Oscillatory Stability Of Converter Dominated Power Systems

This book provides an overview of power electronic converters for numerical simulations based on DIgSILENT PowerFactory. It covers the working principles, key assumptions and implementation of models of different types of these power systems. The book is divided into three main parts: the first discusses high-voltage direct currents, while the second part examines distribution systems and micro-grids. Lastly, the third addresses the equipment and technologies used in modelling and simulation. Each chapter includes practical examples and exercises, and the accompanying software illustrates essential models, principles and performance using DIgSILENT PowerFactory. Exploring various current topics in the field of modelling power systems, this book will appeal to a variety of readers, ranging from students to practitioners.

This book covers modeling, control and stability aspects of hybrid AC/DC power networks. More specifically, this book provides an in-depth analysis of the stability and control aspects of hybrid AC/DC power grids, with comprehensive coverage of theoretical aspects of conventional stability issues (e.g., small-signal stability, voltage stability and frequency stability), emerging stability issues (e.g., converter associated stability) and control strategies applied in this emerging hybrid AC/DC power grids. This book takes a more pragmatic approach with a unique compilation of timely topics related to hybrid AC/DC networks compared with other books in this field. Therefore, this book provides the reader with comprehensive information on modeling, control and stability aspects which need to consider when modeling and analysis of hybrid AC/DC power grids for power system dynamics and stability studies. Each chapter provides fundamental stability theories, some worked examples and case studies to explain various modeling, analysis and control concepts introduced in the chapter. Therefore, postgraduate research students, power system researchers and power system engineers benefit from the materials presented in this book and assist them to model and device new control strategies to overcome the stability challenges of the emerging hybrid AC/DC power grid.

Future power systems will source much of their electrical power from converter-based generation,be it a large scale HVDC link or a smaller system such as the back-to-back converter systems found in modern, variable-speed wind turbines. This is in stark contrast to the original AC power systems which used directly-coupled synchronous generation. The transition from the past power system to the future power system will produce power systems that have both low inertia, which compromises angular and frequency stability, and low short-circuit ratios, which compromises voltage stability.In this thesis, the modelling and control of converter-based generation in low short-circuit ratio systems are investigated. For the modelling of AC power systems and the controllers being applied to the converter(s), the unified linear state-space approach is proposed. In this approach, linear state-space models of the electrical system are combined with linear state-space models in a manner which is highly scalable and sufficiently flexible to allow multiple control algorithms acting in a system instantaneously to be considered with relative ease. Three control algorithms are considered in single converter systems: dq-axis vector current control,proportional resonant control, and power synchronization control. By adopting dq-axis vector current control, the system becomes ill-conditioned at the current level, primarily due to the dynamics of the phase-locked loop, which then causes stability issues for outer feedback loops (for example DC voltage and AC voltage controllers) which accompany the current controller. Proportional resonant control, also employing a phase-locked loop, exhibits poor dynamics in the low short-circuit ratio power system. By mimicking the basic synchronization process of a synchronous generator, power synchronization control is able to perform satisfactorily in a low short-circuit ratio system, much as a synchronous generator can. Two algorithms are considered in the multi-converter, low short-circuit ratio systems: dq-axis vector current control and power synchronization control. Performance issues observed in single converter systems when dq-axis vector current control is applied are observed in the multi-converter systems. Additional sources of undesirable coupling between control loops at the current control level are observed, potentially placing more demands on the design of the outer control loops. Power synchronization control performs satisfactorily in the multi-converter systems; however, oscillatory behaviour does arise, which requires careful tuning of the controllers. In addition, it is shown that the introduction of converters using power synchronization control enables other converters (in the same system) using dq-axis vector current control to exhibit improved performance. This is due to power synchronization control causing a converter to act as an effective voltage source/regulator,and dq-axis vector current control relying on electrical proximity to a strong voltage source. This produces systems with improved conditioning, which will reduce the complexity of the design of outer controllers for dq-axis vector current controlled converters. Keywords: control, modelling, HVDC, power systems, stability, voltage-source converter, weak ACsystems, multiple-converter systems, power system planning.

The dynamics of operation of both machines are well understood, including potential stability issues. With the introduction of converter-interfaced generation, power networks are becoming diverse systems, associated with which is an increased number of stability issues to consider.

Bridging the technical and the economical worlds of the energy sector and establishing a solid understanding of today's energy supply as a complex system– with these missions in mind, the book at hand compactly describes the fundamentals of electrical power supply in a dialogue between technology and non-technology, between academia and practitioners, and between nations and continents. Today, energy supply is a complex global system – it is time for a dialogue of the disciplines. In this book, experts explain in an understandable manner the technical foundations and selected specific aspects of today's electrical power supply. Each chapter supplies a fundamental introduction in layman's terms to the topic and serves technical specialists both as a reference and as an opportunity to expand their knowledge. Practical examples and case studies complete the compendium. Technology and economics in the energy sector work on the same questions out of different perspectives. The increasing complexity and interconnections and the epochal upheavals in the energy sector make a comprehensive understanding of the energy sector as a system an essential requirement. This necessitates an ongoing and successful dialogue between the disciplines and between academia and practitioners. To that aim, this book serves both as a compact reference for everyone interested in the energy sector and as a true translation aid between the professional disciplines.