A method and arrangement for controlling magnetrons.

(54) Description Method and apparatus for controlling the microwave power of several magnetrons by means of only one power supply (56) Published publications: --- (57) Abstract:

A method for controlling magnetrons in terms of their microwave power, where several magnetrons are present. The invention is characterized by connecting two or more magnetron (1,2) in parallel with a power supply (3) for generating high voltage for operating the magnetron, by connecting one control circuit (9) for each magnetron, respectively, to the magnetron (1.2). ), which control circuit (9) comprises a measuring means (10) by which the anode current through the respective magnetron is measured on the high voltage side of the magnetron, in that said measuring means (10) is galvanically separated from a control circuit (19; 20), which control circuit is arranged to control the anode current of the magnetron in response to a signal from said measuring means (10).

Furthermore, the invention includes a device for carrying out the method.

DB 647289

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The present invention relates to a method and apparatus for controlling magnetrons in equipment where microwave energy is utilized for heating purposes.

Microwave heating is a very advantageous technique for a variety of processes involving the supply of thermal energy. A significant advantage is that the heat effect can be controlled without any inertia.

One disadvantage, however, is that microwave equipment is often more expensive than other conventional alternatives. A heating equipment includes power unit with associated control system for driving the magnetron. Such a power unit with control system is the dominant cost of the equipment. Often, a significant number of magnetrons with associated power units and control systems are needed for a shown heating need since the power of the magnetrons is limited.

Microwaves are used almost exclusively as microwave generators for heating purposes. The properties that are crucial are high efficiency in converting direct current to microwave power and having a compact geometry.

A major disadvantage is that the voltage required to obtain a given output power varies from microwave to microwave. This voltage is determined by the magnetron's internal geometry and the magnetic field strength of the cavity.

There are two types of magnetrons, namely those whose magnetic field is generated by a permanent magnet and those where the magnetic field is generated by an electromagnet.

The strength of the permanent magnets varies during manufacture and during operation.

In the construction of the magnetron there is magnetok whose permeability varies with temperature. Along with geometric changes that occur when the temperature of the magnetron changes, the working curve is changed as a diagram of anode voltage plotted against anode current. The output power is proportional to the anode current with good accuracy.

The above is why several magnetrons cannot be directly driven by a common power supply. The above diagram shows a knee, the so-called knee tension, over which the magnetron gives a greatly increased effect.

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If two or more magnetrons are connected in parallel1 to a power supply and the magnetron has slightly different working curves, as is usual, one magnetron gives a higher output power than the other. The one that gives the higher output power gets warmer, whereby the work curve drops so that the power supply. gives a lower output voltage. This, in turn, means that the magnetron that gives the lower power gives even less power, etc., until only one magnetron gives all the power because it is below the knee voltage of the other magnetron.

The basic problem is thus that each magnetron must be individually regulated while at the same time striving to reduce the number of power units with associated control systems.

The present invention solves this problem and offers a solution where magnetons with permanent magnets, respectively, magnetrons with electromagnet can be supplied from one and the same power unit.

Thus, the present invention relates to a method for controlling magnetrons in terms of their microwave power in which multiple magnetrons are present, and is characterized by connecting two or more magnetrons in parallel with a power supply for generating high voltage to operate the magnetrons, one for each magnetron separately a control circuit comprising a measuring means by means of which the anode current through the, respectively, magnetron is measured on the high voltage side of the magnetron, in that said measuring means is galvanically separated from a control circuit, said control circuit being arranged to control the anode current of said magnetron in response to a signal from said measuring means.

The invention further relates to a device for controlling two or more magnetrons from one and the same power unit, the device having substantially the features set forth in the appended claim 10.

The invention will now be described in more detail in connection with various embodiments of the invention shown in the accompanying drawings, in which

Figure 1 schematically shows a wiring diagram according to Figs. a first embodiment of two or more magnetrons connected to a common power unit and with individual control circuits,

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Figure 2 shows a first embodiment of the control circuit associated with the controller,

Figure 3 shows a second embodiment of a control circuit associated with control means,

Figure 4 shows a third embodiment of a control circuit associated with control means,

Figure 5 schematically shows a wiring diagram according to Figs. a second embodiment of two or more magnetrons connected to a common power unit and with individual control circuits,

Figure 6 shows a typical anode voltage anode current (V

Figure 7 schematically shows a circuit which galvanically separates two circuits.

Thus, Figure 6 shows a typical anode voltage - anode current diagram for a magnetron. The curve shown in the diagram shows a knee at the voltage V_Q. Under the knee voltage Vo, the magnetron gives no output. over the knee voltage, the dynamic resistance is low and the voltage search from no output to full output is small. The output power of the microwave is proportional to the anode current 1 ^ with good accuracy.

As mentioned above, there are two types of magnetrons, namely, magnetrons provided with permanent magnets for generating a magnetic field in the magnetron, and partly magnetrons provided with a magnetic winding and a magnetic core for generating the magnetic field. For the former type, the knee tension is fixed. For the latter type, the knee voltage can be controlled as indicated by the dashed curve and the arrow in Figure 6 by controlling the current through the magnetic winding.

As mentioned above, due to variations from magnetron to magnetron the diagram is not quite the same for each magnetron with the same specification.

Thus, this is the root of the problem of feeding two or more magnetrons with a common power unit.

The present invention provides a method and apparatus for controlling multiple magnetrons in terms of their microwave power, wherein two or more magnetrons are connected in parallel with a power supply for generating high voltage to operate the magnetrons. According to. the invention connects one control circuit for each magnetron to each, magnetron. The control circuit comprises a measuring means by which the anode current through the magnetron is measured on the high voltage side of the magnetron. By measuring the anode current on the high voltage side of the magnetron, the anode current will be measured individually for each of the magnetrons while the magnetron's anode is directly grounded, which is extremely important from a safety point of view.

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If the anode current were to be measured on the low voltage side, ie between anode and ground, the magnetron would be raised to a certain potential, which is unacceptable from a safety point of view, provided that not the entire magnetron is surrounded by a grounded housing which is isolated from the magnetron, waveguide and possibly . heating cavity.

The measuring means is arranged to output a signal to a control circuit. Because the measuring means is on the high voltage side, this is galvanically distinct from the control circuit which operates with a relatively low voltage, such as normal mains voltage. The control circuit is arranged to control the anode current of the magnetron and thus output power in dependence on the signal from the measuring means.

According to. In one embodiment, the measuring means is a travel in the punch over which the voltage is measured, the voltage being said signal to the control circuit.

The invention is described in more detail below in case the magnetrons are of the type that are only provided with permanent magnets, in conjunction with embodiments shown in Figures 1-4.

Figure 1 shows a schematic wiring diagram where two or more magnetrons 1,2 of the aforementioned type are present. These are supplied via a common power unit 3 which includes a transformer and a rectifier. For example, the output voltage of the power supply 3 can be 3 "4 KV.

Figure 1 shows two magnetrons 1,2 connected in parallel across the power supply 3 · The anodes 4 of the magnetrons 1,2 are grounded. As indicated in Figure 1, several magnetrons can be connected to the dashed conductors 5,6 in the same way that the two magnetrons 1,2 with associated circuits are connected to the conductors 7,8.

A separate control circuit for each magnetron, generally denoted by the number 9, is connected to the respective magnetron. The control circuit 9 comprises said measuring means 10 arranged to measure the anode current through respective conductors 11,12. Preferably, as mentioned, the measuring means consists of a resistance R over which the voltage is measured via conductors 13,14; 15,16. Said conductors are connected to a measuring circuit 17; 18 of a suitable known type arranged to transmit the measured value in the form of said voltage to an control circuit 19; 20 analogously or digitally.

The measuring means is galvanically separated from the control circuit 19; 20 by a circuit 21 »22. This circuit can have several different designs. Common to various embodiments, however, is that circuit 21; 22 comprises an analog-to-digital converter, for example, a voltage-to-frequency converter and a digital-to-digital converter or a digital-to-analog converter, e.g., a frequency-to-voltage converter, where the converters are galvanically separated from each other. .

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According to an embodiment shown in Figure 7, optocouplers are used. Hereby, circuit 21; 22 includes a voltage-frequency converter 80 which drives a light emittersuch as an LED so that, for example, it emits light pulses with a pulse repetition frequency corresponding to the converter 80 at low voltage. Further, the circuit 21; 22 includes a frequency-voltage converter 82 to which a light-sensitive means 83, such as a phototransistor, which receives light and converts light from the light-emitted means 81, into electrical pulses corresponding to the received light pulses. Converter 82, for example, converts these pulses to a voltage corresponding to the voltage applied to the first mentioned converter. Between the members 81.83, the light is conveniently passed in a light guide 84 such as a plastic or glass fiber.

According to another embodiment, said means for converting a voltage to a frequency may instead be connected to the primary winding of a transformer, the secondary winding of which is connected to a means for converting a frequency to a voltage, the latter voltage being supplied to the control circuit 19, '20. .

The control circuit 19,20 is arranged to control the anode current of the magnetron 1,2 in response to a signal from the measuring means 10. Conveniently, the control means 19,20 is a microprocessor or equivalent in which a set value for the desired output power is input. The voltage across the conductors 23,24; 23,25 to respective power units can also be applied to the control circuit. The control circuit is thereby arranged to calculate the product of the latter voltage and the anode current, which is a relatively accurate measure of the output power of the respective magnetron. The efficiency of the microwaves is about 70%.

Of course, instead the magnetron anode voltage - anode current diagram can be input to the control circuit in order to calculate the current output power. The control circuit 19,20 may be of a suitable known type and may have any suitable detail structure.

Said setpoint is emitted in the form of an electrical signal. The signal preferably represents a measure of the desired anode current. However, the signal may instead constitute an output of a temperature sensor in the volume or range of the microwave in question. emits its effect, whereby a temperature control is actually done by means of the output power. The number 2é; 27 denotes the setting means which is arranged to deliver a set value to the control circuit. given

453 043, this means may be an overall control system in the form of a computer or the corresponding to which the control circuits of all magnetron are connected. Thus, the control circuit receives a set value from the means 26; 27 and an actual value from the measuring circuit 17; 18. The control circuit 19; 20 is arranged to output a control signal via conductors 28; 29 to a control circuit comprising controllers 30; 31 for direct control of the anode current.

The controller can be designed according to several preferred embodiments.

According to a first preferred embodiment, shown in Figure 2, the controller 30) 31 is constituted by a peak voltage assembly 85.

This is connected between the power supply 3 and the measuring means 10 and is arranged to apply a further voltage, for example 200-800 volts, in addition to the voltage from the power supply, over the magnetron 1,2.

The peak voltage assembly comprises a transformer 32 having a rectifier bridge 33, one of which is connected diagonally to the conductors designated 24.35, 25.35 in Figures 1 and 2. The other diagonal points of rectifier bridge 33 are connected to the secondary winding of transformer 32. The primary winding of the transformer is connected to thyristors 36, a triac or the equivalent by which phase angle control is intended to be performed by the power supplied to the top assembly via its terminals 37,38. The top unit can be supplied with, for example, 380 V alternating current.

The semiconductor element 36 may be a so-called SCR (Silicon Control Rectifier) ​​circuit.

Said thyrist 36 is controlled directly via a control conductor designated 28; 29 from the control circuit 19; 20.

In series with the thyristor 36, a choke 43 or leakage transformer may be present.

According to a second preferred embodiment shown in FIG. 3, where the corresponding designations used in FIGS. 1 and 2, there is also provided a peak voltage assembly 86, which comprises a transformer 39 and a first rectifier bridge 40 connected to the secondary inlet of transformer 39. A chopper or equivalent is connected in parallel over a second rectifier bridge 41, which chopper 54 is arranged to supply the primary winding of the transformer at a high frequency ex. Viszo kHz. Thus, in the middle of the chopper 54, a so-called primary switched control is intended to be formed. Parallel across the second rectifier bridge 4l, a capacitor k1 is connected.

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The second rectifier bridge is supplied via the terminals 44.45 eg with 3θ0 V alternating current. The chopper is controlled directly by the control conductor 28; 29 from the control circuit 19; 20. The output voltage of the first rectifier bridge 40 may be e.g. 200-800 volts.

By using a direct voltage intermediate according to. in this embodiment generating a high frequency, a smaller transformer core 39 can be utilized to generate high voltage, as compared to the embodiment shown in Figure 2.

According to a third preferred embodiment, shown in Figure 4, the power supply is arranged to supply a voltage higher than the highest voltage required for the magnetrons 1,2, the tops being arranged to reduce the voltage across the magnetrons.

Between the power supply and each of the measuring means 10 there is a transistor switch 44, or equivalent, connected, each of the transistor switches being arranged to be equipped so that the anode current is limited by the respective magnetron, compared to the anode current which would arise if the top unit was equipped. to not reduce the power supply voltage. The transistor switch 44 is controlled with a control current through a secondary winding 45 by a transformer 46, whose primary winding 47 is supplied with current via the control conductor 28; 29 from the control circuit 19; 20. The task of transformer 46 is to separate the transistor torque switch 44 on the high voltage side from the control circuit 9 which operates on a low voltage.

A throttle 48 and a diode 49 connected parallel to it are present to limit, accommodating the increase of the room with time.

Common to the embodiments described in connection with Figures 1-4 is thus that a common power unit can be used for two or more permanent magnet magnets, by connecting only one cheap and simple top unit to each of the magnetrons. By means of the top assemblies, each of the magnetrons can be equipped to the desired power regardless of the current output power of the other magnetrons.

Also to each magnetron, a glow transformer 50; 51 is connected in the usual manner, which is supplied from a voltage source 52; 53 ·

In case the magnetrons are of the type in which a magnetic winding is present for generating the magnetic fields of the magnetrons it is brought according to. the invention one for each

453 043 magnetron separate magnetizing unit connected to said winding to be equipped by the control circuit so that the magnetic field's strength in the magnetron at the current voltage across the magnetron provides a predetermined anode current through the magnetron.

Figure 5 shows an example of such an embodiment, in Figure 5 certain details corresponding to details in Figures 1-4 have been given the same designations. Thus, in Figure 5 there is found a power unit 3 and conductor 7,8. The measuring means 10, as well as the measuring circuit 17; 18, the circuit 21; 22 and the control circuit 19; 20, and the means 26; 17 may be arranged in the same manner as described above.

The magnetrons 60,61 are provided with an earthed anode 62.63. The magnets 60,61 are thus provided with a magnetic winding 64.65 with associated magnetic core to generate a magnetic field in the magnetrons. Furthermore, such magnetrons may be provided with a permanent magnet, which, however, cannot alone generate a sufficiently strong magnetic field for microwaves to be generated.

For magnet in view, there is a magnet separate for each magnetron in the serger assembly 66; 67, which is a power supply for supplying the magnetic windings 64; 65. As mentioned initially, the anode voltage-anode current curve is moved up and down with the strength of the magnetic field. Thus, in this embodiment, the voltage across the magnetron is substantially constant while the output power is controlled by lowering or raising said curve. This is done by regulating the current through the magnetic windings.

As described above, the control circuit 19; 20 obtains a set value and an actual value.

In this embodiment, the control circuit 19, 20 is arranged to deliver a control signal via a conductor 68; 69 to the magnetizer assembly 66; 67, thereby providing it so that the magnetic field's strength in the magnetron at current voltage across the magnetron provides a predetermined anode current through the magnetron.

The magnetizing assembly 66,67 comprises a rectifier as well as a current regulator such as a transistor or equivalent. The transistor or its equivalent is provided by said control signal.

Any suitable circuit can be utilized here. The magnetizing assembly 66; 67 is supplied via a transformer 70; 71 from a voltage source 72; 73, which may be, for example, 380 Volt AC.

4.

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In the lower part of Figure 5, there is shown an embodiment in which magnet 1 winding 64 is separated from conductor 74 which is connected to anode 75 of magnetron 60.

However, in another embodiment, as shown in the upper part of Figure 5, the magnetic winding of a portion 76 is connected in series to the conductor 77 connected to the anode 63 of the magnetron 61. Between the 1 coil 76 and the anode 63 of the magnetron, there is a grounding point 79, which means that the anode 63 is at ground potential.

It is convenient, however, that the same type of magnetization and control circuit is present in all the magnets supplied by the same power supply, although two variants are shown in Figure 5. It is obvious that further magnetons with the associated control circuit can be connected in parallel across the power supply via the dashed conductors 5,6. Figure 5.

It is further evident that by means of, respectively, control circuit and respective, magnetizing units, the output power of each magnetron can be controlled individually and independently of the current output power of the other magnetron.

Thus, the present invention solves the problem mentioned above by using a common power supply for two or more magnetrons while measuring the anode current of each magnetron on the high voltage side and used to control each magnetron separately. The cost of the individual control circuits is only a fraction of the cost of a power supply.

The present invention is particularly advantageous in many magnetron heating systems. The advantages consist, in addition to requiring only one power supply, in that the weight and material demand for the installation are lower, while the volume is considerably reduced by the fact that several power units are not needed. The required wiring is substantially reduced.

Another advantage that is required is that in a larger plant the power unit can be dimensioned to drive all the magnetrons except for example 2 to 4 pieces. Not all magnetrons are controlled during normal operation. However, when a magnetron needs to be replaced, it is turned off and another previously non-equipped magnetron is ejected to provide microwave power.

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A further advantage is that through the individual regulation where the anode current is sensed, each magnetron can be equipped to compensate for, for example, age changes.

A number of embodiments have been discussed above. It will be apparent that, for example, the couplings and components of one of ordinary skill in the art can be exchanged and altered to achieve the same function without departing from the basic to individually regulate each magnetron by measuring the anode current on the voltage side.

The idea of ​​the present invention is thus not to be considered limited to the above embodiments but can be varied within the scope of the appended claims.

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