Effect of Skewing in a Variable Flux Interior Permanent Magnet Synchronous Machine

The motivation of this article is to minimize the cogging torque and the torque ripple in a 6-pole 27-slot variable flux interior permanent magnet synchronous machine (VF IPMSM) by skewing the permanent magnets (PMs) in several steps. AlNiCo9 is used as the PM material in the rotor as the magnetization level of the AlNiCo9 PM can be changed and controlled by proper current control. The optimum skewing angles to minimize the cogging torque are found analytically and verified by using the finite-element analysis (FEA). The effect of these skewing angles on the back electromotive force and the torque ripple is also studied at different magnetization levels of the AlNiCo9 magnets. An FEA shows that a step skewed PM pole significantly minimizes the cogging torque and the torque ripple in the VF IPMSM. A current pulse in the d-axis is applied to magnetize or demagnetize each step in the step skewed PM pole. The minimum optimum skewing angle is chosen such that each step of the step skewed PM pole is magnetized or demagnetized with minimum nonuniformity.