how do you control the output frequecy of full wave rectifier circuit?

thebluser

what i mean is, if i want to make a certain rectifier circuit to some sort of load, how would i know which diodes and transistors/IGBT's/MOSFET's to use? for example, i have an AC source with 50 hertz and a load that requires 60 hertz, what would i use? can you show me calculations?

berkeman

To convert from 50Hz to 60Hz, you need to use a motor-generator device (a 50Hz AC motor drives the input shaft of a 60Hz generator), or you need to rectify the 50Hz power to DC, and use a 60Hz inverter to generate the output power.

You cannot just use a "rectifier" circuit to change the frequency of the power waveform from 50Hz to 60Hz. If the output frequency were 2x the input frequency, you could use a full-wave rectifier followed by filtering to remove the harmonics.

thebluser

ok so after i doubled the frequency from the rectifier circuit and it comes out as DC, will the DC double again after it will enter another rectifying circuit? or do i need to convert it to ac again and then i could double it?

Windadct

AC to DC is a rectifer, then you have DC - som ripple, but true "frequesncy" as you are using the term. DC to AC is an inverter.

You need a Rectifier + Inverter. An easy way may be to buy a UPS if the load is not too big.

Also -- what is the load - device? a surprising number if devices can run on 50 or 60 Hz.

Berkman - can you explain "If the output frequency were 2x the input frequency, you could use a full-wave rectifier ..." I am perplexed

berkeman

When you full-wave rectify a sine wave, you get a waveform that is 2x in frequency, plus the sub-harmonic at the fundamental, plus higher harmonics from the sharp-edged side of the waveform. If you feed that into another transformer and a filter at the 2x frequency, you can get pretty close to a 2x sine wave out. I've never done it, but it looks pretty plausible.

http://www.eleinmec.com/figures/018_04.gif

Windadct

OK - I see what you mean- that would have a pretty ugly waveform, more humps than a sine, and if directly into a transformer it would saturate due to DC. Some capacitive coupling would take care of that but would be tough to transfer much power without big caps.
Now theBluser needs somethng to run on 100Hz....

berkeman

Don't think it would saturate the transformer. There is an assymmetry to the waveform, but don't get fooled by the fact that we usually take the (floating) output of the first transformer and rectify the output and *then* reference it to ground. Just take the FWR output and put it straight into a 2nd transformer/filter...

After further thought, you are correct. The FWR makes the current always flow one direction through the primary of the 2nd transformer, so it would need to be sized to be able to handle twice the AC flux compared to if the input to the 2nd transformer were AC. Sorry for my mis-statement above.

Windadct

No apologies - just open discussion. In AC inverters any current asymmetry is a problem for down stream magnetics - including motors, so it comes up a lot. Of course these end discussions often drive the OP's batty....

thebluser

thanks everyone :D