Introduction

This thesis adopts bifurcation theory, a nonlinear analysis technique, to investigate various power system stability limits, including small-disturbance rotor-angle stability, resonance stability, converter-driven stability and voltage stability. Power systems are approaching and being operated closer to their stability boundaries to improve their efficiency and to address increasing load demand due to electrification. In addition, with the significant integration of power electronic-interfaced devices, the dynamic response of power systems has become progressively dominated by the characteristics of these components. As the controllers of power electronics operate across a frequency range from several kilohertz down to a few hertz, they can impact a wide variety of dynamic phenomena. This may exacerbate adverse interactions between the power electronics devices and the network, which may, in turn, be detrimental to the stability of the power system. Consequently, there is an increasing necessity to perform comprehensive stability assessments of power systems including multiple converters considering various types of stability simultaneously. This introductory chapter outlines the research topics considered in this thesis. It starts with a description of the definition of power system stability, followed by a discussion on the evolution of modern Voltage Source Converters (VSC) technologies and their impacts on system stability. The chapter then introduces the analytical techniques utilised in this research: bifurcation theory and sensitivity analysis. Following this, a thorough literature review is presented, highlighting the research gaps this thesis addresses and outlining the significant contributions detailed in subsequent chapters.