Introduction
Brushless DC motors are typically
classified by having trapezoidal back emf and are typically driven by
rectangular pulse current
PM synchronous motor differed from
BLDC motor by having sinusoidal back emf and driven by sinusoidal current
Motors are usually designed for
inside rotor and outside rotor. In this magnetic field travels in radial
direction which are usually called as radial flux motor
If magnetic field travels between stator
and rotor in axial direction, called axial motor
All electrical motor is constructed
with winding on stator and permanent magnet on rotor
Magnet poles and Motor phases
It is possible to build PMSM with
any even number of magnet pole and any number of phases greater than or equal
to one
Usually most of the PMSM motor are designed
for 3 phases
The choice of magnet depends on
application and space available for magnet
For high speed motor it’s better to
choose low number of pole count and for high torque motor its better to choose
high pole number.
For high speed motor D:L ration
will be 1:1 or less and for high torque motor forms pan cake like structure
since it can accombadate more magnets
Stator
Stator usually has teeth that protrude
towards magnet on the rotor from outer ring of steel called stator back iron.
In between teeth are called slots where electrical winding is placed
Electrical and Mechanical measures
Mechanical speed – rotor shaft
makes one complete revolution it travels 360 deg mechanical
Electrical speed – movement of rotor
which puts back the rotor in same identical magnetic orientation
Fe is the fundamental electrical
frequency, which determines the speed at which the commutation must occur to
run at given speed. Inverse of the frequency is commutation time period which
determines the time over which to energize the phase completely.
Fe determines the design of power electronics
to keep the motor running
It is Common to use fewer magnet poles
for high speed motor. Higher the magnet poles increase, torque production
efficiency decreases
