Analytical Modeling of a Novel Vernier Pseudo-Direct-Drive Permanent-Magnet Machine

In low-speed high-torque applications, gearboxes are widely used to amplify the output torque of electrical machines, which inevitably introduce side effects caused by mechanical contact. Consequently, a gear-free system has become increasingly interesting. Although a Vernier permanent-magnet machine has good torque capability, the low power factor is its weakness. This paper proposes a novel topology called the Vernier pseudo-direct-drive (VPDD) machine. A two-stepped design methodology is adopted by combining the subdomain analytical method and finite-element method (FEM). According to the results, the exact subdomain analytical model allows a quick pre-optimization of the structure, and the FEM can be used for further adjustment, dealing with the saturation effect and demagnetization. The optimized VPDD is capable of reaching a very high torque density of 91.8 Nm/L, and the torque ripple is negligible. Its power factor is 0.94.