Analysis and Mitigation of the Low Inertia Challenges Due to the High Renewable Penetrations

Abstract

The power system inertia refers to the stored kinetic energy in all synchronous rotating elements, which determines the stability of system frequency as it is the initial resistance to any frequency deviations caused by the generation failure, generation shortfall, a sudden load increase. The integration of the asynchronous renewable generations reduces the overall system inertia thus introduces new challenges for maintaining the stability of system frequency. For a conventional generation dominated system, frequency stability is ensured by the adequate frequency response. However, for a renewable dominated system, the same frequency response reserve is unable to guarantee the frequency stability due to the reduced inertia. When there is a sudden load/generation imbalance, the consequences of the reduced inertia on the system operation are the rapid change in frequency, the potential hazards of the higher rate of change of frequency (ROCOF) to trip the ROCOF-based protection relays for the distributed generators, and the significant frequency drop causing unintentional low-frequency demand disconnection.
Due to the reduced inertia, the system operation planning is shifting from efficiency driven to the balance between efficiency and stability, which is commonly investigated in the unit commitment (UC) to determine the optimal generation scheduling. The existing research in addressing the reduced inertia issues from the perspective of UC optimisation only considers the ROCOF requirements for inertia and ignores the requirements for the maximum frequency drop allowed due to the lack of the representation for the frequency dynamics. The UC is a mixed-integer problem and the transcendental relationship between inertia and the minimum frequency raises the difficulty to not only implement the inertia-related constraint into the UC consideration but also solve the mixed-integer nonlinear-constrained problem. Further challenges from considering the inertia-related constraints into UC is to bring finical incentives for the generator with low output and high inertia contributions. For the current practice, the inertia is provided voluntarily and the significance of inertia is not reflected and rewarded.
This thesis aims to address the challenges of the system operation planning and the market incentives. For the operation planning perspective firstly a frequency mathematical model is proposed that can analyse the representation of the frequency transient dynamics for the initial ROCOF, the minimum frequency and the quasi-steady-state frequency during contingencies; secondly the frequency-related constraints are incorporated into the UC generation scheduling problem for the system operation planning while ensuring the stability of system frequency. Finally, an inertia market is developed for the inertia providers to reward with an incentive for the provision of inertia based on the UC optimisation results.

Date of Award	13 Feb 2019
Original language	English
Awarding Institution	University of Bath
Supervisor	Furong Li (Supervisor) & Roderick Dunn (Supervisor)