MCF8316AEVM: 8A application with fast speed and torque adaption

Dear Support,

I am currently testing the MCF8316AEVM I2C. I connected a 24VDC 200W power supply at the input and I would like to drive a high speed motor to the maximum load supported which is 8A.

Application: we want to use the driver to drive the motor from some 1000 rpm to maximum speed with a fast torque adaption when we apply variable load which could need 7A currents. The speed should remain constant while load is increasing and the motor should be reactive supporting actions less than 1 second and fast starting (1 second max) and decelerating (2 seconds).

Motor parameters: 1 pole pair high speed sensorless motor, 16mm diameter, 24VDC, 40.000rpm, 8,19A stall current, 110µH and 2,9Ohms.

After first MCF8316A_GUI 1.1.8 adjustments, at 25% I2C Speed Command my motor turns well at 10.000rpm (100% = 667Hz = 40.000rpm).

I would need some help regarding the various topics: 

• Maximum current

The GUI is configured to allow the highest current limits settings 8.0A in order to no be limited in current in my application because we want to apply a variable load on the motor axis and have fast and powerful reaction.

Ki Kp are in auto tune and by making some fast tunings it doesn't help me on the torque.

When I apply a load at 25% speed, it not reaches more than 3/4A but I would need 7/8A until the motor stalls.

>>> Do you have any recommendation to adapt the driver to reach higher current? 

• Working at low speed

My motor is not turning so fine at low speeds. 15%/6000rpm is working but I would like to turn less. BEMF voltage I read on the GUI is 19mV/Hz.

>>> Do you have any recommendation to have stable rotation at speed under 5000rpm and still good torque? 

• Heating

To improve the temperature of the motor, I suppose the best is to increase the PWM frequency and currently it is 25 KHz but if I increase, the motor doesn’t work at low speed.

>>> Do you have any recommendation to improve the motor heating? 

• Starting/Decelerating ramp

I configured a fast acceleration 500 Hz/s in order to start fast the motor from idle to maximum speed to around 1 second. This generally works fine.

Then when I set the motor to high speed and then send a lower speed command, the motor doesn’t decelerate fine and often it stalls or blocks by HW_LOC_LIMIT fault.

>>> Do you have any recommendation to decelerate the motor without blocking? 

• Autorestart after blocking

Currently, the motor doesn't restart alone after a wrong starting procedure or when it is in fault after a over load blocking but I would like it retry to auto start/restart every 2 seconds.

>>> Do you have any recommendation to auto restart the motor fast when it is stopped by high load?

Thank you in advance for your help on any topics.

Best Regards,

Julien