Field weakening (Phase Advance) using ST7MC

borisvr · ‎2005-06-01

Posted on June 02, 2005 at 07:36

borisvr · ‎2011-05-17

Posted on May 17, 2011 at 10:18

Hello,

I want to use the ST7MC to control a BLDC in sensorless mode. Due to limited input voltage of 12V and a given motor (10-pole) I have to use the field weakening effect (also known as phase advance mode) to get my desired 7000 rpm.

In AN2009 is a section called ''winding demagnetization'' where an acceleration of demagnetization is described, but I don't know, if I get higher speed.

Can anyone help me with my problem?

Thanks

Boris

gaetano · ‎2011-05-17

Posted on May 17, 2011 at 10:18

Hello,

to speed-up the demagnetization process is a necessary condition to increase the motor speed; but, once this is done, other parameters affect the maximum speed the system can reach.

In fact, only when the demag time is elapsed (D event), the micro is able to detect a zero-crossing event of the BEMF (Z event). At high speed, a long demagnetization time could 'mask' the Z event detection, making it impossible to increase the rotor speed.

Regards,

Tanio

borisvr · ‎2011-05-17

Posted on May 17, 2011 at 10:18

Hello tanio,

thanks for your answer.

But what I want to know is: can I implement the phase advance in the ST7MC micro?

Perhaps you know how to implement it.

Thank you for your reply

Best regards

Boris