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[moved] Maintain v/f ratio in pic microcontroller output

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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.
 

Hello
Are you trying to control 3 phase induction motor with pic18f4550.
I thing PIC18f4550 do not have 6 PWM outputs.
first describe you project completely.
then i can help you in V/F ratio concept
 

Hi abc_de,
Thanks for replying.
Yes I want to control 3 AC phase induction motor. I have generated PWM pulses on my GPIO. Now I want to generate pulses with v/f.
 

Ok
For 3 phase motor control pic18f4550 is insufficient because 2 phase pwm generation is possible but for 3rd phase you have to use timers.
Till now are you able to generate 3 pwms ?
If yes then you can go for V/F ratio.
 
I have generated 6 pwm pulses successfully. Now only v/f is remaining.
Need your suggestions for that....
 

Ok that's great
Now V/F ratio is voltage /frequency. It means you have to keep voltage and frequency ratio constant. Motor current is directly proportional to the relationship of v/f.
For v/f implementation you must be able to control the voltage and frequency let us assume your motor is rated for 220v/50hz and running for specific RPM.
If you have to reduce the speed of motor to Half RPM then you have to apply 110V/25HZ to get half of RPM.
For that you have to create an algorithm by which voltage is reduced as frequency reduce.
Don't forget to click helped me button.
 
I understand the concept. But how to create that "algorithm" in microcontroller?
 

For V/F ratio implementation you have to make two functions or routines
In voltage control routine you have to multiple fraction value with sine look up table values. For example your maximum sine look up table value is 255*.5 then output voltage is half. 255*.2 then output voltage is 5th part of maximum voltage.
For frequency control I don't know how your changing frequency.

- - - Updated - - -

For more help you have to share your algorithms
 

Hii.. abc_de
Good Morning

Ya even i am suffering from same issue.
at last,I want to run IM. Now, i am getting PWM waveforms by using TIMERS where i used diifrent data and pulses generated according to that. I am giving Frequency fromMPLAB X software (using PIC18f4550 with PICKIT3). So, if i give frequency range from 1 to 100Hz from PC i am able to see the waveform of PWM in CRO.
Now, problem is when i am connecting with drive ita working fine but voltage is not changing according to applied frequency :-( :-(

I hope i clearly explained the issue.
Please help me. :-(
 

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