Electric Power Systems Research 154 (2018) 95–109 Contents lists available at ScienceDirect Electric Power Systems Research j o ur na l ho mepage: www.elsevier.com/locate/epsr A novel method of measurement of loss in a track of a turn of a planar transformer for induction heating applications Amira Zouaoui Khemakhem a , Khaled Ben Smida b,∗ , Aymen Ammouri a , Ferid Kourda a a Electrical System Laboratory (LSE), Ecole Nationale d’Ingénieur de Tunis, Tunis-Manar University, BP 37-1002-Tunis le Belvédère, Tunisia b LATIS - Laboratory of Advanced Technology and Intelligent Sytems, ENISO, Sousse University a r t i c l e i n f o Article history: Received 28 February 2017 Received in revised form 9 June 2017 Accepted 24 July 2017 Keywords: Planar transformer Finite element method (FEM) Litz planar Skin and proximity effect a b s t r a c t The new trend in power converters is to design planar magnetic components aimed at low profile. How- ever, at high frequencies, the AC losses induced in the planar inductor and transformer windings become significant due to skin and proximity effects. This paper presents the design of a high-frequency planar transformer (HFPT) for an induction heating system. The aim of this design is to adapt the levels of volt- age and current from the inverter to the resonant tank characteristics. We propose a planar structure of Litz in the primary of our HFPT to reduce the AC resistance of the planar conductor. The Litz structure is obtained with a technique of the turn’s division in four tracks and their intersection so that the current passes all over the turn. For the single secondary turn, the choice of the section is based on an analytical study compared to a 2D finite element modeling (FEM), and is determined according to the shape that represents fewer losses and responds to our needs. 2D finite element modeling (FEM) was performed for three different primary turns’ structures; full coil, a turn with four parallel tracks and our Litz planar turn; to minimize losses. Simulation results show that the planar Litz conductor can lead to a lower AC resistance. The performance of this Litz structure is also verified by measurements on experimental prototypes. © 2017 Elsevier B.V. All rights reserved. 1. Introduction AC Winding resistances depend on both the operating frequency and the winding configuration. At high operating frequencies, the current through a solid wire concentrates along the conductor edges, due to the skin and proximity effects Ref. [1]. HFPT are largely used in many electrical and electronic designs. Switching at higher frequencies is an interesting option to reduce passive components and isolation transformers. In addition they allow adapt different levels of voltage and provide electrical and galvanic isolation between both windings. However, there is not a standardized procedure for design transformers, and every manu- facturer keeps their method confidential. An optimized design can save power, volume, weight and money for both manufacturer and customer. Most of researches have been studied the theory of HFPT and its usage in power systems Ref. [2,3]. ∗ Corresponding author. E-mail address: khaled bensmida@yahoo.fr (K.B. Smida). In this paper, the principle of Litz conductor is applied to planar conductor. The literature has already shown that this technique leads to a reduction in the equivalent AC resistance. In Ref. [11] work was examined on high levels of power and realistic operating conditions, in combination with calorific mea- surements. Several configurations of Litz interconnections are investigated. These include 90 and 120 track angles, wide and narrow tracks, and parallel track structures with only one track crossing. It is shown that the latter performed very well under high power conditions. A planar Litz structure is showcased in Ref. [10], aiming to reduce the high-frequency losses in planar windings. This planar Litz type conductor is constructed by weaving many narrow strands along the length of the conductor in such a pattern that each strand can be subjected to every point of the winding cross sectional areas. Thus, the current is distributed uniformly on the conductors. The measured results showed that the reduction of AC resistance by using Litz winding instead of solid conductor could be as high as 30%. Ref. [7] proposes a manufacturing technique and loss analysis model for PCB windings using the planar Litz structure to obtain a loss reduction of AC power similar of conventional windings of http://dx.doi.org/10.1016/j.epsr.2017.07.026 0378-7796/© 2017 Elsevier B.V. All rights reserved.