A permanent magnet synchronous motor is a
rotating electric machine in which the field excitation is
furnished by permanent magnets. With the advent of high
performance permanent magnet with high coercivity and
residual flux, it is possible for the PM motor to have superior
performance to other type of AC motors, thus it attracts
growing attention for a wide variety of industrial applications
[1][2][3]. Because the excitation of a PM machine is provided
by permanent magnets and there is no need to use brushes and
slip rings, then motor structure is greatly simplified. Also, the
excitation provided by the permanent magnets is current-free
and power lossless, this enables the PM motor to be more
efficient and higher in power density comparing to other
electric motors. Since the armature field and the rotor of the
PM motor are synchronized, and the armature field can be
precisely controlled, accurate torque control is achieved and
high dynamic performance is also assured. It is very
convenient to implement precise speed and position control
with a PM motor. Then by utilizing the back-EMF induced in
the stator windings by the permanent magnets, the control of
the PM motor can be realized without using a position sensor,
which is of particular importance to certain applications where
the use of a rotor position encoder is difficult