induction heating is a method to generate heat by flow of current that produced inductively in metal plate.
the eddy current (also called Foucault currents) which is the cause of heating in transformers.
in Transformers(where eddy current is the evil) the heating is avoided by insulating the plates but here make the eddy current flow in the plate
PWM is pulse width modulation it is used for generation of alternating current.
and IGBT is a power transistor used for amplification in power systems.
and i guess the process is like this
AC(220-230volt)-->DC(10-100volt)-->PWM oscillator--->IGBT based power amplifier--->induction coil