Потери от вихревых токов в массиве постоянных магнитов магнитоэлектрических вентильных двигателей

Abstract

Higher harmonic components of magnetic field in the air gap of permanent-magnet electrical machines cause eddy currents to occur in the bodies of permanent magnets, due to which the latter become heated and partially demagnetized. Expressions for the coordinate components of magnetic induction and eddy current density in the magnet body (given the known value of the n-th harmonic component of magnetic inductance on the magnet external surface) are obtained proceeding from analytical solution of the well-known Maxwell equations for the n-th harmonic component of magnetic field. It is shown that the electromagnetic wave energy enters into the magnet through the external cylindrical surface and lateral radial flat edges. It is also found that the power flux surface density in the first channel is constant, whereas that in the two other channels decreases exponentially in the radial direction. Therefore, it is not expedient to subdivide the pole magnet into elementary tiles in the transverse direction from the viewpoint of losses, because the losses in the first channel remain unchanged (i.e., they are invariant to decomposition), whereas the losses in the second channel increase (the total number of tile lateral edges increases in decomposing the magnet). The article presents a quantitative assessment of losses in samarium-cobalt magnets of a switched motor with a capacity of 15 kW due to a slotted stator surface outline, a non-sinusoidal waveform of the frequency converter voltage, and higher harmonic components of the stator winding MMF.