ElmoMC SimplIQ Software Manual - Manual (Page 114)

SimplIQ Software Manual Commutation
MAN-SIMSW (Ver. 1.4)
8-4
The following table describes the digital Hall sensor reading. The BLDC field angle is the
angle that produces maximum torque for this Hall sensor reading.
Hall A
Hall B
Hall C Electrical Rotor
Position (Degrees) BLDC Field
Angle (Degrees)
0 0 0 Illegal
1 0 0 330 - 30 90
1 1 0 30 - 90 150
0 1 0 90 - 150 210
0 1 1 150 - 210 270
0 0 1 210 - 270 330
1 0 1 270 - 330 30
1 1 1 Illegal
The crude division into six draws a rough torque from the motor, and requires hard
switching of the motor winding currents.
In many application digital Hall sensors are used together with higher-resolution position
sensors. The Hall sensors serve to initialize the field direction and add redundant position
sensing for increased reliability.
8.3.2 Shaft Angle Sensors
The second group of sensors consists of shaft angle sensors. This category includes encoders
of all types (incremental digital and analog, absolute digital and analog), resolvers,
capacitive sensors and others. The
SimplIQ drive can only interface directly with digital and
analog incremental encoders. Shaft angle sensors normally have good resolution, but must
be homed (referenced absolutely) with respect to the rotor electrical angle.
For commutation calculation, it is important to know how many bits the shaft sensor counts
per single electrical cycle. If this number is not an integer, after a certain amount of
movement, the calculated commutation angle may accumulate numerical errors and cause
the motor to lose torque. The numerical commutation error is not a serious issue with linear
motors, because the limited travel also limits the commutation calculation error. With rotary
motors, each mechanical shaft rotation involves an integer number of encoder counts, per an
integer number of electrical cycles. This means that the commutation can be kept as accurate
as:
p1 = mod (encoder, counts per shaft revolution)
and
Electrical rotor angle = 360º * * mod (pl, )
Counts per shaft revolution
Number of pole pairs Counts per shaft revolution
Number of pole pairs