Observer-Based Transient Frequency Drift Compensation in AC Microgrids

This paper proposes a novel solution for transient frequency compensation in weak 3-phase microgrids (MGs) based on a Luenberger observer and a transient frequency detector. Unlike in conventional grids, the low inertia of the generators coupled to an MG could make their rotor speeds to be affected by load changes, varying the grid frequency and compromising the grid quality and stability. This problem has been approached in the literature by the virtual inertia concept. However, the existing solutions are affected by the decoupling of the grid frequency reference and the frequency estimation bandwidth. The proposed paper addresses these problems by the use of a transient frequency drift estimator based on a transient detector and a Luenberger type observer that provides a nearly zero lag frequency estimation. The proposed alternative is analytically compared with the existing techniques and validated through simulation and exhaustive experimental results in an islanded MG. The developed method enables a 1 Hz reduction in the transient frequency deviation when compared with the existing alternatives and improves the system stability.