Review and Analysis of Coaxial Magnetic Gear Pole Pair Count Selection Effects

Abstract

Magnetic gears perform the same function as mechanical gears using magnetic fields instead of interlocking teeth. A review of the design processes used in the literature demonstrates that a critical design parameter, pole pair count, is often given inadequate consideration. In addition to reviewing the existing prototypes, this article uses a parametric simulation study to analyze the impacts of pole pair counts on gear performance and illustrate how the optimal pole counts vary with gear ratio and various design parameters. This article also introduces new ripple factors, which better correlate with torque ripple than the cogging factor ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C_{T}$ </tex-math></inline-formula> ) used in previous articles, and illustrates why designs with noninteger gear ratios tend to have much smaller torque ripples than designs with integer gear ratios. While selecting the pole counts to minimize symmetry can reduce torque ripple, designs without any symmetry are shown to experience unbalanced magnetic forces on each rotor. Thus, it is recommended to select pole counts that result in an even number of modulators but not an integer gear ratio. This article also reveals that for a fixed gear ratio, a nontrivial optimum pole count minimizes the electromagnetic losses.