Evaluation of Grid-Connected Converter Dynamics on DFT-Based Relay Protection

Grid-connected converters are increasingly being deployed in renewable energy-dominated power grids, where accurate relay protection is critical for reliability. However, the dynamic behavior of the Phase-Locked Loop in these converters can introduce frequency deviations that impair the accuracy of relay protection accuracy. Motivated by these challenges, this paper analyzes the link between the PLL frequency deviations and the fundamental RMS values extracted by the Discrete Fourier Transform algorithm. In this study, we performed mathematical derivations and validated them through Controller Hardware-in-the-Loop tests under various system conditions. The results provide theoretical justification for evaluating the adaptability of conventional DFT-based relay protection schemes in systems with prevalent converter-interfaced generation, thereby advancing the field toward more reliable protection strategies in renewable energy-dominated grids.