In inductive power transfer applications that use resonant compensation networks, the commonly employed H-bridge inverter should be kept operating in soft-switching to ensure high power efficiency and low irradiated electromagnetic noise. To achieve so, the zero-crossing detection circuit for the resonant current or voltage must be fast and accurate in any operating condition. This paper researches the concept of an auto-resonant control for the typical H-bridge resonant converter used in wireless charging systems. In the method proposed here, the reference levels for the zero-crossing detection of the inverter's current are automatically adapted depending on the slope of the current itself at the zero-crossing. In this way, it is possible to compensate for the circuit delay even in the presence of parameters' variation and to ensure that the soft-switching is always maintained. The functionality of this control method is proven first mathematically, and then with circuit simulations. The core steps for the implementation are described with the support of functional blocks. Finally, the system start-up strategy is explained, which uses an auxiliary timed oscillator to modulate the inverter with a fixed 50% duty cycle at a higher frequency than the nominal. This guarantees that the start-up is in the inductive region and, thus, the zero-voltage switching turn-on. Once the detection circuits sense the current flow, the oscillator is automatically disabled, and the nominal power transfer starts.

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Generally, high grade products such as pulsed electric field (PEF) treated fruit juices are packaged after their preservative treatment. However, PEF treatment after packaging could avoid recontamination of the product and becomes feasible when electric field pulses of sufficient magnitude can be generated inside closed food containments. Microbial inactivation of 2 log10 was proved by using an electrically conductive plastic packaging material, and in this contribution it is shown that inactivation toward pasteurization level is achievable. Therefore, a series of microbial experiments with Lactobacillus plantarum at different energy levels were performed. The obtained microbial data with the plastic material have been compared with inactivation models from literature as well as with reference experiments. All treatments were done at ~2.3 kV/mm, with treatment times between 10¿600 µs, and the thermal load was below 38C. The maximum obtained microbial inactivation with the plastic packaging material was 5.9 log10 with a specific energy of 255 J/mL.@en

Nowadays Pulsed Electric Field (PEF) treatment of food needs to be performed prior to packaging, either hygienic or aseptic packaging is necessary. New techniques for PEF treatment after packaging can be considered when plastic conductive (film) electrodes can be integrated within the package, so that the package and the product can be treated as a whole. This paper describes a newly developed treatment chamber, which can be used to test the ability of any arbitrary plastic packaging film to be used as electrodes for PEF treatment. Tests with a flexible commercially available electrically conductive copolymer film showed that reduction of Lactobacillus plantarum by PEF was possible. This heat sealable film obeys the mechanical properties of a polymer; however it has an electrical conductivity of 0.75 S m¿ 1 and approximately 2.3% of the surface area is electrically conductive. The maximum obtained inactivation was 2.1 log10 with a specific energy of 17 J ml¿ 1. The microbial experiments gave a consistent outcome compared with finite element simulations and with models from literature. Further research to reach real pasteurisation levels is needed as well as issues concerning utilisation of these film electrodes.@en

Pulsed power (PP) is a technology where energy is released to a load in a short time. Every device using this technology needs electrodes to transfer the electric energy to the load. Recent developments in composite conductive polymers make them suitable as electrodes for new or existing PP applications, where normally metals were used. Composite polymers, consisting of conductive filler and a nonconductive matrix, can solve several specific problems in common and to be developed (PP) applications, due to their ability to conduct current or to store electrical charge, in combination with their elasticity. In general, polymer electrodes behave differently on pulsed stimuli compared to a static load and metal electrodes. An overview of many existing characterization methods and a newly developed technique suited for characterization of conductive polymers for PP applications in particular is described. For three different applications, artificial muscles, cell electroporation, and biofouling prevention, the requirements for the polymer electrodes and specific application-related issues are addressed with examples.@en

Electrically conductive polymer composites consisting of a nonconductive polymer matrix and conductive fillers, such as carbon black, are widely used. This contribution describes a newly developed measurement setup that has been built to investigate the specific electrical properties of polymer composite films for pulsed conditions in the microsecond (10-6 s) range. For an industrially available volume conductive polymer film (Carbostat) the contact resistivity to copper has been investigated. Also, three methods for minimizing the contact resistivity, namely pressing, gluing, and wetting, have been compared for a wide range of applied current densities.@en

The force acting on a current carrying body, which is induced by magnetic fields gained more interest due to new applications. These magnetic techniques are used for decades to accelerate or move objects, for instance for catheter navigation in the human body, metal forming or for fast opening of electrical circuit breakers. Due to the increase in short circuit power in most grid systems, and thereby larger prospective currents, conventional AC and DC switches lose interest. This has led to an increased interest in faster and hybrid switching techniques. For this reason a novel electro-mechanical set-up has been developed, which accelerates a movable electrical contact extremely fast by using the combination of Lenz law and the Lorentz force. This contribution describes the mixed domain simulation environment and the validation of the set-up, which consist of a linear electro-magnetic drive and a mechanical damper system. The prototype used for validation is capable to generate a maximum driving force of approximately 200 kN, which accelerates the movable contact of 2.7 kg to 18 m s¿1. Initial simulations have been compared with the measurements and the results are in good agreement. This tool can be used to develop generic hybrid circuit breakers, reduces the risk for switchgear manufacturers and speed up the introduction of hybrid switch systems, which is urgently needed due to the ever increase of short circuit power in grid systems and the introduction of DC grid systems.@en

Electrically conductive polymer composites consisting of a nonconductive polymer matrix and conductive fillers, such as carbon black, are widely used. This contribution describes the specific electrical properties of polymer composite films for pulsed conditions in the microsecond (10-6 s) range. Investigation of an industrially available volume conductive polymer film (Carbostat) showed that the electrical properties of this material, which can be considered for electrodes in pulsed power applications, are quite different from the properties for DC conditions. Key words: Plastic electrodes; Polymer characterization; Polymer composite; Pulsed power@en

Power electronic switches have been considered for load switching ever since their invention. This is because semiconductor switches enable fast, arc-less, reliable and maintenance-free switching. The main disadvantages in relation to conventional switches (i.e. circuit breakers), however, are their sensitivity to transients, high on-state losses and the presence of leakage current. The advantages of both types of switches can be exploited by combining the semiconductor and the mechanical switch and thereby their disadvantages, arc formation and regular maintenance, can also be eliminated. For hybrid switches (HSs), both zero voltage switching (ZVS) and zero current switching (ZCS) are frequently used. A new hybrid switching topology has been developed where both ZVS and ZCS techniques are applied to the mechanical switch. The `symbiosis' between these solid-state switching techniques and a mechanical switch eliminates several of the disadvantages, resulting in a more reliable direct current (DC) HS that requires less maintenance. The first turn-off measurement (up to 5 kA) from a prototype that has been developed for a 3-kV DC grid is presented.@en

Electrochemistry in pulsed electric field treatment chambers B Roodenburg, Delft University of Technology, The Netherlands - Electrochemistry: introduction - Theory - Experiments - Treatment chamber lifetime - Legislation - Conclusions - References@en

Liquid pumpable food is mostly pasteurised by heat treatment. In the last decennia there is an increasing interest in so-called Pulsed Electric Field (PEF) treatment. During this treatment food is pumped between two metal electrodes and exposed to short high electric field pulses, typical 2¿4 kV·mm¿ 1 during 1¿10 ¿s. During this treatment the stainless steel electrodes are in direct contact with the food product. Associated with the charge that has to be exchanged at the interface of electrode and food, electrode material may be transferred from electrode to food. This transfer of material may cause serious electrode corrosion and adds metals to the food. The magnitude of material transfer depends on many factors such as current magnitude, pulse duration, pulse shape and fluid constitution. In this contribution the effect of three different mono-polar pulse shapes on treatment chamber corrosion is investigated. Experiments are carried out in an aqueous sodium chloride solution. The experiments showed that due to PEF treatment dissolved metals are present in the liquid. The four main elements of stainless steel, iron, chromium, nickel and manganese, have been considered in particular. These elements could only be detected in the liquid when it was repeatedly exposed to a Pulsed Electric Field treatment, which was realised by repeatedly circulating. From the experiments a relationship between dissolved metals in sodium chloride and the transferred charge is derived. With these values an upper limit for dissolved metals caused by PEF treatment can be defined.@en

In the last decennia, there is an increasing interest in pulsed electric field (PEF) treatment. The product is often treated in a continuous flow treatment chamber with stainless steel electrodes and exposed to short pulsed electric fields, typically 2¿4 kV·mm¿ 1 during 1¿10 ¿s. Due to direct contact of the treatment chamber electrodes with the food product, the main elements of these stainless steel electrodes are able to dissolve in the treated product. The magnitude of the material transfer depends on many factors such as current magnitude, pulse duration, pulse shape, and product constitution. In this contribution, the effect of metal dissolving during a monopolar pulse shape, generated by a pulse forming network, is investigated. Experiments are carried out with single and repeated PEF treatments in orange juice. These experiments showed that, due to PEF treatment, dissolved metals are present in the juice. The four main elements of stainless steel, iron, chromium, nickel, and manganese, have been considered in particular. The metal concentrations found do not exceed the legislation values for fruit juices and the EU Drinking Water Directive [EU Drinking Water Directive, http://www.europe.eu.int/.] for human consumption. From the experiments, a relationship between dissolved metals in orange juice and the transferred charge is derived. In addition, a lifetime prediction of the treatment chamber caused by release of metals has been made.@en