Over the last decades, the electrical power system has gone through a fundamental transformation never seen before. The liberalisation of the power industry that set the whole process in motion has opened up the possibility of electricity trading across utility and even national boundaries. The distance between where power is generated and where the final consumption takes place and with it the power transit through the high voltage transmission lines has increased immensely. A further development compounding the competitive electricity market and power transmission over long distances has been the large-scale installation of renewables-based power generation units. In addition to the volatility and stochasticity of the power outputs of these units, utilities now also have to contend with possible bi-directional power flows in the distribution networks.

Due to the different dynamic characteristics of renewable generation units compared with conventional power plants, the increasing share of renewables-based generation capacity in the system can give rise to new dynamic phenomena that can reduce the existing security of the whole system. Additionally, restrictions regarding expansion or reinforcement of the existing network mean that lines have to be loaded up to or near their maximum current carrying capabilities. It can thus be safely concluded that the increasing uncertainty regarding load flows and the use of power plants in a heavily loaded network, together with the new power generation technologies such as wind and solar as well as transmission technologies such as VSC-HVDC, would necessarily lead to the reduction of existing security levels unless appropriate countermeasures are implemented.

This book takes up this most up-to-date topic and provides valuable contributions in the areas of both vulnerability assessment and intelligent control. The use of many of the methods under discussion has been made possible by the powerful computers and communication technologies that are now available. Also, in the last decade, significant advances in the area of computational intelligence have been made. These results are now mature enough for use in the planning and operation of power systems. During a contingency, for example, the operator is often overwhelmed by the rapidly changing situation and the associated flood of information, on the basis of which appropriate steps have to be taken. Clearly, the dispatcher cannot be expected to form an objective judgment on the unfolding situation based on his/her observation and experiences alone. The uncertainties must be assessed by suitable analytical tools in order to make the best possible decision within the shortest time possible, and computer-based decision support systems come in handy here. Other promising techniques in this context are the model based predictive control approaches. If a contingency or unfavourable operating condition is predicted some time ahead of its occurrence, a suitable countermeasure can be devised over the intervening period taking prior experience into account. Also, since the available time for decision and control actions is typically very short, real-time applications are required.

The current challenges, and particularly those ahead in the upcoming years, urgently require the introduction of new methods and approaches to ensure the preservation of the existing level of system security, which is taken for granted and assumed so far to be self-evident. The approaches described in this book grew out of the work of talented and committed young scientists working in the area. On the one hand, the contributions serve as a thought-provoking impulse for practising engineers who are looking for new ways to cope with the challenges of today and the future. However, many of these forward-looking ideas are already ready for implementation. On the other hand, this book also allows graduate students to get an overview of modern mathematical and computational methods. Certainly, the book presupposes a thorough knowledge of power system analysis, dynamics and control. Building on this, however, it introduces the reader to an exciting world of new approaches. The combination of practice-orientation and introduction of modern methods for vulnerability assessment and control applications make this book particularly valuable, and recommended reading for a wide audience in the area of power engineering.

January 2017

Prof. István Erlich
Chair Professor of Department of Electrical
Engineering and Information Technologies
Head of the Institute of Electrical Power Systems
University Duisburg-Essen