Hello,

I am using PIC18f4550. My aim is to control AC induction motor. For that I have generated required PWM pulses for required frequencies. But I need to maintain V/F ratio at the output. Which I am unable to do.

Please suggest me.

 

The PMW modulation frequency determines the AC frequency applied to the motor, and the PWM duty-cycle along with the PWM carrier voltage determines the AC voltage applied to the motor.
So from the modulation frequency you calculate the needed duty-cycle to get the desired motor voltage for the PWM carrier voltage you are using.

 

Thanks crutschow.
Can you please explain briefly ?

 

Change the period register and maintain 50 percent duty cycle.

Better use a v/f converter or a pic with NCO.

If the frequency isn't too fast, consider dds in software.