Analysis of the Power Factor of Stator DC-Excited Vernier Reluctance Machines

Stator dc-excited vernier reluctance machines (dc-VRMs) are a kind of a novel vernier reluctance synchronous machine that employs doubly salient structures; their innovations include stator concentrated dc windings to generate the exciting field. Compared with the rotor wound field machines or stator/rotor PM synchronous machines, these machines are characterized by low cost due to the absence of PMs, a robust rotor structure, and a wide speed range resulting from the flexible stator dc exciting field. In this paper, with the proposed phasor diagram, the power factor of dc-VRMs is analyzed analytically and with the finite-element analysis, and the analysis results are confirmed with the experiment. It is found that, with constant slot sizes and slot fill, the power factor is mainly dependent on the ratio of the dc current to the armature winding current and also the ratio of the armature synchronous inductance to the mutual inductance between the field winding and the armature winding. However, torque will be sacrificed if measures are taken to further improve the power factor.