A novel dual-rotor hybrid machine with synchronous reluctance and surface permanent magnet rotors

The goal of this paper is to investigate a proposed novel dual-rotor hybrid synchronous machine using two different types of rotors, i.e. the synchronous reluctance (SyR) and surface permanent magnet (SPM) rotors. Conventional design of dual-rotor machine utilizes SPM rotors on both inner and outer sides with toroidal winding configuration. However, there are limitations of using the permanent magnet in the inner rotor such as centrifugal forces on the magnets at high rotational speed conditions and relatively low torque density if ferrite permanent magnets are used. This research proposed a novel topology by using a well-designed SyR rotor to replace the inner SPM rotor in the conventional design. The principle of operation including combined space vector diagram of the novel dual-rotor hybrid machine is discussed. Sizing equations of the proposed machine are derived to show the calculation of output power from key dimensions and electrical and magnetic loading conditions. The N-N and N-S configurations of the novel dual-rotor machine are compared. The performance of the novel machines is studied against the conventional dual-rotor surface permanent magnet machine by finite element analysis (FEA) to demonstrate that the proposed machines achieve higher torque densities with less permanent magnet consumption. The proposed N-S machine is also scaled for the traction motor specification and compared to a conventional interior PM machine.