Thanks to Andy's answer I found an answer to my question behind: why is AC rectified to DC, then converted again into AC?
the point is to control the frequency. Once you have DC power, you can
pretty much drive the inverter at any frequency you want.
It is difficult to convert one frequency to another, but it is
relatively easy to convert DC into any frequency you want (and to
rectify AC power to DC).
Details:
Think of the inverter as a switch that reverses polarity. If on one
side you have DC, then you can switch back and forth as you want. The
faster you go, the higher the frequency on the output side. You can
pick any frequency you want, there are no "hard" or "easy"
frequencies. They try to do the same thing with AC power on the input.
Unless the frequencies match up, the output will be an ugly mess. AC
power is very easy to convert from one voltage to another, using a
transformer. But the frequency on the input and output side of the
transformer are the same.
Thanks to M Quack from the physicsforums
charger
... they are powered by apower supply
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