Claudio Carretero

Analysis of the Mutual Inductance of Planar-Lumped Inductive Power Transfer Systems

Mutual inductance is a key parameter of the inductively coupled circuits such as transformers and contactless energy transfer systems. This parameter is particularly required to design the power electronics associated with each application. However, its value is usually extracted from measurements performed in a previously built prototype, which is an expensive and time-consuming task. In this paper, an analysis of the mutual inductance between two planar circular windings is developed. The analysis takes into account the effect of the media that can be part of the complete system. As a result, an analytical calculation of the mutual inductance with respect to the main parameters of the system such as the number of turns of the coils, geometry, frequency of the currents, and the properties of the media can be carried out. The analysis can also be used to explore the tendencies of the mutual inductance for design purposes and, thus, it allows speeding up the design process. The analysis has been verified by means of experimental results.

Series Resonant Multiinverter with Discontinuous-Mode Control for Improved Light-Load Operation

Operation under light-load conditions is a general issue when developing power converters as it can lead to system instability and/or decreased performance. This topic is particularly important for resonant converters as their efficiency significantly reduces when their operation point is set outside their resonant conditions. Considering the importance of efficiency for power converter reliability, environmental impacts, and regulation concerns, a major effort to improve the operation under light-load conditions is justified. Domestic induction heating is an application where variable loads and output power requirements imply operation under a wide range of conditions, including long-term light-load operation. The aim of this paper is to propose an improved control scheme for series resonant multiinverters, which are a cost-effective topology for supplying multiple inductive loads, based on discontinuous-mode operation. Two different control strategies are proposed: regenerative control and direct conduction control. An analytical study is performed, and the main simulation results are presented. An experimental series resonant multiinverter prototype is used to validate the simulation results.

Induction Heating Appliances: Toward More Flexible Cooking Surfaces

Efficient energy management in residential areas is a key issue in modern energy systems. In this scenario, induction heating (IH) becomes an alternative to classical heating technologies because of its advantages such as efficiency, quickness, safety, and accurate power control. In this article, the design of modern flexible cooking surfaces featuring IH technology is presented. The main advantages and technical challenges are given, and the design of the inductor system and the power electronic converter is detailed. The feasibility of the proposed system is verified through a laboratory prototype.

Computational Modeling of Two Partly Coupled Coils Supplied by a Double Half-Bridge Resonant Inverter for Induction Heating Appliances

In this paper, an induction heating system composed of two partly coupled coils connected to a double half-bridge resonant inverter is deeply analyzed. Induction coils are electrically characterized by their electrical equivalents, usually a series RL circuit, where the inductance is determined by the magnetic energy stored in the system and the resistance is associated with the power dissipated in the load, generally, a metallic workpiece. The aim of this work is to obtain the electrical equivalent of an inductor system with two concentric coils used in domestic cookers by means of computational methods, in order to be included into the models used in computational aided electronic tools to simulate the time-domain behavior of the associated electronics. The multiple-coil system is characterized with a frequency-dependent impedance matrix, where the diagonal terms are the impedance of each isolated coil, and the nondiagonal terms are coupling impedance components describing the mutual coupling between coils. The impedance matrix is calculated with finite-element analysis tools, and equivalent passive networks are proposed to perform time-domain simulation with a good accuracy in the frequency range of interest. The proposed system has been experimentally verified, obtaining accurate time-domain waveforms and output power calculation.

Analysis and Modeling of Planar Concentric Windings Forming Adaptable-Diameter Burners for Induction Heating Appliances

Adaptable-diameter inductors are being implemented in domestic induction hobs in order to increase the range of suitable pot diameters and to achieve the better use of the rated power electronics. Such inductors are arranged by means of several concentric planar windings, usually up to three units, each one of them comprising several litz-wire turns. Currently, one resonant inverter is dedicated to supplying each winding. In this paper, a characterization of these inductors in terms of their impedance matrix is derived. The self-impedance of each winding and those caused by the coupling between them are analyzed. The contribution of this paper lies in the understanding and analysis of the coupling between concentric windings. Unlike transformers, where ideally the magnetic path consists of a lossless material, in domestic induction heating, the vessel is part of the flux path. Consequently, the off-diagonal terms of the impedance matrix have been generalized because they have a resistive component in addition to the classical mutual-inductance component. The analysis presented in this paper also includes the losses in the litz wires generated by the currents in each winding as well as the losses produced by the windings over their concentric neighbors.

Multiple-Output Resonant Matrix Converter for Multiple Induction Heaters

Most of the ac-ac converters used in home appliances are based on single-output dc-link inverters, which provide a cost-effective and straightforward solution. However, a two-stage power conversion decreases power density and efficiency. A direct ac-ac conversion has been thoroughly studied in the past. Nevertheless, the complex control scheme and higher cost have prevented it from being used in cost-oriented applications, such as home appliances. This paper proposes a direct ac-ac conversion scheme by means of a multiple-output resonant matrix converter applied to multiple inductive load systems. The proposed topology reduces significantly the number of devices and complexity, leading to an efficient, versatile, and cost-effective solution. The analytical and simulation results have been verified by means of a prototype applied to a novel total-active-surface induction-heating appliance.

Quantitative Evaluation of Induction Efficiency in Domestic Induction Heating Applications

Efficiency of electromagnetic energy transference in coupled pot-inductor systems of induction cooktops is analyzed. The influence of different parameters such as pot properties, number of turns of the windings, frequency of the currents, cable types, and ferrite arrangements is studied by means of an analytical model. The proposed model is a combination of two independent models corresponding to the loaded planar coil impedance and the cable losses, respectively. The two models are related using the global magnetic field of the system. The analysis reveals that it is not possible to experimentally determine induction efficiency by measuring unloaded and loaded winding impedances. In this paper, we propose a practical method to obtain the induction efficiency and compare the results with theoretical predictions. Quantitative results corresponding to different pot materials, frequencies, type of cables, and ferrite arrangements are also presented.

AC Power Losses Model for Planar Windings With Rectangular Cross-Sectional Conductors

In this letter, a method to calculate the ac losses, including skin effect and proximity losses, in planar windings with rectangular cross-sectional conductors is proposed. The aim is proposing proper ac losses expressions similar to the formulas available for round cross-sectional wires, to be used for the calculation of the ac losses and the optimization of planar magnetic windings implemented in the printed circuit board. The proposed model is based on the decomposition into conduction and proximity losses. Conduction losses only depend on the properties of the conductor, whereas proximity losses are calculated by using the orthogonal decomposition of the magnetic fields in which the conductors are immersed. Functions including the frequency and geometrical dependences of the both types of losses are extracted by means of finite element method simulation. Finally, several prototypes are used to verify the proposed expressions and some design considerations are also outlined.

TM-TE Decomposition of Power Losses in Multi-Stranded Litz-Wires Used in Electronic Devices

E-ciency often constitutes the main goal in the design of a power system because the minimization of power losses in the magnetic components implies better and safer working conditions. The primary source of losses in a magnetic power component is usually associated with the current driven by the wire, which ranges from low to medium frequencies. New power system tendencies involve increasing working frequencies in order to reduce the size of devices, thus reducing costs. However, optimal design procedures involve increasingly complex solutions for improving system performance. For instance, using litz-type multi-stranded wires which have an internal structure to uniformly share the current between electrically equivalent strands, reducing the total power losses in the windings. The power losses in multi-stranded wires are generally classifled into conduction losses and proximity losses due to currents induced by a magnetic fleld external to the strand. Both sources of loss have usually been analyzed independently, assuming certain conditions in order to simplify the derivation of expressions for calculating the correct values. In this paper, a unifled analysis is performed given that both power losses are originated by the electromagnetic flelds arising from external sources where the wire is immersed applying the decomposition into transversal magnetic (TM) and transversal electric (TE) components. The classical power losses, the so called conduction and proximity losses, can be calculated considering the TM modes under certain conditions. In addition, a new proximity loss contribution emerges from the TE modes under similar conditions.

Mutual Impedance of Small Ring-Type Coils for Multiwinding Induction Heating Appliances

This paper proposes a model of the mutual impedance between ring-type coils used in domestic induction hobs. Recent developments in these appliances have focused on flexible cooking surfaces, including adjustable-size or total-active surfaces. Flexible cooking surfaces are implemented by means of several small ring-type closely arranged coils, each one supplied by a resonant inverter. The basic winding is a ring-type circular small coil, whose self-impedance has been reported previously. In this paper, the coupling between coils in terms of impedance is derived. The coils are modeled as axisymmetric current density distributions with parallel revolution axes. The mutual impedance between the coils is obtained considering two media representing the load and the ferrite, respectively. Experimental measurements have been performed to validate the results.