This book will serve as a stepping stone for the undergraduate students in Electrical & Electronics Engineering for further specialization. It is a core subject in the curriculum for post-graduate Power Electronics and Power Systems Engineering disciplines offered by most of the universities and educational institutions. The book starts with the fundamental concepts such as phasors and reference frames which are not usually elaborated at the undergraduate level thereby providing smooth transition to more advanced topics as specified in the various syllabi. The book is also suitable for final semester undergraduate students and practising engineers.