Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B6/00—Heating by electric, magnetic or electromagnetic fields
  • H05B6/02—Induction heating
  • H05B6/06—Control, e.g. of temperature, of power
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B6/00—Heating by electric, magnetic or electromagnetic fields
  • H05B6/02—Induction heating
  • H05B6/06—Control, e.g. of temperature, of power
  • H05B6/062—Control, e.g. of temperature, of power for cooking plates or the like

Definitions

• the present invention relates to a ripple current generator for use in an induction heater.
• Generators of this type are known and the one described in the present application comprises an oscillating circuit consisting of a current injection choke, a capacitor, an induction heating coil and a switch. high frequency controlled power.
• induction heating 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 an inductor and which is placed near a body of a conductive object. electricity so that eddy currents develop there and generate a significant amount of heat by the Joule effect.
• Existing devices, implementing this heating principle have the disadvantage of being sensitive to coupling, that is to say that the transmitted heating power varies when the size of the object to be heated varies. More particularly, it is known that when such generators are used in induction hobs intended for heating food contained in a container, the maximum heating power transmitted to the container containing the food to be heated is all the more small that the bottom diameter of this container is small.
• the object of the invention is to provide 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 a high heating power even for small kitchen containers. .
• the generator described here com ⁇ carries a current injection reactor of the saturable type connected in series with a parallel set formed by two branches, ie a first branch B- ⁇ containing the power switch, and a second branch B 2 containing the capacitor connected in series with the induction heating coil.
• the device according to the invention therefore makes it possible to vary the power continuously from a low value of approximately 100 Watts to a value of approximately 2.5 kilowatts regardless of the size of the container used. This advantage is essential in the case of domestic use of the generator in an induction 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 self-injection of saturable current by construction not requiring any additional device to reach saturation and which operates automatically in saturation during the phase of resonance of the oscillating circuit. Besides the reduction in size and price, an important consequence of the use of such a saturable choke is the achievement of self-adaptability of the generator to the load.
• the generator according to the invention makes it possible to obtain heating power. independent of the dimensions of the body to be heated which can vary over a wide range and the value of which is chosen only by the user.
• FIG. 1 shows the diagram of an exemplary embodiment of the generator according to the invention where the power switch used is a power transistor of the IGBT type associated with a power diode;
• FIG. 2 illustrates a graph showing the evolution of the power absorbed as a function of the supply voltage for different diameters d in cm of the utensil containing the food to be heated in the case of a generator of the prior art comprising an unsaturable self;
• FIG. 3 illustrates the evolution of the power absorbed as a function of the supply voltage for different diameters d in cm of the utensil containing the food to be heated in the case of a generator according to the invention and comprising a saturable self;
• FIG. 4 represents an alternative embodiment of the invention in which the switch is a thyristor of the MOS CONT OLLED THYRISTOR (MCT) type voltage symmetrical;
• FIG. 5a shows a perspective view of the E-shaped ferrite parts constituting the magnetic circuit of the current injection choke
• FIG. 5b shows a vertical section of the saturable current injection choke used in the generator according to the invention
• FIG. 5c shows a horizontal section of the saturable current injection choke used in the generator according to the invention.
• FIG. 6 illustrates, on the one hand, an alternation A of the supply current flowing in an oscil ⁇ lant circuit consisting, inter alia, of an inductor for injecting unsaturable current as well as a heating coil by induction and, on the other hand, an alter- nance B of the supply current flowing in a circuit of the same type but with a saturable choke according to the invention;
• - Figure 7 illustrates an envelope E of the supply voltage and, on a very enlarged scale, part of this said voltage applied to the terminals of the power switch in the case of an oscillating circuit comprising a choke unsaturable current injection;
• - Figure 8 is a representation similar to Figure 7, but in the case of an oscillating circuit comprising a self injection of saturable current according to the invention.
• the corrugated current generator 1 is intended to be used in an induction heating device of the hot plate type and is supplied by the mains, said generator in a manner known per se rectifier 2 preceded by an anti-parasite filter 3 and followed by a low-pass filter 4 comprising a coil 5 and a capacitor 7.
• a first output terminal 8 of said rectifier bridge 2 is connected to a first terminal of the coil 5 , the second terminal of the coil 5 being connected to a common terminal to a current injection choke 6 and to the condenser 7.
• the second terminal 9 of the current injection choke 6 is connected to a first terminal 1 • parallel set consisting of two branches B- j ⁇ and B 2 .
• the second terminal 10 of this parallel set is connected to the second terminal of the capacitor 7 and to the second output terminal 11 of the rectifier bridge 2.
• the branch B- ⁇ comprises an electronic switch 12, while the branch B 2 comprises a capacitor 13 mounted in series with a coil forming the inductor 14.
• the coil 5 and the capacitor 7 constitute the low-pass filter 4 which makes it possible to avoid the return to the sector of steep edges of voltages which may appear in the oscillating circuit.
• the graph represents the power absorbed as a function of the supply voltage in a generator of the prior art as described above.
• This graph shows that when the supply voltage varies from 180 V to 270 V the induced heating power does not exceed 2 kilowatts when using vessels having diameters ranging from 95 cm to 150 cm.
• the current injection choke is a saturable choke and is connected in series with a parallel assembly formed by two branches, ie a first branch B- ⁇ containing the switch referenced 12 in FIG. 1 and 21 in FIG. 4 and a second branch B 2 containing a capacitor 13 mounted in series with the induction heating coil 14.
• Said inductor 6 comprises a magnetic circuit which automatically reaches saturation when its winding is traversed by a current of predetermined value.
• This magnetic circuit as shown in FIGS. 5a and 5b comprises two identical pieces 16 in the form of an E in ferrite connected by their respective side bars 17 while the respective central cores 18 are separated by a 4 mm entre ⁇ iron.
• said choke 6 is saturable by construction and comprises a winding of 46 turns formed by 60 strands of 0.2 mm in diameter.
• Said choke 6 is characterized by the fact that it comprises a magnetic circuit which automatically reaches saturation when its current is crossed by a current of predetermined value.
• the switch 12 of the branch B- ⁇ as illustrated in FIG. 1 is a power transistor of the IGBT type connected in series with a power diode 19. The diode 19 allowing the application of a reverse voltage across the power transistor when the latter is blocked.
• a CMD control device referenced 20 controls the high frequency switching of the power transistor during the resonance phase of the oscillating circuit, when the current in the branch B- ⁇ is zero. Said control device 20 also makes it possible to avoid the overvoltage which may develop at the terminals of the power transistor.
• the choke 6 when the choke 6 is saturable, a generator is obtained which makes it possible to induce a heating power which varies over a wide range and whose value does not depend on the dimensions of the container to be heated.
• the power absorbed, for different supply voltages varying from 180 V to 270 V is greater than 2 kilowatts with the exception of the case where the diameter of the cooking utensil is 95 cm and the supply voltage is greater than 230 V.
• 1 high frequency controlled switch is a thyristor 21 of the type MOS CONTROLLED THYRISTOR (MCT) symmetrical in voltage.
• MCT MOS CONTROLLED THYRISTOR
• the impedance of the saturable choke 6 has a value of 250 ⁇ H
• the capacitance of the capacitor 13 has a value of 188 nF
• the impedance of the inductor 14 to vacuum has a value of 66 ⁇ H
• the power switch is chosen so that the breakdown voltage does not exceed 1200 V.
• the tests have been carried out for a value of the saturation current of the inductor 6 of 1 • order of 17 amps at room temperature.
• the tests in FIG. 7 were carried out for a power of 1500 W at a frequency of 29.6 Hz and the tests in FIG. 8 were carried out for a power of 1500 W at a frequency of 31.5 kHz.
• the generator according to the invention therefore makes it possible to obtain a simple and inexpensive device which operates over a wide range of power and whose heating power does not depend on the dimensions of the container containing the food to be heated.
• This device also makes it possible to significantly improve the coefficient of use of silicon for small loads. This allows the user to obtain a high desired power regardless of the load, with an economical switch. In addition, thanks to the reduction of overvoltage at the terminals of the switch 12,21, it is possible to maintain high power on low loads, despite poor coupling.
• the invention also applies to induction heating generators intended to be incorporated into housings of apparatuses such as for example steam cookers, rice cookers, fryers. It also applies to industrial induction heating machines intended for the treatment of metal parts.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• General Induction Heating (AREA)
• Inverter Devices (AREA)
• Cookers (AREA)

Priority Applications (5)

Applications Claiming Priority (2)

Publications (1)

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ID=9452850

Family Applications (1)

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Families Citing this family (9)

Citations (6)

Family Cites Families (7)

• 1993
  • 1993-11-15 FR FR9313587A patent/FR2712763B1/fr not_active Expired - Fee Related
• 1994
  • 1994-11-15 DE DE69405412T patent/DE69405412T2/de not_active Expired - Fee Related
  • 1994-11-15 EP EP95901493A patent/EP0734639B1/fr not_active Expired - Lifetime
  • 1994-11-15 CN CN94194152A patent/CN1067836C/zh not_active Expired - Fee Related
  • 1994-11-15 WO PCT/FR1994/001334 patent/WO1995014364A1/fr active IP Right Grant
  • 1994-11-15 JP JP51425995A patent/JP3724804B2/ja not_active Expired - Fee Related
  • 1994-11-15 US US08/637,721 patent/US5854473A/en not_active Expired - Fee Related
  • 1994-11-15 ES ES95901493T patent/ES2106632T3/es not_active Expired - Lifetime
  • 1994-11-15 KR KR1019960702533A patent/KR100318806B1/ko not_active Expired - Fee Related
  • 1994-11-18 TW TW083110742A patent/TW277178B/zh active

Patent Citations (6)

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