A fully coreless Multi-Stator Multi-Rotor (MSMR) AFPM generator with combination of conventional and Halbach magnet arrays

An axial flux permanent magnet (AFPM) generator is known to be a good candidate for both low and high-speed application. In this paper, a new design of fully coreless multi-stator multi-rotor (MSMR) AFPM generator has been presented with conventional and Halbach magnet arrangement combined with an ironless (epoxy) rotor. For MSMR topology of AFPM machine, back iron is still present in the middle rotor and to maintain the same distribution of magnetic flux, magnets are using on both side of the middle rotor. This paper suggests replacing the middle iron rotors with a single epoxy rotor which reduces the weight of the machine, hence increase power density. On the other hand, for the elimination of iron and magnets in the middle rotor, conventional magnet arrays are used to maintain a continuous flux path. In addition, Halbach array is adopted on the external epoxy rotor to reduce flux leakage on the external sides of the machine. The performance of the proposed generator is investigated in terms of voltage, current, power, power density, and torque ripple. The analytical design approach is first presented and subsequently validated using ANSYS Maxwell® electromagnetic finite element analysis (FEA) software. It is found that a fully coreless MSMR AFPM generator with conventional and Halbach magnet arrays gives higher power density and lower torque ripple with a reduced axial length which is favorable in wind power and pico-hydro applications.