PWM freq selection

[pravin]

Posted on March 22, 2005 at 06:31

PWM freq selection

[pravin]

Posted on May 17, 2011 at 10:18

hello

i'm new to forum & also to motor controller., working on BLDC with ST7FMC1K2T6. following r the parameters of the motor viz,.. no of poles :4 , speed : 10000 RPM, mech/elct freq : 166.66 Hz/333.33Hz respt.., T = 3000 usec & T(step)= 500usec. Based on the above info what must be my PWM value to be set fixed in MCPOHL? Using a sampling in PWM OFF & ON in start up & running mode respt.What changes r expected in library code? will the ratio & value in RAMP[64] struct need to be modified? Kindly respond quikly. Pravin

[gaetano]

Posted on May 17, 2011 at 10:18

Hello,

normally, minimum four BEMF samples for step time is the rule: so, choose the PWM frequency accordingly with your step time. Anyhow, for the info you asked for, it is better to give a look at the literature written for this micro at the following address:

http://mcu.st.com/devicedocs-ST7MC2N6-15.html

where you can find plenty of information for implementing your best driving strategy (not only for PMBLDC motors). Another way, you could take into account, is to use the ST7MC GUI ver 1.1, that helps you to create your configuration files (to be included in the available BLDC library) starting by a visual approach tool. After your system has been configured according to your requirements, some ANSI C header files (ext. ''.h'') can be generated by the GUI, allowing you to work in stand alone manner. The GUI can be free downloaded at the following address:

http://www.softecmicro.com/products.html?type=detail&title=AK-ST7FMC

Hope this can help you effectively. Best regards, Tanio

[pravin]

Posted on May 17, 2011 at 10:18

Hi

This is a sensorless BLDC motor application with PWM freq.18.1Khz,PWM on HIGH side,sampling during PWM OFF time. After alignment & acceleration phase motor is stoping before switching into run mode.stops getting BEMF from motor & once it goes into Z event interrupt routine.In the end,ends up with start up failed RAMP UP(64).Wht could be the cause of failure?wht must be BEMF 0 crssing pattern at MCIA/B/C? PWM OFF sampling is OK? how to set MCRB? thnks in advance Pravin