Electric heating – Inductive heating – With heat exchange
Patent
1996-04-30
1998-12-29
Leung, Philip H.
Electric heating
Inductive heating
With heat exchange
219661, 219663, 219670, 323328, 363 97, H05B 606, H05B 612
Patent
active
058544739
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an alternating current generator, intended to be used in an induction-heating apparatus. Generators of this type are known and the one described in the present application includes an oscillating circuit consisting of a current-injection choke, a capacitor, an induction-heating coil and a power switch controlled at high frequency.
The principle of induction heating is known and consists in applying a current which varies at a relatively high frequency, up to a few tens of kilohertz, to a coil which serves as inductor and which is placed in proximity to a body of an electrically conducting object so that eddy currents are developed therein, and which generates a considerable amount of heat therein joule effect. The existing devices employing this heating principle exhibit the drawback of being sensitive to the coupling, that is to say that the heating power transmitted varies when the dimensions of the object to be heated vary. More particularly, it is known that, when such generators are used in induction plates intended to heat food contained in a receptacle, the maximum heating power transmitted to the receptacle containing the food to be heated is the smaller the smaller the diameter of the base of this receptacle.
In order to remedy this drawback, several solutions have been implemented, some of which vary the inductance of the oscillating circuit so as to modulate the power transmitted. Other techniques use mechanical methods consisting in altering the spacing gap between the inductor and a support plate situated in proximity to the inductor and on which the receptacle is placed, which leads to a variation of the gap containing the support plate, and consequently a variation in the magnetic flux through this gap. Other known solutions consist in varying the output frequency of a semiconductor inverter feeding the induction-heating coil. Solutions are also known consisting in adjusting the DC power supply voltage of the inverter by using a phase-control rectifier in the rectifier circuit. Another solution used consists in varying, in steps, the capacitance and inductance parameters of the switching circuit.
All these solutions, although they allow modulation of the heating power, do not, however, make it possible to avoid the influence of the size of the body to be heated on the power transmitted by the inductor to this body. In fact, as we mentioned previously in the case of the heating of food contained in a cooking receptacle, this influence is manifested by a lowering in the power absorbed when the surface area of the receptacle to be heated, in which the eddy currents are developed, is reduced. This constitutes a drawback for the user, who wants to have high power available in small-size receptacles.
SUMMARY OF THE INVENTION
The object of the invention is to produce a device which makes it possible to induce a power which does not depend on the dimensions of the body to be heated and which makes it possible to obtain high heating power even for cooking receptacles of small dimensions.
According to the invention, the generator described here includes a current-injection choke of the saturable type mounted in series with a parallel assembly formed by two branches, that is a first banch B.sub.1 containing the power switch, and a second branch B.sub.2, containing the capacitor mounted in series with the induction-heating coil.
The device according to the invention thus makes it possible to vary the power continuously from a low value of about 100 watts to a value of about 2.5 kilowatts whatever the size of the receptacle used. This advantage is vital in the case of a domestic use of the generator in an induction heating hob, where the low powers, often necessary for simmering, are obtained without cycling.
Another essential advantage of the generator according to the invention resides in the use of a current-injection choke which is saturable by construction, requiring no additional device for reaching saturation, and which operates auto
REFERENCES:
patent: 3777100 (1973-12-01), Trine
patent: 4002875 (1977-01-01), Kiuchi et al.
patent: 4055740 (1977-10-01), Nakamura et al.
patent: 4320273 (1982-03-01), Kiuchi
patent: 4506131 (1985-03-01), Boehm et al.
patent: 5055648 (1991-10-01), Iceland et al.
patent: 5059762 (1991-10-01), Simcock
Leung Philip H.
Moulinex (S.A.)
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