Method and Apparatus for Determining a Fault Current Portion in a Differential Current

摘要

When determining a fault current portion I_F in a differential current i_diff(t) measured by an inverter, an AC voltage u_AC(t) applied to an AC output of the inverter is measured and a periodic reference function y(t) of alternating sign is generated as a function of the measured AC voltage u_AC(t) in order to determine an AC fault current portion I_FAC in the differential current i_diff(t). The differential current i_diff(t) is multiplied by the periodic reference function y(t), and the product of the differential current i_diff(t) and the reference function (y(t)) is averaged over an integral number of periods of the reference function y(t). The reference function y(t), at least for one operating state of the inverter, is generated with a predefined phase offset with respect to the measured AC voltage u_AC(t) and/or with a frequency which is an integer multiple of the frequency of the measured AC voltage u_AC(t).