Selective Power Control in Grid-Connected AC Microgrids

The increasing penetration of non-linear loads (NLLs) and distributed energy resources (DERs) in low-voltage grids presents significant challenges to power quality and grid hosting capacity (GHC). This paper proposes a centralized multi-mode selective power control strategy for grid-connected AC microgrids (MGs), requiring no prior knowledge of MG parameters. The strategy enhances GHC and power quality at multiple MG nodes through coordinated control. The proposed approach includes two non-simultaneous operation modes. The centralized mode enables multi-frequency power dispatch via a generalized power-based control (GPBC) algorithm, which extends the formulation of the power-based control strategy. It enables selective harmonic/distortion power control, improved disturbance rejection, and more accurate point of common coupling (PCC) power tracking. For the first time, feedback (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$F$</tex-math></inline-formula>), feedforward (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$f$</tex-math></inline-formula>), and disturbance decoupling (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$D$</tex-math></inline-formula>) actions are applied to distortion/harmonic power in MGs. The decentralized mode avoids the need for communication links in harmonic current compensation (HCC), reducing data traffic. Control is achieved by a primary-level selective decentralized voltage-detection-based HCC (VDB-HCC) method. The strategy allows for: resistive load synthesis at the MG PCC to damp upstream grid resonances, sinusoidal current synthesis to enhance current quality and meet power quality standards, and HCC based on voltage measurements to improve voltage quality at internal MG nodes. Comprehensive simulations assess power reference tracking, disturbance rejection, the effect of grid short circuit level, and mode transitions. In decentralized mode, the MG control improved PCC voltage THD from 10.65% to 1.09% under weak grids. In centralized mode, using sinusoidal current synthesis up to the 11th harmonic, PCC current THD was reduced from 61.18% to 3.42% under stiff grids. Experimental results are also evaluated to demonstrate the feasibility of implementation in real-field MG applications.