Solid state pulsed power source for pulsed electric field and plasma treatment of food products

Pulsed electric fields (PEF) for the pasteurisation of food products is a widely investigated area today. The use of submerged streamer discharges for the inactivation of micro-organisms has only recently become an area of interest. For optimisation research of micro-organism inactivation with PEF and submerged streamer discharges, a flexible 2 MW pulsed power source was developed at TNO Prins Maurits Laboratory (TNO-PUL). This bi-polar source uses two stacks of 30 solid state (IGBT) switches for each polarity. An IGBT driver circuit has been developed to distribute the switched voltage equally over the IGBT\´s. The driver circuits are fed from a small DC current through the switch. Difficult high voltage insulation, for the driver electronics, is avoided in this way. Any parameter of the rectangular shaped pulses can be varied independently: pulse amplitude, pulse width and repetition rate for either bi-polar or mono-polar pulse trains. The delay time between positive and negative pulse can be made zero so as to achieve a "charge reversal" pulse pair. The generator flexibility enables a wide range of critical process parameters to be investigated. PEF and submerged streamer chambers with different electrode radii have been characterised electrically. For the inactivation of micro-organisms in food products with submerged streamer discharges different corona electrode arrangements were applied. Experiments have been performed with a full wet process set-up controlling flow rate and temperature. Experiments show which electrical and geometry parameters are relevant for the inactivation efficiency of E. Coli bacteria.