Methods and apparatus for active front end filter capacitor degradation detection

Patent metadata

Field	Value
Publication number	US-9318944-B2
Application number	US-201313872177-A
Country	US
Kind code	B2
Filing date	Apr 29, 2013
Priority date	Apr 29, 2013
Publication date	Apr 19, 2016
Grant date	Apr 19, 2016

Abstract

Apparatus and methods are provided for detecting degradation of delta-connected filter capacitors in an active front end (AFE) power converter, in which delta circuit capacitor leg currents are calculated based on measured branch circuit currents, and filter capacitor impedance values are computed based on the calculated leg currents as well as measured line-to-line voltages and corresponding phase angles for comparison with one or more thresholds to selectively detect degradation of the filter capacitors. Further apparatus and methods are provided for detecting degradation of Y-connected filter capacitors by computation of fundamental frequency RMS impedance values as ratios of RMS capacitor voltages and RMS circuit branch currents, and comparison of the calculated RMS impedance values with one or more thresholds.

First claim

The following is claimed:

1. A power conversion system, comprising:
a power converter input operative to receive multiphase AC input power;
an active front end (AFE) rectifier, comprising a three phase AC input, and a plurality of switching devices operative according to a plurality of rectifier switching control signals to convert power received at the three phase AC input to provide DC output power;
an input filter circuit coupled between the power converter input and the AFE rectifier, the input filter circuit comprising first, second, and third series circuits individually including at least one filter inductor coupled between a corresponding phase of the power converter input and a corresponding phase of the three phase AC input of the AFE rectifier, first, second, and third capacitor circuit branches respectively connected to the first, second and third series circuits, and three filter capacitors connected in a delta configuration with each filter capacitor connected to two of the capacitor circuit branches;
a feedback circuit operatively coupled with the input filter circuit to sense line-to-line voltages across the filter capacitors and filter circuit branch currents flowing in the capacitor circuit branches; and
a degradation detection system operatively coupled with the input filter circuit to calculate fundamental frequency filter capacitor impedance values at least partially according to the line-to-line voltages and according to the filter circuit branch currents, and to selectively detect degradation of one or more of the filter capacitors according to the calculated fundamental frequency filter capacitor impedance values.

2. The power conversion system of claim 1 :
wherein the individual series circuits of the input filter circuit include a first filter inductor connected to the corresponding phase of the power converter input and a second filter inductor connected between the first filter inductor and the corresponding phase of the three phase AC input of the AFE rectifier; and
wherein the individual capacitor circuit branches of the input filter circuit are connected to a node joining the first and second filter inductors of the corresponding series circuit.

3. The power conversion system of claim 2 , wherein the degradation detection system is operative to:
filter the line-to-line voltages and the filter circuit branch currents to obtain filtered line-to-line voltages and filtered circuit branch currents at a fundamental frequency of the multiphase AC input power;
calculate RMS line-to-line voltages according to the filtered line-to-line voltages;
calculate RMS circuit branch currents according to the filtered circuit branch currents; and
calculate the fundamental frequency filter capacitor impedance values according to the RMS line-to-line voltages and according to the RMS circuit branch currents.

4. The power conversion system of claim 3 , wherein the degradation detection system is operative to:
calculate the fundamental frequency filter capacitor impedance value Z ab.60Hz of a first filter capacitor according to the following equation:

Z

ab
⁢
.60
⁢
Hz

=

[

[

V

c
.
ab

⁢
.60
⁢

hz
.
rms

-

V

c
.
ca

⁢
.60
⁢

hz
.
rms

·

Cos
⁡

(

φ
ca

)

]

2

+

[

V

c
.
ca

⁢
.60
⁢

Assignees

• Royak Semyon
• Breitzmann Robert J
• Rockwell Automation Tech Inc

Inventors

• Royak Semyon
• Breitzmann Robert J

Classifications

• G01R31/64

  Testing of capacitors · CPC title

• H02M1/32

  Means for protecting converters other than automatic disconnection · CPC title

• H02M7/219

  in a bridge configuration · CPC title

• H02M5/4585

  having a rectifier with controlled elements · CPC title

• G01R31/42

  AC power supplies · CPC title