Evaluation and control design of virtual-synchronous-machine-based STATCOM for grids with high penetration of renewable energy

Abstract

Because renewable energy sources are environment-friendly and inexhaustible, more and more said renewable energy power plants have been integrated into power grids worldwide. To compensate for their inherent variability, STATCOMs are typically installed at the point of common coupling (PCC) to help their operation by regulating the PCC voltage. However under different contingencies, PCC voltage fluctuations in magnitude and frequency may impede the STATCOM from tracking the grid frequency correctly, hence worsening its overall compensation performance, and putting at risk the operation of the power plant. Further, the virtual synchronous machine (VSM) concept has recently been introduced to control grid-connected inverters emulating the behavior of rotating synchronous machines, in an effort to eliminate the shortcomings of conventional d-q frame phase-locked loops (PLL). In this paper, the VSM concept is extended by developing a STATCOM controller with it, which then behaves like a fully-adjustable synchronous condenser, including the adjustment of its “virtual” inertia and impedance. The proposed controller is compared against existent d-q frame STATCOM control strategies, evincing how the VSM-based approach guarantees not just better synchronization, but an improved voltage regulation performance at the PCC, attained through its virtual impedance, as well as a lower sensitivity to system disturbances, attained through its virtual inertia. The paper will include the complete design procedure for the VSM-STATCOM, and the verification of key results through detailed simulation studies.