Frequency converter and method for identifying and blocking a fault current in a frequency converter
In a frequency converter operated for safety of personnel and/or fire protection via a ground fault interrupter is frequently not able to distinguish between an actual fault current and an operationally generated leakage current. The proposed method addresses this problem by determining a course of a magnitude of a current flowing through the frequency converter, predefining a signal portion which is independent of switching processes within the frequency converter while the frequency converter operates fault-free, checking whether the determined course satisfies a criterion that is predetermined depending on the signal portion, and interrupting the current the determined course fails to satisfy the predetermined criterion.
1. A method for at least one of identifying and blocking a fault current in a frequency converter, comprising the steps of:
determining a course of a magnitude of a current flowing through the frequency converter;
monitoring a switching signal for semiconductor power switches of the frequency converter,
disregarding in the so determined current flow substantially Dirac-shaped switching peaks characteristic of a fault-free operation of the frequency converter to predefine for the determined course a signal portion which is independent of switching processes within the frequency converter while the frequency converter operates fault-free,
checking whether the predefined signal portion comprises substantially rectangular pulses following the substantially Dirac-shaped switching peaks, and interrupting the current if the course of a magnitude of the substantially rectangular pulses is greater than a predetermined threshold value.
2. The method of claim 1 , further comprising the step of determining a course of a magnitude of a differential current between at least two phase conductors of the frequency converter.
3. The method of claim 1 , wherein the predefined signal portion comprises at least one spectral band.
4. The method of claim 3 , wherein a fault current in an intermediate circuit of the frequency converter is indicated by a common mode current of the predefined signal portion having an enhanced signal portion in a frequency range of less or equal to three times a frequency of a supply network, thereby.
5. The method of claim 1 , wherein the predefined signal portion comprises at least one time segment.
6. The method of claim 1 , further comprising the step of suppressing pulses of an inverter, through which a fault current flows, so as to interrupt the current flowing through the frequency converter.
7. The method of claim 6 , wherein the current is interrupted by decoupling the frequency converter from a supply network forming a source of the current.