Coordinated multi-mode selective power control for provision of ancillary services in advanced AC microgrids

Abstract

The transition from traditional to modern power systems is facing technical bottlenecks at the distribution level with the random and steady-growing installation of distributed energy resources (DERs) and non-linear loads (NLLs). To avoid the high costs associated with reinforcing the pre-existing grid, arranging DERs and loads in advanced microgrid (MG) models emerges as the most promising solution to improve grid hosting capacity. This work proposes the coordinated multi-mode selective power control strategy for the provision of ancillary services in advanced AC microgrids. The proposed control is integrated into the secondary-level hierarchical control of centralized MG architectures. It relies on a central controller (CC) to steer DERs via a communication infrastructure to achieve the control goals at the MG point of common coupling (PCC). The proposed strategy comprises two harmonic-support operation modes, which are interchangeable according to a well-defined sequence of CC decisions. Regardless of the operating mode, active and reactive power dispatchability are provided at the MG PCC. The centralized mode offers multiple PCC line-frequency power dispatchability, through the formulation of the proposed so-called generalized power-based control (GPBC). The GPBC algorithm is a generalization of the well-established power-based control for MGs. This approach introduces selective distortion and harmonic power compensation, along with improved load disturbance rejection and more accurate PCC power tracking capabilities compared to previous formulations. In such a centralized mode, the MG is controlled as a single controllable entity at selective frequencies, with distortion or harmonic power sharing among DERs, and capable of performing sinusoidal current or resistive load synthesis from an upstream grid perspective. Still in centralized mode, the so-called PQD/H strategy is proposed to compose the DER local control, which enables active, reactive, harmonic, or distortion power tracking commands from the CC. Conversely, the decentralized mode overcomes the dependence on the communication link to perform harmonic current compensation (HCC), and also significantly reduces data packet traffic requirements. This mode is less sensitive to coupling caused by line impedances, which can be critical in long-wiring MGs. The local control of DERs integrates a selective decentralized voltage detection-based HCC (VDB-HCC) method, which is enabled when the MG operates in this mode. Lastly, some ancillary services that advanced MGs can provide by adopting the proposed multi-mode selective power control is evaluated, with the GPBC algorithm running at the MG secondary level background. The merits of the proposed strategy are comprehensively evaluated in this PhD thesis through both simulations and experimental results, particularly under non-ideal conditions (i.e., voltage distortions and insertion of communication link latency) to ensure robust real-field implementation. Finally, the proposed strategy does not require knowledge of grid parameters and offers a novel approach for coordinating DERs in advanced MGs, representing a significant step toward advancing the electric sector with smarter grid implementations.