Induction heating apparatus using a saturable reactor for power control purposes

An induction heating apparatus comprising:

• a power converter adapted to connect to a source of alternating voltage for converting the frequency of the source voltage to a high frequency, including a gated switching device, a resonant circuit including an induction heating coil connected to the gated switching device, a gating circuit providing gating-on pulses that drive said gated switching device into conduction successively, whereby an energization current substantially at said higher frequency is produced in said induction heating coil, a zero crossover detector for detecting the instant when said alternating voltage is substantially at zero to trigger said gating circuit to generate a train of gating-on pulses, first delay means for delaying the generation of said gating-on pulses for a predetermined period from the instant when said power converter is connected to the alternating voltage source, whereby said induction heating coil is electromagnetically coupled to a magnetic cooking ware placed in overlying relation therewith to be heated;
• a transformer having a closed magnetic circuit and provided with three parallel limbs connected together by transverse members, a control winding arranged on the central limb and series-connected load windings wound in opposite directions and arranged one on each outer limb and connected in series with said induction heating coil to thereby be energized by said energization current, said transformer including an air gap in each of said outer limbs so that the variation of a current through said control winding linearly alters the magnitude of the current passing through said load windings;
• and
• a power control circuit comprising means for detecting electrical power representative of said electromagnetic coupling, means for comparing the detected power with a reference value to produce a DC control current with which said control winding is energized, manually adjusting means for controlling said reference level, and second delay means connected between said comparing means and said control winding for delaying the application of said DC control current for a predetermined period from the instant when said power converter is connected to said source voltage for energization.