Generating 3-phase sine wave..

[sirvo]

Heello...

I'm trying to generate a 3-phase ~60Hz sine wave and i think it would be nice using any 16f7x7 with 3 CCP modules. The problem is that it will take a month to get these here where I live.

As I've been playing with 18f2550 @ 20MHz and got USB working really fine, I was trying to figure out if it is possible to create a windows interface to control a 3-phase sine wave.. then I would create sags, swells, harmonics and so...

The ideia is to control the 3-phase amp. and also its frequencys...(never exceeding ~62Hz..)

So, any ideias of where should I start figuring this out?

Is a RC low pass filter enought to generate a sine wave from a pic's pin pwm?

Well,, thanks for the attention!

[skimask]

More information than you can shake a stick at here...doesn't delve too much into the 3 phase aspect though...
http://www.picbasic.co.uk/forum/show...light=inverter

[Luciano]

Hi Sylvio,

(Somehow related).

Speed Control of 3-Phase Induction Motor Using PIC18 Microcontrollers

Microchip AN843: (PDF)
http://ww1.microchip.com/downloads/e...tes/00843a.pdf

(Code and PDF).
http://www.microchip.com/stellent/id...pnote=en012011

Example of 3-phase bridge driver chip:
http://www.irf.com/product-info/data...ata/ir2136.pdf

Best regards,

Luciano

[sirvo]

Well.. Thank you Skimask and Luciano. Excelent readings!

So, I've bought a 16F777 and it has 3 CCP modules. As suggest in the readings above, it becomes easier to create an analog output when using high PWM frequencys. Using @ 20Mhz and Mister_E's PicMultiCalc, it turn out that it can generate frequencys > 20Khz, what is enought to this application.

Timer2 is responsable to control the PWM frequencys (all the same).

Timer1 is responsable to create the interruption to supply the new duty cycle value.

Now, let'ss think about the sine table and the software. Just to remember, I'll create an interface to control sine frequency, amplitude and also the sine table, as it would be interesting to create harmonics, sags and swells.

The sine table could be in the pic's data memory or it could be sent throught USART everytime that the user changes the interface option, like frequency. Do you think that it would work in real time using USART?


Thanks again!

[sirvo]

Well, things have been working until now...

When Timer1 interrupts, a INDEX var is summed and another position in a sine table is selected.. then a new value is output throught HPWM.

The sine table is filled with 72 number.. So, to create a 60Hz sine wave, o must read it at approx. 4.32KHz.

So, When I set timer1 to 64386 (1:1 prescaler @ 20MHz), it should interrupt at ~4.32KHz and create de 60Hz sine wave... but, it is generating a 26Hz... if I set timer1 to 65000, it decreases the 26Hz to 20Hz ... I didnt get iT! It should read the table faster, shoul'nt it?

Well, thanks!!!

[skimask]

So, When I set timer1 to 64386 (1:1 prescaler @ 20MHz), it should interrupt at ~4.32KHz and create de 60Hz sine wave... but, it is generating a 26Hz... if I set timer1 to 65000, it decreases the 26Hz to 20Hz ... I didnt get iT! It should read the table faster, shoul'nt it?

I'm guessing here, wild stab, since I don't see any other code here...
It might be reading it faster, but it might be missing/skipping a Tmr1 interrupt due to how long it takes to accomplish your interrupt code.
Try increasing the number by small amounts, see if it actually increases up to a point, and then drops off.