Induction cooktop designs typicallty run on rectified but unfiltered AC power at 120 Hz. This voltage varies from zero to about 160 volts peak and is used to directly power a quasi resonant circuit running at about 24 KHz. The width of the 24 KHz cycle power pusles is used to control the power level, but this method has trouble doing lower power levels. Many of the units resort to on/off cycling to achive the lower power settings.
An alternative way to control the power would be to keep the width of the 24 KHz power pulses the same, but vary the number of oscillations created within each AC cycle. Since quasi-resonant circuts require that each cycle be initiated individually, and there are about 200 of them within each AC cycle, very fine control can be achieved even at low power levels.
Experiments are currently under way. The final design will be posted here when completed.