Impact of Loading Effect from Liquid Foods on the Performance of Unipolar and Bipolar Square Pulse Generator

Different shapes of pulse voltages such as square pulse, exponential pulse and oscillatory pulse voltages were used for processing of food using PEF technique. However, each type of food offers different loading effect to the pulse generator due to its varying impedance based on the type of food and volume of food to be treated. This paper analyzes the impact of loading effect from different volumes of juice samples on the output parameters of high voltage square pulse generator. A unipolar square pulse voltage of positive and negative polarity and a bipolar square pulse voltage were generated at a pulse repetition rate of 50 Hz and 1 kHz. The juice samples of different volumes were considered as RC parallel branch and connected as a load across the pulse generator. This work was carried out as a simulation in MATLAB platform along with a mathematical modelling of pulse generator and load. The results obtained in simulation is validated using a low voltage unipolar pulse generator. From the simulation and experimental results, it is evident that, the loading effect offered by the juice samples on the magnitude and shape of the pulse voltage depends on the volume of sample to be treated and pulse repetition frequency. This paper also presents an output equation from state space model considering the effect of juice sample impedance, circuit parameters and duty cycle of converter switches. By controlling the duty cycle, a constant output voltage can be maintained across pulse generator irrespective of different volumes of juice samples.