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Expert: cleggsan Date: 12/20/2006 Subject: PWM concept and inverter
Question I was told the output of PWM is a sequence of squarewave.This squarewave actually come from the AC fed into the inverter input which contains 'unwanted frequency'.Then when using the PWM this sinusoidal AC converted into 'squarewave sinusoidal AC'.A sequence of s/wave that repeated after certain interval and behave like pure sinusoidal AC.Is it correct the way I understand it?
Another thing we also have quasi-square wave inverter which also a squarte wave.Whats the different with PWM?
And how the designer/vendor decide to use PWM or quasi squarewave for their technology?Which one is better?
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The text above is a follow-up to ...
-----Question-----
Most inverter use PWM concept.TYhe output of itis a square wave, but how can it(squarewave) relates to inverter fucntion.Meaning to say whenwe have the square wave, what and when the inverter use it and for what purpose?
-----Answer-----
PWM or pulse width modulation is a means whereby the amount of energy is controlled by the width of the pulses. They can easily be converted, by rectification and filtering, back to a dc power level. The dc is then converted back to an ac output. Or, in some systems the PWM output is kept at the right frequency, 60 Hz, and converted directly to ac with filters.
NOTE: A square wave is the product of a series of sine waves. Filtering out the unwanted sine waves will leave on the sine wave of interest.
The above is a good overview of how they are designed.
A square wave - or more precisely, a rectangular wave where the ON portion is different from the OFF duration - can be represented by a series of sine waves. This is fourier analysis method which is the basis of non-sinusoidal wave form analysis techniques.
I really don't understand the question in total. There are many designs for inverters and it depends on the application, end product and user requirements as to what may or may not work best in a given situation.
You are asking design engineering questions without the knowledge of system topology and theory of operation.
Please read the wikipedia article mentioned above and it will teach you the basic ideas.
If you want to dig deeply, I suggest you enroll at the university where you can be instructed in control theory and power system design methods.
