Re: SSAC PWM Transformer (SS Variac Update)

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

Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

They're actually trying to make a transformer (i.e. where VA in == VA 
out).. if all you want is a smoothly varying AC voltage at essentially 
constant current, it's been done...  A single PWM chopper in a bridge 
rectifier in series does very nicely.  I used a fairly run of the mill 555 
circuit driving a fairly run of the mill VMOS fet to do this 10 years ago 
for an AC fan speed controller for a PSC motor fan (where you wanted to 
keep the waveform sinusoidal for low noise at low speeds). At that time, 
the mfr was using a small 3A variac, and was looking for a lower cost, 
lower mass replacement. The FET chopper worked fine from a fan standpoint, 
but the regulatory aspects killed it, and, I couldn't get the BOM cost down 
to $3-5 (we were getting the variacs for $30, so after the usual BOM 
multiplier for assembly/test costs, the chopper was more expensive).

Technology marches forward, and the company now uses a fairly sophisticated 
3 phase PWM inverter to do the speed control.


At 07:04 PM 4/23/2003 -0600, you wrote:
>Original poster: "David Sharpe by way of Terry Fritz 
><teslalist-at-qwest-dot-net>" <sccr4us-at-erols-dot-com>
>
>All
>
>I've not been working on the IGBT SS Variac yet, but is in sight.
>While
>looking at electronics URL's at work today, I found these two papers.
>One covers single phase PWM SS Transformer (read SS Variac with
>duty cycle control), and one paper covers three phase voltage control.
>
>VERY interesting and germane for those power electronics EE's out
>there willing to take on the challenge.
>
>  http://www.iee.uz.zgora.pl/English/publications/5%5B5%5DPESC02.pdf
>
>Discusses single phase SS PWM AC transformers, and was disclosed at
>the PESC 2002 (Power Electronics Specialists Conference) sponsored by
>IEEE et al.  Deriving equations, possible circuit topologies etc. are
>discussed.
>Single quadrant (powering) and dual quadrant (bi-directional)
>topologies are
>discussed.  The single quadrant straight buck converter looks to me to
>be the
>most interesting, due to use of standard totem pole power devices with
>copack
>diodes, IGBT clocking frequencies were fixed arbitrarily at 5kHz, and
>simple
>low pass filtering for utility wave reconstitution to transformer
>load.
>
>  http://www.iee.uz.zgora.pl/English/publications/5%5B6%5Dspedam02.pdf
>
>Covers three phase solid state AC PWM duty cycle voltage control for
>the
>real high power interests out there.  VERY interesting reading, and
>maybe
>another electromechanical bastion is about to fall...
>
>Regards
>Dave Sharpe, TCBOR
>Chesterfield, VA. USA