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 (S1-S6) 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 (Lu, Lv, Lw) 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 (Cab, Cbc, Cca) connected in a Delta configuration with each filter capacitor (C) connected to two of the capacitor circuit branches ; a feedback circuit operatively coupled with the input filter circuit to sense line-to-line voltages (V c.ab , V c.bc , V c.ca ) across the filter capacitors (Cab, Cbc, Cca) and filter circuit branch currents (I c.a , I c.b , I c.c ) 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 (Z ab.60Hz , Z bc.60Hz , Z ca.60Hz ) at least partially according to the line-to-line voltages (V c.ab , V c.bc , V c.ca ) and according to the filter circuit branch currents (I c.a , I c.b , I c.c ), and to selectively detect degradation of one or more of the filter capacitors (Cab, Cbc, Cca) according to the calculated fundamental frequency filter capacitor impedance values (Z ab.60Hz , Z bc.60Hz , Z ca.60Hz ). 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 (S1-S6) 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 (Lu, Lv, Lw) 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 (Cab, Cbc, Cca) connected in a Delta configuration with each filter capacitor (C) connected to two of the capacitor circuit branches ; a feedback circuit operatively coupled with the input filter circuit to sense line-to-line voltages (V c.ab , V c.bc , V c.ca ) across the filter capacitors (Cab, Cbc, Cca) and filter circuit branch currents (I c.a , I c.b , I c.c ) 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 (Z ab.60Hz , Z bc.60Hz , Z ca.60Hz ) at least partially according to the line-to-line voltages (V c.ab , V c.bc , V c.ca ) and according to the filter circuit branch currents (I c.a , I c.b , I c.c ), and to selectively detect degradation of one or more of the filter capacitors (Cab, Cbc, Cca) according to the calculated fundamental frequency filter capacitor impedance values (Z ab.60Hz , Z bc.60Hz , Z ca.60Hz ). <EOS>