Overview of Field Modulated and Magnetically Geared Electrical Machines-Part I: Origins and History

Field modulation and magnetic gearing effects in electrical machines can be derived from the well-known field harmonic theory. This two-part series of papers reviews the origins, history, and relationship of different types of electrical machine technologies and topologies with field modulation and magnetic gearing effects, as well as recent developments. In this Part I, the origins and early development of field modulated and magnetically geared machines are reviewed, including switched reluctance machines, stator-PM machines, vernier PM machines, multi-port machines, and brushless doubly-fed machines, etc. The general principle of field modulation and magnetic gearing effects and the torque production mechanism of field modulated and magnetically geared machines are introduced based on the field harmonic theory. The common features of field modulated and magnetically geared machines are summarized based on the evolution of machine topologies and general principles of field modulation and magnetic gearing effects. It is shown that electrical machines can be unified by magnetic gears, various field modulated and magnetically geared machines can be obtained by different combinations of magnetic field excitations and modulators, which provides guidelines for developing more novel machine topologies with synergies of different field modulated and magnetically geared machines.