The growth of distributed generation (DG) has reshaped distribution networks on a global scale. DGs operating at the distribution level have the flexibility to function either as grid-following or grid-forming systems, depending on grid power availability. A robust islanding detection and control transfer mechanism is imperative to ensure a seamless transition between these modes during unintended islanding events. A unified control scheme (UCS) is proposed to facilitate dual-mode operation for 3-phase grid-tied DGs. Rapid and smooth transfer is achieved between operating modes based on a proposed grid-current feed-forward (GCFF). The proposed control structure elegantly combines state feedback-based active islanding detection with transfer of control logic (TCL), requiring minimal alterations to conventional power converter control architectures for DG. The GCFF is engineered to optimize both islanding detection and transfer speed while mitigating voltage transients during the process. It is specifically designed for DG systems equipped with swift active islanding detection capabilities. The integrated controller structure and GCFF enable the detection and control transfer within a single fundamental operational cycle. This capability holds true even in scenarios involving considerable mismatch between local loads and generation, as validated by comprehensive simulations and rigorous hardware testing in the laboratory.Â

The integration of renewable energy resources is a prevailing trend in modern power systems. Wind and solar energy are key among these renewables, linked to the grid via power electronic converters. These converters require precise synchronization of their output with the grid, achieved through a phase-locked loop (PLL). The PLL’s ability to accurately track the grid voltage phase directly impacts synchronization stability. Moreover, stability relies on the converter’s controller, loads, and grid stiffness. The inclusion of these cross-linked dynamics culminates in a complex analytical model. However, commonly used reduced-order models often omit load dynamics, limiting the obtained insights. Addressing these limitations, this paper introduces a comprehensive method to model a 3- phase grid-tied inverter with an SRF-PLL and local loads, utilizing dynamic phasors. The approach evaluates the impact of system parameters, especially load configuration, on synchronization stability via eigenvalue analysis of the linearized state-space model. This model is apt for investigating weak grids and islanded distributed generation (DG) with diverse local loads. The model showcases stability boundaries, aiding the design of robust renewable energy systems.

This paper presents a method for islanding detection of power-electronic interfaced grid-tied distributed energy resources. A dynamic phasor-based modeling approach is used to synthesize a state-space model of the islanded network. This model leads to the formation of a  generalized framework wherein the application of state feedback is designed to destabilize the islanded network. The proposed method can detect islands within one fundamental cycle of operation with passive loads of unity, lagging, and leading power factors. The detection scheme has a zero Non-detection Zone (NDZ), and detection times are within the  criteria suggested in IEEE Std. 1547-2018.