Development Of High Voltage Square Wave Pulse Source Used For Pulse Electrical Field Sterilization

As a new non-thermal sterilization,pulsed electric field sterilization technology can retain nutrients and flavor of food extremely with the advantage of short sterilization time and less energy consumption.So far,exponential decay wave is widely used for sterilization in domestic.Research is shown that square wave can get better sterilization effect.So it is the trend of sterilization to use high voltage square wave pulse source.The liquids in the treatment chamber may be breakdown abnormally which influence the safety of the pulse source and the normal operation of the system under pulse voltages because of the high conductivity.A new high voltage pulse square wave source circuit is proposed which based on the principle of the inductive energy storage pulse source.This circuit can avoid the problems above.The simulation results show that the voltage amplitude and waveform can meet the requirements.The amplitude is changed by varying the equivalent impedance in the treatment chamber The main parameter and structure of pulse source are designed and manufactured based on the simulation results.The IGBT stacks are used as the solid switch of the pulse source.In order to make the control signal synchronous,the control signal is formed by single IGBT,Rogowski coil and waveform shaping circuit.The simulation result shows that the output waveform can meet the requirements.A voltage-sharing method based on the RCD circuit is proposed to solve the program of series IGBT voltage-sharing.The simulation shows that this method obtains better voltage-sharing effect.Treatment chamber filled with liquid food is a key device of the new high voltage square wave pulse source.The amplitude of output voltage is affected by equivalent impedance of the treatment chamber.It is difficult to measure the equivalent impedance of the high conductivity liquid food,so that the square wave pulse method is proposed.Three measurement programs are designed according to the square wave pulse method,and one of them is selected to be used.The equivalent impedance of water,orange juice,beer and milk in the treatment chamber are obtained after measurement.The effect of pressure on pulse electrical field sterilization and liquid breakdown voltage are analyzed.An improve program is proposed to solve the problem of unstable pressure and low flow.The system pressure is stable after improvement,and the sterilization can be carried out under different pressure.