RU2240659C2 - Sectionalized-inductor inductive heating device (alternatives) - Google Patents

Abstract

FIELD: induction heating; inductors for heating to different temperatures and devices for methodical heating of blanks.

SUBSTANCE: proposed heating device incorporating sectionalized inductor wherein various areas of part corresponding to different sections of inductor are heated to different temperatures is characterized in that each section is supplied with power from respective matching transformer; primary windings of these transformers are interconnected in series and their secondary windings are connected in parallel with respective inductor sections. Such connection of transformer windings makes it possible to set any desired reasonable current ratio in sections and, hence, desired power distribution by varying turn ratio of matching transformers and to maintain it constant in case of load variation due to re-distribution of transformer voltages. Several alternatives are possible for connecting resonance-tuned capacitor with such connection of transformer windings. Proposed alternatives provide for designing sectionalized-inductor systems where system cost is limited and at the same time desired output power distribution among sections is required due to dispensing with intricate control circuits, switching devices, and additional variable inductive components.

EFFECT: simplified design while maintaining resonance for all sections, enhanced efficiency, reduced cost and size of device.

5 cl, 8 dwg

Description

The invention relates to induction heating, in particular to devices of induction heating with a multi-section inductor, in which the heating of different areas of the heated object corresponding to different sections of the inductor is carried out to different temperatures, as well as to devices for methodical heating of workpieces. In particular, methodical heating devices are characterized in that the impedance of each individual part depends on its position in the inductor system, so the power applied to different sections of the inductor has different values. For methodical heating devices, the heating mode is most often used in which the power consumed by each part is kept constant, although there are other heating modes in which the power consumption in each section of the inductor system is specified by a certain law. From the foregoing it follows that in both cases a field with a variable intensity along the length of the inductor is necessary. This problem in known devices, as a rule, is solved in two ways: by changing the number of turns of the inductor per unit length, or by changing the operating current along the length of the inductor, for example, by dividing it into several sections with different currents. The use of an uneven pitch of turns for the implementation of various heating modes has been studied in sufficient detail in the literature on methodological heating; see, for example, S. Yaitskov Accelerated isothermal induction heating of forging blanks. M .: Mashgiz, 1962. An induction heating installation is known from patent sources, including an external winding connected to a power source, in which the redistribution of heating power over the zones is achieved due to a predetermined uneven step of the winding turns in its different zones, and all winding zones are connected in series and connected to the same power source (SU No. 1152096, H 05 V 6/36). The most serious drawback of this method is the limitation of the change in the pitch of the coil of the inductor caused by technological difficulties, since its minimum value is limited by the thickness of the insulation, the maximum by the permissible length of the inductor. In addition, in areas of the inductor with a low magnetic field strength, a large winding pitch is used, which leads to distortions of the magnetic field and an increase in the scattering flux. The above disadvantages are eliminated using a sectioned inductor with separate section power. In such a structure, various voltages are applied to the sections, the multiplicity of which is set by the transformation coefficients of the matching transformers. In this case, either the transformation coefficients are selected at which the necessary power distribution is achieved, or current stabilizers are used in sections, in any of these options the device turns out to be complicated and expensive. Another method of obtaining the desired power distribution can be the operation of each section at its own resonant frequency, which allows you to change the power consumption, since the active impedance of the heated part depends on the frequency. However, the need to power each section with its own source requires the use of its own control unit, as a result, the device becomes complex and expensive (see, for example, international application WO No. 9903308, publ. 21.01.1999). Known devices for induction heating with a sectioned inductor, sections of which are powered from one high-frequency power source. In this case, the sections are connected in parallel through the corresponding thyristor switches and to control the temperature released in the zone with which the corresponding section is connected, the power transmitted to each zone is determined by the combination of closed switches and the period of time for which the sections are connected to the power source (US patent No. 5349167). Such devices require the installation of temperature sensors in each heating zone and feedback from the control device, as a result of which the device also turns out to be complex and expensive. In addition, the presence of switches in the power circuit reduces the efficiency of the device and further increases its cost.

Closest to the first of the variants of the claimed invention is a multi-zone induction heating device, the description of which is given in US patent No. 5059762. In this device, the winding is divided into several sections defined by soldering and associated with the corresponding zones of the heated object. Redistribution of power in the appropriate sections from one source while maintaining resonance in the specified device is performed using additional reactance, which shunts the heating sections through soldering. In this device, reactances are made on the basis of saturable inductive elements that have control windings made so that the direct current supplied to them changes their reactance and the resistance of the section as a whole. The disadvantages of this device are the large dimensions due to the presence of additional windings, which, in addition, increase the inductive energy of the circuit, and hence the power of the capacitor bank, and a complex heating process control circuit.

The objective of the invention is to simplify the device of induction heating while maintaining resonance in all sections, as well as increasing efficiency, reducing its cost and dimensions by eliminating complex control circuits, switching devices and additional reactive elements.

The problem is solved in that in an induction heating device with a sectioned inductor, powered by one high-frequency power source, in which the sections are determined by soldering, and a resonant circuit formed by an inductor and a resonant capacitance, the power supply of each section is provided by a matching transformer, and the primary windings of matching transformers are connected in series with each other, and their secondary windings are connected in parallel with the corresponding sections of the inductor. This inclusion of transformer windings allows you to set any reasonable multiplicity of currents in the sections, and therefore the necessary power distribution by the transformation coefficients of the matching transformers and keep it constant when the load changes due to the redistribution of transformer voltages.

In this case, several options for connecting a resonant capacitance with this inclusion of transformer windings are possible. Firstly, it is possible to connect the resonant capacitance in series with the primary windings of the transformer. In this case, the system is reduced to one resonant capacitance located along the primary winding of the transformer. This arrangement of the capacitance allows you to compensate for the reactive energy of the entire inductor, as a result of which the converter operates on an active load, although the transformer units transmit the full power of the inductor. Secondly, it is possible to connect the resonant capacitance in series with one of the secondary windings of the matching transformer. Here, the capacitance compensates for the reactive energy of one section due to the series connection with it, part of the reactive power of the remaining sections is compensated by the capacitive section through electromagnetic coupling. In the third case, the resonant capacitance is included in the circuit of each section of the inductor in series with the secondary winding of the transformer. In this circuit, matching transformers have only the active component of power, since here the inductance of each section of the inductor is compensated by its own capacitance.

The closest analogue to the second variant of the device according to the claimed invention is the device according to US patent No. 3209114, in which the windings of a multi-section inductor are powered from one high-frequency power supply, and each section of the inductor is included in its resonant circuit, in which a resonant capacitor is connected in parallel to each section of the inductor and linear variable inductance element with a wide range of inductance regulation for redistributing power in sections during heating. A disadvantage of the device is the difficulty in creating and the high cost of such a linear variable inductive element, as well as a significant increase in the dimensions and mass of the device, while at the same time complicating the heating control circuit.

The objective of the second embodiment of the invention is also to simplify the induction heating device while maintaining resonance in all sections, reducing its cost, dimensions and weight.

In the second embodiment of the invention, the problem is solved in that in the induction heating device with a sectioned inductor powered by one high-frequency power source and a series resonant circuit formed by the inductor and the resonant capacitance, the power supply to the inductor sections is provided by corresponding matching transformers, while the primary windings of matching transformers connected in series to each other, their secondary windings are connected in series with the corresponding section an inductor, and a resonant capacitance connected in parallel branches formed by the inductor sections with respective secondary windings of a transformer that also provides a multiplicity of predetermined currents in the sections. In this embodiment, the total current of all sections of the inductor passes through the capacitance, therefore the reactive energies of all sections are compensated.

Further, the invention is disclosed using the figures in which: FIG. 1 is a diagram with a resonant capacitor connected in series to the primary windings of a matching transformer; figure 2 - diagram of the operation of the circuit in figure 1; figure 3 - circuit with a resonant capacitor connected in series with one of the secondary windings of the transformer; figure 4 - diagram of the circuit of figure 3; 5 is a diagram with resonant capacitors connected in series to each of the secondary windings of the transformer; 6 is a diagram of the operation of the circuit in figure 3; 7 is a diagram with a parallel connection of a resonant capacitor; Fig.8 is a diagram of the operation of the circuit in Fig.7.

All diagrams are constructed under the condition that the inductive and active resistances of the sections are equal, and also under the condition that the sections have the same power, the specified current multiplicity is 1: 1.5: 2.

The following notation is used in the drawings: high-frequency voltage source 1, matching transformers 2, 3, 4 with primary windings 2 ₁ , 2 ₂ , 2 ₃ , secondary windings 2 ₂ , 3 ₂ , 4 ₂ , inductor sections 5 ₁ , 5 ₂ , 5 ₃ , resonant capacitance 6. The indices L ₁ , L ₂ , L ₃ indicate the inductance of the sections of the inductor.

The device according to the first embodiment of the invention is shown in FIGS. 1, 3 and 5. In this device, a multi-section inductor, powered by source 1, consists of sections 5 ₁ , 5 ₂ , 5 ₃ . The inductor sections are powered from a single source by means of corresponding matching transformers 2, 3 and 4, the primary windings of which 2 ₁ , 3 ₁ , 4 _{1 are} connected in series, and the secondary windings 2 ₂ , 3 ₂ and 4 _{2 are} connected in parallel to the corresponding sections of the inductor 5 ₁ , 5 ₂ and 5 ₃ . The resonant capacitance 6 is connected in series with the primary windings of the transformer.

The device in figure 3 differs only in that the resonant capacitance 6 is connected in series with the secondary winding 4 _{2 of the} transformer 4.

In the device of FIG. 5, a resonant capacitance is included in the circuit of each section of the inductor. Here, the resonant capacitance 6 _{1 is} connected in series with the secondary winding of the matching transformer 2 ₂ . in the circuit of the section of the inductor 5 ₁ , the resonant capacitance 6 _{2 is} connected in series to the secondary winding 3 ₂ in the circuit of the second section of the inductor and so on.

The device according to the second embodiment of the invention is presented in Fig.7. In this embodiment, the multi-section inductor 5 consists of sections 5 ₁ , 5 ₂ and 5 ₃ . All sections of the inductor are powered from one high-frequency power source through the corresponding matching transformers 2, 3 and 4, the primary windings of which 2 ₁ , 3 ₁ and 4 _{1 are} connected to each other in series, and the secondary windings 2 ₂ , 3 ₂ and 4 ₂ are connected each in series with the corresponding section of the inductor 5 ₁ , 5 ₂ and 5 ₃ . In this embodiment, the resonant 6 capacitance is connected parallel to the branches formed by the sections of the inductor with the corresponding secondary windings of the matching transformers, forming a series resonant circuit with all sections.

The operation of the device in figure 1 is illustrated by the diagram of the operation of this option with the methodical heating in figure 2, which shows the voltage diagrams of the primary windings of the transformers U2 ₁ , U3 ₁ and U4 ₁ and the current sections of the inductor I5 ₁ , I5 ₂ and I5 ₃ . It can be seen from the diagram that at various sections resistances the system provides the multiplicity of current specified in the transformation coefficients in the sections. In figure 2, the primary voltage of the transformers are equal, since the diagrams are constructed from the condition of equal power sections. In this embodiment, the system is reduced to one resonant capacitance 6 located in the primary winding circuit of the transformers. This arrangement of the capacitance allows you to compensate for the reactive load of the entire inductor, as a result of which, the source converter 1 operates on an active load. But since the capacitance is switched on in the primary winding, the overall power of the matching transformer is overestimated due to the reactive power of the inductor, that is, the transformer transmits the total power of the inductor. This is confirmed by the diagrams in figure 2, which shows that the sum of the voltage of the transformer has a reactive component. The advantage of this circuit is the small capacitance of the capacitor or capacitor bank, since it is brought to the secondary side of the transformer through the square of the transformation coefficient. The disadvantage of this circuit is the high voltage at the resonant capacitance. Thus, such a circuit is best used in induction heating devices with a low voltage output, since it is difficult to optimally design a capacitance for low voltage.

In the structure with the arrangement of the resonant capacitance 6 along the secondary winding shown in FIG. 3, the capacitance compensates for the reactive energy of one section 5 ₃ due to the series connection with it, the reactive power of the remaining sections 5 ₁ and 5 _{2 is} compensated by the capacitive section via electromagnetic coupling. The reactive voltage of the secondary winding of the transformer 4 ₂ is equal to the sum of the reactive voltages of the secondary windings of the remaining sections, as can be seen from the diagram in figure 4. From this we can conclude that the more sections are used (that is, the smaller the resulting inductance is connected to the capacitance), the higher the reactive component of the voltage on the transformer in the section where the capacitance is turned on, in this case, on the transformer 4. Thus, the structure applicable with a minimum number of sections of the inductor.

The operation of the variant of the device shown in FIG. 5 is characterized in that the matching transformers 2, 3, 4 have only the active power component, since here the inductance of each section of the inductor 5 ₁ , 5 ₂ , 5 _{3 is} actually completely compensated by its own capacitance, respectively, 6 ₁ , 6 ₂ , 6 ₃ , connected in series with the secondary winding of the corresponding transformer. Diagrams of voltages and currents for the operation of this circuit are shown in Fig.6. In this scheme, it is necessary to fulfill the condition for the resonance frequencies to coincide in the sections, that is:

,

,

where C ₆₁ , C ₆₂ , C ₆₃ are the capacitors of the capacitors in the respective sections, and L ₁ , L ₂ and L ₃ are the inductances of the corresponding sections of the inductor 5 ₁ , 5 ₂ and 5 ₃ .

The diagram of Fig.6 shows the voltage and currents in the mode of stabilization of power in sections, subject to the specified conditions. The diagram shows that the voltages on the primary windings of the transformers do not have reactive components and coincide with each other, which is evidence of the constancy of power consumption in sections. Changes in inductances L ₁ , L ₂ , L ₃ during heating, disproportionately to each other due to the presence of leakage inductance, can lead to the appearance of transformer reactive voltages as a result of violation of condition (1). However, this effect will be significantly less with an increase in the number of sections, since the range of variation of the load inductance within each section will decrease with an increase in their number. That is, using this scheme, you can get a stable heating mode, despite the fact that it is significantly cheaper and simpler in comparison with the known analogues.

The operation of the second embodiment of the device is explained using the example shown in Fig. 7 with the corresponding diagrams presented in Fig. 8. In this structure, the total current of all sections of the inductor passes through capacity 6, therefore the reactive energies of all sections are compensated, although all sections of the inductor will transmit reactive power, since they have different reactive components. However, the total power of the entire transformer system will have only the active component, due to the fact that the inductive nature of one section is compensated by the capacitive nature of the other, which is confirmed by the diagrams of Fig. 8. Thus, this structure can be effectively used with a large number of sections of the inductor. The advantage of this system is the achievement of relatively small reactive powers of transformers when using only one resonant capacitance.

The proposed variants of the invention make it possible to design systems with a partitioned inductor for applications where the cost of the system is limited, but a given distribution of allocated power is required in sections, due to the elimination of complex control circuits, switching devices and additional variable inductive elements.

Claims (5)

1. A high-frequency induction heating device with a sectioned inductor, powered by sections from a single high-frequency power source and a resonant circuit formed by an inductor and a resonant capacitance, characterized in that the power of each section is provided by a matching matching transformer connected to the power source, while the primary windings matching transformers are connected in series, and their secondary windings are connected in parallel with the corresponding sections of the inductor. 2. The high-frequency induction heating device according to claim 1, characterized in that the resonant capacitance is included in the primary winding circuit of the matching transformer in series with them. 3. The high-frequency induction heating device according to claim 1, characterized in that the resonant capacitance is connected in series with one of the secondary windings of the transformer. 4. The high-frequency induction heating device according to claim 1, characterized in that a resonant capacitance is connected in series with each secondary winding of the transformer. 5. A high-frequency induction heating device with a sectioned inductor, with sections powered by a single high-frequency power source and a resonant circuit formed by an inductor and a resonant capacitance, characterized in that the power of each of the sections of the inductor is provided by a matching matching transformer, sections of the inductor are connected in series with their supply the secondary windings of the transformer, forming parallel branches, and the resonant capacitance is connected in parallel with these branches with it resonance circuit with each section of the inductor, the primary windings of the matching transformers are connected in series.

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