Efficacy Analysis of Power Swing Blocking and Out-of-Step Tripping Functions in Grid-Following VSC Systems

TL;DR

This paper analyzes the effectiveness of traditional power swing blocking and out-of-step tripping functions in grid-following VSC systems, revealing fundamental differences from synchronous generator systems and validating findings through simulations.

Contribution

It provides a detailed analysis of GFL-VSC power swing dynamics and highlights the need to revise legacy protection settings for these systems.

Findings

LOS in GFL-VSC caused by PLL divergence, unlike SG systems

Legacy settings may malfunction in GFL-VSC systems

Simulation validates theoretical analysis

Abstract

Power flow oscillations can occur in power systems after major disturbances such as system faults, which may result in significant power swings and even lead to system collapse. This paper provides a detailed analysis of the efficacy of the legacy power swing blocking and out-of-step tripping functions in grid-following voltage-source converter (GFL-VSC) systems. First, the power swing dynamics of GFL-VSC are characterized, considering the outer power control loops and phase-locked loop (PLL). It is found that the loss of synchronism (LOS) of the GFL-VSC system is caused by the divergence of the output angle of the PLL, which is fundamentally different from that of synchronous generator (SG)-based systems, whose LOS originates from the divergence of power angle differences between power sources. Therefore, the legacy setting principles for power swing blocking and out-of-step tripping function designed for SG-based systems can not be directly applied to GFL-VSC systems, and may even malfunction. Time-domain simulations are performed in the PSCAD/EMTDC platform to validate the correctness of the theoretical analysis.