Using 3-phase PWM-mode with ST7MC

ralf2399 · ‎2005-09-08

Posted on September 08, 2005 at 15:08

ralf2399 · ‎2011-05-17

Posted on May 17, 2011 at 10:18

Hello,

I'm using the using the ST7MC1 controller in 3-phase pwm mode like it is described in the application note for pmsm. This works fine now. Now I want to use this mode in conjunction with the current or voltage controlled mode to enable sampling of the three signals MCIA/B/C. My question is: Is it possible to use these modes in combination? If yes, how are the three inputs sampled in this mode?

In the datasheet it is described that in voltage mode the inputs are sampled at the end of the pwm off time on channel U, but what happens if I have configured 3 independend pwm signals?

In current mode it is described that the window generator configures the sampling point, but what happens if I use 3-phase mode? Are all 3 pwm-signals configured in the way lowside on and highside off?

Can anybody help me in using BLDC and 3-phase-mode in combination?

Best regards,

Ralf

gaetano · ‎2011-05-17

Posted on May 17, 2011 at 10:18

Hi,

what you wrote about the different sampling modes regarding the use of ST7FMC in voltage or current mode is related exclusively to the BLDC motor when driven in six-steps mode and without sensors. But, the embedded MTC peripheral is differently configured when 3 independent PWMs are generated like you are doing with PMSM motor. So you cannot mix the two methods.

Best regards,

Tanio

ralf2399 · ‎2011-05-17

Posted on May 17, 2011 at 10:18

Hi,

thank you for this very fast reply!

Now I have a further question:

In 3-phase-mode it is possible to use a digital tacho generator. In the app note for pmsm this signal is also used for synchronization of the sine modulation. How is this signal evaluated by the ST7MC? Is in this case also used the internal comparator with a certain threshold for switching? If yes, is it possible to read out the output of the comparator over the HST-bit? Can I set the reference voltage of the input comparator? Or is the whole function realized in a digital way (edge triggered IO-port)?

Best regards,

Ralf

tomas23 · ‎2011-05-17

Posted on May 17, 2011 at 10:18

Hello,

I suppose that that you cannot switch one input to the analog comparator while another input is used as digital input for tacho. The bits ISx are shared and used for selection of tacho input.

Tomas