Understanding Sine Wave Production with an LC Filter and Inverter PWM Waveform

[raikko62]

Hi,

Could someone please explain how EXACTLY a sine wave is produced using an LC filter from a PWM waveform generated by an inverter.

Thanks

 

[hisham.i]

Hi raikko

In order to create a sine wave, the duty cycle of the pwm signal should be varied in a

sinusoidal manner, this can be done using micro controller, and each pwm period an interrupt is

generated, and the duty cycle takes a new value in the interrupt service routine. (Note that

the values that the duty cycle should take are saved in an array; say up to 200 elements).

This will generate a sine wave which has also the carrier frequency part of its harmonic

components, so we put a low pass filter (LC filter) in order to eliminate the switching

frequency.

 

[raikko62]

Thanks for the reply.
However what I wanted to know is how the LC filter works in eliminating the carrier frequency of the generated PWM signal.

 

[olivermsun]

Kind of the same way FM demodulation works on your radio, I would imagine?

 

[alexyoung]

hello how is everyone. Could someone kindly send me a link for a pure sinewave imverter circuit/ Thank you

 

[jim hardy]

for an intro to one technique
try a google on

magic sinewave tinaja

However what I wanted to know is how the LC filter works in eliminating the carrier frequency of the generated PWM signal.

the series L is high impedance at carrier frequency so attenuates carrier by voltage divider action
the paralllel C is low impedance at carrier frequency so shunts carrier attenuating it further.

you can also shape a square wave into a pretty decent sinewave with tuned filters that attenuate the harmonics

 

[alexyoung]

Thank you for your support but I went to the magic sinwave site but I did not see a circuit please help me on this . thank you

 

[raikko62]

@olivermsun and @jim hardy - Thanks for the answers