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
  • H05B6/64—Heating using microwaves
  • H05B6/66—Circuits
  • H05B6/666—Safety circuits

Definitions

• the invention relates to a device for supplying a non-linear load which is connected to an alternating current distribution network.
• the supply device comprises a rectifier connected to the terminals of said network and formed by a full-wave diode bridge, the output of which is connected by two supply lines to the primary winding of a high voltage transformer, the secondary winding being connected by two supply lines to the non-linear load, a high frequency interference suppression filter positioned at the output of said rectifier and consisting of an inductor and a capacitor, a high frequency switching element positioned on one supply lines and having a trigger connected to a control circuit and a device for measuring the intensity of the current flowing in the supply line containing the switching element.
• Said intensity measurement device makes it possible to detect a value of current flowing in the supply line containing said switching element.
• the value thus detected is sent to the control circuit which applies trigger signals to the trigger of the switching element.
• the trigger signals sent to the control circuit make the switching element conductive by authorizing the passage of current from the other supply line connected to the primary winding to the supply line containing the switching element.
• the average intensity delivered at each pulse being a function of the switch control frequency, said control frequency can be controlled by the measured value of said average intensity so that the latter remains constant.
• the object of the invention is to remedy these drawbacks by implementing an intensity measurement device correcting the frequency of the triggering signals of the control circuit.
• the measuring device comprises a sensor intended to take the intensity on the supply line and associated with a storage device which makes it possible to store a voltage proportional to the intensity passing through the average switching element on a period of the high frequency oscillation, a device for squaring the rectified mains voltage
• the intensity of the current in the supply line is measured at each opening of the switching element, this calculation making it possible to take into account all the variations in the average intensity of the pulses.
• the frequency of the trigger signal is corrected either increasing or decreasing, thereby acting on the power supplied to the non-linear load.
• the power absorbed by the load can therefore be adjusted at each switching and, therefore, the absorbed intensity can be kept close to a sinusoidal shape and said absorbed power controlled by a set value.
• FIG. 1 represents an example of mounting of a device for measuring intensity according to the invention and positioned in a supply circuit of a magnetron;
• FIG. 2 represents a circuit of a device for measuring the intensity of a non-linear load adapted to be mounted in the circuit of FIG. 1.
• the circuit is intended more particularly for supplying a non-linear load such as a magnetron 1 of a microwave oven from an alternative distribution network arriving at terminals 3 and 4 of the circuit.
• a rectifier 5 which is formed by a full-wave diode bridge and the output of which is connected to two lines 6 and 7 supplying a high voltage transformer 8.
• a filter high frequency interference suppression is positioned at the output of said rectifier 5 and consists of a self-inductance 9 and a capacitor 10.
• Lines 6 and 7 are connected respectively to the ends 11 and .12 of the primary winding 13 of the transformer 8.
• the supply line 7 also includes a switching element 14 having a trigger 15 connected to a control circuit 16 as well as a switching aid device 16 '.
• Said switching element 14 is constituted by a unidirectional current switch.
• the unidirectional switch 14 is connected, for example, in series with a diode 20 preventing reverse current to the source, thus ensuring a better ratio: average current injected on effective current in the primary circuit.
• the diode 20 can be mounted in parallel with the unidirectional switch 14.
• the circuit also includes a capacitor 18 connected in parallel to said winding 13, as well as an inductor 17 connected in series with the assembly thus constituted by the capacitor 18 and the primary winding 13.
• the inductor 17 is coupled to a secondary winding 21 the ends of which are connected to the heating element 20 of the magnetron 1.
• the secondary winding 19 of said transformer 8 comprises respectively two terminals 21 and 22 connected respectively to two supply lines 23 and 24 connected one 23 to the cathode 2 of magnetron 1 and the other 24, to the anode 25 of said magnetron which is also connected to ground 26.
• the frequency of the trigger signals varies according to the value of the current flowing in the supply line 7.
• the value of said current is analyzed by an intensity measurement device 28.
• the measurement device 28 comprises a sensor 30 intended to take the intensity from the supply line 7 and associated with a storage device 34 which makes it possible to memorize a voltage proportional to the intensity crossing the switching element 14 averaged over a period of the high frequency oscillation, a device 43 for raising the square of the mains voltage straightened
• the sensor 30 comprises a winding, for example, that of a high frequency intensity transformer 29.
• the winding 30 has two terminals 31 and 32, one of which 32 is connected to ground.
• a resistor RI is connected in parallel to the winding 30 at the terminals 31 and 32.
• the terminal 31 is connected to one of the inputs 33 of the storage device 34 constituted, for example, by a sample-and-hold amplifier controlled by the activation of 'a clock clk has on an input 35.
• the activation of the clock clk has controls a switching device not shown forming an integral part of the amplifier 34 which triggers the measurement of the value of the intensity of the line of power supply 7 by memorizing it at a so-called sampling instant.
• This selected sampling instant corresponds to the instant when the switch 14 is open and the current in lines 6 and 7 is zero, the voltage stored at said instant then being equal to the average value of the current in the switch 14 with the time constant of the high frequency intensity transformer 29.
• the sensor 30 is constituted by a winding 31 carried out on the magnetic circuit of the self-inductance 17 charged by an integrator circuit with resistance R and capacitor C.
• the senor 30 is constituted by a high-pass filter associated with an RC integrator circuit connected directly to the terminals of the self inductance 17.
• the measuring device 28 is connected by a line 28A to the supply line 6, for example, upstream of the capacitor 18 connected in parallel with the primary winding 13, and this line 28A takes the mains voltage straightened
• the second input 44 of the multiplier 41 receives the reference power Po of the non-linear load at start-up, this value being corrected during operation.
• the output S lf of said multiplier 41 is connected to a first input 45 of the error amplifier 46.
• the output 47 of the square elevation device 43 is connected to an input 48 of the first multiplier 38.
• the output S 2 of said multiplier 38 is connected to a second input 49 of the error amplifier 46.
• the output 50 of the error amplifier 46 is connected to an input 51 of the control circuit 16.
• the measuring device intensity according to the invention operates in the manner described below.
• the sample-and-hold amplifier 34 thus makes it possible to store the value of the current flowing on the supply line 7.
• the amplifier 34 delivers, at a determined instant, the corresponding value I to a multiplier 38 which makes it possible to carry out the product of said intensity by the absolute value of the square of the rectified mains voltage
• the multiplier 41 performs the product of the absolute value of the rectified mains voltage
• taken from the supply line 6 by the reference power P Q of the load and delivers, on its output S lf the product P 2
• This product P 2 is sent to the input 42 of the error amplifier 46.
• the amplifier 46 compares the input signals 42 and 49, that is to say if in equilibrium condition we have (u) .
• P 0 ⁇ (u) 2 > .I ..
• the output signal 50 of said error amplifier 46 is sent to the input 51 of the control circuit 16 which controls the switching element 14, so that the enslavement of the resulting switching frequency ensures both a variation in the intensity taken from the sector proportional to the voltage delivered by said sector and a power consumption equal to the set power P Q.

Landscapes

• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Control Of High-Frequency Heating Circuits (AREA)
• Dc-Dc Converters (AREA)
• Measurement Of Current Or Voltage (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

Family

ID=9416095

Family Applications (1)

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Citations (4)

• 1991
  • 1991-08-09 FR FR9110176A patent/FR2680297B1/fr not_active Expired - Fee Related
• 1992
  • 1992-07-08 DE DE69201445T patent/DE69201445T2/de not_active Expired - Fee Related
  • 1992-07-08 WO PCT/FR1992/000656 patent/WO1993003587A1/fr active IP Right Grant
  • 1992-07-08 EP EP92915711A patent/EP0597897B1/de not_active Expired - Lifetime

Patent Citations (4)

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