Semi-planar power combiner structure for IGBT-based pulsed power modulators

A semi-planar, rotationally symmetric power combiner has been realized using a hard-wired parallel circuit of four power transfer stages which feed into a common radial transmission line. For testing purposes, the radial transmission line is terminated with a matched ohmic resistor. The power combiner is designed to produce a double exponential pulse by optimizing the transmission line geometry with the help of electrodynamic modeling using CST Microwave Suite. Each of the four stages contains three parallel capacitors of 200nF each, the geometrical circuit inductance, a switch, and are discharged into the common resistive load. The switch is realized with an industrial type IGBT module, at a DC link voltage of up to 4.5 kV. Lifetime estimations show a permissible peak current of up to 2kA for a single IGBT module, at pulse durations of around 1 μs. Hence, a peak current of over 6 kA can be achieved by paralleling four of these power transfer stages in the semi-planar power combiner structure. First experimental results show that the semi-planar power combiner is a suitable functional unit for pulsed power applications. The circuit was characterized at a DC link voltage of up to 4 kV, a peak current of 1.68kA, and a pulse duration of 1μs per IGBT module. The low switching losses of the IGBT when using a hard gate drive allow using the IGBT at high pulse repetition rates (PRF) up to kHz, at pulse durations around 1μs. The circuit presented is suitable to be used as a modular component of an inductive voltage adder to increase the available voltage and peak power levels, respectively.