METHOD AND APPARATUS FOR DETERMINING A FAULT CURRENT PORTION IN A DIFFERENTIAL CURRENT

摘要

When determining a fault current portion (IF) in a differential current (idiff(t)) measured at an inverter (1), an AC voltage (uAC(t)) applied to an AC output of the inverter (1) is measured and a periodic reference function (y(t)) of changing sign is generated on the basis of the measured AC voltage (uAC(t)) in order to determine an AC fault current portion (IFAC) in the differential current (idiff(t)). The differential current (idiff(t)) is multiplied by the periodic reference function (y(t)), and the product of the differential current (idiff(t)) and the reference function (y(t)) is averaged over an integral number of periods (T) of the reference function (y(t)). In this case, the reference function (y(t)) is generated, at least for one operating state of the inverter (1), with a predefined phase offset with respect to the measured AC voltage (uAC(t)) and/or with a frequency which is an integer multiple of the frequency of the measured AC voltage (uAC(t)).