Hi,

I was just reading about pure sine wave inverters and how they generate the suare pulse that feeds the transistors by comparing a trinagle wave and a 60 hz sine wave. My question is: why isn't a 60 hz square pulse generated with a dc offset and fed to the transistors, then filtered?

Thank you.

 

I don't know, but would guess that in power conversion, efficiency is important, and it's better to generate an approximately correct waveform in the first place, than to apply massive subsequent waveshaping and filtering at high power. Not only would it be expensive, they would lose some of the power.

 

If you calculate the size of the filter needed to get a decent sinewave, you will see why they don't.

 

Hi,

I was just reading about pure sine wave inverters and how they generate the suare pulse that feeds the transistors by comparing a trinagle wave and a 60 hz sine wave. My question is: why isn't a 60 hz square pulse generated with a dc offset and fed to the transistors, then filtered?

Thank you.

What actually happens is that the Square Wave is Modified by a technique called Pulse Width Modulation. The "ON" and "OFF" time of the Transistors is varied; the variation follows the Sine Wave.

Read http://fab.cba.mit.edu/classes/MIT/961.04/topics/pwm.pdf

The transistors are operated in ON/OFF mode since the power dissipation is least in these 2 states.