Re: MOSFET/IGBT power supply?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Eddie Burwell by way of Terry Fritz <twftesla-at-qwest-dot-net>" <eburwell-at-columbus.rr-dot-com>

At 08:08 AM 6/20/02 -0600, you wrote:
>Original poster: "Mr Gregory Peters by way of Terry Fritz
<twftesla-at-qwest-dot-net>" 

<snip>

>Firstly, I would rectify the 240 VAC 3 phase supply using a six pulse
>rectifier, giving me 340 VDC. I would then switch this using mosfets or
>igbts at the line frequency (50Hz). Switching would be done using, say,
>a 555 timer. I would control the RMS current draw by varying the pulse
>width. This would then be fed to my 10kW single phase pole pig. I guess
>the core would heat up a bit, but apparently silicon steel isn't too bad
>at handling a square wave for short periods. Questions:
>
>1. Is this possible?

yes

>2. What complications would I run into?

Your DC filter caps would need to be able to handle the ripple current.
any other problems would be specific to your circuit design. 

>3. Can the pole pig really handle a low frequency (50Hz) square wave?

Sure. Square wave will probably have slightly higher core losses than sine
wave.   For tesla coil duty it should be no problem. You could also up the
frequency of operation which would allow you to push more power through a
given core. this would also increase core losses. 

>4. Suggestions? 

Look at Marco Denicolai's power supply for his project Thor at:
http://personal.inet.fi/atk/dncmrc/thor.htm
High frequency switchers have the advantage of being light weight although
they are more challenging to develop.
You could use the same series resonant circuit with the pig at a much lower
frequency. I would recommend a "soft switching" or resonantly commuted
design over a "hard switched" design.
There are so many possibilities that it comes down to the question of "what
are your objectives?" Simplicity? Weight? Power? Efficiency? Aesthetics?
Robustness?


Eddie Burwell

>
>Cheers,
>
>Greg Peters
>Department of Earth Sciences,
>University of Queensland, Australia
>Phone: 0402 841 677
>http://www.geocities-dot-com/gregjpeters
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