Fault Analysis and Control of Inverter-Interfaced Energy Systems for Reliable Protective Relaying

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Green energy and smart grid initiatives are driving the move from legacy power systems toward sustainable systems with new features such as microgrids and renewable energy sources (RES). Bridging the gap between the renewable energy industry and relay manufacturers, this research will respond to growing challenges related to protective relaying to ensure the fault resiliency and reliability of next-generation power systems. The following issues will be investigated.1. Microgrid fault analysis: Lack of accurate fault analysis algorithms for microgrids forces protection engineers either (i) to use conventional short-circuit calculation tools that fail to provide reliable microgrid protection or (ii) to employ detailed time-domain microgrid simulation models that are time-consuming and commercially infeasible. For these reasons, optimal protection coordination of directional overcurrent relays (DOCRs) has been limited to microgrids that employ synchronous generators (SGs), whereas modern microgrids are typically powered by inverter-interfaced distributed generators (IIDGs). To address this gap, sequence-component inverter fault models will be developed that include consideration of different control modes, inverter current limits, and reactive current generation (RCG) requirements, and will then be integrated into new microgrid short-circuit calculations. The resultant fault analysis algorithms will be exploited for the creation of new protection coordination indices and the optimization of DOCR operation.2. Microgrid phase selection: To improve microgrid reliability and resiliency during faults, phase selection methods (PSMs) should accurately trip faulty phases. Significant differences between IIDG and SG fault current signatures can cause the misoperation of existing PSMs. This research will address this problem at its source, i.e., the inverter side, by developing new control algorithms in the sequence-component control frames to enable accurate operation of the PSMs used by commercial relays.3. Distance protection of renewable energy systems: Distance relays are normally utilized as either primary or backup transmission system protection. Inverter-interfaced RES can cause unreliable relay impedance measurements, thus impairing the operation of distance relays. This research will develop new fault ride-through and RCG techniques that can provide ancillary services to distance relays, leading to accurate impedance measurements without the need for relay communication or upgrades.The fault analysis and inverter control algorithms developed through this program will be crucial for (i) fault-resilient and sustainable microgrid operation, (ii) greater RES penetration, and (iii) cost-effective protective relaying. The industrial beneficiaries include Canadian utilities, relay manufacturers, and the renewable energy industry.