The dissipation models of AMB and its computational methods

Active magnetic bearing (AMB) is a kind of advanced high speed bearing, it is used to suspend rotor without contact between stator and rotor by magnetic power. At present researches on active magnetic bearing mainly focus on power amplifier and control system, but the researches on its power losses are very few. Because active magnetic bearing is turning at high speed, its power losses can not be neglected. Power losses can increase the temperature of AMB, make stator and rotor thermal deformation, have an effect on bearing’s orientation, even make stator and rotor produce distortion, and influence active magnetic bearing normaloperation. At the same time, it can reduce insulation capability of windings; shorten its life-span. So it is important to estimate the power losses to insure AMB normal operation. There are three kinds of power losses in AMB, including copper losses, iron losses and windage losses. It is necessary to research and compute the three kind of power losses. This paper investigated present researches on power dissipation of AMB, summarized three dissipation models, gave their computational methods and their application range. Copper losses can be computed by ohm law. Iron losses consist of eddy losses and hysteresis losses. Eddy losses are generally proportional to the square of frequency. Hysteresis losses are generally proportional to frequency. So hysteresis losses are very low in iron losses at high frequency and can be ignored, but it will account for the large proportion of iron losses at low frequency. And iron losses depend on the arrangement of magnetic pole, such as alternating pole (NSSN) and paired pole (NNSS). At present the analysis of iron losses are based on such assumptions as material linearity and neglect of magnetic saturation, but material nonlinearity must be token into account when AMB rotates at high speed, so actual iron losses are larger than computational results. Windage losses can be described by fluid state in air gap and corresponding empirical formula, and in high-speed motors the surface speed of the rotor is typically between 150 and 400 m/s. At this range the windage losses are proportional to the cube of the surface speed. Index Terms – active magnetic bearing; copper losses; iron losses; windage losses.