this book provides a review of the flexible high voltage direct current (hvdc) options for efficient power transmission. it is designed to highlight the relative merits of both flexible ac transmission systems (facts) and hvdc, enabling the power engineer to make informed choices when planning, designing and operating existing and future power transmission systems. starting with a full introduction to the topic, covering the technical and economic bases for developing flexible hvdc systems, the authors go on to describe to principles and components of current converter technology, including semiconductor power devices. the following chapters analyse alternative proposals for self-commutating conversion, such as pulse width modulation (pwm) and multi-level conversion. the final chapter is on the application of various converter configurations to hvdc transmission, looking at system control and comparing the technologies.