Stability Issues with Network Impedances and its Mitigation in Islanded Microgrids

Inhalt:
The paper presents the effect of network impedances between parallel operated Distributed Generations (DGs) on the transient stability of Low Voltage (LV) microgrids intended for islanded operation. A simulation model is developed using simplified models of DGs. These simplified models are used to simulate electrical (excluding switching) as well as control dynamics for each DG to setup and facilitate system level simulations [1, 2, 3]. The paper focuses on the operation of DGs in grid forming mode using a droop based primary control. These DGs are connected through adjustable cable impedances to a resistive load bank at the point of common coupling (PCC). The effect of varying individual impedances between DGs and PCC under loading conditions on the microgrid stability is investigated. The location of load between DGs and its impact is also discussed. Finally, a control modification utilizing concept of Virtual Impedances (VIs) in Voltage Source Inverters (VSIs) is proposed to improve the transient stability of the discussed microgrid.