A Research For The Control And Detection Of Pulsed Electric Field Equipment

Pulsed Electric Field(PEF) sterilization technology is a promising non-thermal sterilization technology. It has the advantages of short sterilization time, low processing temperature, good sterilization effect, and little effect on the flavor and nutrition of food, etc., which make the technology having broad application prospects in the food processing field. Our research team has developed a pilot-scale single polarity sterilization equipment to provide 30 k V, 2.5μs square wave pulse, and the equipment has a good effect in sterilization. A control and detection system was designed on the basis of the bipolar PEF sterilization equipment that our team are developing in this paper, and the problems in the equipment operation had been researched in depth. All the work provided a guarantee for the stable operation of the equipment. The main work and results were listed as follows:1. Research on the structure of high-voltage pulse power, the chamber and energy efficiency was done from the perspective of waveform, and the waveforms of the capacitor discharge circuit were simulated through the PSpice. Through the research and analysis on the independent developed PEF sterilization equipment, a conclusion was drawn: the closer waveform is to a square wave, the higher energy efficiency is. The electrical conductivity, the inductance of line and the synchronization of switches have important influence on the waveform.2. A control and detection system was designed for the bipolar PEF sterilization equipment. The overall structure of the PEF sterilization equipment was designed depending on the requirements of the sterilization system, and the voltage amplitude control module, the waveform parameters control module and the flow rate control module were designed respectively. Besides, a resistive voltage divider and a close-loop Hall current sensor were used to detect the voltage and the current respectively.3. The waveform characteristics of the PEF sterilization equipment was studied, and the influence that the electrical conductivity have on the waveform, the causes of waveform jitter and discharge phenomenon were analyzed. There is approximately linear relationship between the fall time of the waveform and resistance within a certain range, which means that the falling time of waveform under high conductivity is shorter. The waveform jitters dues to the changing of the chamber resistance which is caused by the non-uniform flow rate of the peristaltic pump. Discharge is caused by the presence of gas in chamber. Through wavelet analysis of waveforms at two resolution levels, we can get an eigenvalue, which helps us to define the discharge.4. Through the analysis of the control requirements of the PEF sterilization equipment, the control system software was designed, and the electrode corrosion during the equipment operation, energy efficiency and equipment stability were analyzed. By calculating the theoretical power consumption and energy efficiency of the PEF sterilization equipment, a conclusion that energy efficiency under high electrical conductivity is much higher than the energy efficiency under low conductivity was made. The larger the power of the chamber is, the higher the energy efficiency is. The resistance for protection increases the rise time of waveform and causes a waste of energy.In this paper, the existing problems on the device were analyzed through the principle analysis, waveform analysis, simulation, etc. The discharge phenomenon detection has been achieved, and a complete control and detection system for the bipolar PEF sterilization equipment was built. Through Lab VIEW programming, the PEF sterilization equipment can be controlled remotely, which increases the safety of the operation.