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This article presents an inductively coupled heating application, that is, a combination of wireless power transfer and induction heating. The addition of a secondary inductor with a resonant capacitor directly beneath and attached to the ferromagnetic load allows us to improve induction heating adaptation of loads of different sizes to the primary inductor, enhancing power distribution and extending load distance while avoiding increased power losses and stress on electronic components. The extended distance can be used to implement the seamless induction concept, where the typical ceramic glass is substituted by the kitchen surface itself. Finite-element analysis simulations are carried out to determine the suitability of each possible design, and a scoring system is applied to determine the optimal solution, bearing in mind the delivered power, power factor, power distribution, and efficiency. A near optimal design is chosen to develop as a prototype. The prototype is tested under working conditions up to 3680 W at several distances, validating the simulations’ impedance parameters and verifying power distribution with a water boiling test and a dry test with a thermographic camera.

Inductive devices are extensively employed in power electronic systems due to their magnetic energy storage and power transfer capabilities. The current trend is towards increasing the frequency of operation in order to reduce the size of the magnetic components, but the main drawback is that the parasitic capacitance effect can become significant, and degrade the performance of the system. This work analyses the influence of this stray capacitance, and considers how to improve the performance of the device. In general, the impact of the stray capacitance on a magnetic component can be reduced by two methods: reducing the parasitic capacitance between turns of the winding or, alternatively, modifying the arrangement of the connection between turns. To evaluate the last option, an approximated expression of the first self‐resonant frequency of the magnetic device is proposed. This gives a rapid assessment of the performance of different devices maintaining the overall equivalent inductance. The proposed expression accounts for the influence of the connection between turns in the bandwidth of the component. Finally, some numerical results are verified with planar coils manufactured on two‐layer printed circuit boards.

This study presents design guidelines for planar induction systems whose winding is considerably farther from its load than in usual arrangements. Optimum efficiency design is paramount for larger distances due to the magnetic field dispersion. To this end, a parameterised finite element model is used to ascertain the system''s parameters in this new configuration. This model is used to test variations in frequency, inductor-load distance and inductor diameter. From simulation results, efficiency, output power, power loss volumetric density and near field measurement predictions are obtained. Graphical representation of these results is used to determine the viability of each possible design, choosing one to develop a prototype. Moreover, a study was carried out with Pareto techniques to determine the effect of ferrite coverage and thickness, as well as its distance to the aluminium shielding on efficiency and near field predictions in order to develop a second prototype. The validity of the model is confirmed by experimental tests in small and operating signal regimes.

In this work, a hybrid wireless power transfer system which combines induction heating (IH) and inductive power transfer (IPT) functionalities is proposed to improve the performance of a domestic induction heating application with small loads weakly coupled to distant inductors. Considering the basic single-inductor domestic IH application, the addition of a secondary inductor with series compensation capacitor directly attached to the small ferromagnetic cookware. This inductor allows to adapt the primary inductor to the load size, extending load distance while avoiding increased power losses and stress in electronic components. The extended distance can be used to implement the glassless induction concept, where the ceramic glass of typical cooktops is substituted by the kitchen surface itself. The design of the secondary coil is carried out by means of a combination of Finite Element simulations and electrical simulations. A design process including the housing of the resonant capacitors and the selection of the secondary winding number of turns and cabling is presented. As a result, a prototype is implemented and tested under working conditions up to 1500 W at several distances. Experimental results validate the electrical modelling and simulation. Moreover, thermal results confirm the feasibility of the proposal and validate the adopted strategies for the capacitor housing. IEEE

Domestic induction heating appliances are evolving from surfaces with three to five fixed cooking areas to flexible cooking zones. These are able to adapt to a number of vessels of any size and shape by using multiple coils. Some state-of-the-art induction systems make use of overlapped inductors in two layers, which combine the high efficiency of large inductors with the high flexibility of small adjacent coils. The main drawback of this concept is the unequal distance between different coils and the vessel, which implies that each coil presents a different impedance depending on its layer. This paper presents an induction system conformed by nonplanar inductors. These inductors are designed in such a way that they can be assembled in overlapping structures, while preserving equivalence among them, i.e., they all present the same impedance. This paper includes the finite-element method modeling of the nonplanar coil, an analysis on the an experimental verification.

This paper explores the magnetic flux emissions of induction heating systems compared with inductively coupled heating systems. Inductively coupled heating uses a resonator coil attached to the ferromagnetic load in order to improve energy transfer from the appliance to the load. The magnetic flux emissions of both kinds of systems are simulated, and their dependence on coil current and turn number is outlined. The paper focuses on emitted near field, whose measurement and limits are determined by norm. Several prototypes are developed and tested to verify the simulations.

The following paper describes the design and optimization method for a small inductor in printed circuit board, which is later used in the implementation of a flexible cooking surface prototype. The method combines analytical developments with finite element analysis (FEA) simulations, providing an important decrease of the computational costs. This is followed by the corresponding calculations in order to minimize conduction and proximity losses in the winding by optimizing the copper volume in the winding and the conductor cross-section dimensions. A parametric analysis is carried out to define the induction system that leads to the optimal efficiency, which, moreover, proves extra-thin PCBs as the most suitable solution. A laboratory prototype of a flexible cooking surface was implemented and tested under real working conditions. The empirical characterization produced good results, which are consistent with the simulations. Additionally, the correct thermal behavior of the arrangement and its adaptability to different pot sizes was verified.

This paper introduces the design of a three inductor system that uses a combination of induction heating and wireless power transfer, called inductively coupled heating, in order to heat an additional zone while feeding only one of the inductors. Since no more degrees of freedom are added, the delivered power to the second zone is entirely dependant on the system's geometry and resonant capacitors. Therefore, the ratio of the delivered power to each of the zones becomes very relevant to the design. A finite element model is used to simulate the magnetic fields generated by inductor currents and calculate the impedance matrix. With the impedance, capacitor values are selected with the objective of achieving a high power ratio between the second and first zone, as well as minimizing stress in the electronics. A prototype was used to validate the impedance results.

This work introduces a design method for dual wireless energy transfer and induction heating, allowing for more flexibility in features and usability. A parameterized finite element model is used, along with the development of the analytic equations that rule the system in order to determine its most relevant characteristics. Parametric studies are carried out with this model in order to understand the behavior of the system and achieve a suitable design. This is determined by the calculation of the power factor and supplied power to the system according to the frequency. The representation of these results helps determine the viability of each possible design, choosing one to develop a prototype. The validity of the method is tested via experimental measurements in small signal regime and real operation signal conditions.

Printed circuit board technology provides a cost constrained manufacturing option for low profile inductors due to its highly standardized process, however, the transferred power is limited by the losses in the winding, which may produce overheating. In this work, PCB inductors are evaluated for a high power application as domestic induction heating appliances. Moreover, in the seek of flexible cooking surfaces which can adapt to the size and shape of the pot, the use of partially overlapped inductors generating coil arrays is considered. The work includes the analysis of the coupling between overlapped coils when placed under a dissipative material, a study of the losses in the winding considering rectangular cross section conductors and presents the main implementation techniques. The method is employed for the design of a prototype which was tested under real working conditions delivering up to 4.2 kW.

Domestic induction cookers are evolving from fixed cooking areas to flexible surfaces in such a way that the pot can be placed at any position. This implies the use of a larger number of reduced-sized inductors, which present a lower efficiency. As a solution to increase the efficiency while maintaining the flexibility, we propose the use of partially overlapped inductors of a larger size. This concept is currently in use in wireless power transfer systems, where the transmitter arrangement consists of several overlapped coils. The aim of this paper is to evaluate this concept applied to domestic induction heating appliances, with special emphasis in analyzing the effects of introducing the multicoil system with dissipative media. Moreover, the losses in the winding will be studied in detail. The system will be prototyped and tested, delivering up to 3.7 kW.

Printed circuit board (PCB) implementations provide high repeatability and ease of manufacturing as well as potential cost savings for many applications. An optimization procedure is proposed for designing PCB inductors for use in domestic induction cooktops. Cables for classical inductors are built of multistranded round litz wire for efficiency reasons. A planar litz structure in a PCB has been applied to achieve a similar performance to that of traditional constructions (in terms of maximum output power, inductive efficiency, and thermal behavior). The inductor performance has been optimized by a finite-element-analysis-tool-based method taking into account the power losses in rectangular cross-sectional tracks of the cable as well as the geometrical constraints of PCB implementations and the requirements of the associated electronics. Finally, the proposed method has been validated by means of experimental measurements under large-signal conditions on a PCB inductor prototype.

PCB technology provides an alternative to conventional Wireless Power Transfer (WPT) coils made of wound copper wire. The most common wires for conventional coils are either a single wire or a multistranded cable conforming a litz wire structure. On the other hand, the implementation on printed board is suitable for medium-low power applications, presenting advantages as low cost, high repetibility and compact design. Moreover, for reduced losses, the litz wire structure can be adapted to a PCB implementation. In this paper, a mathematical description of the PCB litz structure is presented together with a method to automatically generate PCB layouts of custom coils. Following this method, several prototypes were built and tested. The experimental characterization of the samples shows that coils with PCB litz structure present reduced losses.

This paper presents a design method for domestic induction systems whose winding is considerably farther from its load. To this end, a parametrized finite element model is used to ascertain the system's parameters. This model is used to test variations in frequency, inductor-load distance and inductor diameter. From simulation results, efficiency, output power, power loss volumetric density and near field measurement predictions are obtained. Graphical representation of these results is used to determine viability of each possible design, choosing one to develop a prototype. Validity of the model is confirmed by experimental tests in small and operating signal regimes.

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.

The operation of a domestic induction cooktop is based on the wireless energy transfer from the inductor to the pot. In such systems, the induction efficiency is defined as the ratio between the power delivered to the pot and the consumed power from the supplying converter. The non-transferred power is dissipated in the inductor, raising its temperature. Most efficiency-measuring methods are based on measuring the effective power (pot) and the total power (converter output). While the converter output power is directly measurable, the measurement of the power dissipation in the pot is usually a cause of inaccuracy. In this work, an alternative method to measure the system’s efficiency is proposed and implemented. The method is based on a pot with a reversible base to which the inductor is attached. In the standard configuration, the inductor is placed below the pot in such a way that the delivered power is used to boil water, and the power losses are dissipated to the air. When the pot base is flipped, the inductor is immersed into the water. In this case the losses in the inductor also contribute to heating up and boiling the water. The induction efficiency is calculated from the boiling rates in both configurations. A commercial inductor was tested under real working conditions with consistent results.

This work presents a method for calculating losses in PCB windings used in multi-coil contactless charging systems. This includes an electromagnetic model which combines analytical developments with FEM simulations in order to calculate the frequency-dependent resistance in a rectangular cross-sectional conductor. The obtained resistance per unit length is then applied to a PCB winding composed of multi-stranded turns in which strands rotate their positions building a Litz structure. The proposed model considers a generic case of a multi-coil assembly in which one of the inductors is supplying power to the load. As other coils may be positioned in the immediate vicinity of an alternating magnetic field source, these coils will produce a loss contribution due to proximity effect. The model has been experimentally validated and the results present consistence when compared with the calculations.

In this work, a design calculation method for common-mode chokes (CMC) is presented. With this purpose, a similar method to that employed in a typical inductor design where the input current characteristics define both the maximum magnetic flux and the winding losses has been adapted. In order to get a suitable design that provides a CMC optimization, considerations with regard to both current components, the common-mode (CM) and the differential-mode (DM) current, have been taken into account. Therefore, the CM current contributes to the magnetic flux in the core, which is associated to the core saturation and core losses, whereas the DM current generates the copper losses. Finally, a CMC for domestic induction heating appliances is designed.

In this paper, an elliptic inductor intended to implement low-cost flexible active surfaces for induction cooktops is presented. A 3-D Finite Element Analysis (FEA) platform including the parameterization of the geometry has been developed for simulation purposes. By means of this platform, the main parameters of the induction system, such as the equivalent impedance including the dependence of the position of the pot, the ferrite sizing and the wiring requirements, are analyzed. Finally, experimental results of the developed inductor prototype at both small and large signal levels are shown.

In this paper, the design and implementation of small inductors in printed circuit board (PCB) for domestic induction heating applications is presented. With this purpose, we have developed both a manufacturing technique and an electromagnetic model of the system based on finite-element method (FEM) simulations. The inductor arrangement consists of a stack of printed circuit boards in which a planar litz wire structure is implemented. The developed PCB litz wire structure minimizes the losses in a similar way to the conventional multi-stranded litz wires; whereas the stack of PCBs allows increasing the power transferred to the pot. Different prototypes of the proposed PCB inductor have been measured at low signal levels. Finally, a PCB inductor has been integrated in an electronic stage to test at high signal levels, i.e. in the similar working conditions to the commercial application.

In this paper, a power control strategy focused on improving the efficiency of induction heating appliances is presented. This strategy uses the distance between the inductor and the load as a control parameter, which is combined with the switching frequency of the resonant inverter. Therefore, a study of the efficiency of the involved subsystems is carried out. From these analyses, the theoretical efficiency of the combined converter-inductor system is analyzed. In order to verify experimentally the proposed power control strategy, an experimental setup has been built in which both distance inductor-vessel and switching frequency can be varied. By using this setup, a mixed electric-calorimetric energy balance is performed with the objective of measuring the impact of the proposed strategy in the appliance efficiency. The calorimetric method shows that the efficiency tendency of the appliance follows the predictions of the theoretical analysis.