Envelope dynamics of resonant inverter driven electromagnetic levitation melting system with experimental verification

The paper presents a methodology for nonlinear envelope dynamics derivation of a levitation melting type induction heating system, fed by a resonant inverter, based on recently established work piece electro-mechanical model. The work piece under consideration is formed by an aluminum sphere, floated by conical-shaped copper coil. Resonant power converter is used to drive the induction heating system due to the fact that significant impedance of the work piece coil at high operation frequency (several tens of kilohertz) limits the power transferred to the load and therefore needs to be cancelled by corresponding capacitive impedance. Since the application requires levitation of the object being heated up, low-frequency (several hertz) dynamics appears, related to floating body movement. As a result, high-frequency electrical signals become modulated by low-frequency oscillations induced by mechanical side dynamics. It is known that power transfer in sinusoidal excited electrical system is governed by magnitudes and related phases of currents and voltages. Consequently, in order to assess both the low-frequency dynamics of levitated object mechanical motion and the amount of power transferred, information regarding envelope behavior of electrical-side signals is sufficient. Once established, envelope model of the electrical subsystem combined with typical model of the mechanical subsystem describe mechanical side parameters (position, speed and acceleration) exactly as if full electrical model would have been utilized. Moreover, envelope model significantly decreases simulation time and memory requirements of simulation platform. The proposed modeling approach is validated by comparing full and envelope model simulation results, accompanied by results obtained from experimental prototype.