DESIGN AND ANALYSIS OF HIGH-SPEED BRUSHLESS PERMANENT MAGNET MOTORS.pdf
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DESIGN AND ANALYSIS OF HIGH-SPEED BRUSHLESS PERMANENT MAGNET MOTORS
Z.Q. Zhu, K. Ng, and D. Howe
University of Shefield, UK
INTRODUCTION
High-speed brushless permanent magnet machines are
likely to be a key technology for electric drives and
motion control systems for many applications, since
they are conducive to high efficiency and a high power
density, small size and low weight [I] . However, due to
the high fundamental operating frequency a more
detailed consideration of various operational issues,
such as stator iron losses and rotor parasitic eddy
current losses, and the influence of the winding
inductances on the dynamic system performance, is
advisable at the design stage [2-51.
The paper reports on the design of a 20,00Orpm, 3-
phase brushless permanent magnet dc motor for use in
a friction welding unit, in which studs up to 3mm
diameter and welded by coordinating the rotational
speed of the motor with the force applied by a linear
permanent magnet servo-actuator. The motor consists
of a stator having 3 teeth, which carry non-overlapping
windings, and a 2-pole diametrically magnetised
sintered NdFeB magnet rotor, as shown in Fig.]. The
airgap flux density distribution is essentially sinusoidal.
The advantages and disadvantages of such a motor
topology for this and other high speed applications are
discussed, and an optimal airgap diameter is derived.
The effect of the stator tooth tip geometry on the
waveform of the induced emf is investigated by finite
element analysis, and validated by measurements,
whilst the merits of laminated silicon iron and soft
magnetic composite materials for the stator core are
considered.
GENERAL DESIGN CONSIDERATIONS
The higher the operating speed of a motor the smaller is
its physical size for a given output power. Hence, in the
case of a permanent magnet machine, the lower will be
the volume of magnet material. Therefore, high speed is
particularly appropriate when rare-earth permanent
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