Permanent Magnet Assisted Synchronous Reluctance Motor: an Alternative Motor in Variable Speed Drives
The design and performance of a permanent magnet assisted synchronous reluctance motor (PMASynRM) is investigated using finite element method. The motor is called PMASynRM when the share of reluctance torque is significant compared to the PM electrical to
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Abstract The design and perfonnance of a pennanent magnet assisted synchronous reluctance motor (PMASynRM) is investigated using finite element method. The motor is called PMASynRM when the share of reluctance torque is significant compared to the PM electrical torque. The advantages of adding PMs to the synchronous reluctance motor rotor construction are the increased motor power factor and thus reduced motor stator ohmic losses. The ohmic losses represent the majority of the motor total losses. The advantage of reluctance torque is the decreased need of expensive pennanent magnet (PM) material, which makes this solution thus cheaper than the respective pennanent magnet motor. The advantages of PMASynRM compared to the induction motor (1M) are the synchronous rotation speed, possibility of sensorless rotation control, higher power factor and better efficiency.
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Introduction
An interesting alternative for today's high efficiency variable speed drives is the PMASynRM drive, which belongs to the family of brushless synchronous AC motor drives. These drives consist of sinusoidal current driven machines, which use a quasi-sinusoidally distributed AC stator winding and frequency converter. The design of brushless synchronous AC motors has not matured yet to a similar degree, on which e.g. the designing of induction machines is. During the recent years there has been a considerable increase of interest in using brushless synchronous AC machines in applications where previously asynchronous machines have been used. Traditionally brushless synchronous AC machines have been used in low-power servo drives, but with the recent development in both pennanent magnets and power electronics also medium and large power drives are gaining more interest. The suitability of a brushless synchronous AC motor to a particular application is, however, dependent on the motor design. Selecting the parameter to fulfill the requirements of applications is clearly an optimization problem. The
F. Parasiliti et al. (eds.), Energy Efficiency in Motor Driven Systems © Springer-Verlag Berlin Heidelberg 2003
102 main types of brushless synchronous AC motor are surface mounted permanent magnet (SPM) or interior permanent magnet synchronous motor (lPM), synchronous reluctance motor (SynRM) and the combination of these two types namely permanent magnet assisted synchronous reluctance motor (PMASymRM). Even though the IPM motor has a reluctance torque component the share of it is remarkably lower than electric torque especially if the pole-pair number is big. The family of brushless synchronous AC machines is shown in Fig. 1. The dotted areas represent steel, the white areas represent air or some nonmagnetic material and dark grey areas represent permanent magnets.
a)
b)
c)
d)
Fig. 1. Brushless synchronous AC machines a) surface mounted pennanent magnet motor, b) Interior pennanent magnet motor, c) Synchronous reluctance motor and d) pennanent magnet assisted synchronous reluctance motor.
The SPM motor (Fig. la) operates purely with magnet a
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