High speed operation of electrical machines, a review on technology, benefits and challenges

The High Speed (HS) technology, in electrical machine based drive systems, is reviewed in this paper by investigating around 200 different machine's data that are reported in the literature or open sources. This study includes information regarding clarifying the maximum power vs. speed capability, potential applications, different machine types, design limitation issues consisting of thermal, electro-magnetic, mechanical, control, inverter and power electronics. The limitations of electrical machines in HS technology are classified by introducing HS-index, which is the product of the machine nominal power and nominal speed (= n × P
_out
). It is shown that HS-index behavior changes by speed, because limitation factors for HS power capability take different physics/nature, as speed increases. It is found that in relatively low speeds, n <; 20 krpm, maximum mechanical stress in the rotor, and in high speeds, n > 20 krpm, additional losses in the machine dictates the maximum power capability. The survey shows that Induction Machine (IM) and Permanent Magnet (PM) machine have relatively superior performance. The maximum rotor surface speed, v
_max
, is limited to 250-300 m/s (can reach 550 m/s) and is independent of n and output power. The HS-index is a function of v
_max
²
and almost independent of n for n <; 10-20 krpm. However, for n > 20 krpm is proportional to v
_max
³
/n
²
due to thermal limitations. The maximum power is almost cubically (P
_out
∝ d
^2.6
) proportional to the rotor diameter.