MCF8329A: Sensorless Vector control of slotless motors

Tool/software:

Hi there,

I am trying to drive a slotless motors using MCF8329A. While I am getting a good sine wave current with different slotted motors I have tested with the chip (using both standard demo board from TI and custom board with the same chip) when I use a slotless motor the result is quite pour. The phase current (measured with a current probe and oscilloscope) is extremely noisy; the Id has a saw shape with the frequency of the sine instead of regulating at 0, while Iq has an acceptable relatively stable line (not perfect but far away from the Id form). Do you know if this is due to the slotless motor construction? Do you have any idea what can cause this behavior? These are the pictures of the phase current for reference:

1. Slotless motor

2. Slotted motor:

If you need any additional information please let me know.

With kind regards,

Alexander.