A PMU-Based Control Scheme for Islanded Operation and Re-synchronization of DER

Abstract

This article proposes a novel synchrophasor-based control scheme enabling controlled islanding, islanded operation and automatic re-synchronization of a distributed energy resource (DER) in a distribution network. The performance of the proposed control system is studied using a test power system model. The DER controller uses a centralized architecture, receiving phasor measurement unit (PMU) measurements from both the transmission and distribution grids. In simulation, the frequency control function inside the proposed controller uses frequency estimates calculated using a new formula that exploits the bus voltage in rectangular form (real and imaginary values). The performance of the proposed frequency computation method is studied and compared with the conventional washout filter (WF) approach used by most power system software tools. The study also discusses why unwrapped bus angles are necessary to perform the automatic re-synchronization process. The performance of the proposed controller is evaluated using both deterministic and stochastic load models, allowing the assessment of variability in distribution grids. The implementation of the proposed control scheme and the simulation of the test system is carried out leveraging rich features of Modelica language and the Open-Instance Power System Library (OpenIPSL).