Optimizing underfrequency load shedding strategies in converter-dominated networks

The integration of renewable energy resources into the power grid has introduced challenging problems that need to be overcome to ensure system stability and reliability. This paper applied an Integrated Protection-Planning Simulation (IPPS) technology to evaluate an innovative Underfrequency Load Shedding (UFLS) scheme with the objective of complying with NERC Standard PRC-006-5 considering penetration of Inverter-Based Resources (IBR). IPPS technology creates a simulation platform that allows the modeling of highly detailed protection models in transient stability analysis. This paper took advantage of the new features enabled by IPPS and modeled a novel UFLS relay logic with Rate-of-Change-of-Frequency (RoCoF) supervision. The RoCoF-supervised UFLS has the advantage of avoiding misoperation at industrial motor loads and allowing for reduced UFLS time delay. A sudden loss of generation condition was simulated in IPPS according to the PRC-006-5 standard requirements. The protection logic of both the conventional UFLS program and the RoCoF-supervised UFLS scheme have been examined by incrementally increasing the IBR penetration level. The IPPS tool provided accurate simulation results including frequency profile and Volts per Hertz values at all generation buses. The performance of the novel UFLS scheme has been compared with the conventional scheme to validate its effectiveness. An automatic load restoration scheme to prevent frequency overshoot after UFLS occurs has also been implemented along with the addition of a Battery Energy Storage Systems (BESS) to provide fast frequency response and further alleviate system-wide frequency decay.