Abstract
The modern power grid is evolving towards net-zero carbon emissions by deploying an increasing amount of renewable resources. Inverter-based renewable generation has increasingly replaced conventional generation in recent years, resulting in lower system inertia. However, the impact of renewable generation on power system planning and operation is not sufficiently investigated, especially the capability of renewable penetrated power systems to resist and recover from major disturbances, which is a critical concern for system operators.Power system resilience generally represents the capability of the system recovering from a degraded state to normal operation in an acceptable period of time. Novel metrics and evaluation methodologies are needed to depict the systems’ ability in response to events such as varying loads, changes in non-dispatchable generation, transmission line opening, or generating power shedding, and to quantitatively evaluate system performance in various time scales. Also, systematic methodologies are required to assess the evolution of system performance during various stages of specific event processes.
In this dissertation, the operational metrics based on adaptive capacity of the transmission network, bus voltage and generation limits, transient stability principles, and frequency are proposed and validated in several power systems with renewable generation. Based on the proposed metrics, the resilience-oriented operation management strategies are designed and validated to enhance system resilience using the modified IEEE 39-bus test system.
The frequency resilience in such a low inertia system is critical for emergency mitigation. A resilience metric based on frequency recovery is proposed to quantitatively represent system resilience in terms of the rate of change of frequency. Application of grid-forming converters provides a means to improve system resilience by providing virtual inertia. An under-frequency load shedding strategy is applied to further support frequency recovery in cases with high penetration of grid-forming inverters.
Furthermore, the protection issues caused by increasing penetration of inverter-based renewable resources are verified and interpreted in the modified IEEE 9-bus system. The impact of inverter controllers on superimposed quantity-based protection is investigated under fault conditions. A protective relay including incremental quantity-based directional element and voltage restrained time overcurrent element is implemented to enhance system resilience considering fault current characteristics of inverter-based resources.