Hybrid Voltage Sag Mitigation for Renewable Integrated Weak Distribution Systems Using a Load Management and Robust Inverter Control Approach

This paper proposes a novel approach for mitigating voltage sags in weak distribution systems. The proposed system utilizes Inverter-Based Resources operating in a special mode during voltage sags, even for unbalanced voltage events. This allows the inverters to remain connected and support the grid. A Decoupled Double Synchronous Reference Frame - Phase Locked Loop ensures fast and precise phase detection under unbalanced voltage conditions. Additionally, Flexible Positive and Negative Sequence Control enables independent control of positive and negative sequence current components. Furthermore, a Load Management Scheme (LMS) is proposed to mitigate voltage sags during large machines starting events. The LMS employs real-time monitoring of connected loads and implements a predefined load-shedding strategy to bring the voltage back within the Computer Business Equipment Manufacturers Association (CBEMA) acceptable limits, based on the severity of the voltage sag. The combined application of these schemes significantly enhances power quality, particularly regarding voltage sag issues in weak distribution systems.