6.1.1. Definition

A hybrid excitation synchronous machine (HESM) is a machine associating the features of permanent magnet synchronous machines (PMSM) and coiled rotor synchronous machines (CRSM). It is a class of synchronous machine where the excitation flux is obtained by the contribution of two sources: one part of the excitation flux is created by permanent magnets; the other part by one or more excitation coils. This definition shows that the hybrid excitation concept is not linked to the synchronous machine. We could, for instance, design linear hybrid excitation actuators, or even hybrid excitation DC machines. We will exploit this to explain the simple functioning principle of hybrid excitation structures. The aim of such an association is obviously to associate the advantages of the two types of classical synchronous machines, i.e. a high mass and volume torque for PMSM and control of the excitation flux for CRSM.

In the first approach, excitation flux exc can be written as the sum of two fluxes: one generated by magnets a (which we will refer to as the magnet flux) and one generated by the excitation coils f (called the flux of excitation coils). This is summarized by the following equation: