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Improving the cooking experience of induction-heating users involves, among other factors, an optimized power distribution at the bottom of the cooking vessel. Conventional ferromagnetic cookware presents high efficiency but unequal temperature distribution with flat inductors, which subsequently leads to uneven cooking results. In this work, we propose an alternative to the traditional cookware arrangement by inserting some aluminum pieces in the ferromagnetic bottom of cookware. This arrangement combines the optimal inductive performance of the ferromagnetic iron an the high thermal conductivity of aluminum. The performance of the proposed arrangement is analyzed by means of a multiphysics tool including electromagnetic and heat transfer sub-models which is applied to predict both the equivalent electrical circuit and the temperature distribution in cookware. As a result, a balanced trade-off between efficiency and temperature distribution is evidenced with the proposed solution. Experimental results also corroborates the predictions of the proposed solution. Author

This paper presents the optimization procedure of an inductive power transmission (IPT) system which utilizes large size spiral printed circuit board (PCB) coils for high- power transfer. Printed circuit boards for coil assembly provides advantages in the manufacturing process through the use of cost- effective flexible fabrication techniques. Furthermore, this kind of construction offers a low profile device, which is of great interest for applications with space constraints. PCB-based IPT system coils can achieve high energy efficiency by applying litz-structure braiding techniques, as investigated in this work, where the objective was to obtain an optimized balance between the conduc- tion losses and proximity losses associated with the number and dimensions of the traces. Considering the geometrical dimensions and manufacturing constraints, we will proceed to obtain the characteristics of the coil to achieve optimal performance. The estimation of coil losses were in part based on finite element simulations, and the results were conveniently processed with the appropriate mathematical methods. Numerical simulation and experimental results were conducted for validation on a prototype suitable to transfer up to 3.3 kW for a transmitter- receiver distance of 10 cm. In the experimental arrangement, a maximum efficiency in the coils of 93% has been measured, and the overall efficiency of 88% has been reached for the entire IPT system.

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.

Wireless inductive power transfer (IPT) systems incorporate magnetic flux concentrators in order to improve some features, as coupling and efficiency, and also to reduce electromagnetic emissions. Usually, flux concentrators consist of ferrite cores, which are arranged according to the size and shape of inductive power pads and also according to the application. Ferrite is the most common magnetic material due to its optimal balance between performance and cost. Despite the availability of ferrite cores with a wide set of shapes and sizes, in some applications, the optimal matching between inductive power paths and flux concentrators becomes problematic. In this article, magnetic cement concrete is evaluated as a size-adaptable material for the arrangement of flux concentrators of IPT systems. Both cement powder and concrete are magnetically characterized at different temperatures, field levels, and frequencies, and measurements show that the achieved levels of permeability, Curie’s temperature, and losses make this material attractive for potential flux concentrator uses. A potential IPT application is evaluated by means of a finite-element study and the results are applied to a prototype design. Feasibility of the use of the magnetic cement is tested by means of different power pads according to different flux concentrator arrangements.

Multi-stranded litz wires are commonly used in magnetic devices for power electronics applications at medium-high frequency range, from several kHz up to hundreds of kHz. For these applications, litz-wire structure favours the uniformity of driven current in the cross-sectional area of conductors, alleviating ac losses (skin and proximity effects) and improving the global efficiency of the application. These features are achieved by means of a special cable arrangement consisting of many isolated fine copper strands twisted together according to the manufacturing process. Often, the manufacturing process involves several twisting steps where bundles of moderate number of strands are successively twisted resulting in intricate cable structures. We present a mathematical description of the trajectories of copper strands with the purpose of obtaining the cable losses by means of Finite Element Analysis (FEA) simulation tools. Moreover, a nomenclature for this multilevel structures is also proposed. Parameters as the number of twisting steps, number of strands, strand diameter or pitch length, are included in this representation, allowing to compare the performance of different manufacturing solutions.

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

This article introduces the design of a system capable of heating two magnetically independent ferromagnetic loads placed on different horizontal planes, which uses a combination of induction heating and inductive coupling, called inductively coupled heating. The system uses a single primary inductor acting as a transmitter to transfer power to a secondary inductor attached to the bottom load, which is connected electrically with a third inductor that heats the top load. Since power of the whole system is supplied by a simple half-bridge inverter, the ratio of the delivered power to each of the loads, which is critical for cooking results, is entirely dependent on the system's geometry, coil's number of turns, and compensation capacitors. 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 and inductors’ number of turns are selected with the objective of achieving a high power ratio between the top and bottom zones, as well as minimizing stress in the electronics. First, a prototype was built to validate the impedance results in the small-signal regime, and then, the full power regime was used to verify power and current simulations

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.

We present a semianalytical model for calculating the forces exerted on cookware in domestic induction heating applications. The developed model is based on the Maxwell''s stress tensor and is also based on the existing semianalytic expressions of the electromagnetic fields in planar induction heating systems, which are expressed in terms of Fourier-Bessel series. Taking advantage of the axial symmetry of usual domestic induction heating systems, the flux of the vertical component of the Maxwell''s stress tensor is analytically integrated and the vertical force is obtained. The proposed model captures both eddy currents and magnetization that occurs in typical ferromagnetic cookware. The model is verified by means of two-dimensional Finite Element simulations and also is tested by means of measurements of the change of the weight experimented by cookware due to the forces during the heating process.

We analyze the feasibility of heating non-metallic cookware, unappropriate for heating by means of induced currents, with the purpose of extending the applicability range of the current induction heating cooktops. In order to turn materials as glass, ceramic, wood or plastic into suitable for the induction heating technology, we propose the use of thin layers of a metal (not necessarily a ferromagnetic material) which can be deposited on a surface by means of a thin or thick layer technology. For this purpose, the inductive performance of these layers is investigated by means of an analytical electromagnetic model, finite element simulations and experimental measurements. Calculations point out that for a specific induction arrangement working at a fixed frequency, it exists a thickness which maximizes the induction efficiency for each layer material. The suitability of this result is tested by means of a set of samples with copper thin layers whose thicknesses range from one hundred of nanometers to tens of micrometers, which are implemented using a phase vapor deposition (PVD) technology. The obtained induction efficiency and equivalent resistance are compared with those obtained with conventional ferromagnetic materials. As a proof of concept, the inner and outer bottoms of two glass pots are covered with a copper layer of $2~{\mathrm {\mu }}\text{m}$ , and $1.5~{\mathrm {\mu }}\text{m}$ , respectively, and 1 kW is inductively supplied by means of a series resonant inverter, reaching the boiling water conditions.

Purpose Litz wire manufacturing using mechanical procedures presents several limitations regarding reliability and repeatability, especially when a small strand diameter is used. This paper aims to propose a power supply design for Litz wire manufacturing using a high-frequency high-performance resonant converter. Design/methodology/approach This paper proposes the design of a resonant power supply for induction heating specially designed to tackle with the challenge of heating Litz wires quickly. Findings The proposed converter enables the removal of the isolating coating from the Litz wire through induction heating, improving significantly the manufacturing process. Originality/value The proposed converter improves significantly the manufacturing process of Litz wire through induction heating, with economic and reliability benefits.

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.

We analyze the forces exerted on the pots used as loads of induction heating appliances. These forces depend on the parameters of the induction heating system and also depend on the arrangement and geometry of the application. Forces can be calculated by means of finite element tools but not straightforwardly because the materials of pot combine both eddy currents and ferromagnetism. For this reason, the Maxwell’s stress tensor is used. The exerted force causes the change of the weight of the pot when power is supplied, with respect to the off state. The change of weight is theoretically analyzed and experimentally measured. As it is also shown, the change of weight is also related with the electromagnetic properties of materials and the operating frequency, and this fact can be used to characterize the induction loads. Calculations are validated by means of an experimental setup arranged by means of load cells.

Litz wires with large number of strands are usually manufactured by twisting several bundles of a moderate number of strands. Apart from manufacturing advantages, this technique also provides extra characteristics as current balancing between strands and, consequently, power loss balancing and optimal use of cross sectional copper area. However, complex twisting configurations carry analysis, modeling and design problems which make choosing the parameters of a particular arrangement difficult. A complete 3D finite element model that explicitly includes the effect of twisting at several bundle levels is introduced. This model captures the twisting details and allows observing the actual current density in the strands at the different positions in the wire for both net driven current and induced current by an external field. The model is implemented by using the rigourous mathematical description of trajectories of strands and it is used to analyze the effect of several parameters as bundle levels, pitch and isolation between strands.

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.