Enhanced DC-Link Voltage Synchronization Control for Grid-Forming Photovoltaic Systems Considering PV Power Dynamics and Grid Strength Adaptability

Abstract

The integration of large-scale photovoltaics induces significant challenges of low inertia and weak damping within power grids. To effectively address these issues, grid-forming (GFM) strategies have been adopted in photovoltaic systems (PV). In such systems, the front-stage converter is tasked with maximum power tracking, while the back-stage adopts dc-link voltage-synchronized control. However, conventional modeling of the photovoltaic and front-stage dynamics via a constant power source (CPS) model tends to neglect the intrinsic impedance of the front-stage converter, leading to inaccuracies in stability identification. To rectify this oversight, this paper introduces an equivalent circuit model of the PV front-stage converter, which features a power source combined with parallel impedance (PPI), precisely capturing the PV front-stage dynamics and facilitating the stability analysis of the back-stage converter. Furthermore, to address the issue of the low-frequency oscillation induced by the conventional matching control, an enhanced dc-link voltage synchronization strategy is proposed in this paper. This strategy integrates a proportional loop in parallel with a low-pass filter loop. The dc-link voltage regulation, grid strength adaptability, and grid support capability of the PV-GFM system with the proposed strategy are quantified analytically and verified by case studies.