A front-end PFC stage for improved performance of flexible induction heating appliances

Flexible cooking surfaces, eg. fully active surfaces, have gained lately an increasing importance in the domestic induction heating. Multi-inverter structures are a cost-efficient solution to develop this technology. However, they add control restrictions that can be solved with a power factor corrector (PFC) stage as proposed in this work. The proposed converter and modulation strategy work with zero voltage switching (ZVS), decreasing the switching losses, enabling a higher working frequency and, therefore, decreasing the magnetic devices size. The bus voltage is controllable and can be increased, easing the load power control and decreasing current through load and inverter and, so, the power losses. Besides, the switching frequency is constant in the mains cycle and can be modified to synchronize the load inverter and the PFC stage avoiding intermodulation noise. A 3.6 kW prototype has been implemented fulfilling the EMC requirements. The experimental waveforms and efficiency have been measured to prove the feasibility of this proposal

Analytical solution of the induced currents in multilayer cylindrical conductors under external electromagnetic sources

We present a closed-form solution for the induced losses in round conductors consisting of several concentric layers. The geometry under study corresponds to an infinitely-long and isolated multilayer cylinder where layers can have different electromagnetic properties and the number of layers is not restricted. The multilayer conductor is under an external time-varying magnetic field which induces currents and, accordingly, generates Joule dissipation. Total induced losses are obtained by integrating the losses of each layer. Mathematical expressions of the current distribution in each layer are derived from the solution of Maxwell''s equations. These expressions consist of a combination of Bessel functions of different kinds and orders. The current distribution in a particular layer not only depends on the properties of the layer but also on the properties of the rest of layers. Consequently, matrix formalism is adopted for describing current distribution of layers. Matrix description is numerically solved and results are compared with finite element simulations for different arrangements and cases

Tumor location on electroporation therapies by means of multi-electrode structures and machine learning

Electroporation is a phenomenon produced in the cell membrane when it is exposed to high pulsed electric fields that increases its permeability. Among other application fields, this phenomenon can be exploited in a clinical environment for tumor ablation therapies. In this context to achieve optimum results, it is convenient to focus the treatment on the tumor tissue to minimize side effects. In this work, a pre-treatment tumor location method is developed, with the purpose of being able to precisely target the therapy. This is done by taking different impedance measurements with a multi-output electroporation generator in conjunction with a multi-electrode structure. Data are processed by means of a vector of independent artificial neural networks, trained and tested with simulation data, and validated with phantom gels. This algorithm proved to provide suitable accuracy in spite of the low electrode count compared to the number of electrodes of a standard electrical impedance tomography device

Etapas ac-ac directas con un número reducido de dispositivos operando en modo discontínuo

El calentamiento doméstico por inducción se basa en generar el calor directamente en elrecipente mediante la aplicación de un campo magnético variable de alta frecuencia. Dada lapotencia requerida, sistemas de potencia a eleveda frecuencia son empleados. Los esquemastradicionales emplean dos grandes bloques: una etapa previa rectificadora, encargada degenerar un bus de tensión contínua con el que alimentar a la segunda de las etapas, lainversora. Ésta es la encargada de generar la corriente de alta frecuencia con la que alimentarel inductor. Esquemas clásicos emplean topologías de dos dispositivos como el semi‐puenteresonante serie, dada la potencia alcanzada, sin embargo, etapas de un solo dispositivo hansido también empleadas con el fin de reducir costes, elevando la complejidad de control delconjunto. En esta ponencia se expone un nuevo concepto: la unión de ambas etapas en unconjunto, lo que se denomina como etapas directas ac‐ac, puesto que no existe unaconversión intermedia a un bus de contínua. La etapa conjunta se basa en la topología 1SWZVSen modo cicloconvertidor con dos elementos unipolares y bidireccionales en serie,logrando un dispositivo bipolar y bidireccional, que gobierna el sistema. Adicionalmente, se hapropuesto un modo de operación discontínuo que permite incrementar la eficiencia delconjunto para potencias elevadas

Constant-current gate driver for GaN HEMts applied to resonant power conversion

New semiconductor technology is enabling the design of more reliable and high-performance power converters. In particular, wide bandgap (WBG) silicon carbide (SiC) and gallium nitride (GaN) technologies provide faster switching times, higher operating temperature, and higher blocking voltage. Recently, high-voltage GaN devices have opened the design window to new applications with high performance and cost-effective implementation. However, one of the main drawbacks is that these devices require accurate base current control to ensure safe and efficient operation. As a consequence, the base drive circuit becomes more complex and the final efficiency is decreased. This paper presents an improved gate driver circuit for GaN devices based on the use of a constant current regulator (CCR). The proposed circuit achieves constant current regardless of the operating conditions, solving variations with temperature, aging and operating conditions that may degrade the converter performance. Besides, the proposed circuit is reliable and cost-effective, being applicable to a wide range of commercial, industrial and automotive applications. In this paper, its application to a zero-voltage switching resonant inverter for domestic induction heating was performed to prove the feasibility of this concept. © 2021 by the authors. Licensee MDPI, Basel, Switzerland