Protective circuit and method for multi-level converter

• US 7,573,732 B2
• Filed: 05/25/2007
• Issued: 08/11/2009
• Est. Priority Date: 05/25/2007
• Status: Active Grant

• Current Assignee: GE Infrastructure Technology, LLC (GE Vernova, Inc.)
• Original Assignee: General Electric Company
• Inventors: Teichmann, Ralph, Dai, Renchang, Roesner, Robert, Tan, Zhuohui, Delmerico, Robert William, Wang, Changyong
• Primary Examiner(s): Laxton; Gary L
• Application Number:
  US11/753,794
• Publication Number:
  US 20080291708A1
• Time in Patent Office: 809 Days
• Field of Search: 363/34, 363/35, 363/37, 363/50, 363/55, 363/56.01, 363/56.02, 363/56.05, 363/95, 363/98, 363/132, 363/51, 361/111
• US Class Current: 363/51
• CPC Class Codes: F03D 15/00 Transmission of mechanical power
• CPC Class Codes: F03D 9/255 connected to electrical distribution networks; Arrangements therefor
• CPC Class Codes: H02H 7/12 for static converters or rectifiers for discharge lamp power supplies using static converters H05B41/2851, H05B41/2921, H05B41/2981
• CPC Class Codes: H02J 3/01 Arrangements for reducing harmonics or ripples
• CPC Class Codes: H02M 1/0048 Circuits or arrangements for reducing losses using snubbers H02M1/34
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• CPC Class Codes: H02M 5/4585 having a rectifier with controlled elements
• CPC Class Codes: H02M 7/487 Neutral point clamped inverters
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
• CPC Class Codes: Y02E 10/72 Wind turbines with rotation axis in wind direction
• CPC Class Codes: Y02E 10/76 Power conversion electric or electronic aspects
• CPC Class Codes: Y02E 40/40 Arrangements for reducing harmonics

Abstract

A protective circuit for a multi-level converter including a DC link capacitor bank includes: an energy absorbing element; switches, wherein at least two of the switches each couple the energy absorbing element to the capacitor bank; and a controller configured to provide control signals to the switches to selectively actuate the switches to enable control of energy dissipation and to enable control of voltage balance on the capacitor bank of the multi-level converter.

Claims

1. A protective circuit for a multi-level converter including a DC link capacitor bank, the protective circuit comprising:

an energy absorbing element;

switches, wherein at least two of the switches each couple the energy absorbing element to at least one mid-point of the capacitor bank, the at least one mid-point at a floating potential between a positive voltage rail and a negative voltage rail; and

a controller configured to provide control signals to the switches to selectively actuate the switches to enable control of energy dissipation and to enable control of voltage balance on the capacitor bank of the multi-level converter during transient conditions, and further configured to provide control signals to multi-phase converter phase leg switches during normal operating conditions.

2. The protective circuit of claim 1 wherein the energy absorbing unit comprises an element selected from the group consisting of resistors, batteries, ultracapacitors, and combinations thereof.

3. The protective circuit of claim 1 wherein the controller is configured for providing pulse width modulation control during normal operating conditions and for actuating the switches during transient conditions.

4. The protective circuit of claim 3 wherein the transient conditions include low voltage, no voltage, low power factor conditions, and power generation start-up under light load conditions.

5. The protective circuit of claim 3 wherein the transient conditions include low voltage, no voltage, and low power factor conditions, and power generation start-up under light load conditions.

6. The protective circuit of claim 1 wherein the converter comprises a three level converter.

7. The protective circuit of claim 6, further comprising two diodes, wherein the energy absorbing element comprises at least two energy absorbing elements, wherein the capacitor bank comprises at least two capacitors, and wherein

a first one of the switches and a first one of the energy absorbing elements are coupled across a first capacitor,

a second one of the switches and a second one of the energy absorbing elements are coupled across a second capacitor,

a first one of the diodes is coupled in parallel to the first energy absorbing element, and

a second one of the diodes is coupled in parallel to the second energy absorbing element.

8. The protective circuit of claim 7 wherein the controller is configured for obtaining an error signal representative of the voltage imbalance at a neutral point of the capacitor bank, using a neutral point regulator to provide a neutral point command for driving the error signal towards zero, obtaining a signal representative of the combined voltage across the capacitor bank, using an over voltage regulator to provide a voltage command for maintaining the voltage within a threshold.

9. The protective circuit of claim 8 wherein the controller further comprises a summation element for obtaining the sum of the neutral point command and the voltage command, and a difference element for obtaining a difference of the voltage command and the neutral point command.

10. The protective circuit of claim 6, further comprising two diodes, wherein the capacitor bank comprises at least two capacitors and wherein

a first one of the switches is coupled to one side of the capacitor bank,

a second one of the switches is coupled to the other side of the capacitor bank,

the diodes are coupled in series across the energy absorbing element, and

a connection point of the diodes is coupled to a neutral point of the capacitor bank.

11. The protective circuit of claim 6 wherein the switches comprise at least three switches, wherein the energy absorbing element comprises at least three energy absorbing elements, and wherein

a first one of the switches and a first one of the energy absorbing elements are coupled between a first phase leg of a machine side converter and a neutral point of the capacitor bank,

a second one of the switches and a second one of the energy absorbing elements are coupled between a second leg of the machine side converter and the neutral point of the capacitor bank, and

a third one of the switches and a third one of the energy absorbing elements are coupled between a third phase leg of the machine side converter and the neutral point of the capacitor bank.

12. The protective circuit of claim 1 wherein the energy absorbing element comprises at least two energy absorbing elements with at least one of the energy absorbing elements having a smaller rating than another of the energy absorbing elements and being coupled to a neutral point of the capacitor bank.

13. A power generation system comprising:

a multi-level converter, wherein the multi-level converter comprises a DC link capacitor bank; and

a protective circuit, wherein protective circuit comprises;

an energy absorbing element;

switches, wherein at least two of the switches each couple the energy absorbing element to at least one mid-point of the capacitor bank, the at least one mid-point at a floating potential between a positive voltage rail and a negative voltage rail; and

a controller configured to provide control signals to the switches to selectively actuate the switches to enable control of energy dissipation and to enable control of voltage balance on the capacitor bank of the multi-level converter during transient conditions, and further configured to provide control signals to multi-phase converter phase leg switches during normal operating conditions.

14. The power generation system of claim 13 further comprising a wind turbine generator coupled to the multi-level converter.

15. The power generation system of claim 13 further comprising a renewable energy source generator coupled to the multi-level converter.

16. The power generation system of claim 13 further comprising a machine coupled to the multi-level converter.

17. The power generation system of claim 16 wherein the machine comprises a motor.

18. The power generation system of claim 17 wherein the motor comprises a motor incorporated in an assembly for obtaining oil, gas, or combinations thereof.

19. A method for providing energy dissipation control and voltage balance control for a multi-level converter including a DC link capacitor bank comprising at least one mid-point at a floating potential between a positive voltage rail and a negative voltage rail, an energy absorbing element, and protective switches, wherein at least two of the protective switches each couple the energy absorbing element to the capacitor bank, the method comprising:

providing control signals to the protective switches to selectively actuate the protective switches to enable control of energy dissipation and to enable control of voltage balance on the capacitor bank of the multi-level converter during transient conditions; and

providing control signals to multi-phase converter phase leg switches during normal operating conditions.

20. The method of claim 19 wherein providing control signals comprises providing pulse width modulation control signals to phases leg switches of the multi-level converter during normal operating conditions and providing control signals for actuating the protective switches during transient conditions.