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.

Addressing LV network power quality issues through the implementation of a microgrid

“…Short-circuit protection in a microgrid should be in such a way that faults are detected and isolated within a given time frame. In addition, fault isolation in autonomous operation should ensure that the fault current provided by the voltage source is sufficient to operate protection devices [5]. A total of twelve short-circuit tests were conducted to determine if an inverter/ both inverters will be able to clear faults during autonomous operation and restore microgrid voltage within 200ms after fault isolation.…”

Distributed Power-Generation Systems and Protection

“…The synchronous condensers or the storage devices, such as flywheels, batteries, and ultra-capacitors, can be used as FCSs for injecting high currents during faults [9]. The storage device-based FCS usually contains a storage element, a power electronic converter, a triggering circuit, and a charging module [123]. As soon as a fault is detected, the FCS is used to restore the system voltage, injecting as much current as necessary.…”

Feasibility of an efficient add-on protection system for a real-world Microgrid in islanded mode

“…Furthermore, the requirements assumed should be questioned for the backup power supply use case. Using fuses in IMO requires dedicated highly rated equipment [2,5]. Trying to sustain fuses for protection in GPO the minimal requirements on add-on measures to achieve a reliable protection in IMO are yet unknown.…”