The Optimal Design and an Analysis of a Hybrid W-Shaped IPM Rotor of Coaxial Magnetic Gear

This paper presents a hybrid, W-shaped interior permanent magnet (HWIPM) rotor of a coaxial magnetic gear (MG). To reduce the usage of rare-earth PM material, it proposes a topology of inner rotor in a MG with two types of PM materials. The key point about this idea is that NdFeB PM is applied in combination with ferrite PM to form a hybrid PM excitation. This new type of HWIPM rotor is introduced, and the structure and principles of the operation are explained in details. The optimization and analysis results, using finite element method, showed that this structure could improve torque density and reduce cogging torque, while the cost of rare-earth PM consumption decreased, compared with conventional flat type interior PM-MG. A prototype was fabricated and the performances were experimentally verified. The experimental results showed that the proposed MG had superiorities of low cogging torque, low PM cost, and high torque density compared with conventional coaxial MGs.