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. ... Read more

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. ... Read more