The operation and simulation of a.c. and d.c. machines and a large number of variable-speed drives, including some of the most recently introduced modern drives, are discussed here, and a general theory applicable during their steady-state and transient operation is presented. Although the detailed mathematical analysis given relies mainly on space-vector theory, the relationship to other theories, including the matrix theory of generalized machine theory, is also emphasized. Many of the equations are given in their state-variable or analytical forms so that they can be used directly for computer simulations or for hand calculations. The novel features of this book include: the `exact' and `simplified' performance analysis of a.c. machines and a large number of variable-speed drives are described; both the large- and small-signal equations are given; the effects of magnetic saturation are incorporated into the different models of smooth-air gap and salient-pole machines; the space-vector model is extended to the double-cage induction machine and the salient-pole synchronous machine; it is demonstrated how all the various machine models used in the matrix model of electrical machines can be obtained from the simple space-vector model without having to use matrix transformations; a systematic approach is given for the a priori deduction of all the transformations used in generalized machine theory; and permanent-magnet machines both the surface-mounted and with interior magnets are discussed. Electrical machines and drives can be used without any prior knowledge of space-vector or other theories; it is aimed at students, teachers, and those researching in industry and universities, who require a deep understanding of the various aspects of the operation and the theories of electrical machines and drives and their simulation.