Influence of converter current limiting and prioritization on protection of highly IBR-penetrated networks

TL;DR

This study analyzes how grid-forming (GFM) and grid-following (GFL) inverter-based resources (IBRs), with LVRT current limiting and positive/negative-sequence prioritization, affect line-distance and alpha-plane line-differential protection in a highly converter-dominated network. Using EMT simulations on a modified IEEE 39-bus system, the authors implement a mho distance relay and an alpha-plane differential algorithm, evaluating ABG and internal/external faults under various control settings. Key findings show that phase-to-ground loops can cause substantial misplacement of fault location for distance protection, and external faults can momentarily push differential quantities into the alpha-plane trip region, especially under GFL with negative-sequence priority, highlighting reliability concerns for traditional protection. The results underscore the need to revise protection strategies to account for converter dynamics, current limitation, and sequence prioritization in modern grids with substantial IBR penetration.

Abstract

This paper investigates how grid-forming (GFM) and grid-following (GFL) control strategies in inverter-based resources (IBRs) influence line distance and differential protection in converter-dominated transmission systems. A modified IEEE 39-bus system is evaluated with GFM and GFL units equipped with low-voltage ride-through logic, current limiting, and positive- or negative-sequence prioritization. Distance protection is implemented with a mho characteristic, while line differential protection uses an alpha-plane approach. Results show that phase-to-ground loops in distance protection can substantially overestimate the fault location near the Zone-1 reach. For line differential protection, external faults may cause the operating point to briefly enter the trip region of the alpha-plane, even for the healthy-phase in ABG faults under GFL control and during the initial moments of the fault, demanding strong external security measures. These findings highlight that modern converter controls, together with current limitation and sequence-current prioritization, can compromise the reliability and security of traditional protection schemes.

Figures (10)

• Figure 1: Grid-forming converter interface to the AC network
• Figure 2: Control structure of the grid-forming unit
• Figure 3: P and Q control schemes
• Figure 4: Control structure of the grid-following unit
• Figure 5: IEEE 39-bus with embedded GFM/GFL units