Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: With technological advances in solid-state switches the modernization of conventional pulsed
power supplies utilizing thyratrons has become possible. A novel pulsed power supply is designed
where two series-stacked IGBTs (rated at 1700 V and 300 A each) are used to replace a thryatrondriven
pulsed power supply for a mini CO2 TEA laser.
The mini CO2 TEA laser is firstly characterized in order to optimize the design of the pulsed power
supply. It is found that stable laser discharges can be obtained with electrode voltage rise-times of
150 ns or less. Furthermore, the optical output energy and the efficiency of the laser have been
significantly increased by reducing the peaking capacitor size of the pulsed power supply.
The two stacked IGBTs switch a C-C transfer loop and the generated pulse is stepped up by a pulse
transformer and is compressed by a two-stage magnetic pulse compression unit. Theoretically and
through measurements it is shown that automatic voltage sharing between the two IGBTs can be
obtained if the turn-on time of the IGBTs is much faster than the transfer time of the switched C-C
transfer loop. Lifetime tests reveal that high-power IGBTs are able to reliably switch pulses with
peak currents between 4 and 5 times the rated average current of the device. Under laser fault
conditions, i.e. laser arcing or missing laser discharges, the reliability of the pulser can be increased
by using over-voltage snubbers. In addition, it was found that the internal diode of IGBT modules
can eventually fail under the prevalence of laser fault conditions.
A modular construction approach is used where components of the pulsed power supply are preassembled.
A new rectangular layout of the magnetic pulse compression unit is utilized in order to
minimize size and simplify the final construction and assembly. / AFRIKAANSE OPSOMMING: Nuwe ontwikkeling in vastetoestand-skakelaars het die modernisering van laser-pulskragbronne
moontlik gemaak. ’n Nuwe kragbron wat gebruik maak van twee seriegeskakelde IGBT’s is
ontwerp om ’n Tiratron-gedrewe laserkragbron te vervang, wat vir ’n mini-C02-TEA-laser gebruik
word.
Die laser is vooraf eers gekarakteriseer om sodoende die laserkragbron te optimeer. Daar is bevind
dat stabiele laserontladings verkry kan word met spanningstygtye van 150 ns of minder. Verder kan
die uittree-energie van die laser beduidend verhoog word deur die uittreekapasitore (eng.: peaking
capacitors) van die laserkragbron te verminder.
Die twee serie-geskakelde IGBT’s skakel ’n C-C oordraglus. Die spanning van die gegenereerde
puls word deur ’n pulstransformator verhoog en die stygtyd van die puls word met ’n twee-stadium
magnetiese pulskompressor verlaag. Teoreties en deur metings kan getoon word dat eweredige
spanningsverdeling tussen die twee IGBT’s outomaties verkry kan word indien die skakeltye van
die IGBT’s baie vinniger as die oordragstyd van die C-C oordraglus is. Toetse het getoon dat
IGBT’s pulse met piekstrome van tussen vier tot vyf keer die gespesifiseerde gemiddelde stroom
betroubaar kan skakel. Tydens laserfouttoestande kan die betroubaarheid van die IGBT verhoog
word deur oorspanningsgapsers te gebruik, maar onder fouttoestande wat voortduur, kan die IGBT
se interne diode vemietig word.
Die komponente van die laserkragbron is as modules vervaardig, wat op ’n maklike wyse
gemonteer kan word. ’n Nuwe reghoekige uitleg is gebruik vir die konstruksie van die magnetiese
pulskompressor, waarmee die grootte van die pulskompressor geminimeer en die konstruksie
vergemaklik is.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53359 |
| Date | 12 1900 |
| Creators | Stehmann, Timo |
| Contributors | Von Bergmann, H. M., Mouton, T., Stellenbosch University. Faculty of Science. Dept. of Physics. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 188 p. : ill. |
| Rights | Stellenbosch University |
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