Torsional shear stress minimization techniques and implications on electromagnetic performance of flux-modulated double rotors

Magnetic geared machines are based on the flux-modulation principle and typically constructed with a flux-modulated double rotor (FMDR). The modulator experiences high torsional stresses when designed for high torque transmission. This result in modulator deformation and pose a significant risk of failure of the FMDR. In this paper, the FMDR design options are investigated with mechanical and electromagnetic FE modeling. The addition of filler material in between the poles reduce the shear stresses by 61.7% to 87.2% at the cost of 2.6% to 3.2% lower pull-out torque. Increase in pole number is shown to increase localized stress levels in bridged modulators. Electromagnetic simulations show that the highest pull-out torque is at an optimal pole number. The trade-off between FMDR weight, losses and shear stress are discussed. A scaled-size prototype FMDR with a bridged modulator is constructed. The FMDR is tested and achieves comparable results with the FE simulations. At field intensity levels above 600 kA/m in the periphery of the FMDR, the end effects are prominent and experiences a reduced pull-out torque 28.7% lower in comparison with 3D simulations. The losses at different load levels of the FMDR are also compared and experimental result confirm the FE results.