Investigation and Suppression of Cross-Phase-Count Magnetic Field Modulation in Compound Permanent Magnet Vernier Machines

Recently, compound permanent magnet vernier machines, such as the double-stator, double-rotor, or hybrid-excitation topologies, have the advantages of enhanced torque capacity and compact structure. They inherently rely on the magnetic field modulation (MFM) effect. However, the design of a compound machine structure increases the number of parts involved in MFM, thereby making the modulation effect more complex. Additionally, due to the different parameter design of field sources, their interactions and influences on the air-gap field have not been fully understood. As to multiphase motors, the philosophy of cross-phase-count MFM to be studied in this paper becomes crucial. Through compound permanent magnet vernier machine topologies, this article reveals and features the adverse influence of the field modulation between armatures with different phase counts. Also, various rotor structures are studied to explore the approaches to suppressing this influence. It is concluded that the cross-phase-count effect is subject to not only modulation-sensitive parameters but also the design of rotor topology.