Abstract
D.Ing. (Electrical and Electronic Engineering)
Solid state converters are showing considerable progress in all applications for
power electronics, mainly because of the advances made in the field of power
semiconductor devices. Higher frequencies and power ratings of converters are
therefore possible, leading to more and more applications for these solid state
converters in induction heating. The available knowledge in this fast evolving field is
however limited, leading to numerous research possibilities. It is none the less
important to learn to crawl before attempting to run and a systematic line is therefore
followed in this research.
The combination of the heating-coil and work-piece is a challenging electromagnetic
problem, resembling a transformer with a short circuited secondary. The
heating of the work-piece to above the Curie temperature causes considerable
variations in the parameters of the load. A study of the influence of temperature on
the physical properties of the heated material is therefore made to obtain an
understanding of these variations and is aided by Finite Element Simulations.
Numerous circuit topologies and switching strategies are possible candidates for
induction heating, and a collection of more than thirty converters is presented. Each
of these has its own advantages and disadvantages, of which a good understanding
is necessary to obtain the most suitable converter for a certain application in this field.
The behaviour of some of the most popular converters under typical load variations
is investigated to facilitate the final decision.
This knowledge is then applied to some every day applications. A converter is
chosen both for an induction cooker and a surface heater, after the specific
requirements for each have been identified. A detailed design procedure and
experimental results are presented...