ElmoMC SimplIQ Digital Servo Drives-Bell Command Reference - Manual (Page 299)

SimplIQ compensates, however, for a non-sinusoidal winding shape. This assures that
a 1 Amp effective current demand always produces the same torque, regardless of the
motor angle. When winding compensation applies, the winding current waveforms
become more complex.
For Iq=1, Id=0 the phase current peak value of 1 Amp is no more guaranteed, but the
RMS value of 0.707Amp remains.
9.1.2 Output Transformation: Calculating Phase
Voltages
This block transforms the outputs of the Q and D controllers – namely Vq and Vd – to
motor phase voltages.
In the simplest sinusoidal, non saturated case, we have
cos( cos(
sin( si
) 90 )
) ( 90 ) n
a q d
b q d
o
o
c a b
V V V
V V V
V V V
θ θ
θ θ
+ +
+ +
= − −
=
=
In the 3-phase case
) cos( 90
) sin( 90
cos( )
sin( )
a q
b
o
d
a
c d q
d c
o
V
V
V V
V V
V
V
V
V
θ θ
θ θ
+ +
= + +
=
= −
= −
In the 2-phase case (stepper)
The math is significantly more complex accounting for winding corrections.
With winding corrections:
- Predicted values are added to the voltages to overcome rotating inductance
effects and BEMF.
- Voltages are converted to PWM values, using the available DC supply voltage.
- The neutral point voltage is set.
- Vector saturation is applied as needed.
- If saturation occurred, anti windup corrections are returned to the Q and D
controllers.
The final PWM values are sent to the switching transistors.
9.2. Cogging Correction
Cogging is a magnetic friction – it comes from the magnetic asymmetry of the motor.
The cogging generates torques or forces that are independent of the motor current.
SimplIQ for Steppers Application Note The Current Controller
MAN-STECR (Ver. 1.1)
100