UM-YROTATE-IT-RX62T Datasheet, PDF (17/54 Pages) Renesas Technology Corp – Low Cost Motor Control Kit based on RX62T

RX62T
YROTATE-IT-RX62T Motor Control Kit
10. Permanent magnets AC Brushless motor model
The synchronous permanent magnets motor (e.g. sinusoidal Brushless motor) is widely used in the industry. More
and more home appliance makers are now using such AC Brushless motor, mainly because of the intrinsic motor
efficiency.
The permanent magnet motor is made with few components:
1. A stator formed by stacking sheared metal plates where internally the copper wiring is wound, constructing
the stator winding
2. A rotor in which permanent magnets are fixed
3. Two covers with ball bearings that keep together the stator and the rotor; the rotor is free to rotate inside
the stator
“a” winding
“b” winding
i_a
Motor axis
+
(shaft)
v_a
“c” winding
“a” winding
magnetic axis
How current flows
into “a” winding
i_c
i_b
+ ^vc
v_b
+
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 v_a(t), v_b(t), v_c(t) to the stator windings, the relations between phase voltages and currents
are:
UM-YROTATE-IT-RX62T Rev.1.00
Jan 15, 2014
Page 17 of 51