Analysis of Load Dynamics in Induction Melting Furnace and Improved Power Quality With Phase Shift Modulated LLC Resonant IGBT Inverter

A dynamic load profile is experienced by the power topology to which the induction melting furnace (IMF) is coupled when an iron scrap is being melted in the furnace. This load profile necessitates continuous correction in silicon-controlled rectifier (SCR)-based front-end converter as well as adjustment in the switching frequency of an inverter in a conventional 12-pulse SCR current source inverter (CSI-SCR) design. This correction on both sides of the converter results in harmonics and interharmonics, which gets injected into the supply line current, degrading the distribution grid’s power quality. The line current total harmonic distortion (THD) is observed to be around 16%–19.5% which is beyond the permissible limit (< 12%) as per IEEE 519–2014 standard. This article investigates the dynamic load profile of the IMF system based on simulation and extensive practical field data from existing running IMF. In this article, LLC resonant insulated gate bipolar transistor (IGBT) inverter is proposed for an iron scrap melting application. In the proposed topology, in which the practical load profile of the furnace is taken into account, the front-end converter is an uncontrolled diode rectifier, and the power to the furnace load is controlled by a combination of phase shift modulation (PSM) and frequency control of the IGBT inverter. A prototype model of 100 kW is designed, fabricated, and tested in the field to validate the concept. The proposed topology reduced the line current THD from 19.5% to 11.6%, meeting the required standard. In addition, the system efficiency has improved by 2.05%.