Method and apparatus for active front end filter capacitor degradation detection

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.

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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