Fast frequency containment in power systems with volatile inertia

This doctoral thesis addresses the critical challenges posed by the integration of renewable energy sources (RESs) into modern power systems, focusing on the impact on frequency stability in the face of volatile inertia. With RESs rapidly penetrating into power grids to achieve global decarbonisation goals, the intermittent nature of these sources introduces operational complexities that demand novel strategies for preserving the active power balance. Traditional frequency control practices, built upon stable inertia contributions, face significant disruptions due to the reduced or absent inertia inherent to RESs. Consequently, the system frequency dynamics become swift and unpredictable, rendering conventional methods of frequency protection and control obsolete.

This research unveils a comprehensive methodology for detecting, locating, and estimating the magnitude of loss of generation (LoG) events in power systems characterised by substantial RES integration. Using the superimposed circuit methodology, nodal current injections from RESs are estimated, forming a system of linear equations that pinpoint LoG events by changes in the nodal currents with unparalleled accuracy. This method transcends traditional reliance on frequency measurements and knowledge of system inertia, making it robust and versatile in real-world applications.

Central to this research is the exploration of optimal fast frequency containment (OFFC), which consists of active power injections from RESs to swiftly arrest frequency deviations resulting from LoG events. A new paradigm emerges for OFFC, strategically decomposing the frequency response into transient and steady-state deviations. This approach yields an optimal allocation of power resources to effectively counteract LoG events. Contrary to conventional step-function injections, the proposed methodology ensures that transient deviations are prioritised, thereby conserving energy resources and minimising the time required for frequency to be recovered within statutory limits. The allocation of resources for correcting steady-state deviations subsequently follows if resources are available after mitigating the transient deviation, promoting the preservation of steam turbines' lifespan.

In conclusion, this research highlights the critical intersections between RES integration, frequency stability, and LoG event dynamics. By introducing pioneering methodologies and challenging established assumptions, this thesis contributes to the evolution of power grid management strategies in an era of escalating renewable energy adoption. The insights derived bridge theoretical discourse with practical implications, empowering power systems to effectively navigate the complexities of renewable energy integration while ensuring resilience and stability.