Fault current source to ensure the fault level in inverter-dominated networks

Abstract

This paper addresses the issue of ensuring the fault level in inverter-dominated islanded networks. This issue is particularly gaining significance with the advent of microgrids. It is proposed to add one component to the network which supplies the fault current when required and which keeps the network alive long enough for all inverters to resume operation, if they have switched off during the transient. This component is named a Fault Current Source (FCS). If the network is in normal operation, the FCS charges its internal energy buffer and then remains dormant. As soon as a phenomenon is detected which is representative of a fault, the FCS attempts to restore the system voltage which was present just before the fault, thereby injecting as much current as necessary. Once the fault is cleared, the FCS provides the reference needed by all inverters to restart operation. Subsequently the FCS switches off again. A prototype FCS has been built and tested. Preliminary test results are presented in this paper, full results are to be presented during the conference.