I. Introduction
IN the last few years, several studies dealing with the design of high-speed electrical drive systems have been published, e.g., [1], [2]. The scaling and the speed limitations of high-speed electrical machines are analyzed in [3]– [5]. However, the use of ultrahigh-speed systems in industrial applications has been limited, mainly by the absence of reliable bearings for rotor support and long lifetime of several thousand hours. Promising candidates for high-speed bearings with longer lifetimes are contactless concepts such as active magnetic bearings (AMB) or gas bearings. The scope of this paper is the magnetic bearing, as it is the only contactless bearing technology that can be operated in vacuum or low-pressure environments, such as high-speed optical scanning systems or reaction wheels for attitude control of satellites in orbit. The focus will be on low-power ultrahigh-speed electrical drive systems.