Research On High-Voltage Pulse Generator Based On Step-up Pulse Transformer For Pulsed Electric Fields Processing

In recent years, the consumers’ demands on the nutrition and safety of food products are increasing, and the traditional food processing technologies are facing the great challenging of emerging technologies. As an innovative nonthermal processing technology mainly for liquid and pumpable foods, pulsed electric field (PEF) technology is predominantly used for the inactivation of microorganisms and enzymes at ambient or mild temperature, thereby preserving the fresh flavor, functional properties, and integrity of heat-sensitive compounds. It presents an attractive prospect in the field of liquid food processing with excellent treatment efficient and low operating costs.This research focuses on the developing of a high voltage pulse generator based on the step-up pulse transformer, which is capable of providing the monopolar quasi-square pulses with peak voltage of1kV, pulse width of3μs, and pulse frequency of1kHz. The main results and conclusions were listed as follows:(1) The present high-voltage pulse generator consisted of three parts, including the main circuit, a control unit and a human-machine interface. Besides, the designs of main circuit and control circuit were introduced.(2) The pulse generator was powered by the220V supply, which was rectified, filtered, inverted, boosted, and half-wave rectified, finally obtaining the monopolar quasi-square wave pulses. Based on the above five steps, the variations of voltage waveform and frequency were achieved (from the sine wave of220V and50Hz to the quasi-square wave of1kV,3μs and1kHz). This study described the design method of main circuit and the calculation method of parameters, and demonstrated the reasonableness of design method based on the Pspice simulation and experimental waveforms.(3) The control unit of pulse generator was consisted of the PWM control circuit, the signal amplification circuit, the driver circuit, and the fault protection and feedback circuit. For the selection of control circuit, four different PWM circuits were presented and compared. The protection circuit was mainly composed by a double over-current protection circuit, double over-voltage protection circuit and dual-voltage protection circuit. The experimental results indicated that the protection circuit could ensure the system operating stably.(4) Development of the pulse transformer is one of the key technologies of the pulse generator system. This study presented the design method of toroidal transformer, established a theoretical model, and gave the calculation method of some important parameters, finally built a pulse transformer with the ratio of1:16based on the series connection of four toroidal transformers, and the correctness of calculation and analysis were validated by experimental results.