Induction heating is becoming more popular around the
globe. It is a fast, safe, energy efficient method of cooking
and is used in both residential and commercial cooking
environments. In induction heating, a high frequency
magnetic field is generated by a coil in the cooker and
absorbed by the pan material. This is much more efficient
that either gas or electric heating in which much of the heat
generated rises past the surface of the pan and never
contributes to the heating of the contents. The two most
common topologies for induction cooking applications are
the quasi−resonant boost converter, which requires 1200 V
or higher, IGBT switches, and the resonant half−bridge
circuit which uses 600 or 650 V IGBTs.
Both of these circuits employ an RLC tank circuit which
is comprised of a capacitor (or equivalent series of
capacitors), an inductor (heating coil) and a resistance (the
pan). The pan acts as a core to the air core coil that it is placed
on. In a normal magnetic component, the device is designed
to minimize the core loss by selecting the proper material for
high efficiency. In the case of induction heating, the goal is
exactly the opposite and the core should be very lossy, to
convert the magnetic field generated by the power converter,
into heat.
This application note examines some of the common
materials used in the construction of IH cookers. These
include several alloys of stainless steel, iron as well as
aluminum, although it is not a magnetic material.