System and method for unified common mode voltage injection

Patent metadata

Field	Value
Publication number	US-9755545-B2
Application number	US-201414550297-A
Country	US
Kind code	B2
Filing date	Nov 21, 2014
Priority date	Nov 21, 2014
Publication date	Sep 5, 2017
Grant date	Sep 5, 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 three-level CMV 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; 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 three-level CMV limit for further modifying the at least one modified voltage command to achieve a second function in association with operation of the power conversion system; wherein the second CMV injection module comprises: a min-max classifier for determining an instantaneous maximum voltage, an instantaneous medium voltage and an instantaneous minimum voltage from three- phase AC voltage command signals; a CMV limit calculator for calculating a maximum CMV limit and a minimum CMV limit based on instantaneous maximum voltage, the instantaneous medium voltage, the instantaneous minimum voltage and the three-level CMV limit; wherein modifying the at least one voltage command includes adding the first CMV signal into the at least one voltage command; and wherein the first CMV signal is generated based at least in part on the instantaneous maximum voltage and the instantaneous minimum voltage.

2. 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.

3. The power conversion system of claim 2 , 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.

4. The power conversion system of claim 1 , wherein the CMV limit calculator computes the maximum CMV limit and the minimum CMV limit based at least in part on a minimum pulse width requirement of a pulse width modulator (PWM).

5. The power conversion system of claim 1 , 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 a maximum CMV limit, a minimum CMV limit, and a three-phase AC current command.

6. The power conversion system of claim 1 , 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 a maximum neutral point current, a minimum neutral point current, a pre-calculated neutral point current with zero CMV injection from the second CMV signal and a gain signal generated from regulation of a DC voltage difference at the DC link.

7. The power conversion system of claim 1 , wherein the second CMV injection module further comprises an inverse function calculator for calculating the second CMV signal based at least in part on a maximum neutral point current, a 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 a neutral point reference current.

8. The power conversion system of claim 1 , wherein the second CMV injection module further comprises a DC voltage balance regulator for generating a gain signal based at least in part on a DC voltage difference signal at the DC link.

9. The power conversion system of claim 1 , 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, an instantaneous current signals corresponding to the maximum, medium, and minimum voltage signals, and wherein the original neutral point current is used for generating a neutral point reference current.

10. The power conversion system of claim 1 , wherein the first function includes increasing a direct current (DC) voltage utilization or reducing a total harmonic distortion at the output of the at least one multi-level power converter.

11. The power conversion system of claim 1 , wherein the first CMV signal (u 0 ) given by:

u
0

=

max
⁡

(

u

dm
,
a
,
b
,
c

)

+

min
⁡

(

u

dm
,
a
,
b
,
c

)

2

where max(u dm,a,b,c ) represents the instantaneous maximum voltage and min(u dm,a,b,c ) represents the instantaneous minimum voltage.

12. 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 three-level CMV limit; using the second CMV signal 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; wherein the at least one voltage command is modified by adding the first CMV signal into the at least one voltage command; wherein generating the second CMV signal comprises: determining an instantaneous maximum voltage, an instantaneous medium voltage and an instantaneous minimum voltage from three-phase AC voltage command signals; calculating a maximum CMV limit and a minimum CMV limit based on the instantaneous maximum voltage, the instantaneous medium voltage, the instantaneous minimum voltage and the three-level CMV limit; and wherein the first CMV signal is generated based at least in part on the instantaneous maximum voltage and the instantaneous minimum voltage.

13. The method of claim 12 , wherein

Assignees

• Gen Electric

Inventors

• Lei Qin
• Shen Jie
• Schroeder Stefan

Classifications

• H02M1/12 Primary

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

• H02M7/487 Primary

  Neutral point clamped inverters · CPC title

• H02M7/483

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

• H02M2001/123

  Electricity · mapped topic

• H02M1/123

  Suppression of common mode voltage or current · CPC title