Download DTI 100kV/100A opening switch work at the APS

“Testing a 100kv / 20A SolidState Fast Switch and ModAnode Regulator at the APS”
ASD – RF Group
Argonne National Laboratory
Office of Science
U.S. Department of Energy
A U.S. Department of Energy
Office of Science Laboratory
Operated by The University of Chicago
“Testing a 100kv / 20A Solid-State Fast Switch
and Mod-Anode Regulator at the APS”

Mercury - containing ignitron crowbars are commonly
used to protect klystrons from arc damage. When an arc
occurs, the crowbar closes and rapidly discharges the energystorage capacitor.

An alternative way to protect a klystron is to use a switch
that opens during an arc, using series arrays of insulated-gate
bipolar transistors (IGBTs).
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Ideal switch:
1) Zero resistance or forward voltage drop in the on-state.
2) Infinite resistance in the off-state.
3) Switch with infinite speed.
4) Would not require any input power to make it switch.

Choice involves voltage, current, switching speed, drive circuitry, load,
and temperature effects.

Most desirable primary characteristics are fast switching speed, simple
drive requirements and low conduction loss.
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High Power MOSFET:

Has high input impedance and fast switching speed.

For low voltage applications, power MOSFETs offer extremely low on-resistance, RDS(on),
and approach the desired ideal switch.

In high voltage applications, MOSFETs exhibit increased RDS(on) resulting in lower
efficiency due to increased conduction losses.
BJTs

Low conduction loss.

BJTs and IGBTs have similar ratings in terms of voltage and current.

The presence of an isolated gate in an IGBT makes it simpler to drive than a BJT. BJTs
require that base current be continuously supplied in a quantity sufficient enough to
maintain saturation.
•
BJTs have a much slower performance than MOSFETs.
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IGBTs

IGBT technology offers a combination of the low conduction loss of a BJT and
the switching speed of a power MOSFET.

IGBTs, like MOSFETs, are transconductance devices and can remain fully on
by keeping the gate voltage above a certain threshold.

The IGBT has high input impedance and fast turn-on speed like a MOSFET.

Although turn-on speeds are very fast, turn-off (tailing) of the IGBT is slower
than a MOSFET. Until recently, the feature that limited the IGBT from serving a
wide variety of applications was initial IGBTs had current fall times of around
three microseconds.
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STAGE 1 M ODIFICATIONS, UVC 1.9 MW DC POWER SYSTEM FOR SR (SECTORS 38 + 40) and RF1 DRIVES TEST BED
FUSED DISCONNECT
MOTORIZED/FUSED
DISCONNECT
MATCHING
TRANSFORMER
VAC
SCR'S
SGR3
M
13.2 1.4
KV KV
:
REGULATOR
TR SET
0 - 1400 VARIABLE VAC
Vc
FAST
SWITCH
V MA
1.9M W
I Fil.
0 TO
-95KVDC
@20A
Vc
KLY
LLRF TEST
BED
CROWBAR
LLRF
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+
HLRF
to
TEST BED
V MA
I Fil.
OUTSIDE
BUILDING 420
-
Typical
100KW RF
KLY
RF1
HLRF
to RF1
Typical
700KW RF
+
INSIDE
BUILDING 420
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Major parameters for fast opening switch transmitter system from Diversified Technologies, Inc. (DTI).
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DTI SOLID STATE OPENING SWITCH / MOD ANODE SUPPLY
D
C
-100KV
@20A
INPUT
C
FAST
+
K
2mH
1?
FIL.
PWR
25VDC
20A
H
FAST
OPENING
SWITCH
MOD ANODE
REGULATOR
(LINEAR)
WIRE
TEST
DUMP
RELAY
10K
1K
13M
1uF
MA
100M
13M
VIN
Vc
4M
VMA
Vc-VMA
IMA
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Solid-state switch plate rated at 3.3 kV, 100A continuous; 36 plates are connected in series to
achieve over 100 kV switch capability.
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Ch.1 = cathode voltage
Ch.2 = cathode current
Ch.3 = diode current
Ch.4 = over current fault
Input = 80kV from spotknocker (fault caused by arc test – output to ANL dummy load)
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Ch.1 = cathode voltage
Ch.2 = cathode current
Ch.4 = over current fault
Input = 100kV from spotknocker
(fault caused by arc test – output connected to ANL dummy load)
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Series opening switches have substantial advantages over
crowbars in the protection of RF amplifiers (klystrons).
1) Nearly immediate resumption of operation after an arc, during klystron conditioning.
2) Solid – State opening switches use no ignitron crowbars, therefore no mercury.
3) IGBTs can be much less expensive than vacuum tubes due to expected longer
lifetimes.
4) Removal of crowbars can significantly lower stresses on upstream power
components.
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5) Opening switches are made with excessive voltage capability, so the switch can
operate even if several devices fail (IGBTs always fail shorted).
6) Because the energy – storage capacitor does not discharge during an arc, the RF
could be turned again immediately after the arc clears. It is possible the beam may
be retained during an arc.
-
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At APS, the accelerator beam will continue for approximately 30µs without RF. If
a fault would clear within this time and the opening switch were to reclose, it is
possible that no beam restart would be required.
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