to selectively electrically couple the second AC terminal to one of the first DC terminal, the second DC terminal, and the common node according to a second set of switching control signals, and

a third set of switching devices coupled with the DC connection and the third AC terminal, the third set operable in one of three states to selectively electrically couple the third AC terminal to one of the first DC terminal, the second DC terminal, and the common node according to a third set of switching control signals; and

a switch control system providing the sets of switching control signals by space vector modulation to equalize the voltages across the capacitors in open-loop fashion during operation of the power conversion system;

wherein the switch control system comprises an even-order harmonic elimination space vector modulation system coupled with the three-level switching network, the space vector modulation system providing the sets of switching control signals by space vector modulation according to an even-order harmonic elimination vector switching sequence ensuring half-wave symmetry at all times to balance the voltage at the common node.

2. The power conversion system of claim 1, wherein the space vector modulation system provides the sets of switching control signals according to the position of a reference vector in a space vector modulation diagram having 19 stationary space vectors that represent 27 switching states for the three-level switching network and defining six sectors positioned around an origin, the sectors each having six triangular segments, each segment defined by a unique set of three space vectors at the corners of the corresponding triangular segment;

wherein the vector switching sequence provides for switching vector sequencing when the reference vector is in a given segment using switching states corresponding to the three space vectors defining the given segment; and

wherein the vector switching sequence defines a sequence of switching states corresponding to the three space vectors defining each segment, with the vector switching sequences defined for diagram segments that are symmetrically opposite relative to the diagram origin providing for symmetrically opposite coupling of the AC terminals with the first and second DC terminals.

3. The power conversion system of claim 1, wherein the multi-phase AC connection is a three phase connection that receives or supplies three-phase electrical power.

4. The power conversion system of claim 1, wherein the three-level power conversion system is an inverter with the DC connection receiving DC electrical power, and wherein the three-level switching network provides the sets of switching control signals according to the even-order harmonic elimination vector switching sequence to provide multiphase AC electrical power at the AC connection.

5. The power conversion system of claim 1, wherein the three-level power conversion system is a rectifier with the AC connection receiving AC electrical power, and wherein the three-level switching network provides the sets of switching control signals according to the even-order harmonic elimination vector switching sequence to provide DC electrical power at the DC connection.

6. A space vector modulation control system for providing switching control signals to a three-level power conversion system having a DC connection with a pair of capacitors connected in series between first and second DC terminals and connected to one another at a common node, the control system comprising:

driver means for selectively actuating individual switches or pairs of switches in a switching network of the power conversion system for selective coupling of individual AC terminals of the power conversion system to one of the first DC terminal, the second DC terminal, and the common node; and

switch control means for controlling the driver means by space vector modulation to ensure half-wave symmetry at all times and to balance the voltages across the capacitors in open-loop operation of the power conversion system.

7. The control system of claim 6, wherein the switch control means comprises:

an even-order harmonic elimination vector switching sequence; and

processing means for controlling the driver means according to a reference vector and according to the vector switching sequence.

8. The control system of claim 7, wherein the processing means controls the driver means according to the position of the reference vector in a space vector modulation diagram having 19 stationary space vectors that represent 27 switching states for the three-level switching network and defining six sectors positioned around an origin, the sectors each having six triangular segments, each segment defined by a unique set of three space vectors at the corners of the corresponding triangular segment;

wherein the vector switching sequence provides for switching vector sequencing when the reference vector is in a given segment using switching states corresponding to the three space vectors defining the given segment; and

wherein the vector switching sequence defines a sequence of switching states corresponding to the three space vectors defining each segment, with the vector switching sequences defined for diagram segments that are symmetrically opposite relative to the diagram origin providing for symmetrically opposite coupling of AC terminals of the power conversion system with the first and second DC terminals.

9. The control system of claim 7, wherein the even-order harmonic elimination vector switching sequence comprises a machine readable medium having vector sequence listings for each segment of a space vector modulation diagram defining stationary space vectors representing switching states for the switching network and defining a plurality of sectors positioned around an origin of the space vector modulation diagram, the sectors each having a plurality of triangular segments, each segment defined by a unique set of three space vectors at the corners of the corresponding triangular segment, wherein the individual vector sequence listings define a sequence of switching states corresponding to the three space vectors defining each segment, with the vector switching sequences defined for diagram segments that are symmetrically opposite with respect to the diagram origin comprising symmetrically opposite switching states.

10. The control system of claim 9, wherein the vector sequence listings for each segment include three or more switching state entries, each entry indicating one of three possible switching state levels positive (P), zero (0), or negative (N) for each of three or more switching groups of a power conversion system, and wherein the vector sequence listings for each pair of first and second diagram segments that are diametrically opposite relative to the diagram origin comprise symmetrically opposite switching states, with positive (P) levels in the entries of the listing for the first segment corresponding to negative (N) levels in the entries of the listing for the second segment and vice versa.

11. The control system of claim 10, wherein the machine readable medium comprises vector sequence listings corresponding to six segments for each of six sectors defined by the space vector modulation diagram having 19 stationary space vectors that represent 27 switching states for the switching network.

12. The control system of claim 11, wherein the individual vector sequence listings for each segment include seven switching state entries.

13. A vector switching sequence for space vector modulation of a switching network in a three-level power conversion system, the vector switching sequence comprising:

a machine readable medium comprising vector sequence listings for each segment of a space vector modulation diagram defining stationary space vectors representing switching states for the switching network and defining a plurality of sectors positioned around an origin of the space vector modulation diagram, the sectors each having a plurality of triangular segments, each segment defined by a unique set of three space vectors at the corners of the corresponding triangular segment, wherein the individual vector sequence listings define a sequence of switching states corresponding to the three space vectors defining each segment, with the vector switching sequences defined for diagram segments that are symmetrically opposite with respect to the diagram origin comprising symmetrically opposite switching states to ensure half-wave symmetry at all times.

14. The vector switching sequence of claim 13, wherein the vector sequence listings for each segment include three or more switching state entries, each entry indicating one of three possible switching state levels positive (P), zero (0), or negative (N) for each of three or more switching groups of a power conversion system, and wherein the vector sequence listings for each pair of first and second diagram segments that are diametrically opposite relative to the diagram origin comprise symmetrically opposite switching states, with positive (P) levels in the entries of the listing for the first segment corresponding to negative (N) levels in the entries of the listing for the second segment and vice versa.

15. The vector switching sequence of claim 14, wherein the machine readable medium comprises vector sequence listings corresponding to six segments for each of six sectors defined by the space vector modulation diagram having 19 stationary space vectors that represent 27 switching states for the switching network.

16. The vector switching sequence of claim 15, wherein the individual vector sequence listings for each segment include seven switching state entries.

17. The vector switching sequence of claim 14, wherein the individual vector sequence listings for each segment include seven switching state entries.

18. A method for space vector modulation control of a three-level power conversion system, the method comprising:

providing a space vector modulation vector switching sequence comprising vector sequence listings for each segment of the space vector modulation diagram, the individual vector sequence listings defining a sequence of switching states corresponding to the three space vectors defining each segment, wherein the vector switching sequences defined for diagram segments that are symmetrically opposite with respect to the diagram origin comprise symmetrically opposite switching states;

obtaining a reference vector representative of a desired state of the power conversion system;

determining a reference vector segment location in a space vector modulation diagram defining space vectors representing switching states for the switching network and defining a plurality of sectors positioned around an origin of the space vector modulation diagram, the sectors each having a plurality of triangular segments, each segment defined by a unique set of three space vectors at the corners of the corresponding triangular segment; and

providing switching control signals to the power conversion system to ensure half-wave symmetry at all times according to the vector sequence listing for the reference vector segment location.

19. The method of claim 18, wherein providing the switching control signals according to the vector sequence listing for the reference vector segment location comprises:

computing switching times for application of the individual switching states of the vector sequence list based on the reference vector segment location; and

applying the switching states of the vector sequence list to control the power conversion system according to the computed switching times.