System and method for unified common mode voltage injection

Patent metadata

Field	Value
Publication number	US-9634576-B2
Application number	US-201414317361-A
Country	US
Kind code	B2
Filing date	Jun 27, 2014
Priority date	Jul 3, 2013
Publication date	Apr 25, 2017
Grant date	Apr 25, 2017

Abstract

A power conversion system includes at least one multi-level power converter and a controller coupled to the at least one multi-level power converter. The controller includes a first CMV injection module and a second CMV injection module. The first CMV injection module generates a first CMV signal for modifying at least one voltage command to achieve a first function in association with operation of the power conversion system. The second CMV injection module generates a second CMV signal based at least in part on a local limit either for modifying the at least one voltage command or for further modifying the at least one modified voltage command to achieve a second function in association with operation of the power conversion system.

First claim

The invention claimed is:

1. A power conversion system, comprising: at least one multi-level power converter; and a controller coupled to the at least one multi-level power converter, the controller comprising: a first common mode voltage (CMV) injection module for generating a first CMV signal for modifying at least one voltage command to achieve a first function in association with operation of the power conversion system; a second CMV injection module for generating a second CMV signal based at least in part on a local limit either for modifying the at least one voltage command or for further modifying the at least one modified voltage command to achieve a second function in association with operation of the power conversion system; and a summation unit to receive and combine the first CMV signal and the second CMV signal with the at least one voltage command to provide modified voltage command signals.

2. The power conversion system of claim 1 , wherein the first CMV signal is generated based at least in part on an instantaneous maximum voltage and an instantaneous minimum voltage identified from a plurality of voltage commands.

3. The power conversion system of claim 1 , further comprising a direct current (DC) link coupled to the at least one multi-level converter, the DC link comprising at least two DC capacitors defining at least one DC neutral point therebetween, wherein the second CMV signal is used to modify the at least one voltage command to regulate the DC current component flowing from or to the DC neutral point of the DC link in order to reduce the voltage difference between two the DC capacitors substantially to zero.

4. The power conversion system of claim 3 , wherein the second CMV signal is further used to modify the at least one voltage command to regulate the AC current component flowing from or to the DC neutral point of the DC link in order to substantially reduce the voltage difference between the two capacitors to zero.

5. The power conversion system of claim 1 , wherein the second CMV injection module comprises a min-max classifier for determining an instantaneous maximum and an instantaneous minimum voltage from three-phase AC voltage command signals.

6. The power conversion system of claim 5 , wherein the second CMV injection module comprises a CMV limit calculator for calculating a maximum CMV limit and a minimum CMV limit based at least in part on measured DC voltages at a DC link.

7. The power conversion system of claim 5 , wherein the second CMV injection module comprises a CMV limit calculator for calculating a maximum CMV limit and a minimum CMV limit based at least in part on a carrier band voltage.

8. The power conversion system of claim 5 , wherein the second CMV injection module comprises a CMV limit calculator for calculating a maximum CMV limit and a minimum CMV limit based at least in part on a minimum pulse width requirement of the PWM.

9. The power conversion system of claim 6 , wherein the second CMV injection module further comprises a NP current calculator for calculating a maximum neutral point current, a minimum neutral point current, a first CMV corresponding to the maximum neutral point current, and a second CMV corresponding to the minimum neutral point current based at least in part on the maximum CMV limit, the minimum CMV limit, and three-phase AC current command or feedback signals.

10. The power conversion system of claim 6 , wherein the CMV injection module further comprises a NP current calculator for calculating a maximum neutral point current, a minimum neutral point current, a first CMV corresponding to the maximum neutral point current, and a second CMV corresponding to the minimum neutral point current based at least in part on the switching state of the converter at each instantaneous time.

11. The power conversion system of claim 9 , wherein the second CMV injection module further comprises a reference NP current calculator for calculating a neutral point reference current based at least in part on the maximum neutral point current, minimum neutral point current, and a gain signal.

12. The power conversion system of claim 11 , wherein the second CMV injection module further comprises an inverse function calculator for calculating the second CMV signal based at least in part on the maximum neutral point current, the minimum neutral point current, the first CMV corresponding to the maximum neutral point current, the second CMV corresponding to the minimum neutral point current, and the neutral point reference current.

13. The power conversion system of claim 11 , wherein the second CMV injection module further comprises a DC voltage balance regulator for generating the gain signal based at least in part on a DC voltage difference signal at the DC link.

14. The power conversion system of claim 11 , wherein the second CMV injection module further comprises a NP current pre-calculator for calculating an original neutral point current flowing from or to the DC neutral point based at least in part on the instantaneous maximum, medium, and minimum voltage signals, the instantaneous maximum, medium, and minimum current signals, and wherein the original neutral point current is used for generating the neutral point reference current.

15. A method for operating a power conversion system having a multi-level converter and a controller coupled thereto, the method comprising: generating a first common mode voltage (CMV) injection signal; using the first CMV injection signal to modify at least one voltage command to achieve a first function in association with operation of the power conversion system; generating a second CMV signal based at least in part on a local limit; using the second CMV signal either to modify the at least one voltage command signal or to further modify the at least one modified voltage command to achieve a second control function in association with operation of the power conversion system; and combining the first CMV signal and the second CMV signal with the at least one voltage command to provide modified voltage command signals.

16. The method of claim 15 , wherein generating the second CMV signal comprises:
determining an instantaneous maximum voltage and an instantaneous minimum voltage based at least in part on a plurality of voltage command signals;
calculating a maximum CMV limit and a minimum CMV limit based at least in part on a global limit and the local limit;
calculating a neutral point maximum current, a neutral point minimum current, a first CMV corresponding to the neutral point maximum current, and a second CMV corresponding to the neutral point minimum current based at least in part on the maximum CMV limit, the minimum CMV limit, a plurality of instantaneous current command signals, and the switching state of a converter circuit; and
calculating the second CMV signal based at least in part on the neutral point maximum current, the neutral point minimum current, the first CMV corresponding to the neutral point maximum current, the second CMV corresponding to the neutral point minimum current, and a neutral point reference current.

17. The method of claim 15 , further comprising:
generating a gain signal based at least in part on a DC voltage difference signal at a DC link; and
calculating the neutral point reference current based at least in part on the maximum neutral point current, minimum neutral point current, the original neutral point current and the gain signal.

18. The method of claim 17 , further comprising:
calculating an original neutral point current flowing from or t

Assignees

• Gen Electric

Inventors

• Shen Jie
• Schroeder Stefan
• Chen Kunlun
• Yang Shuitao
• Qu Bo
• Lei Qin

Classifications

• H02M1/12

  Arrangements for reducing harmonics from AC input or output · CPC title

• Y10T307/707

  Cross-Sectional Technologies · mapped topic

• H02M2001/123

  Electricity · mapped topic

• H02M7/483

  Converters with outputs that each can have more than two voltages levels · CPC title

• H02M7/487 Primary

  Neutral point clamped inverters · CPC title