Patent ID: 8829919
Filing Date: 2014-09-09
Classification: G01R

Abstract:
1. A method for monitoring a condition of a capacitor in a capacitor arrangement of a DC-voltage intermediate circuit of a power electronics appliance at a place of usage by measuring a DC voltage over the capacitor arrangement as the capacitor discharges the DC voltage as a function of time, the method comprising the following steps: pre-charging the capacitor in the intermediate circuit to a pre-determined DC voltage by using a pre-charging circuit, removing the pre-charging circuit from the intermediate circuit, measuring the DC voltage of the intermediate circuit by sampling at regular time intervals, determining a drop of the DC voltage as a function of time based on the measured DC voltage of the intermediate circuit, determining an actual capacitance value of the capacitor in the intermediate circuit based on the drop of the DC voltage, comparing the actual capacitance value of the capacitor, to a first pre-determined limit of the actual capacitance value of the capacitor, based on the drop of the DC voltage, performing a first necessary condition monitoring procedure when the actual capacitance value of the capacitor, as determined by a measurement of the DC voltage, indicates that the actual capacitance value of the capacitor is substantially close to the first pre-determined limit, determining the actual capacitance value of the capacitor in the intermediate circuit, and the pre-determined change of the actual capacitance value of the capacitor in the intermediate circuit with an equation as follows: where “C “v” is a pre-determined change in the DC voltage of the intermediate circuit, “t” is a related discharge time, and “R