Design and Retrofit of Consequent-Pole Permanent Magnet Machines with High Component Commonality and Enhanced Magnet Utilization

The spatial asymmetry of the air-gap flux density in consequent-pole permanent magnet (CPPM) machines leads to large cogging torque (Tc) and abundant even-order harmonics in the back electromotive force (BEMF). Conventional suppression methods rely on iterative parameter optimization, which often compromises structural modularity and component commonality. To address this issue, this paper proposes a design strategy based on preselection of a conventional reference machine. The strategy mitigates these drawbacks at the topological level and avoids multi-parameter optimization. First, an analytical Tc model is established. It accounts for parameter uncertainties and unequal pole widths, and reveals that the fundamental period of Tc is always equal to one slot pitch. Second, an analytical total-flux model is developed to evaluate the effects of parameter optimization on the total flux and the flux contribution per unit volume of permanent magnet (PM) material. On this basis, reference-machine selection criteria are proposed. Stator slot skewing is used to reduce Tc, and full-pitch windings are used to suppress even-order harmonics. The designed CPPM machine inherits the stator components and rotor PMs of the reference machine. A non-magnetic shaft is used to reduce unipolar end leakage flux. Only the iron-pole arc width is optimized through a single-parameter sweep. Finite-element (FE) analysis results show that the optimized CPPM machine exhibits reduced Tc and suppressed even-order harmonics. Compared with the reference machine, the optimized machine uses half the PM material. Its output torque reaches 81.33% of the reference value; its torque per unit PM volume increases by 62.66%; and the cost share of rare-earth PM material decreases from 34.00% to 21.58%. Finally, prototypes of both the reference and the proposed CPPM machines are fabricated. Measurements of the end leakage flux at the shaft extension and the output torque validate the theoretical analysis and optimization results.