Semiconductor-based marx circuit for soft-switching operation

Summary

For a test setup for the application of a pulsed electric field (PEF) to biological tissue a semiconductor-based pulse circuit has been developed. The pulse application to biological tissue causes pore formation in the cell membranes enabling a more energyefficient extraction of valuable substances from the cells in comparison to other extraction methods. The test-setup has been designed for the application of an electric field strength of up to 2 kV/cm to the sample at a pulse length in the microsecond range requiring a pulse voltage of up to 20 kV. The high-voltage pulses are generated by means of a 30- stage Marx generator equipped with IGBT switches. A design goal for the pulse circuit was an energy-efficient operation of the pulse generator. The pulse circuit has been designed as RLC series resonance circuit operated approximately critically damped. This design allows for an operation of the IGBTs under soft-switching conditions. In normal operation, the IGBTs operate as closing switches only. However, in case of a flash-over at the sample fast breaking of the circuit is required. When switching-off the pulse current the surge-voltage caused by the circuit inductance is limited within the safety margin of the device by means of active clamping across the IGBTs at each stage omitting freewheeling diodes. The paper describes the design of the 30-stage pulse generator and presents results of first tests. Under soft-switching conditions a rise time of the voltage across the terminals of the Marx generator of less than 100 ns at a charging voltage of 1 kV per stage has been achieved. For the tests the pulse current rises initially with a rate of approximately 400 A/µs up to a crest value of approximately 500 A. Voltage clamping when switching off the pulse current has been tested successfully. Thereby, a nearly linear decay of the current has been observed. During voltage clamping inductive energy from the pulse circuit is partly stored back to the capacitors and partly dissipates as heat at the switches.

Additional informations

Keywords

Electroporation, Semiconductor-based marx generator, soft switching, power electronics