This paper first reviews mechanism and waveform consideration for liquid food sterilization, and then presents how to generate bipolar narrow pulses. In this research, a bidirectional flyback converter with energy recovery circuits is proposed to generate bipolar narrow pulsed electric fields for liquid food sterilization, which includes sterilization of drinking water, alcoholic beverages, fruit juice, etc. Since in the converter, leakage inductance is around 1 % of the magnetizing inductance, capacitors are used to resonate with the leakage inductor to recover the trapped energy and to reduce switching loss, improving efficiency about 13%. In addition, the energy recovery capacitor can reduce voltage stress significantly. Experimental results obtained from a prototype with the output of ±6 kV ~ ±20 kV, depending on loads, and peak power of 250 kW have confirmed these discussions.
This paper proposes a wide pulse combined with narrow pulse generator for solid food sterilization. The proposed generator is composed of a full-bridge converter in phase-shift control to generate high dc-link voltage, and a full-bridge inverter associated with an L-C network and a transformer to generate wide pulses combined with narrow pulses. These combined pulses can prevent undesired strong air arcing in free space, reduce power consumption and save power components, while can sterilize food effectively. The converter and inverter can be operated at high frequencies and with PWM control, thus its weight and size can be reduced significantly and its efficiency can be correspondingly improved. Experimental results obtained from a prototype with ±10 kV wide pulses combined with ±10 kV narrow pulses and with 10 ~ 50 kW peak output power, depending on pulse width of the output pulses, have demonstrated its feasibility.
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