Analysis of Design Topologies for Variable Flux Permanent Magnet Motors

This article presents a comprehensive analysis and evaluation of four topologies for variable flux motors (VFMs) employing AlNiCo permanent magnets (PMs) on their rotors. The investigated topologies are featured with different torque capabilities such as normal saliency, inverted saliency, reluctance torque dominated, and magnet torque dominated. Three rotors employ solely AlNiCo as the PM material while the fourth rotor adopts a combination of AlNiCo and rare-earth magnets connected in series. A new procedure is proposed for evaluating and analyzing VFMs. This procedure considers the irreversible demagnetization performance of hybrid-PM VFMs and determines their safe and critical demagnetization currents. Initially, design maps are created for relating magnet dimensions with key performance metrics of the VFMs under study. Then, a detailed electromagnetic performance evaluation is conducted describing the magnetization-state-dependent operation of the four rotors. It is revealed that, full reliance upon AlNiCo magnets lead to sacrificing the reluctance torque capability of the inverted saliency VFMs. In addition, as the reluctance torque proportion is increased, the on-load demagnetization risks increase along with increasing the magnetization requirements. On the other hand, positioning the PMs magnetically in series can reduce these drawbacks with the main tradeoff being the increased risk of rareearth magnet irreversible demagnetization. Finally, experimental tests are conducted on two different motors for validating the analysis.