Electro-mechanical modeling of electromagnetic levitation melting system driven by a series resonant inverter with experimental validation

Abstract

In this paper, decoupled electro-mechanical modeling of a resonant-inverter-fed electromagnetic levitation melting system (in which a conductive body is floated by Lorentz force and heated-up by high frequency magnetic field-created eddy currents) is carried out and validated experimentally. The work piece considered is formed by a metallic sphere placed in a conical-shaped coil. The proposed model consists of an electrical side subsystem formed by series resonant circuit with time-varying resistance and inductance, a typical second-order mechanical subsystem and a highly nonlinear link between the two. It is also shown that the power conversion process is similar to that of a loosely-coupled transformer, on which any wireless power transfer system is based. Therefore, the system should be powered by a resonant high-frequency AC source to both stabilize vertical axis dynamics and maximize the transferred power. Moreover, operation under resonant conditions yields an explicit relation between operation frequency and vertical position of levitating sphere, leading to possibility of position-sensorless implementation. 1 kW-rated experimental prototype, based on 210Vdc-fed inverter, operating at switching frequency of around 25 kHz is built and tested to validate the derived model. The inverter forces 300A current flowing through 8-turns conical coil in which a 2.27 g sphere is levitated. Simulation and experimental results are shown to accurately resemble each other, verifying well the proposed modeling approach.