Hybrid Excited PM Synchronous Generators: Analysis, Design and Comparison

This paper deals with synchronous generators characterised by a hybrid excitation: permanent magnet (PM) and excitation current. Two structures with fractional slot windings are analysed. The first generator is characterised by a radial flux only, while the second generator is characterised by a flux in both radial and axial direction. The analysis includes the computation of the main generator parameters, flux linkage and voltage according to different excitation currents. The two hybrid excited PM generators have a constant magnetic flux produced by the permanent magnet together with a variable magnetic flux due to the excitation current. As a consequence, it is possible to operate at constant output voltage in a wide load and speed range. The advantages and disadvantages of the topologies are presented, together with an analysis of the output quantities.