Design of Hybrid Variable Flux Motors for Enhanced Wide-Speed Performance

The paper presents a detailed study about Variable Flux Machines (VFMs) with series rare-earth and AlNiCo magnets. A tangentially magnetized series hybrid VFM is first compared to a VFM with AlNiCo magnets, and the Finite Element Analysis (FEA) results show the benefits of the series hybrid configuration in terms of higher power capability at high speeds, more stable magnet operation at full load and lower magnetization current requirement. The effects of saliency, magnet orientation and magnet grade on the hybrid VFM performance are then investigated using FEA. Among the various simulated designs, the V-shaped hybrid VFM with normal saliency and higher grade rare-earth magnets is found to have the best overall performance. The selected design is then optimized using Genetic Algorithm (GA) based procedure that aims to maximize the machine output torque, while satisfying the VFM demagnetization/magnetization requirements. The optimized design can achieve high torque at low speeds and maintain constant power at high speeds by utilizing lower magnetization levels.