Interharmonic Current Differential Protection Scheme for Converter-Based Hybrid AC/DC Microgrids

The limitation of fault currents from converter based distributed generators (CBDGs) in hybrid AC/DC islanded microgrids poses a significant challenge for microgrid protection. This paper presents a novel interharmonic current differential protection scheme for the AC side of hybrid AC/DC islanded microgrids supplied by CBDGs. During faults, the proposed scheme exploits the varying interharmonic components of the currents at both terminals of the faulted line, arise due to variations in the droop-based no-load frequency limits of the interlinking converters (ICs) and the CBDGs. By leveraging these variations, the scheme effectively detects and isolates internal faults within the AC sub-grid, enhancing system reliability. The effectiveness of the suggested scheme is assessed using an enhanced IEEE33-bus hybrid AC/DC microgrid modelled in PSCAD/EMTDC, demonstrating its ability to reliably detect and isolate faults under various operating conditions. Additionally, the scheme is further evaluated using a real-time hardware-in-the-loop experimental setup implemented on an RTDS platform, validating its practical applicability. The simulation and experimental results validate that the presented protection scheme accurately discriminates between normal and faulty conditions across various fault locations, types, and resistance values. This discrimination is achieved without requiring high-bandwidth communication, overcoming a key limitation of existing protection schemes and improving feasibility in real-world deployments.