Method and apparatus for active front-end filter capacitor degradation detection

Abstract

Apparatus and methods are provided for detecting degradation of a delta-connected filter capacitor in an active front end (AFE) power converter, wherein the delta circuit capacitor arm current is calculated based on the measured branch circuit current, and based on the calculated The filter capacitor impedance value is calculated from the arm current and the measured line-to-line voltage and corresponding phase angle for comparison with one or more thresholds to selectively detect filter capacitor degradation. Also provided is a method for detecting star-connected filter capacitors by calculating the fundamental frequency RMS impedance value as the ratio of the RMS capacitor voltage to the RMS circuit branch current, and comparing the calculated RMS impedance value to one or more threshold values. Apparatus and methods for degradation.

Description

Background technique [0001] Motor drives and other power conversion systems operate using power from an AC power source and typically include input filters to reduce switching noise associated with the operation of the power converter and, inter alia, to control the Total Harmonic Distortion (THD) generated by high frequency operation. In particular, many power conversion systems utilize inductor-capacitor (LC) or inductor-capacitor-inductor (LCL) input filter circuits associated with each AC input to control the harmonic content of the connected grid. Such filter circuits suffer from damage or deterioration of filter capacitors. Filter capacitor degradation, in turn, can be expensive in terms of replacement part cost, labor for inspection and replacement, and downtime of the power conversion system and any associated machinery. However, assessing the performance and any degradation of the input filter capacitors has so far been difficult, and visual inspection by maintenanc...

AI Technical Summary

Problems solved by technology

Filter capacitor degradation in turn can be expensive in terms of replacement part cost, labor for inspection and replacement, and downtime of the power conversion system and any associated machinery

However, to date, assessing the performance and any degradation of the input filter capacitors has been difficult, and visual inspection by maintenance personnel may not necessarily be able to identify initial capacitor degradation

Some conventional power converters employ fuses in series with filter circuit capacitors, but in practice the fuses either do not open fast enough to prevent capacitor degradation, or frequently open while healthy capacitors are functioning normally causing excessive system result of downtime

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