hello everybody
May i ask about DC to AC some question


How can the non-sinusoidal Ac voltage improvement to become a pure sinusoidal waveform

who can answer me this question ~what way can be improve~~~thk for u guy reading this topic thank q very much..

 

Hello,

Take a look at SPWM:
http://www.educypedia.be/electronics/powercontrolspwm.htm

Greetings,
Bertus

 

Most simple and common solution is to add an LC low pass filter to whatever signal shape is at the output.
Here typical filters for ground referenced and not ground referenced filters:

 

You cannot use an LC filter on a low frequency inverter because the inductor will be huge, expensive and have a high resistance that causes it to overheat and has a high voltage loss and the filtered voltage from a square-wave is far too low anyway.

 

Well, you are right, an LC-filter for a low frequency inverter will be huge, expensive and inefficient. That's the price anybody would have to pay, who wants to produce a sinusoidal waveform out of a 50-60Hz square wave...
Also, to make a "nicely" shaped sine wave, one simple LC stage (2nd order LP), would hardly be enough.

That's also one reason why most frequency inverters switch (PWM) the voltage at several kHz and then LC-filter the output.

In fact (although many topologies exist), the principle is roughly the same in a normal SMPS (Switched Mode Power Supply), keeping the reference voltage at a constant level, instead of letting it change as a 50-60Hz sine wave.
Or even further, in a class D amplifier, where the reference voltage is the audio frequency wave.