Methods and apparatus for active front end filter capacitor degradation detection

A method for detecting filter capacitor degradation in an active front end (AFE) motor drive, the method comprising:

• measuring line-to-line voltages across filter capacitors connected in a delta configuration with each filter capacitor connected to two of three capacitor circuit branches in a filter circuit of the motor drive;
• measuring filter circuit branch currents flowing in the capacitor circuit branches;
• using at least one processor, calculating fundamental frequency filter capacitor impedance values at least partially according to the line-to-line voltages and according to the filter circuit branch currents;
• using the at least one processor, comparing the calculated fundamental frequency filter capacitor impedance values with at least one threshold;
• and
• selectively detecting degradation of one or more of the filter capacitors at least partially according to the comparison of the calculated fundamental frequency filter capacitor impedance values with the at least one threshold.

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 Y configuration with each filter capacitor connected between a corresponding one of the capacitor circuit branches and a common connection node;
• a feedback circuit operatively coupled with the input filter circuit to sense capacitor 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 capacitor 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.