can any one help me in solving out this thing ? I need to change the frequency of the 230v ac power supply using the microcontroller(89c51). and what if the load takes high current ? which is the best method ?

 

If your little friends told this was possible on the cheap then they were wrong. The only way I can see this happening is to use a motor coupled to a generator that will produce the correct output.

 

i just had this thought because i thought of the thing which we do with lower power. ie first to bring ac to dc(after stepping down) then use an oscillator for the desired freqency.

 

that is the principle used in Variable frequency drives.
try a google search on those and inverters,IGBT etc.
first the ac is rectified and then a desired frequency of output ac is obtained by controlling the firing rate of the IGBT/mosfet etc.

 

If your little friends told this was possible on the cheap then they were wrong. The only way I can see this happening is to use a motor coupled to a generator that will produce the correct output.

No. Explanation below.

i just had this thought because i thought of the thing which we do with lower power. ie first to bring ac to dc(after stepping down) then use an oscillator for the desired freqency.

It is indeed possible to do that. Computer PSUs work that way. The current is first converted to DC and then pulse modulated to feed a high frequency transformer. the advantage of doing this is that high frequency transformers are smaller that 50Hz ones with the same VA rating.

that is the principle used in Variable frequency drives.
try a google search on those and inverters,IGBT etc.
first the ac is rectified and then a desired frequency of output ac is obtained by controlling the firing rate of the IGBT/mosfet etc.

Indeed.

 

I forgot to mention that my assumption was that with a sine wave in he would want a sine wave out. The AC-DC-AC conversion doesn't produce a sine wave out -- does it?

That is why I suggested the motor generator combination.

 

I forgot to mention that my assumption was that with a sine wave in he would want a sine wave out. The AC-DC-AC conversion doesn't produce a sine wave out -- does it?

That is why I suggested the motor generator combination.

It is still possible to produce a sine wave using a signal generator. Although a motor generator combination might be simpler to implement.

 

yes i think the pulse generated will be smoothen by passing thru an induction coil.

 

yes i think the pulse generated will be smoothen by passing thru an induction coil.

I don't think it will be a sine wave, though.