how to produce 120 deg phase generation in pwm generator

[poornimargowda]

Please can anybody help me about how to generate 120 deg phase shifted pwm waveform for ac motor control?

 

[FvM]

Depends on how you generate the "pwm waveform". The phase shift applies to the modulating sine waveform, not the pwm carrier. Assumed you are generating the sine by a lookup table, the 120 and 240 degree phase shift isn't but an offset to the table index.

 

[poornimargowda]

Depends on how you generate the "pwm waveform". The phase shift applies to the modulating sine waveform, not the pwm carrier. Assumed you are generating the sine by a lookup table, the 120 and 240 degree phase shift isn't but an offset to the table index.

Hi, thank you for your reply. But one thing i did not understand for controlling the speed of the motor. Suppose if we modulate the 50 hz frequency with the carrier for generating pwm signal then what is the need of varying the motor frequency again from 1 Hz to 128 Hz in some cases?

Please reply me. actually i am controlling the ac motor using MC3PHAC controller but i did not get the internal working of this controller. So please help me...


Regards,
Poornima

 

[FvM]

https://en.wikipedia.org/wiki/Variable-frequency_drive

 

[poornimargowda]

Hi FVM, thank you for your reply. One more help i need. Please can you explain me the internal operation of MC3PHAC controller . Its a DSP based controller. I googled for it but did not get the right information. Please help me since i am doing my M.Tech project on this.

Thanks,
Poornima

 

[jayanth.devarayanadurga]

It is explained in the datasheet. It is just a 3 phase motor controller.

 

[poornimargowda]

Hi thank you for your reply.
I have read the datasheet but only the configuration in standalone and master mode is explained. i want the internal block diagram of mc3phac.

Regards,
Poornima