Électrotechnique et électroénergétique INVERTER-INDUCTOR CIRCUIT FOR EDDY CURRENT TREATMENT OF FERROMAGNETIC PIECES TEODOR LEUCA 1 , ADRIAN TRAIAN BURCA 1 , MIHAI MARICARU 2 , NISTOR DANIEL TRIP 1 , IOAN FLOREA HĂNŢILĂ 2 Key words: Surface heating, Periodic non-sinusoidal regime, Inverter-inductor circuit. This paper presents an effective procedure for analyzing the operation of the medium frequency heating system for ferromagnetic pieces. Given the non-sinusoidal shape of the output voltage of the inverter, it was taken into account the harmonics of capacities within the system, selecting the most important ones. At the working frequency of the installation, the depth of penetration of the electromagnetic field is very low compared to the other geometric dimensions and therefore it is suggested the adoption of a uniform environment for this superficial area. The thermal diffusion problem has been solved analytically, using the separation of the solution in spatial eigenfunctions. 1. INTRODUCTION In order to account for the nonlinearity of the B-H relationship and the pronounced non-sinusoidal form of the inverter’s voltage, the speciality literature provides some important methods, used for solving the eddy currents problem. The static permeability method, corrected by several criteria [1], is used by most commercial software (FLUX, COMSOL etc.). The phasor representation of the electromagnetic field can also be used. The harmonic balance method, which can be relatively easily applied to non-linear electric circuits, raises significant problems in the case of electromagnetic field issues [2]. A huge nonlinear algebraic system, involving all Fourier series coefficients must be solved. In the case of the brute force method, which aims to obtain the asymptotic solution to the electromagnetic field problem, it is difficult to formulate the boundary conditions for the considered inductor-inverter circuit. The only method that seems to be particularly effective in treating the periodic nonlinear regime is described in [3] and is based on the polarization method [4]. For medium frequency, the depth of penetration of the electromagnetic field in ferromagnetic pieces is very small compared to other geometrical dimensions of 1 University of Oradea, Universitatii str., no. 1, Oradea, 410087, Romania; tleuca@uoradea.ro 2 “Politehnica” University of Bucharest, 313 Splaiul Independenţei, 060042, Bucharest, Romania Rev. Roum. Sci. Techn. – Électrotechn. et Énerg., 60, 1, p. 7–16, Bucarest, 2015