driving STEVAL-IHM023V2 without controller

[florian]

Posted on March 19, 2014 at 17:24

We are working with the STEVAL-IHM023V2 to drive a brushless DC motor of 24V. The set up is to be used in an academic environment and will be used as set up for students. As it is their task to make the control algorithm (from current set point to switching pattern based on Hall sensors) we did not buy the controller of ST. The tests we did so far were successful but it is not possible to keep one leg of the inverter open (in a stable way). The only way we found so far to keep both upper and lower switch open was to keep both connection points floating (which cannot be the right option). Is there anyone who has tried to do the same and knows a solution?

#steval-ihm023v2

[Gigi]

Posted on April 01, 2014 at 13:48

Ciao Florian,

this is a typical problem of 6-step drive. Usually to modulate the voltage applied to the motor a PWM signal si applied to the high side switches and this solve the problem of discharging of the boot capacitor. If you need to apply 100% of duty, this means maximum voltage and so the high side closed for two consecutive steps, then you have a limitation in the minimum duration of the two step that must be less than the discharging time, and this give you a limitation in the minimum speed of the rotating field. To increase the duration of the discharging of the boot cap one option can be to increase the capacintance values. For instance doubling it you shall increase to 36ms the maximum Ton time of each high side switches. Ciao Gigi P.S. What is missing in the analysis is that when a inductive motor is present (like in case of motor) the free weeling diodes of LS switches allows to charge the boot capacitor so just applying the PWM on the HS is sufficient. While if you have only resistive load then you need to apply a complementary PWM in both high side and low side to cherge the boot cap. 

[florian]

Posted on April 01, 2014 at 15:25

Hello Gigi,

that could be an explanation for the problem... But if you ask me, that should be a paragraph of text in the datasheet ;) By the end of the week I will test the board on the motor.Thank you for your help and I'll let you know if everything works fine.Kind regards,Florian

[florian]

Posted on April 03, 2014 at 08:29

The motor is turning around smoothly :)