An application of the impedance boundary condition for the design of coils used in domestic induction heating systems

Abstract

Purpose -The aim of this paper is to propose a design procedure based on the impedance boundary condition in order to simplify the design of inductors for domestic induction heating systems. Design/methodology/approach -An electromagnetic description of the inductor system is performed to substitute the effects of a component, named system load, for a mathematical condition, the so-called impedance boundary condition. This is suitable to be used in electromagnetic systems involving high conductive materials at medium frequencies, as it occurs in an induction heating system. Applying this approach, a simplified electrical model arises from the general system. Findings -A considerable reduction in the efforts devoted to design a coil for induction heating purposes is achieved, because the solution considering the variation of three physical parameters are projected to a one-dimensional space only depending on a single parameter named corrected penetration depth. This proposal assesses the working conditions of standard induction systems. Practical implications -This work is performed to achieve a better understanding of the fundamentals involved in the electromagnetic modeling of an induction heating system. The main goal is the definition of a better coil design process because it is probably the most time-consuming task in the construction of a complete induction system. Originality/value -In this paper, the so-called corrected penetration depth is defined. This single parameter allows explaining the influence of the physical parameter of the inductor load and the excitation frequency in the equivalent of the complete inductor system. The numerical results carried out considering the corrected penetration depth instead of the physical load properties have been validated experimentally. IntroductionDomestic induction heating systems are usually fed by a power electronic inverter working at a switching frequency ranging from 20 to 100 kHz, thus, the inductor system is viewed as an electrical equivalent impedance (Acero et al., 2010). The inductor system is made up of a coil placed between an electrical conductive medium, which is the load to be heated up by the system, and a magnetic insulator playing the role of flux concentrator (Acero et al., 2006) as can be seen in Figure 1. In order to improve the complete system performance, the inductor system equivalent impedance must be adapted to the power converter; consequently, efficient coil optimization is the goal of the system design process. However, such coil design process has to deal with several geometrical constraints and a wide load variety; therefore, roughly iterative simulation procedure is carried out with analytical (Hurley and Duffy, 1995) or numerical methods (Enokizono and Tanabe, 1995;Bay et al., 2003;Lavers, 2008). Such numerical simulations are based on the induction load modeling considering an homogeneous linear medium. Then, the load is characterized by means of its physical properties, for instance, electrical conductivity s and magnetic perme...