WO2022064285A1 - Système électronique pour alimenter des machines ou un appareil avec une fréquence radio comprenant un transformateur élévateur et un oscillateur utilisant un amplificateur à semi-conducteurs - Google Patents

Système électronique pour alimenter des machines ou un appareil avec une fréquence radio comprenant un transformateur élévateur et un oscillateur utilisant un amplificateur à semi-conducteurs Download PDF

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Publication number
WO2022064285A1
WO2022064285A1 PCT/IB2021/055871 IB2021055871W WO2022064285A1 WO 2022064285 A1 WO2022064285 A1 WO 2022064285A1 IB 2021055871 W IB2021055871 W IB 2021055871W WO 2022064285 A1 WO2022064285 A1 WO 2022064285A1
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WIPO (PCT)
Prior art keywords
electronic system
group
power
transformer
electronic
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PCT/IB2021/055871
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English (en)
Inventor
Alessandro Tonello
Fulvio PERRI
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Stalam S.P.A.
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Priority to EP21736386.0A priority Critical patent/EP4218365A1/fr
Publication of WO2022064285A1 publication Critical patent/WO2022064285A1/fr

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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
    • H05B6/68—Circuits for monitoring or control
    • H05B6/686—Circuits comprising a signal generator and power amplifier, e.g. using solid state oscillators
    • 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
    • H05B6/46—Dielectric heating
    • H05B6/48—Circuits
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B40/00—Technologies aiming at improving the efficiency of home appliances, e.g. induction cooking or efficient technologies for refrigerators, freezers or dish washers

Definitions

  • the present invention refers to a Solid State (SS) Radio Frequency (RF) electronic system for use mainly, but not exclusively, in I.S.M. (ISM - Industrial Scientific Medical) with high load impedances, and in particular to a Radio Frequency (RF) apparatus for drying and heat treatments of raw materials, semi-finished and finished industrial products that implements this system.
  • SS Solid State
  • RF Radio Frequency
  • Radio Frequency (RF) electronic systems suitable for use in I.S.M. (ISM - Industrial Scientific Medical) with high load impedances are made using traditional “triodes” or even, although not frequently, “tetrodes” or “pentodes”, or vacuum thermionic valves such as active components that generate RF.
  • this type of RF electronic systems is widely used in dielectric heating for drying and heat treatments of raw materials, semi-finished and finished industrial products, or in all those RF machines designed for sectors such as food, agro-industrial, officinal, pharmaceutical, nutraceutical, textile, technical textiles, latex, glass and basalt fibers, wood and paper, bricks and technical ceramic products, expanded technopolymers, and many others, etc., and more generally to treat products where the volumetric or endogenous heating turns out to be convenient and decisive in technological processes compared to exogenous heating systems, such as traditional thermal ones.
  • a drying and/or pre-cooking machine for industrial and/or food products with dielectric heating, it is equipped with an RF electronic system, or RF generator, generally based on a single self-excited oscillator with thermionic valve, (also called “thermionic tube”), able to shift frequency, with respect to the natural oscillation frequency dictated by its resonant circuit, depending on many factors, mainly related to the high and variable load impedance, moreover if characterized from important reactive components.
  • the thermionic tube is powered at very high voltages and, consequently, operates with relatively moderate currents, essentially behaving like a constant voltage generator.
  • the output circuit of the thermionic tube is substantially characterized by a resonant LC circuit with a high quality factor (Q), tuned for example to about 27.12 MHz, which transfers the power to the load through a coupling and/or adaptation network equipped with inductive/capacitive elements and/or through a variable capacitance and mechanically controlled divider.
  • Q quality factor
  • the RF energy transits into a secondary paired/tuned circuit, with a lower quality factor (Q), which substantially represents the use or load circuit, electrically similar to a L/C resonance passive circuit.
  • Q quality factor
  • This second parallel resonant circuit, in the preliminary phase, can be tuned by means of mobile short circuits applied to tuning inductances placed in parallel to the RF applicator, or between the sides of the "distributed" capacitor, which constitutes the element that applies RF to the product to be treated.
  • the product flows through a tunnel, made with metal surfaces to confine the RF electromagnetic field radiated inside, on a conveyor belt (this in the case of a continuous machine, but from the point of view of operation the considerations are similar also in the case of a static machine also called “batch") adjacent to the electrode connected to ground, which therefore constitutes the "cold armature" of the resonance capacitor.
  • This second resonance circuit for reasons related to managing the impedance adaptation to the RF generator or to the first resonance circuit, is tuned to a slightly different frequency than that used to tune the thermionic tube circuit, for example to about 28 MHz or even about 26 MHz.
  • the dielectric variation with respect to air caused by the product passing between the plates of the RF applicator since it is always characterized by a complex permittivity that is variable and very different from vacuum, is the cause of the "slipping" of the tuning of the secondary circuit, affecting only moderately also on the primary circuit due to the low coupling coefficient between the resonance levels of the two circuits.
  • the primary circuit therefore allows a greater quantity of RF energy to pass through (highlighted by the voltage present between the armatures of the RF applicator) and the required function of dielectric heating of the product can thus be performed.
  • the transfer of RF energy between the generator and the load is substantially linked to the differentiation of the oscillation frequencies between the two resonant circuits of the generator and the load, an operation which in any case always involves a variation in the overall oscillation frequency of the system, depending on the variation of the load or of the power supplied, also resulting from the coupling and/or adaptation network interposed between them.
  • this RF equipment is closely linked to the skills and abilities of the designer specialized in RF settings and of the operator adequately trained in the management of technological processes. For example, it is the task of the designer specialized in RF settings, based not only on circuit simulations with dedicated software but also on specific empirical experiences, to adjust the oscillation frequency of the RF generator, the quality factor (Q) of the output circuits, the percentage of "slipping" of the overall system frequency as a function of the coupling and/or adaptation of the load and of the previously chosen quality factor (Q).
  • Figure 1 shows a typical simplified circuit diagram, but not exclusive or limiting, representative of an RF apparatus for drying and heat treatments of raw materials, semifinished and finished industrial products that uses a thermionic valve, in this case a triode, as an active component for the generation of RF.
  • a thermionic valve in this case a triode
  • the apparatus essentially has a DC High-Voltage power supply (also called “HVDC”) which supplies the high voltage to the RF system, also known as the “RF generator”, and a thermionic valve for generating the RF connected to a tuned LC plate circuit, which also sets the frequency of the power oscillator.
  • HVDC DC High-Voltage power supply
  • a triode grid feedback network determines the reaction for controlling the thermionic valve in percentage terms and also, within certain limits, affects the overall oscillation frequency of the RF system.
  • the plate power of the triode, through the tuned LC circuit, is applied to the use group or circuit indicated in figure 1, through a coupling and/or adaptation network (also called "Matching Network") which, in addition to adapting the impedances of the load circuit to those of the RF generator output, it also allows to perform a precise control of the delivered power.
  • Said coupling and/or adaptation network is generally made by means of passive resistive and/or reactive components suitably interconnected, adjustable in fixed and/or continuous mode, which allow the technician specialized in RF settings to be able to partially compensate any high reactive components of the downstream impedances as well as to adjust their values in the upstream module, so that the power transfer between the RF generator and the use group or circuit can be adjusted in a controlled manner.
  • Said use group or circuit can be electrically comparable to a tunable network, adjustable by the technician specialized in RF settings, which interacts, as for the previously indicated circuit elements, with the overall oscillation frequency of the RF apparatus and with the displacement of the same according to the applied load.
  • RF applicator consisting of cylindrical metal bars, equipped with concentric cylindrical insulators, interconnected by conducting elements
  • Such a circuit is in fact electrically similar to a capacitor "C”, which can be represented in a “concentrated” way since in first approximation it consists of two conductive plates, of which the upper one connected to the high RF voltage and the lower one to ground, spaced and separated from a dielectric material.
  • Said RF applicator has the function of applying the RF to the product or products that are inserted between the plates (i.e. between the conductive plates) of the capacitor, also known as "RF electrodes", and by means of them drying and/or thermally treating the dielectric products subjected to the RF field.
  • the RF electrodes in this exemplary case, there is also an inductive component "L” electrically connected between the ends of the capacitor plates and equipped with a movable conductor terminal (called “shunt") which makes it possible to make the inductance value adjustable in such a way that by conveniently detuning the resonant frequency of the use circuit with respect to that generated by the oscillating circuit of the triode, and also with the interaction of the coupling and/or adaptation network, it is possible to obtain the desired RF electromagnetic field intensity between the plates of the RF applicator, necessary for the desired technological process.
  • inductive component "L” electrically connected between the ends of the capacitor plates and equipped with a movable conductor terminal (called “shunt") which makes it possible to make the inductance value adjustable in such a way that by conveniently detuning the resonant frequency of the use circuit with respect to that generated by the oscillating circuit of the triode, and also with the interaction of the coupling and/or adaptation network, it is possible to obtain the desired RF electromagnetic field
  • the positioning of the inductive component "L" with respect to the longitudinal development of the RF applicator also makes it possible to modulate the amplitude of the field intensity between the electrodes, thus subjecting the products to be treated to distribution profiles of the RF power delivered according to specific technological treatment needs.
  • the cooling system must be optimal in terms of thermo-hygrometric characteristics in the case of air, and thermochemical -physical in the case of water, conditions that require dedicated and expensive systems, moreover due to their interaction with high voltage parts, which also require frequent checks and maintenance, actively involving user customers, especially if the environments are harsh (dusts, mists, acids, etc.);
  • the current electronic RF generation system with thermionic valves despite the difficulties of designing and setting up with the load (since in fact generation, coupling and/or adaptation and use must be "functionally integrated" circuits), being powered at high voltages, that is, already having a high output impedance, it lends itself well to operating circuits with high load impedances, even considerably variable, and with important reactive components.
  • An invention which, in order to be fully and adequately applicable for typical uses in ISM fields with high load impedances, requires that it is possible to emulate the electronic behavior and the typical operation of thermionic valves for these applications, thus exploiting the advantages that still make them very widespread in these specific sectors, but at the same time using the considerable intrinsic advantages of the Solid State (SS) technique.
  • SS Solid State
  • An object of the present invention is to improve the state of the prior art in the terms and aspects clearly highlighted above, in particular with reference to an SS RF electronic system for use in ISM fields with high load impedances that emulate the typical operation of thermionic valves for similar uses, and in particular to an RF apparatus, for drying and heat treatments of raw materials, semi-finished products and finished industrial products, which implements this system.
  • a further object of the present invention is to provide an SS RF electronic system for use in ISM fields with high load impedances that allows the use of the same broadband, thus eliminating the need for an accurate and customized setup for any specific impedance value or variation range around it.
  • a further object of the present invention is to provide an SS RF electronic system for use in ISM fields with high load impedances that allows for controllability of the power supplied with continuity, both in continuous and pulsed mode or in any case that can be modulated according to predefined signal trends, both in the time and frequency domain, even remotely.
  • Another object of the present invention is to provide an SS RF electronic system for use in ISM fields with high load impedances that is robust with respect to possible load mismatches, caused by considerable impedance variations and with important reactive components thereof.
  • Still another object of the present invention is to provide an SS RF electronic system for use in ISM fields with high load impedances which has a modular and low cost cooling system.
  • a further object of the present invention is to provide an SS RF electronic system for use in ISM fields with high load impedances that allows the use of interchangeable and modular groups.
  • Still another object of the present invention is to provide an SS RF electronic system for use in ISM fields with high load impedances whose operation is not affected by external agents, such as dust, humidity, aggressive atmospheres, etc.
  • a further object of the present invention is to provide an SS RF electronic system for use in ISM fields with high load impedances which allows a standardized and economical industrial construction.
  • a further object of the present invention is to provide an SS RF electronic system for use in ISM fields with high load impedances that is light and space-saving, consequently also allowing for ease of packaging and subsequent simpler and faster transport.
  • SS Solid State
  • RF Radio Frequency
  • a Radio Frequency (RF) apparatus for drying and heat treatments of raw materials, semi-finished products and finished industrial products which implements said system according to claim 48.
  • RF Radio Frequency
  • FIG. 1 shows the simplified circuit diagram typical of an RF apparatus for drying and heat treatments of raw materials, semi-finished and finished industrial products that uses a thermionic valve as an active component for the generation of RF, that is, made according to the state of the prior art;
  • FIG. 2 shows the circuit diagram of an SS RF electronic system for use in ISM fields with high load impedances according to the present invention
  • figure 3 shows an enlarged scale view of the final power group of the SS RF system of figure 2;
  • figure 4 shows the basic circuit diagram used for the realization of the first stage of RF output transformation of the final power group of the SS RF electronic system of figure 2;
  • figure 5 shows the circuit diagram used for the realization of the second stage of RF transformation of the voltage/impedance booster group of the SS RF electronic system of figure 2.
  • the number 1 indicates an SS RF electronic system for powering machines or equipment, typically but not exclusively for use in ISM fields, with RF signals at high load impedances according to the present invention.
  • Said system essentially comprises at least one power supply group 2, at least one RF signal generation group 3, at least one logic interface and RF signal control group 4 and, preferably, at least one power pre-amplification group 5 and/or at least one power division group 6 as well as at least one transmission line la designed to be powered by at least one power division group 6 or by at least one power pre-amplification group 5 or by at least one RF signals generation group 3 with a respective percentage of power.
  • the percentage could be 100% in the case of a single transmission line la.
  • the transmission line la comprises at least one final power group 7 and at least one voltage/impedance booster group 8.
  • the power supply group 2 can essentially comprise a first power supply 2a, for example a switching power supply, used to supply one or more previous stages to the power division group 6 of the electronic system 1.
  • a first power supply 2a for example a switching power supply
  • switching power supplies constitutes the current system of greatest use, as the operating logic and the components used allow to obtain high efficiencies, thus helping to maximize the overall energy efficiency of the electronic system where employees.
  • the first switching power supply 2a can then comprise one or more sub-power supplies 2b (figure 2 shows the sub-power supplies 2b detached from the first switching power supply 2a, but which are in fact included therein), for example switching sub-power supplies (or "POL", acronym for "Point of Load”), used to power one or more stages following the power division group 6 of the electronic system 1.
  • switching sub-power supplies or "POL", acronym for "Point of Load”
  • the power supply 2a constitutes what is usually defined "auxiliary power supply” whose function is substantially that of supplying all the elements of the system with the exception of the power stages, that is, with the exclusion of the at least one final power group 7.
  • This power supply can be either a switching power supply, direct from the mains, with power proportional to what is absorbed by the auxiliary and low power stages (RF drivers), or a secondary power supply, scaled by the DC-DC switching power supplies 2b, previously defined POL.
  • the first power supply 2a comprises three switching sub-power supplies 2b, each dedicated to the respective final power group 7, which can each supply a continuous supply voltage between about 24 V and about 60 V.
  • the first switching power supply 2a and consequently also the switching sub-power supplies 2b are provided with means or components for stabilizing the voltage and limiting the current, and with means or components for remote control, so as to allow an external operator the variation of the supply voltage and consequently also of the power at least of the RF signal generation group 3.
  • This group 3 can comprise a waveform generator with high stability, "DDS" or stabilized by means of a quartz crystal, by way of non-limitation, for example exactly at 27.120 MHz ( ⁇ ⁇ 10' 7 PPM of thermal variation per degree centigrade), but which could be indifferently at any frequency of the bands for use in ISM fields, such as, for example, from 12 to 82 MHz, and in particular at the typical frequencies for uses without limitations of restrictions in the radiated amplitudes established by the international ITU - CISPR standards that beyond at 27.12MHz ⁇ 0.163MHz they are also 13.56MHz ⁇ 0.07MHz and 40.68MHz ⁇ 0.02MHz (and also 6.78MHz ⁇ 0.015MHz and 433.92MHz ⁇ 0.87MHz, albeit with limitations in some "regions ").
  • DDS high stability
  • quartz crystal by way of non-limitation, for example exactly at 27.120 MHz ( ⁇ ⁇ 10' 7 PPM of thermal variation per degree centigrade), but which could be indifferently at any
  • This group 3 preferably comprises an oscillator, a circuit for controlling the duty cycle and for modulating the pulse width ("Pulse-Width Modulation"), as well as a low power amplification chain, for example an amplification chain up to a value between about 1W and about 5W, for example up to about 2W.
  • the low power amplification chain is downstream and/or upstream of the oscillator and the circuit for controlling the duty cycle.
  • the circuit for controlling the duty cycle and for modulating the pulse width allows, by means of an electric and/or electronic retroactive feedback circuit, to protect the internal electronic system 1 from any overloads.
  • the circuit for controlling the duty cycle and for modulating the pulse width reduces the duty cycle, defined as the ratio between width and period of the pulse.
  • reaction times of the reduction of the duty cycle on the electronic system 1 are very fast, in the order of about 100-800ns, for example 200ns; the reaction times of the retroactive feedback are also very fast, in the order of about 400-600ns, for example 500ns; the total reaction time of the system is attested to be in the range between approximately 500ns and 1400ns, and therefore fast enough to ensure complete protection for all the groups included in said system.
  • the same circuit for the control of the duty cycle and for the modulation of the pulse width which performs the protection function indicated above can conveniently also constitute the fundamental element for regulating the power delivered to the load, both in continuous and pulsed mode or in any case it can be modulated according to predefined signal trends both in the time and frequency domain, even in remote mode.
  • maximum efficiency is achieved, since the RF apparatus and the adaptation networks have been studied and calculated for this power level.
  • an attempt will be made to maintain the power at the maximum peak level, as a function of the supply voltage supplied by the one or more sub-power supplies 2b, by acting on the duty cycle to modulate it.
  • an efficient method for controlling and varying the power is to divide the wave flow into variable cycle pulse packets. For example, with an "on/off impulsive cycle of 50%, the power applied to the product will be halved, while at the same time keeping the peak power value of the impulse high, thus ensuring high energy efficiency of the RF system.
  • the power variation applied to the product can be carried out by adjusting the one or more sub-power supplies 2b, but combined with the previous one it has a purely coarse pre-setting function, while the subsequent fine tuning is obtained through the aforementioned duty cycle control.
  • Said logic interface and RF signal control group 4 can essentially comprises a logic unit designed to manage the control of operating parameters of the electronic system 1, for example the interface with the operator, the screen, the network, the connectivity and, as already mentioned, the control of the parameters relating to the variation of the duty cycle and of the pulse width.
  • the logic interface and RF signal control group 4 also comprises hardware components for the logic unit, for example a luminous alphanumeric display, for example using "OLED" technology, a power supply, an alphanumeric keypad, a spare battery and a ventilated container.
  • the output signal from this latter group enters the power pre-amplification group 5.
  • the group 5 helps to raise the power of the RF signal however, in other embodiments, this group 5 could be directly integrated within the RF signal generation group 3 or it could not be present.
  • Said group 5 essentially comprises a pre-driving sub-group 5a and a driving sub-group 5b.
  • the pre-driving sub-group 5a can comprise one or more power amplifiers which increase the power level of the output signal from the RF signal generation group 3, which must be specified that it has already been increased by the low power amplification chain present in the aforementioned group 3.
  • the pre-driving group 5a can raise the power from about 2 W to a range between about 5 W and about 25 W, for example up to about 10 W.
  • the driving sub-group 5b essentially comprises an input transformer, for example a 9: 1 input transformer, one or more power amplifiers used to further raise the power level of the output signal from the pre-driving sub-group 5a, and an output transformer, for example a 1 :4 output transformer.
  • an input transformer for example a 9: 1 input transformer
  • one or more power amplifiers used to further raise the power level of the output signal from the pre-driving sub-group 5a
  • an output transformer for example a 1 :4 output transformer.
  • the one or more power amplifiers of the driving sub-group 5b can raise the signal power level for example from about 10 W, also wanting from a range between about 5 W and about 25 W, up to about 100 W, and also up to about 150 W.
  • the one or more power amplifiers can be of any type suitable to reach the desired power level, for example they can be integrated and/or hybrid amplifiers.
  • the output signal power from the driving sub-group 5b enters the power division group 6.
  • Said group 6 essentially comprises a power divider 6a ("splitter").
  • said power divider 6a is an isolated RF power divider with two, three or more ways which divides the power of the output signal from the driving sub-group 5b or from the RF signals generation group 3 in an equal or differentiated manner and almost independent of the load conditions between at least two, three or more transmission lines la of the electronic system 1.
  • the electronic system 1 comprises the power divider group 6, it will also comprise at least two transmission lines la.
  • the signal power input to the isolated three-way power divider 6a is about 100 W transmitted through a transmission line having an impedance of about 50
  • said divider will provide three power signals of approximately 33 W through three transmission lines each having approximately 50 of impedance.
  • the electronic system 1 could also not provide for the power division group 6, for example in the case where the electronic system 1 provides for a single transmission line la.
  • the RF signal generation group 3, the logic interface and RF signal control group 4 and the pre-driving sub-group 5a can be provided, for example, in a single printed circuit in order to simplify the construction of the complex section of the electronic system 1.
  • a dedicated printed circuit is provided both for the driving sub-group 5b and for the power division group 6.
  • the three printed circuits are suitably housed on a sheet-like component, such as for example an aluminum plate having a thickness of about 2 mm and the indicative dimensions of about 160 mm in width and 168 mm in length, such as to also constitute an effective dissipative element of the local heat produced by these circuit sections.
  • a different sizing of the sheetlike component can be provided on the basis of any particular design requirements, for example a smaller or greater number of printed circuits, or can be used a dissipating mechanical support with fins, to facilitate the dissipation of heat.
  • the electronic system 1 comprises three high-level amplification groups 7 and three voltage/impedance booster groups 8.
  • the electronic system 1 comprises only a single transmission line la.
  • the final power group 7 essentially comprises a power amplification sub-group 7b.
  • the power amplification subgroup 7b comprises a Solid State (SS) power amplifier 7b 1. More in detail, the SS power amplifier 7b 1 advantageously comprises two transistors 7b 1 ', 7bl", for example two lateral diffusion transistors (called “LDMOS").
  • LDMOS Solid State transistors
  • the two transistors 7b T, 7b 1" are suitably placed with the two sections available in parallel and with each other in a "Push-Pull" configuration.
  • VDMOS vertical diffusion transistors
  • GaN Gallium Nitride
  • SS power amplifier 7b 1 has the advantage of allowing not only a broadband use of the electronic system 1, but also of obtaining energy efficiency values close to 80% and even more in the case of use in "high energy efficiency" operating classes (for example D and E), and gain values even higher than 20 dB per amplifier stage and/or transistor module.
  • the final power group 7 may then comprise an input transformer 7a, for example an 9: 1 input transformer, placed upstream of said power amplification sub-group 7b, and an output transformer 7c, for example a 1 :4 output transformer, located downstream of said power amplification sub-group 7b.
  • an input transformer 7a for example an 9: 1 input transformer, placed upstream of said power amplification sub-group 7b
  • an output transformer 7c for example a 1 :4 output transformer, located downstream of said power amplification sub-group 7b.
  • the final power group 7 can have an equalization/coupling network 7d, for example positioned before the input transformer 7a.
  • Said equalization/coupling network 7d comprises one or more electrical and/or electronic circuits whose main purpose is to improve the amplitude-frequency transfer function in the field of use, mainly for broadband applications of the electronic system 1, which, as seen previously, they can be, for example, included in the range from about 12 MHz to about 45 MHz, even up to 80 MHz and more.
  • 1 input transformer 7a it is used to substantially perform the adaptation of the "Gate" impedance or of the input of said at least one SS power amplifier 7b 1.
  • the 9: 1 input transformer 7a can be made by means of a ferrite core, of adequate dimensions and magnetic permeability to treat the input power of the transmission line, with a primary winding of one turn and a secondary winding of three turns, i.e. with a 1 :3 turn ratio corresponding to a 1 :9 impedance ratio.
  • the input transformer 7a could also be made with a primary and secondary winding having a different number of turns and therefore a different impedance ratio.
  • the 9: 1 transformer 7a can for example transform the input impedance of about 50 into an output impedance from "Gate” to "Gate” of about 5.5 (being the two "LDMOS” transistors 7b 1', 7b2"arranged in counterphase).
  • the SS power amplifier 7b allows a power amplification capable of reaching, for example, nominal values of about 1300 W per transistor.
  • V d is the power supply voltage
  • Z is the impedance
  • P out is the output power.
  • an output transformer 7c is provided, for example a 1 :4 balanced transformer for adapting the impedance of "Drain" or of the output of said SS power amplifier 7b 1.
  • This transformer having to work with a high bandwidth in order to cover the wide ranges of the expected use frequencies and also for the needs of wide variability of the load impedances, must be designed in a very precise way and at the same time guarantee a high efficiency., for example higher than about 96%, considering the high powers involved in the system.
  • the 1 :4 balanced transformer 7c is made using two coaxial transmission lines according to the configuration, defined as "equal delay", with primary windings placed in parallel and secondary windings placed in series, as shown in figure 4.
  • the use of coaxial transmission lines allows to save from the point of view of simplicity and manufacturing costs of the transformer, while at the same time extending the frequency transformation range.
  • the output transformer 7c it would also be possible to use other methods for the construction of the output transformer 7c, for example by means of a multilayer printed circuit made of a specific material, such as polytetrafluoroethylene (“PTFE”), ceramic or the like.
  • PTFE polytetrafluoroethylene
  • the two coaxial transmission lines can each be made by means of four flexible cables insulated in PTFE having an impedance of approximately 12 Q which, when placed in parallel, give the resulting impedance values of approximately 3 Q.
  • the arrangement of the two lines in series allows to reach nominal impedance values of the order of 6 Q and 1.5 Q, as required, from the parallel side.
  • the two coaxial transmission lines can also be coated with one or more sleeves in magnetic material, suitable for obtaining low losses.
  • each line is coated with three sleeves side by side made of ferrite, according to a Nickel-Zinc mixture, having magnetic permeability ⁇ 150.
  • Said mixture is able to work at quite high temperatures (>100°C), and has a high "Curie point”.
  • sleeves with different mixtures can be used, as long as they are able to guarantee low losses with the desired magnetic permeability.
  • the output transformer 7c can be closed in a container, for example an aluminum container, which will contribute to its cooling.
  • a container for example an aluminum container
  • the transformer 7c can be embedded in a special resin, for example an epoxy or high temperature silicone resin.
  • This resin loaded with ceramic powders, such as Aluminum Nitride powders ("AIN"), will be used to transfer the generated heat to the outside and will irremovably block all parts, also ensuring a better mechanical resistance to vibrations.
  • AIN Aluminum Nitride powders
  • the final power group 7 can also comprise elements placed downstream or subsequently to the output transformer 7c, for example capacitors and/or inductances and/or resistors and/or filters, adapted to compensate for low and/or high band frequencies in which the output transformer 7c must operate.
  • elements placed downstream or subsequently to the output transformer 7c for example capacitors and/or inductances and/or resistors and/or filters, adapted to compensate for low and/or high band frequencies in which the output transformer 7c must operate.
  • a suitable voltage/impedance booster group 8 can therefore be conveniently provided and inserted.
  • the main objective of this group is to considerably raise the voltage/impedance, while at the same time guaranteeing solidity and robustness of the electronic system 1 when stressed, even considerably, by possible load mismatches, due to strong variations in impedances and also with important reactive components.
  • Said group 8 can comprise a first step-up transformer 8a, a power sensing sub-group 8b and finally a second step-up transformer 8c.
  • the first step-up transformer 8a for example a 1 :9 balanced-balanced step-up transformer, is used for a first impedance boost.
  • said 1 :9 balanced- balanced step-up transformer can, for example, raise the input impedance to group 8 from about 6 to about 54 .
  • this 1 :9 balanced-balanced step-up transformer 8a can be built using techniques similar to those used for the construction of the 1 :4 balanced transformer 7c, i.e. by means of coaxial transmission lines coated with ferrite sleeves, with variable mixture and having magnetic permeability values /q included, for example, between about 100 and about 800, in order to widen the band of use.
  • the particular method of connection of the coaxial lines of the transformer 8a also allows to obtain the galvanic separation of the final power group 7 from the load, that is the electrical isolation of the DC power supply voltage from the RF load.
  • the 1 :9 balanced-balanced step-up transformer 8a can also be closed inside a container, for example made of aluminum or other metal alloy.
  • a power sensing sub-group 8b is subsequently provided.
  • Said group 8b mainly comprises one or more balanced directional couplers, for example a double balanced directional coupler 8b 1, 8b2 with opposite lines in phase and able to work with maximum rated input powers which can reach values up to about 3000 W.
  • Such balanced directional couplers 8b 1, 8b2 with opposite lines in phase have the purpose of analyzing the load and monitoring the RF power levels transited without simultaneously suffering losses on the transmission line la and on the load.
  • the balanced directional couplers 8b 1, 8b2 allow the measurement of the direct component of the RF power, i.e. the one that reaches the load from the source, and of the reflected component of the RF power, i.e. the one that is sent back from the load to the source since it is not absorbed from the dielectric load subjected to the treatment.
  • a further function is to use the RF power value reflected at the output either from the final power group 7 or from the transformer 8a, once transformed into a direct voltage inside or outside the one or more balanced directional couplers 8b 1, 8b2, to activate, for example by means of an activation signal sent by the logic interface and RF signal control group 4, in communication with the couplers 8b 1, 8b2, a special electronic "trigger” or threshold circuit (in communication with the output of the RF signal generation group 3).
  • the electronic "trigger" circuit acts first by blocking, then reducing and subsequently increasing, according to a programmed ascent ramp, the output power from the RF signal generation group 3, for protecting the electronic system 1 from a mismatched load.
  • This voltage is therefore supplied for reading the reflected RF power not only to the electronic “trigger” or threshold circuit dedicated for protection, but also to the logic interface and RF signal control group 4 for software management of the system when overloaded.
  • the electronic "trigger" or threshold circuit can be conveniently placed upstream and/or downstream of the balanced directional couplers 8b 1, 8b2 of the power sensing subgroup 8b or integrated directly into the eventual printed circuit dedicated to groups 3, 4 and 5 a.
  • the balanced directional couplers 8b 1 and 8b2 with opposing lines in phase can be equipped with circuits and/or systems that detect and measure the direct and reflected components of both RF voltages and RF currents, allowing to obtain a very flexible and precise controllability of the RF power delivered by the electronic system 1 to the load, for example by means of the principles described above in relation to the electronic "trigger" or threshold circuit, which can be managed both in continuous and pulsed mode or in any case modulated according to predefined signal trends and in the domain of time and frequency.
  • a second step-up transformer 8c can be conveniently provided downstream of the power sensing sub-group 8b.
  • Said step-up transformer 8c for example a 1 :9 balanced-balanced step-up transformer, allows a further increase or elevation of the output impedance and at the same time guarantees, in addition to the feature of its use at a wide frequency band, also a significant robustness and solidity with respect to possible load mismatches, caused for example by considerable variations in load impedances even with important reactive components.
  • the 1 :9 balanced-balanced step-up transformer 8c can be suitably designed following the known Guanella scheme, described for example in the document "Novel Matching Systems for High Frequencies", Brown-Boveri Review, Vol 31, September 1944, Pag. 327-329", which substantially consists of the configuration having primary windings placed in parallel and secondary windings placed in series shown in figure 5.
  • Said 1 :9 balanced-balanced step-up transformer 8c is capable of transform for example from about 54 Q of input impedance to about 486 Q of output impedance.
  • the 1 :9 balanced-balanced step-up transformer 8c is therefore composed of three pairs of coupled cores, for example three pairs of coupled toroidal cores, each pair wound with a respective balanced bifilar line.
  • said bifilar lines can be spaced apart by means of a spacer element in order to maintain both a good parallelism between the wires and a stable and controlled distance.
  • Said spacer element can be, for example, a bar made of silicone elastomer material.
  • bifilar lines have an impedance which for a correct and good operation of the step-up transformer 8c must be approximately three times the low input impedance, therefore in this case said bifilar lines have an impedance value of approximately 162 .
  • the output of the 1 :9 balanced-balanced step-up transformer 8c is isophase and balanced, for this reason, in order to obtain an even higher impedance, the secondary windings of each 1 :9 balanced-balanced step-up transformer 8c of each transmission line la of the electronic system 1 can be connected in series which, as previously mentioned, in the embodiment of the present invention shown in the figures, are equal to three.
  • an output impedance from the electronic system 1 for example equal to approximately 1458 (486 multiplied by three step-up transformers 8c in series) corresponding to an effective voltage value of approximately 3201 V, and a consequent value peak-to-peak voltage of about 9053 V.
  • the maximum final RF power that can be transferred to the load by the electronic system 1, also considering any losses along the three transmission lines, is between about 6500 W and about 7500 W, for example on average equal at approximately 7000 W.
  • the step-up transformer 8c can comprise one or more compensation elements of the parasitic capacitances and/or parasitic inductances or connection upstream and/or downstream thereof.
  • the step-up transformer 8c could include inductive and/or capacitive elements in parallel and/or in series at the output of said step-up transformer 8c, present or not selectively present in at least one of them.
  • the step-up transformer 8c can be connected to a supporting printed circuit and closed in a container, preferably made of plastic material in order to increase the degree of insulation in a simple way, but if desired also in metallic material, such as copper or aluminum, clearly sized to guarantee the necessary electrical insulation from parts with high RF voltages.
  • the step-up transformer 8c can also be immersed in a low-loss resin loaded with ceramic powders, for example Boron Nitride or Aluminum Nitride, in order to increase the dielectric strength of the insulation system and at the same time facilitate cooling for thermal conduction.
  • ceramic powders for example Boron Nitride or Aluminum Nitride
  • the electronic system 1 also comprises a suitable cooling group (not shown in the figures) for the disposal of the dissipated power, for example a liquid cooling group, for example with water, or by means of another suitable liquid.
  • a suitable cooling group for the disposal of the dissipated power, for example a liquid cooling group, for example with water, or by means of another suitable liquid.
  • the liquid cooling group in addition to its high efficiency, since the heat can be selectively extracted from where it is generated, also allows a heat removal capacity that is from about five times up to about a hundred times better than a group of air cooling, on average about twenty times better, thanks to the considerable thermal capacity of liquids compared to gasses.
  • the acoustic pollution in the working environment of the electronic system 1 is also improved, and it is easier to avoid unwanted overheating or unwanted movements of air in the environments where the apparatus is used, especially in applications where the thermo-hygrometric and purity conditions must be kept stable and controlled.
  • said liquid cooling group can comprise one or more recirculation pumps, one or more water tanks, one or more radiators, one or more fans for the water-air exchange and one or more feeders, to power one or more fans, as well as systems that use heat exchangers or heat pumps.
  • the cooling group can comprise one or more flexible connecting cables between said cooling group and the group(s) of the electronic system 1 which require(s) removal of the heat dissipated by the components which, kept at a controlled temperature, they allow to avoid drifts and system operation instability even in harsh environments.
  • Object of the present invention is also a Radio Frequency (RF) apparatus for drying and heat treatments of raw materials, semi-finished products and finished industrial products which uses one or more electronic systems 1.
  • RF Radio Frequency
  • the thermionic valve that generates the RF is replaced, based on specific application needs, with one or more electronic systems 1.
  • the modularity feature of the electronic system 1 allows to combine more than one electronic system 1 in order to reach higher powers, and at the same time to be able to distribute the power delivered to the load in a differentiated way and according to settable and defined profiles, unlike the thermionic valve systems where instead the volumes necessary for the RF generator and the non-fractionability of the RF applicator are such as not to allow it, except with complexity and in a very coarse, fixed and inflexible way.
  • the modularity feature of the electronic system 1 avoids the complete blocking of the working cycle of the machine in the event of a fault, while at the same time allowing the replacement of the damaged electronic system 1, unlike thermionics valve systems where the uniqueness of the RF generator connected to the RF applicator does not make it possible, thus determining the complete stop of the manufacturing process and for the necessary repair time.
  • an electronic system 1 fails, the RF powers supplied by the other electronic systems 1 can be remodeled in an appropriate manner, thus maintaining full operation of the machine and the working process, and only for the time necessary for its replacement, which can also be performed with the machine switched on ("hot swapping").
  • This replacement given the conception of the electronic system 1, is designed to be carried out also by not highly qualified personnel, unlike the thermionic valve systems where their replacement requires specialization and, above all, a lot of attention due to the high voltages involved.
  • a single logic unit can control many electronic systems 1 side by side by serial connection, making it easy to manage and set the profiles of the RF powers delivered in the time domain and in the space domain determined by the size of the RF applicator, also through intuitive operator interface systems, such as for example "touch screen” panels conveniently programmed with synoptic graphics and detailed in the individual iconic elements, for example with active graphics, which can be modulated or set in the process variables.
  • said apparatus designed for machines for uses mainly, but not only, in ISM fields with high load impedances essentially comprise one or more electronic systems 1 that emulate the operation of a thermionic valve, at least one network of coupling and/or adaptation downstream of said electronic system and at least one RF applicator arranged downstream of said at least one coupling and/or adaptation network.
  • the coupling and/or adaptation network can be tuned by the operator and includes one or more electrical and/or electronic circuits designed to filter and/or modulate and/or stabilize and/or modify and/or compensate the impedance connected to said electronic system 1 in a fixed or variable manner.
  • the RF applicator it can be as described in the state of the prior art, i.e. composed of a facing pair of a multiplicity of electrically interconnected cylindrical conductive tubes, electrically similar to two facing conductive plates between which the dielectric material to be treated is interposed, or composed of structures and geometries studied and created ad hoc according to the expected product and technological process through an appropriate method of application of the RF electromagnetic field, such as pairs of concentric cylindrical electrodes, or pairs of facing perforated plates, or sheets shaped according to specific geometric profiles, etc.
  • any other types of RF applicators or circuits suitable for use typically, but not exclusively, in ISM fields can be connected (for example probes or passive devices for thermo-medical treatments, or specific circuits for the excitation of ionized gases, or electrodes for the generation of electric arcs for particle treatments, etc.), which can be electrically represented by high load impedances, even considerably variable and/or with high reactive components.
  • the output RF voltage from the electronic system 1, after having been modified in amplitude and phase by the coupling and/or adaptation network whose function can also be to compensate for the higher reactive components of the load impedances, is applied to the element, for example to one of the plates of the RF applicator called "live", while the other element of the RF applicator, for example the other plate, is connected to ground.
  • the dissipation due to dielectric losses which it is created allows to generate volumetric or endogenous energy in the same, thus allowing to obtain the expected treatment effects.
  • the SS RF electronic system for use in ISM fields with high load impedances just described at the conceptual and operating principle level allows, therefore, the replacement of the thermionic valve technology, managing to obtain output voltages/impedances that are comparable to the latter as they are completely similar in the typical values, while at the same time maintaining a good level of robustness and solidity with respect to possible load mismatches.
  • the SS RF electronic system for use in ISM fields with high load impedances just described, in the case of using multiple systems, in the event of breakage, it allows to avoid total machine downtime and to replace the group that has failed simply by "removing" the broken group from its seat and inserting the new one, while avoiding the intervention of a specialized technician for the repair.
  • the SS RF electronic system for use in ISM fields with high load impedances just described is suitable for broadband use, thus avoiding the need for complex circuit setup case by case, when application and uses require the use of differentiated RF frequencies, or such as to be convenient also for the success or optimization of technological processes.
  • all the elements that make up the electronic system 1 are all designed and built to operate at broadband, thus making it possible to set different RF frequencies for the various systems used, thus allowing to easily create "multifrequency" apparatus and machines, a feature that greatly expands the areas of use for special applications and especially those of technical-scientific research.
  • the SS RF electronic system for use in ISM fields with high load impedances just described allows a high purity of the electromagnetic spectrum and frequency stability, thus responding in the best way to the increasingly stringent regulations in the field of Electromagnetic Compatibility (ITU, CISPR, IEC, EU directives and specific regulations for areas or countries, such as the FCC in the USA, Canada and other countries of South East Asia).
  • ITU Electromagnetic Compatibility
  • CISPR Magnetic Compatibility
  • IEC Electromagnetic Compatibility
  • the SS RF electronic system for use in ISM fields with high load impedances just described, as well as perfect controllability, even remotely, of the RF power delivered to the load both in continuous and pulsed mode also allows to exploit the considerable advantages of modularity, for example in the construction of complex machines such as to require differentiated treatments.
  • the SS RF electronic system for use in ISM fields with high load impedances just described allows a simplified and economical industrial construction of machines and plants that use it since they are not strictly dependent on the type of process and features of the products/loads to be dealt with, with the consequence also of a considerable improvement in production management and in the optimization of delivery times.
  • the SS RF electronic system for use in ISM fields with high load impedances just described allows savings in terms of transport and packaging costs thanks above all to the compactness and intrinsic lightness of the SS compared to the thermionic valves technology where, due to the natural use of electronic circuits, it is confirmed to involve considerable volumes, dimensions and weights.

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Abstract

La présente invention concerne un système électronique radiofréquence (RF) à semi-conducteurs (RF) destiné à être utilisé principalement, mais pas exclusivement, dans l'I.S.M. (ISM-domaine industriel-scientifique-médical) avec des impédances de charge élevées, et en particulier un équipement radiofréquence (RF) pour des traitements thermiuques et de séchage de matières premières, de produits industriels semi-finis et finis mettant en oeuvre ce système.
PCT/IB2021/055871 2020-09-25 2021-06-30 Système électronique pour alimenter des machines ou un appareil avec une fréquence radio comprenant un transformateur élévateur et un oscillateur utilisant un amplificateur à semi-conducteurs WO2022064285A1 (fr)

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IT102020000022726A IT202000022726A1 (it) 2020-09-25 2020-09-25 Sistema elettronico a radio frequenza allo stato solido per utilizzi in ambiti i.s.m. (industriale scientifico medicale) ad alte impedenze di carico
IT102020000022726 2020-09-25

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1954098A1 (fr) * 2005-11-25 2008-08-06 Matsushita Electric Industrial Co., Ltd. Dispositif de commande de puissance pour chauffage dielectrique a haute frequence et son procede de commande
JP2009252346A (ja) * 2008-04-01 2009-10-29 Panasonic Corp マイクロ波処理装置

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1954098A1 (fr) * 2005-11-25 2008-08-06 Matsushita Electric Industrial Co., Ltd. Dispositif de commande de puissance pour chauffage dielectrique a haute frequence et son procede de commande
JP2009252346A (ja) * 2008-04-01 2009-10-29 Panasonic Corp マイクロ波処理装置

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
EHRAT K.: "SPECIAL HIGH-FREQUENCY ENGINEERING NUMBER", 30 September 1944 (1944-09-30), Switzerland, pages 327 - 329, XP055809605, Retrieved from the Internet <URL:https://library.e.abb.com/public/dadf14b477e54194ba7613a3aae11e7a/bbc_mitteilungen_1944_e_09.pdf?x-sign=lWb6zmbVjwsVidyeEEIqKcRGbQm7nu2SHtvRAO9177wOzUNw0KaE8CNmiu5MYIfM> [retrieved on 20210601] *

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