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Re: [TCML] solid state varaic
There is much information in the Internet on "AC Choppers". Several Articles of
interest:
http://www.scribd.com/doc/7031043/A-New-Configuration-of-Single-Phase-Symmetrical-PWM-AC-Chopper-Voltage-Controller
http://www.waset.ac.nz/journals/waset/v56/v56-20.pdf
http://elth.ucv.ro/fisiere/anale/2006/3_2.pdf
My favored design is use a totem pole phase rectifier (doubler)
feeding a totem pole
switching element (IGBT, FET) with appropriate LC low pass filtering and a zero
cross detector. Line impedance (inductance) makes circuit operate similarly to
a current source inverter, which is exactly what you want; adjustable constant
current control by cycle control, and Vo control by DC of PWM. A 555 could
be used for PWM element and the reset pin controlled by a comparator circuit
with hystersis (identical to a DRSSTC OC control) would limit the output current
by dynamic cycle by cycle control of the 555. Simple, robust, and proven.
Regards
Dave Sharpe, TCBOR/HEAS
Chesterfield, VA. USA
On Wed, Jul 28, 2010 at 9:27 PM, Henry Hallam <henry@xxxxxxxxxxxxxxxx> wrote:
> Steve,
> Any more details or references on the hysteretic control scheme?
> Sounds interesting.
>
> Thanks
> Henry
>
> On Tue, Jul 27, 2010 at 8:38 PM, Steve Ward <steve.ward@xxxxxxxxx> wrote:
>> Scott,
>>
>> Yes, what you describe can be known as a synchronous-buck converter, which
>> are popularized by class-D audio amplifiers. Basically a half or
>> full-bridge configuration of switches, and a LC output filter. The PWM
>> control can come from a variety of techniques from classic controls theory
>> and standard PWM generating chips, or to something more clever like
>> hysteretic control laws, or "one cycle control" techniques. Each control
>> scheme has advantages, the hysteresis one is my favorite due to the
>> simplicity and robustness and almost guaranteed stability, the disadvantage
>> (and lack of presence in industry) is possibly due to the shift in switching
>> frequency of these control schemes, which can possibly increase the cost of
>> the EMI filter at the front end to pass emissions, but for us tesla coilers,
>> we dont care about minor EMI problems so its a good solution.
>>
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--
Dave Sharpe, TCBOR/HEAS
Chesterfield, VA USA
Sharpe's Axiom of Murphy's Law
"Physics trumps opinion!"
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