Adaptive Overcurrent Relay Protection Strategy for Demand-side in Offshore DC Microgrids

The integration of renewable energy sources such as solar, wind, waves, and tidal energy by utilizing microgrids is becoming increasingly popular. For offshore applications that operate in an islanded mode, DC microgrids are preferred over AC microgrids due to their ease of the integration of energy storage systems (ESS) and renewable energy sources (RES). DC microgrids mitigate challenges faced by AC microgrids, such as voltage imbalance, harmonic currents, and frequency deviations. However, DC microgrids face unique challenges, particularly in protection systems, due to a lack of standards, limited research, and insufficient expertise. Current protection strategies need modification to adapt to the integration of multiple renewable energy sources, ESS, and various loads. This paper proposes an adaptive approach utilizing rule-based algorithm for DC microgrid protection systems to govern the overcurrent protection setting. Hence, the DC microgrids can dynamically adjust overcurrent settings in response to the change of load conditions, ensuring reliable fault detection and system stability in the presence of various operating scenarios. First, the protection system of the DC microgrid is modelled, and current for several schemes of demand are monitored. Then, the protection system is controlled by coordinating the current-time curve of the overcurrent relay setting. This can be achieved by controlling the pick-up current, the time multiplier settings (TMS), and the high-set current. The setting will adapt accordingly based on predefined rule-based algorithm. Finally, the simulation result will verify that the rule-based algorithm works properly to make the protection relay setting adaptive for the demand side of the DC microgrid application.