User Manual

Brushless Motor Connections and Operation
120 Advanced Digital Motor Controller User Manual V2.0, July 8, 2019
Bandwidth is in rad/sec and according to Nyquist criteria the current loop bandwidth can-
not be more than the half of the current loop sampling time. Most commonly the current
loop bandwidth is set to the 1/10-1/20 of the current loop sampling time. The current loop
sampling time is at 1kHz. So if we choose as current loop bandwidth the 50Hz then:
1Hz = 2π rad/sec
So for 50Hz Bandwidth = 50*2π rad/sec = 314.
Usually even smaller bandwidth can be as effective as the 50Hz. It is better to start with
the smaller possible gains and then tune according to the behavior of the motor. Test in
open loop with caution.
Example calculation for 50Hz bandwith, 11mOhm Phase resistance and 90uH Phase In-
ductance
Ki = 0.011 * 314 = 3.45
Kp = 0,00009 * 314 = 0.028
FOC Testing and Troubleshooting
Verify that FOC is operating correctly by monitoring the following values with the PC
Utility:
Optimal performance is achieved when:
• FOC Quadrature Amps are close to 0.
• Motor Amps and FOC Torque Amps values are close.
• FOC Angle Correction is stable for stable motor Power.
Check also when changing motor power how fast FOC Flux Amps is corrected to zero.
Tune FOC PI as necessary.
Instable FOC correction is generally a sign of imperfections of the angle sensing (noise,
non-linearity, bad calibration, ...). Bad angle sensing causes the wrong values of Id and Iq
to be measured, which the FOC algorithm falsely attempts to correct, worsening the cur-
rent instability.