Some info on an induction cooktop by westing house.
In each of the electronics modules, the 240V, 60 Hz domestic line power was converted to between 20V to 200V of continuously variable DC by a phase-controlled rectifier. That DC power was in turn converted to 27 kHz 30 A (peak) AC by two arrays of six paralleled Motorola automotive-ignition transistors in a half-bridge configuration driving a series-resonant LC oscillator, of which the inductor component was the induction-heating coil and its load, the cooking pan.
Below is a circuit of an induction cooktop of one kind.The full PDF can be found here.
http://www.datasheetarchive.com/control%20circuit%20of%20induction%20cooker-datasheet.htmlNow here is some information that is starting to explain as to what i was seeing in my scope at the lower time scale.
Quote:High frequency alternating current is generated in the heating coil of the cooker by a resonant power inverter employing one semiconductor switch. An anti-parallel diode (DP) is placed parallel to the IGBT to assure a path for current flow in the opposite direction when the transistor is off.
In Fig. 1, L is the inductance of the heating coil and CRES is the resonant capacitor. The controller maintains the resonance of this circuit by monitoring the current flowing in the coil and switching on at the zero crossings of this current and switching off at the proper instant to assure that the input current to the cooker remains within a sinusoidal envelope at the mains frequency.
The whole PDF can be found here-http://www.uzay.tubitak.gov.tr/tubitakUzay/yayinlar/Ertan_baris%20colak_14-05-04.doc
And yet some more info on the induction circuit-•DC power supply for inverter (can be rectified mains)
•Inverter circuit (usually an IGBT)
•Resonant circuit, comprising work coil, matching capacitors and inductor.
•Driver circuit.
The rest can be found here-http://imajeenyus.com/electronics/20060908_induction_cooker/index.shtml
The definition of a resonant circuit-An electric circuit with inductance and capacitance chosen to allow the greatest flow of current at a certain frequency.
This is exactly how the induction cooker circuit is designed to work-and dose.Maybe some should widen there ideas on resonant circuit's?