Design, Analysis of a Seven-Phase Fault-Tolerant Bi-Harmonic Permanent Magnet Machine With Three Active Air Gaps for In-Wheel Traction Applications

For the requirements of in-wheel traction systems, a new motor is proposed based on a specific property of multiphase machines: the ability in vector control to develop smooth torque at low speeds by using simultaneously the first and third harmonics to generate p and 3p polarities. From an initial fault-tolerant seven-phase axial–flux machine with two outer axial rotors for small vehicles such as moto/scooter is born the proposed motor just by adding magnets in the cylinder closing the two 2p-pole axial rotors of initial in-wheel motor, this addition creates thus a third radial rotor with 6p poles without changing the global volume. With an increase by 51% of the torque density, this more expensive motor can be considered in comparison with the initial in-wheel motor as a modular solution. With the same volume, a higher torque for higher acceleration and slopes can be obtained. The possibility to use different polarities with a strong non-sinusoidal back-emf without torque ripples is verified in 3D-FEM simulation and in a manufactured 28 slots – 12/36 poles prototype. Experimental results are given to prove the effectiveness of the proposal.