Static state estimation of islanded AC/DC Hybrid microgrids

Abstract

In this work, a static state estimation (SSE) approach for the hybrid AC/DC microgrid (MG)s operating in islanded mode is studied. In the islanded mode, the Interlinking Converter (IC) is critical for maintaining equal or normalized power between the AC and DC parts of the Microgrid (MG). Since the power exchange between AC and DC parts of the MG is determined from AC MG frequency and DC bus voltage, these also need to be considered as system variables along with bus voltages. Hence, in the proposed approach, the Weighted Least Squares (WLS) method is used to estimate the steady-state frequency (ω), along with AC bus voltages (magnitude and phase) of AC MG and DC bus voltages of DC MG simultaneously. Further, to incorporate frequency and droop equation of IC measurement, the Jacobian matrix of WLS is revised. The developed WLS-based Static SE is tested on two test systems: i) 12 bus system (6 bus AC and 6 bus DC) and ii) 71 bus system (38 bus AC and 33 bus DC). Moreover, the impact of accuracy classes of measurements is studied on a large Hybrid AC/DC MG (906 nodes AC MG and 118 node DC MG). All the SE results have been validated by comparing the obtained results with the corresponding true values (calculated from load ow analysis).