Novel Mitigation Techniques for Subsynchronous Interactions

Abstract

Fixed Series Compensation (FSC) is quick to deploy, reliable, has a low environmental impact and is scalable in the event of future capacity expansion. Particularly, when compared to building new transmission lines, which often suffer from right of way issues and long lead times. FSC also helps enhance transient stability limits and enhance voltage stability by providing dynamic reactive power. Networks across the UK and Europe are now turning to series compensation as a solution; for example, FSC banks have been installed for the first time in 2015 by Scottish Power Transmission to increase the power flow capacity from Scotland to England. However, the presence of series capacitors can induce subsynchronous frequency current components that can interact with power system elements. The interaction with the turbine-generator rotor in the form of Subsynchronous Resonance (SSR) can cause dangerous amounts of shaft stress and fatigue and has been cited as a barrier to FSC deployment by some operators. Furthermore, the interaction with Type 3 wind turbines in the form of Subsynchronous Control Interactions (SSCI) can cause serious overvoltages, which are dangerous for both the wind turbine converter as well as the system. The goal of this thesis is to develop novel mitigation solutions for such subsynchronous interactions. The solutions proposed exploit existing resources and incur minimum additional costs for both operation and installation. The thesis presents an exhaustive literature survey of existing SSR analytical techniques, modelling, and mitigation methods to develop a clear understanding of the underlying assumptions and identify relevant gaps. The thesis studies the impact of including dynamic load modes on SSR damping, which has traditionally been neglected in SSR studies, and uses these findings to propose a novel mitigation solution using Variable Frequency Drive (VFD) interfaced auxiliary power plant induction motors. Next, the thesis looks at how Battery Energy Storage System (BESS) controls in a dispatchable wind farm interact with SSCI. With increasing penetration of wind power displacing synchronous generation, wind farms are expected to follow dispatch schedules by using BESS. The thesis proves how a dispatchable wind farm is inherently able to damp SSCI. The SSR studies use PowerFactory while the SSCI studies use MATLAB/Simulink.

Date of Award	31 Dec 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Joseph Mutale (Supervisor) & Vladimir Terzija (Supervisor)