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A high performance 8khz pulse width modulated voltage fed inverter for induction heating

Chapter One 1.


 1.1 Background to the Work

 Induction Heating is the process of contactless and direct heating of a work piece by a varying magnetic field. This technique has become state of the art and is diversifying to numerous heating operations thereby replacing older and more traditional techniques of heating, ranging from industrial to domestic needs. Its attraction everywhere and especially in industry is based on fast start up, fast heating, energy saving and environmental friendliness, contactless and direct heating of work piece. Induction heating today has found its way into processes like; i. Pre-Heating of metal work pieces: as in forging, extrusion, and rolling. ii. Heat Treatment operations: as in hardening, annealing and tempering. iii. Others such as: melting, welding, brazing, semi-conductor growth, non-metal to metal boding, liquid heating, etc. A pulse width modulated/frequency modulated Voltage Source Inverter (VSI) is built to power a crucible type Induction Furnace developed based on a new per-unitized model. The Induction Furnace is one type of diverse induction heating loads. Since the early days of induction heating, the need for improved power supply equipment presented the challenge against its rapid development. The basic task has always been the development of large power source for low, medium and high frequency applications with improved efficiency. Supply frequency systems, motor-generators, spark-gap generators and vacuum oscillators belong to the early power supplies in use [1]. The growth of semiconductor technology began to introduce static power switches dominated by the thyristor for induction heating [2]. New device optimization has continued to improve the operating frequency, power level, simplicity and efficiency of induction heating power supplies. The introduction of the Insulated Gate Bipolar Transistor (IGBT) in mid 1980s began to oust other members of the thyristor family due to its ease of control and switching speed [3]. These very important features which conduce to induction heating together with continued improvements in the power handling capability of the IGBT has made it a device of choice. Various designs of saturable core reactors operating at mains frequency have their harmonics harnessed to constitute source of low (supply) frequency induction heating systems. Much earlier, motor-alternator sets were used to provide the medium frequency power needed for induction heating works. It has the drawbacks of fixed frequency operation, bulkiness, high noise level and high fault infestation resulting in long downtimes. A number of such units imported into this country have broken down and become abandoned due to lack of maintenance expertise. One such unit for a 50kg crucible induction furnace is installed for the Federal Government Science Equipment Development Institute Enugu (SEDI-E). SEDI-E needs a replacement of the power supply unit of its induction furnace which broke down more than seven years ago and is still in that state for want of capability to resuscitate or replace the power unit. Spark gap and Vacuum Tube Oscillators were also used to generate high frequency induction heating power. Vacuum tubes have low efficiency and very high tube voltage. They are continually declining in popularity. Spark gap oscillators are auto-tuned to resonance but have high peak voltages than would appear in the motor-generator set or vacuum tube generator. They have however faded out.

Project detailsContents
Number of Pages168 pages
Chapter one Introduction
Chapter two Literature review
Chapter three  methodology
Chapter  four  Data analysis
Chapter  five Summary,discussion & recommendations
Chapter summary1 to 5 chapters
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