Protection challenges and solutions on power systems towards 100% inverter-based resources and energy storage systems

Abstract

The decarbonization of the energy sector, driven by the Paris Agreement and the European Green Deal, is increasing the share of renewable energy sources (RES) in power systems. Unlike traditional systems, RES-based systems rely on power electronic converters, which creates unprecedented challenges for reliability and resilience. The future power system is expected to combine a low-level AC layer with an upper-level High Voltage Direct Current (HVDC) backbone, which requires new understanding of fault protection, stability, and interaction between AC and DC components, as well as new models and simulation tools. This is especially critical in systems moving towards 100 percent converter-based generation. Protection systems detect, locate, and isolate faults to protect assets while the rest of the system keeps operating. Traditionally, they rely on the large fault currents supplied by synchronous machines. In modern systems, converter controls limit the fault current contribution to about 120 percent of rated current, so relays that distinguish faults from normal overcurrents based on current level may operate incorrectly. In addition, inverter-based resources (IBR) may not inject enough negative and zero sequence current for directional relays to work properly, and converters hold the voltage at a fixed value only within their reach, beyond which it drops quickly. As a result, existing protection schemes may not provide the expected accuracy and reliability. This report reviews the protection challenges identified in recent academic literature for power systems with high shares of converter-based resources. It covers the specific characteristics of RES, the challenges for protection with intelligent electronic devices (IED), the challenges of converter control during faults, and the main solutions proposed in research over the last decade.