Microchip Technology DM164130-2 Fiche De Données
F1 LV Evaluation Platform Motor Control Add-ons
DS41629A-page 26
2012 Microchip Technology Inc.
11. Enter the % Drive number into the % Drive start-up value.
12. Click the Parameters tab and verify or enter the following nominal values:
12. Click the Parameters tab and verify or enter the following nominal values:
a) Blanking: 100 us
b) Slow Step: 200 ms.
c) Open Loop: 500 ms.
d) Run: % Drive entered in step 13.
e) Stop: 2 less than Run
f) Stall: 900 us
g) Error Scale: 3
b) Slow Step: 200 ms.
c) Open Loop: 500 ms.
d) Run: % Drive entered in step 13.
e) Stop: 2 less than Run
f) Stall: 900 us
g) Error Scale: 3
13. Click the Operate tab and select Closed-Loop mode.
14. Hold your breath, cross your fingers, and slowly increase the speed control to the
14. Hold your breath, cross your fingers, and slowly increase the speed control to the
point where the motor starts. With any luck, your motor will start and immediately
lock onto the BEMF feedback to become fully operational in Closed-Loop mode.
When that happens, you can increase the speed control to the desired rate. Click
on the RPM label to perform one reading of the motor RPM.
lock onto the BEMF feedback to become fully operational in Closed-Loop mode.
When that happens, you can increase the speed control to the desired rate. Click
on the RPM label to perform one reading of the motor RPM.
Now that you are able to operate the motor in closed loop, at least at slow speed, you
need to complete the optimization of the other motor parameters. The following
procedures describe each parameter and its adjustment.
need to complete the optimization of the other motor parameters. The following
procedures describe each parameter and its adjustment.
2.4.3.1
BLANKING
The blanking interval is required so the BEMF sense does not falsely trigger on the
flyback voltage caused by commutation. You can observe this pulse on any motor lead
while the motor is running. The flyback pulse voltage occurs immediately following the
unmodulated drive period. The width of the flyback pulse varies depending on the
inductance of the motor windings and the motor load current. Measure this pulse under
worst-case motor operation and set the blanking time to at least the measured time
plus some margin. The blanking time must be less than 50% of the minimum
commutation period, and ideally much less than that. You may notice during
measurement that some modulation pulses immediately following the flyback pulse
extend beyond the mid-level of the drive voltage. Treat those pulses as part of the time
that must be blanked.
flyback voltage caused by commutation. You can observe this pulse on any motor lead
while the motor is running. The flyback pulse voltage occurs immediately following the
unmodulated drive period. The width of the flyback pulse varies depending on the
inductance of the motor windings and the motor load current. Measure this pulse under
worst-case motor operation and set the blanking time to at least the measured time
plus some margin. The blanking time must be less than 50% of the minimum
commutation period, and ideally much less than that. You may notice during
measurement that some modulation pulses immediately following the flyback pulse
extend beyond the mid-level of the drive voltage. Treat those pulses as part of the time
that must be blanked.
2.4.3.2
SLOW-STEP DWELL TIME
During start-up, the motor windings are energized for a short period to pre-position the
rotor. Slow step is the length of time that the windings are energized. Large high inertia
motors take longer to reach the position, and therefore need extra time. Experiment
and use the shortest time that works.
rotor. Slow step is the length of time that the windings are energized. Large high inertia
motors take longer to reach the position, and therefore need extra time. Experiment
and use the shortest time that works.
2.4.3.3
OPEN-LOOP DWELL TIME
The open-loop time is the amount of time that the motor operates in Open-Loop mode
before the ramp-up to BEMF detection starts. The open-loop voltage and commutation
rate is the same that you entered in the start-up parameters. Small low inertia motors
start well going straight from slow step pre-position into the ramp-up to BEMF
detection. For those motors you can enter an open-loop time of zero. Larger motors
need time to stabilize at the open-loop rate before ramping up. Experiment to find the
value that works best for your motor.
before the ramp-up to BEMF detection starts. The open-loop voltage and commutation
rate is the same that you entered in the start-up parameters. Small low inertia motors
start well going straight from slow step pre-position into the ramp-up to BEMF
detection. For those motors you can enter an open-loop time of zero. Larger motors
need time to stabilize at the open-loop rate before ramping up. Experiment to find the
value that works best for your motor.
2.4.3.4
RUN/STOP PERCENTAGE
The run value should match the start-up drive value to ensure a smooth transition from
open loop to ramp-up. Once BEMF lock is obtained, most motors are able to maintain
lock below the start-up drive value. Experiment to find the stop value that ensures
reliable motor operation at slow speed.
open loop to ramp-up. Once BEMF lock is obtained, most motors are able to maintain
lock below the start-up drive value. Experiment to find the stop value that ensures
reliable motor operation at slow speed.