Since the past three decades, new economic, social, and legislative developments have demanded a review of traditional power transmission theory and practice and the creation of new concepts to allow full utilization of existing power generation and transmission facilities. In this respect, the vision of Flexible AC Transmission System (FACTS) was formulated by the Electric Power Research Institute, Palo Alto, California, in the late 1980s. FACTS emerged as a technology in which various power electronics-based static controllers enhance controllability and increase power transfer capability over existing transmission corridors.
FACTS controllers can be broadly classified into two categories. The first one comprises thyristors. Examples include the static VAR compensator, the thyristor-controlled series capacitor, and the phase shifter. The second category comprises self-commutated static converters as controlled voltage sources. Examples include the static compensator (STATCOM), the static synchronous series compensator (SSSC), the unified power flow controller (UPFC), the interline power flow controller (IPFC), and the generalized unified power flow controller (GUPFC).
Com pared to thyristor-based FACTS controllers, voltage-sourced converter (VSC)-based FACTS controllers generally possess superior performance characteristics. As a consequence, VSC-based FACTS controllers have gained in popularity over the years. Now, for proper planning, design, and operation of power system networks incorporating VSC-based FACTS controllers, a power flow solution of the network(s) incorporating them is required. Therefore, development of suitable power flow models of VSC-based FACTS controllers is of fundamental importance.
Although a number of books on modeling and applications of FACTS controllers exist, very few books dwell on their power-flow modeling. In addition, I have experienced that slow learners face difficulty in comprehending Newton’s method, particularly when proceeding from a single variable to multiple variables. The same holds true for the concept of exchange of real and reactive powers by FACTS controllers, especially the independency of reactive power exchange by individual VSCs, unlike the exchange of real power. This provided the motivation for writing this book.
This book begins by introducing different VSC-based FACTS controllers and their working principle. The way in which these FACTS controllers exchange real and reactive power with the system is explained in detail. The concepts are supplemented with a few solved problems on some typical FACTS controllers. Subsequently, the book presents an introduction to Newton’s method and its application in solving nonlinear algebraic equation(s), proceeding in a lucid, step-by-step way from a single variable toward multiple variables. It also introduces the reader to the concept of the power flow problem and the application of Newton’s method to the solution of the power flow problem.
This is followed by a systematic and generalized approach for the Newton power flow modeling of VSC-based FACTS controllers, which is developed from the first principles. Because of the unique modeling strategy, existing Newton power flow codes can be reused even after inclusion of FACTS controllers. Practical device constraint limits of these FACTS controllers are also accommodated in the power flow models. A large number of case studies have also been included for the validation of the power flow model of each of the FACTS controllers.
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