Advanced Grid-Interface Three-Phase Converters: Grid-Support Capabilities and Grid Impact Analysis

Abstract

The increasing penetration of power electronic converter–interfaced resources is fundamentally transforming modern power systems by displacing conventional synchronous generators, thereby introducing new challenges to system reliability and stability. To address existing challenges and technical gaps, this dissertation develops advanced grid-interface three-phase converters with grid-support capabilities and systematically assesses their impacts on power system operation, including dynamic behavior, small-signal stability, fault current characteristics, protective relay performance, and black-start restoration. Control frameworks are developed for both grid-forming inverters (GFIs) and newly proposed grid-supporting rectifiers (GSRs), enabling grid-regulation support and enhancing overall system stability. Impedance-based small-signal assessments incorporating the generalized Nyquist criterion (GNC) are conducted, with emphasis on (i) comparative stability analysis between conventional grid-tracking rectifiers (GTRs) and the proposed GSR under weak-grid conditions (Chapter 3), and (ii) stability of grid–GFI interconnections during black-start operations, particularly during restoration initial stages (Chapter 5). The proposed converters exhibit more benign impedance characteristics and enhanced stability performance, therefore reducing adverse dynamic interactions and enabling stable operation under weaker grid conditions. In addition, a GFI control strategy with improved fault ride-through capability is proposed. The impacts of inverter-interfaced distributed energy resources on grid fault current characteristics and protective relay performance are analytically investigated, focusing on potential issues of desensitization effect and selectivity deterioration (Chapter 4). Furthermore, a black-start-friendly GFI control is developed, and the feasibility of black-start operations supported by GFI-based renewable resources is systematically studied (Chapter 5). The effectiveness of proposed grid-support control strategies the and the accuracy of the grid-impact analyses are validated by comprehensive simulation studies and hardware experimental results. Overall, this dissertation provides a comprehensive control, modeling, and assessment framework for grid-interface converters in future converter-dominated power systems. The proposed GFI and GSR control strategies, together with impedance-based stability and protection analyses, contribute practical insights for the improving the stability, protection reliability, and restoration capability of low-carbon power grids.