High voltage pulse generator

Details High voltage pulse generator High voltage pulse generator

1999-03-24

2001-04-10

Mayekar, Kishor (Department: 1741)

Chemical apparatus and process disinfecting, deodorizing, preser

Chemical reactor

With means applying electromagnetic wave energy or...

C435S173100, C099S451000

Reexamination Certificate

active

06214297

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to methods and systems for generating high-voltage pulses. More particularly, the present invention relates to the design of a PEF treatment system for generating high-voltage bipolar and/ or unipolar pulses used to induce stress and mortality in biological cells.
BACKGROUND OF THE INVENTION
PEF technology has found a wide range of applications in different areas such as, for example, bio-fouling control, non-thermal food processing, odor control, and NOx removal. Extensive research has been conducted to study the efficacy of using PEF as a non-thermal food pasteurization/sterilization method. However, the application of PEF treatment is not straightforward due to a number of factors. Factors affecting PEF treatment include, for example, electric field strength, treatment temperature, stage of microbial growth, and total treatment time.
In typical PEF treatment systems, high voltage pulses are induced in food products by specially designed PEF treatment chambers. Fluid food products are primarily conductive due to the existence of charge carrying particles such as, for example, proteins, vitamins and minerals. Therefore, application of a high-voltage across a treatment chamber results in a large flux of current flowing through the food product. This same current must also flow through the high-voltage pulse generator that is generating the high-voltage pulse(s).
In this regard, a PEF treatment chamber generally has two electrodes that convert high-voltage pulses to pulsed electric fields. Food product residing in between the electrodes is exposed to this field. For effective treatment, the design of the treatment chamber should guarantee a uniform field distribution inside the treatment zone. However, due to the large contact area between the two electrodes, the resistance therebetween is typically small and often in the range of half an Ohm to a couple of Ohms. Consequently, it is difficult for conventional high-voltage pulse generators to drive a PEF treatment chamber that has such a small resistance.
Accordingly, conventional high-voltage pulse generators are disadvantageous for a number of reasons. One disadvantage is that few high-voltage pulse generators can maintain the extremely high currents required due to the low resistances of treatment chambers. Additionally, conventional high-voltage pulse generators only provide for unipolar pulses that cause the deposition of protein and other charge carrying particles on electrodes. Therefore, methods and apparatuses for providing high-voltage pulses that do not suffer from these and other disadvantages are desirable.
SUMMARY OF THE INVENTION
According to the present invention, methods and systems for generating high-voltage unipolar or bipolar pulses for inducing changes in biological cells is provided. The methods and systems are particularly suited for the pasteurization and/or sterilization of, but not limited to, pumpable food products. In accordance with present invention, a power source charges an energy storage component, either a capacitor or a pulse forming network (PFN). The particular composition of the energy storage component also influences the shape of high-voltage pulse that is applied (ie., substantially square pulse, exponential decay pulse, etc.) Multiple switches that are in circuit communication with the energy storage component are closed and then opened periodically to discharge the energy storage component. The switches are preferably controlled by a trigger control system. The periodical discharges result in application of high-voltage pulses to the load, where specially designed treatment chambers are connected, exposing biological cells inside treatment chambers to intense electric field(s). A high-voltage pulse transformer is preferably connected between the switches/energy storage component and the treatment chambers, to allow the switches to operate at different voltage and current levels or to operate with other desired features. Repetitive application of short duration, intense electric fields induces stress or mortality in biological cells which results in the inactivation of food-borne spoilage and pathogenic micro-organisms.
According to one embodiment of the present invention, a system for generating high-voltage bipolar pulses to induce stress and mortality in biological cells is provided. The system includes, for example, a power source, an energy storage component in circuit communication with the power source and for storing energy from the power source, a plurality of switches for opening and closing periodically to discharge the energy storage component, and a load comprising at least one Pulse Electric Field (PEF) treatment chamber in which biological cells are subjected to PEF treatment. The system may additionally include, for example, a pulse transformer in circuit communication with the energy storage component and the load and for allowing a plurality of voltage and current levels to be generated at the load. The energy storage component include, for example, at least one capacitor such that the energy storage component has a discharge time constant that is larger than the time interval between the closing and opening of the switches.
According to a second embodiment of the present invention, a system for generating high-voltage bipolar pulses to induce stress and mortality in biological cells is provided with an H-bride switching configuration. The system includes, for example, a power source, an energy storage component in circuit communication with the power source and for storing energy from the power source, a plurality of switches for opening and closing periodically to discharge the energy storage component which are configured in an H-bridge configuration, and a load comprising at least one Pulse Electric Field (PEF) treatment chamber in which biological cells are subjected to PEF treatment. The load is preferably in circuit communication with the switches through a bridge portion of the H-bridge configuration.
It is therefore an advantage of the present invention to provide a high-voltage pulse generator system for effective PEF treatment that generates bipolar and/or unipolar high-voltage pulses.
It is a further advantage of this invention to provide a high-voltage pulse generator system for effective PEF treatment that reduces or eliminates protein build-up on PEF treatment electrodes.


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