PWM and Filter LC

[ricperes]

Hello,

I am creating a PWM signal by comparing a sine wave (50Hz) and a triangular wave arrier (10kHz) ,in ordem to control a full bridge inverter.

II had been try filter this pwm signal to obtain a sinusoide, with a LC filter. I use this equation to find a cut-frequency of the filter (and the values of L and C) Fc=1/(2*PI*SQRT(LC)) but i didn't have a good result, can someone help me please?

 

[Tony Stewart]

With 1- 2 decades of separation between 100 and 10kHz you can expect 40 dB/ decade rolloff with a simple 2nd LPF above a breakpoint. But if you choose say 500 Hz for minimal phase shift of the fundamental you get less attenuation but with higher order filters can also improve this with a notch at 10kHz.

 

[ricperes]

With 1- 2 decades of separation between 100 and 10kHz you can expect 40 dB/ decade rolloff with a simple 2nd LPF above a breakpoint. But if you choose say 500 Hz for minimal phase shift of the fundamental you get less attenuation but with higher order filters can also improve this with a notch at 10kHz.

I made a test right now, with :

Freq triangular : 10khz
Freq sin : 50 hz

and replace Fc by 1kHz on Fc=1/(2*PI*SQRT(LC)) and i got a good result ... what ou think about this value (1khz to cut-frequency) ?

Thanks