High-Voltage Pulse Generator Based On Series-Connected IGBTs For Pulsed Electric Fields (PEF) Sterilization

In order to improve the development of high-voltage pulse generator used in pulsed electric fields (PEF) sterilization technologies, a solid state high-voltage pulse generator was developed based on series connected IGBTs. Moreover, combined with the characteristics of pulses and collinear treatment chamber used in PEF sterilization, a solid-state was constructed that can handle more than30kV. And it can also output a adjustable pulse width and frequency quasi-square wave pulse with30kV voltage when utilized in high-voltage pulse generator.The results and conclusions were listed as follows:(1) Driver circuit and protective circuit of IGBTs were designed based on DSP、fiber optic transmission and M57962L. Experiments demonstrated that a protective circuit system had a response time of6.5μs, and its overall protective time was less than the short-circuit time of IGBT15μs. On this basis, a drive circuit based on optical fiber was designed to drive64series IGBTs (with the block voltage of1200V) and the series fault feedback circuit. Moreover, the drive signal can obtain a maximum delay time difference less than100ns.(2) The switching process and power loss of IGBTs were analyzed. And the curve fitting of IGBTs was acquired between equivalent thermal time constant and equivalent transient thermal resistance, which proved that there exist junction temperatures while IGBTs were working and need for thermal design. By thermal analysis, the thermal resistance of radiator was1.7℃/W.(3) The parameters of IGBTs were extracted from Hefner model, and a relative simulation model was established. Compared with the experimental and simulation results of IGBTs switching transient process, it can be demonstrated that the simulation model can be utilized to analyze the series connected IGBTs, to help designing IGBTs’series circuit and to predict the work state of IGBTs.(4) Turn on and turn off delays was analyzed by circuit simulation method, showed that the average work voltage of IGW60T120was600V and the safety delay time was less than70ns. Additionally, through analyzing the gate characteristics of IGW60T120by both simulation and mathematical methods, the results showed that each additional5Ω of gate resistance was equivalent to add27.5ns for driver signal delay and the gate voltage fluctuations on a small scale has a little influence on IGBTs switching processes.(5) Based on the experience formula of RCD snubber circuit, new methods for calculating snubber capacitor and snubber resistor were obtained by simulation. According to combine these methods with equivalent model of collinear sterilization treatment chamber, the range of snubber capacitor and snubber resistor of IGBTs series circuit were and, respectively.(6) The discharge circuit of high-voltage pulse generator was analyzed based on collinear treatment chamber. Results proved that, in PEF sterilization, energy utilization of quasi-square wave pulses was larger than exponential wave pulses, the food temperature rise caused by quasi-square wave pulses and exponential wave pulses were and ΔT=U02·Ce-0.82, respectively, and the temperature rise was relatively small. When applied these results to collinear treatment chamber, the efficiencies of quasi-square wave pulses was, and exponential wave pulses was86.3%.(7) Finally, through high-voltage texts, the results proved that the designed solid-state can handle30kV voltages, and the high-voltage pulse generator can provide relatively stable quasi-square wave pulses for PEF sterilization. Thus, the methods for series connection of IGBTs are feasible.