Multi parameter analysis of layer insulation of segmented magnets

Abstract:
Eddy current losses in permanent magnets (PM) and their mitigation are significant factors in designing inverter fed electric drives. Especially with the need for high power density drives a trend towards increased rotational speeds and therefore higher fundamental frequencies and inverter switching frequencies is observable. Frequency components of concentrated windings and fractional slot windings are widely minded when designing sintered rare earth magnets for permanent magnet synchronous machines (PMSM). On the other hand, inverter related losses are rarely simulated in Finite Element Method (FEM) co-simulations and can contribute as a major factor to the power loss in PMSM. In the worst case this neglection can lead to the thermal demagnetization of the permanent magnets. Segmentation provides an effective measure against eddy current losses [5-6]. However, there is little scientific information and common miss-believes on the requirements of insulation layer thickness and insulation properties in between magnet segments. Whilst decreased insulation gaps in between the magnets enhances the magnetic properties of the magnets, insufficient insulation does not inhibit eddy currents between the single magnet segments. This paper states the results of FEM simulations conducted to estimate the impact of insulation layer resistance on eddy current losses in permanent magnets. A comprehensive analysis of potential influences, e.g. geometry and magnetic field frequency, on insulation requirements in between magnet segments is given. 3-D FEM simulations with Ansys Maxwell do neglect the change of electric displacement field and can therefore not take parasitic capacitance effects into account. A simple analysis of the effects of parasitic capacitance in magnet segmentation is given. Furthermore, a crude analytic model is given for quick practically oriented estimations of insulation requirements.