Advanced Virtual Impedance for Power-Sharing Improvement in Microgrids Using Different SOGI Methods: A Comparative Study

The droop control strategy is necessary for the operation of a microgrid (MG) to control power sharing among parallel-connected distributed generations (DGs). However, the main drawback of this control strategy is poor power sharing due to line impedance mismatch. To overcome this, the virtual impedance (VI) control concept is adopted as a practical solution and effective enhancement to improve power sharing. Despite this improvement, conventional VI-based methods still face challenges in harmonic power sharing under nonlinear load conditions. This article proposes an advanced VI-based control scheme for three-phase voltage source inverters (VSIs) forming a stand-alone MG. It is designed using the second-order generalized integrator (SOGI) method and its variants—ESOGI, MSOGI, and DSOGI—to accurately estimate and compensate for harmonic components in the αβ reference frame. Therefore, improvements in both power and harmonic sharing are expected. To this end, a detailed structural relationship among the different SOGI variants is identified and then compared using a testbed consisting of three DG-based MG simulated in MATLAB/Simulink. Results demonstrate that the proposed approach significantly improves performance, reducing total harmonic distortion (THD) from 5.2% with the classical SOGI to 1.9% with the DSOGI, and decreasing power-sharing error from 7.8% to 1.2%, confirming its effectiveness under various operating conditions. Each variant exhibits specific advantages and limitations.