Adaptive Dual Setting Optimal Protection Coordination for Hybrid AC/DC Microgrid

Abstract

The integration of AC and DC subgrids equipped with variable penetration DERs makes the protection of Hybrid AC/DC microgrids complex and challenging. Diverse topological and operational uncertainties result in variable short-circuit levels of the system. The adaptive relay settings are quite imperative to ensure effective protection coordination for such a dynamic system. This work proposes an adaptive dual-setting scheme for the optimal protection coordination of hybrid AC/DC microgrids(HMG), utilising a novel hybrid relay characteristic. The optimal relay settings are updated offline for the most prominent system operating conditions. Additionally, a fail-safe contingency plan, based on a non-intrusive load detection and communication coordination approach, is employed for system changes other than pre-considered operating conditions. This eliminates any central controller-based communication overhead and reliability concerns. A new performance evaluation framework is also designed to investigate the feasibility of overcurrent protection for low-voltage DC subgrid faults. The effectiveness of the proposed work is validated on a modified MV CIGRE-based 7-bus HMG system, and an extended 39-bus HMG based on the IEEE 33-bus test system, using a real-time digital simulator and a numeric relay development environment for hardware-in-loop (HIL) simulations. The results demonstrate improved performance compared to previous adaptive protection coordination schemes under various network reconfigurations, load-switching scenarios, variable DG penetration, and other system operating conditions.