Datasheet

7. Permanent magnets brushless motor model
The synchronous permanent magnets motor (sinusoidal brushless motor) is widely used in the industry. More and more
home appliance makers are now using such brushless motor, mainly because of the intrinsic motor efficiency.
The permanent magnet motor is made with few components:
 A stator formed by stacking sheared metal plates where internally the copper wiring is wound, constructing the
stator winding.
 A rotor in which permanent magnets are fixed.
 Two covers with ball bearings that keep together the stator and the rotor; the rotor is free to rotate inside the
stator.
PMAC Motor Model
The working principle is quite simple: if we supply the motor with a three-phase system of sinusoidal voltages, at
constant frequency, in the stator windings flow sinusoidal currents, which create a rotating magnetic field.
The permanent magnets in the rotor tend to stay aligned with the rotating field, so the rotor rotates at synchronous speed.
The main challenge in driving this type of motor is to know the rotor position in real-time, so mainly implementation
are using a position sensor or a speed sensor.
In our implementation, the system is using either one or three shunts to detect the rotor position in real-time.
Let’s analyse the motor from a mathematic point of view.
If we apply three voltages va(t), vb(t), vc(t) to the stator windings, the relations between phase voltages and currents
are:
dt
d
iRv
dt
d
iRv
dt
d
iRv
c
cSc
b
bSb
a
aSa






- 
i
is the magnetic flux linkage with the i-th stator winding.
- R
S
is the stator phase resistance (the resistance of one of the stator windings).
+
+
+
v
a
v
b
v
c
i
a
i
c
i
b
“a” winding
How current flows into
“a” winding
“a” winding
magnetic axis
“b” winding
“c” winding
Motor axis
(shaft)