BOOK OF ABSTRACTS 2012 International - Ness Engineering, Inc.

DESIGN OF AN 80KV, 40A RESONANT SWITCHMODE POWER
CONVERTER FOR PULSED POWER APPLICATIONS
Paul Nonn, Andrew Seltzman, Jay Anderson
University of Wisconsin, Physics, Madison, WI, USA
94
3O6
A unique switchmode power converter has been designed to supply a stable 80kV, 40A, 10ms
pulse to a klystron tube presenting an 1800 ohm load. The supply is powered from a 900v, 0.5F
electrolytic capacitor bank capable of sourcing the required input current over the pulse duration.
The supply uses a low inductance IGBT network to switch power from the capacitor bank into the
primaries of a three phase resonant transformer system. The resonant transformer assembly
utilizes three magnetically separate microcrystalline iron cores in order to provide suitable voltseconds
and low magnetic loss at switching frequencies of 18.5 to 25kHz. The transformers are
driven by independent full H-bridges with a 100% duty cycle square wave of variable frequency
and corresponding phase offset. The use of a full duty cycle square wave in conjunction with a
resonant transformer allows soft switching during the current zero crossing in the transformer
primary. The subsequent reduction in junction heating allows operation of the IGBT network at
higher then rated current without damage during the output pulse. Each transformer has a large
leakage inductance secondary of 1.36mH with a parallel 50nF capacitor resonator, providing a
boost ratio in excess of 60:1 at resonance and rated load while using a turns ratio of 13.5:1. The
primary consists of a parallel pair of open air 10 turn helical copper straps around both sides of a
square type core, while the secondaries consist a parallel pair of oil insulated coils, each with two
135 turn layers connected in parallel. The secondaries of the three transformers are connected in a
wye configuration to a doubling rectifier, boosting the output to 80kV. The high switching
frequency in addition to an LC harmonic filter provides a stable output and a reduction in filter
capacitance allowing large values of dv/dt during the leading and trailing edge of the pulse. Ramp
up times to 80kv of