All Solid-State Rectangular Sub-Microsecond Pulse Generator for Water Treatment Application

Low-temperature plasma with reactive species including the hydroxyl radical is found very effective for the degradation of many pharmaceuticals and macromolecular organic matter in wastewater. The most efficient way is to excite plasma directly in the wastewater using high-voltage sub-microsecond pulses which prevents the corona discharges developing into arc discharges. Recently, plasma generated with high-voltage pulses of only several hundred nanosecond durations has been found to be especially efficient. Therefore, an all solid-state sub-microsecond pulse generator prototype based on the Marx concept is constructed, with MOSFET power semiconductor devices. This pulse generator is able to generate rectangular pulses with adjustable durations in impedance-varying wastewater. The sub-microsecond signals are generated by field-programmable gate array, and simulations of the driving circuits are carried out to optimize the driving signals so as to trigger the switches synchronously in a few nanoseconds. First, experiments show that sub-microsecond pulses with amplitudes over 7 kV and a minimum pulse duration of about 100 ns can be generated. Both rise time and fall time are about 22 ns. Pulse frequency up to 30 kHz is achieved. Besides, most of these parameters can be adjusted. The pulse generator itself is compact and portable.