• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
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    • 专利摘要:
    Dual frequency resonant power converter suitable for use in induction heating applications. The invention relates to a dual frequency resonant power converter, suitable for use in induction heating applications, comprising a power stage formed by a branch of square voltage generation VO, LF frequency fO, LF and current io, LF, connected to a branch of square voltage generation VO, HF frequency fO, HF and current iO, HF . Advantageously, the output of the frequency generating branch fO, LF is connected to an impedance ZLF comprising at least one capacitor Cr, LF and a coil Lr, LF ; the output of the frequency generating branch fO, HF is connected to an impedance ZHF comprising at least one capacitor Cr, HF ; the outputs of the impedances ZLF and ZHF are connected to the input of an induction load (Req, Leq) with current iO ; and the output of the induction load (Req, Leq) is connected to the inputs of both branches of voltage generation VO, LF and VO, HF . (Machine-translation by Google Translate, not legally binding)
    公开号:ES2626572A1
    申请号:ES201630084
    申请日:2016-01-25
    公开日:2017-07-25
    发明作者:Héctor SARNAGO ANDÍA；Óscar Lucía Gil；José Miguel BURDÍO PINILLA；Alejandro NAVAL PALLARÉS
    申请人:Universidad de Zaragoza；
    IPC主号:
    专利说明:

    DUAL FREQUENCY RESONANT POWER CONVERTER SUITABLE FOR USE IN INDUCTION HEATING APPLICATIONS
    FIELD OF THE INVENTION
    The present invention is part of the technical field corresponding to resonant power generation techniques. More specifically, the invention relates to a simultaneous dual frequency converter whose preferred application is induction heating techniques, both for industrial and domestic use.
    BACKGROUND OF THE INVENTION
    15 Induction heating is a booming technology that is displacing other traditional heating techniques, such as gas or resistive heating, due to the great advantages it presents in terms of performance, efficiency, lack of contact and precise control. This has caused the applications of induction heating to extend significantly from the industrial field to other fields
    20 technicians, such as domestic applications or medical technologies.
    Induction heating procedures are based on subjecting a conductive and / or ferromagnetic material that is desired to be heated to an alternating magnetic field. How
    Consequently, heating of the material occurs, mainly due to two physical phenomena: induced currents and magnetic hysteresis. In most induction heating processes, both industrial and domestic, induced currents are the predominant heating mechanism. Thus, a magnetic field of a certain frequency, applied to a material with a conductivity and permeability
    30 relative to vacuum permeability, will generate induced currents with a certain penetration depth. As a consequence, said excitation frequency is of fundamental importance in the depth of the heating and, consequently, in the industrial process to be carried out.
    35 Figure 1 of this document shows a known induction generator, based on a complete bridge inverter consisting of two branches equipped with two
    transistors (SHA, SLA and SHB, SLB), where the inverter load is formed by a Cr, HF capacitor, an induction coil and the part to be heated (represented respectively as Leq and Req). According to the number of switching devices, the inverter topologies commonly used in induction heating are full-bridge (as shown in the figure), half-bridge or resonant inverters composed of a single active device. The complete bridge topology is commonly used for output powers greater than 5 kW, and is the standard option for industrial systems. In contrast, the half bridge topology is preferred for domestic induction systems of up to 5 kW, while resonant inverters
    10 single switching are used in small induction heating generators and domestic systems up to 2 kW.
    There are industrial processes of induction heating in which it is essential to precisely apply several excitation frequencies, with a given power distribution. This need is critical in parts of complex geometry, being a representative example the heating of gears in its upper (tooth) and lower (valley). However, the known techniques for the application of induction with several simultaneous frequencies are limited in terms of the ability to control the operating frequencies, as well as the power applied by the generator. These
    20 techniques are currently divided into three groups, represented in Figure 2:
    a) Heating with double coil and double converter (Figure 2a): it is the technique that has a simpler implementation, and consists of using two generators or power stages and their corresponding coils, to generate with each of
    25 of them the required frequencies. The main advantage of this alternative is its ease of realization, since it is based on the simultaneous use of two single frequency generators, which also allows precise control of the power supplied with each coil. However, this option poses significant disadvantages, such as its high cost (for requiring the use of
    30 two single frequency generators) or its difficulty of assembly, as well as limited performance, since the heating of the piece is not carried out simultaneously. Additionally, the electromagnetic coupling between the coils can cause serious problems in the overall control of the generation system.
    35 b) Heating with single coil and double converter (Figure 2b): this implementation consists of using two independent power stages to generate each of
    the required and coupled frequencies, typically, by a transformer, as described for example in patent EP1363474B1. Its use allows greater performance and control of the applied power. However, this technology has a high cost due to the need for several power converters.
    e) Heating with single coil and single converter ("Simultaneous Dual Frequency",
    or SDP) (Figure 2c): this implementation consists of the use of a single coil and a single generator or power stage, capable of simultaneously generating the two required excitation frequencies. In this way, the current distribution ratio (or RRC) is defined as the ratio between the low frequency current value, iO.LF, and high frequency, iO • HF, that is, RRC = io, lF, rmslio, HF.fl1lS 'This alternative has higher performance and better process optimization than double coil heating techniques, and is currently implemented in two different ways: either using several generators or power stages coupled through a transformer ( which implies greater complexity and costs), or using a single power stage feeding a multi-resonant network, as described, for example, in patent application EP2148551A1. This last implementation is more competitive in terms of costs. However, and as a consequence of the specific design of its unique power stage, this technology has serious limitations regarding the independent control of the delivered power and its efficiency. First, the stage presents a fixed RRC ratio for each output power, given by the value of the components of the resonant tank of the circuit, which reduces flexibility to the power stage and makes its adaptation to different industrial processes complex. Secondly, operation at different RRC points can lead to non-optimal operating conditions, typically involving a strong switching of the devices, rather than a soft switching or ZVS ("Zero Voltage Switching"), drastically reducing efficiency. of the power stage.
    As described in the previous paragraphs, it is necessary, in the present technical field, to propose alternatives that allow solving the problems present in the state of the art, with the aim of obtaining induction generators of multiple frequencies that are not limited as far as to the distribution of power, and that do not require the duplication of the generation stage, with the substantial increase in costs that this entails.
    The present invention is intended to solve said problems, by means of a novel dual frequency resonant power converter, which allows to improve industrial induction heating processes, providing greater performance and new applications of induction heating by means of a single converter. This results in a beneficial impact on the quality of industrial induction heating processes and, consequently, also on the environment.
    BRIEF DESCRIPTION OF THE INVENTION
    An object of the present invention is, therefore, to provide an induction technology based on a power stage capable of generating two excitation frequencies simultaneously, and comprising a single converter capable of controlling the delivered power, at each frequency. , in optimal switching conditions.
    Said object of the invention is preferably carried out by means of a dual frequency resonant power converter, suitable for use in induction heating applications, which comprises a main power stage formed by a square voltage generating branch VO. LF of frequency fO.LF and current io.LF, connected to a square voltage generation branch VO.HF of frequency fO.HF and current io.HF.
    Advantageously, the generator of the invention further comprises the following configuration: - the output of the frequency generating branch fO.LF is connected to an impedance ZLF comprising at least one capacitor C ', LF and a coil L, .LF; -the output of the frequency generating branch fO • HF is connected to an impedance Z HF comprising at least one Cr • HF capacitor; where C, .LF, L ', LF and Cr • HF form the resonant tanks of the main power stage; -the outputs of the impedances ZLF and Z HF are connected to the input of an induction load (Req, Leq) with current io; and -the output of the induction load (Req, Leq) is connected to the inputs of both voltage generation branches VO.LF and VO.HF, so that io = iO.LF + io.HF.
    In a preferred embodiment of the invention, the induction load (Req, Leq) comprises a Leq coil and a heating part Req. More preferably, the frequency fO.LF has a value of 0.1-100 kHz, and the frequency fO • HF has a value of 100-1000 kHz.
    In another preferred embodiment of the invention, the converter comprises a stepbridge-type power electronics, consisting of four transistors (SH.LF, SL.LF, SH.HF,SL.HF) grouped into two pairs, where one of these pairs (SH.LF, SL.LF) forms the branch ofgeneration of square voltage VO.LF of frequency fO.LF and current iO • LF, and other suchpairs (SH.HF, S L.HF) form the square voltage generation branch VO.HF of frequency fO.HF
    10 And current ÍO • HF.
    In another preferred embodiment of the invention, the main power stage comprises at least one transformer in the frequency branch fO.LF and / or in the frequency branch fO.HF.
    In another preferred embodiment of the invention, the converter comprises one or more bridge type inverters, connected to the main power stage of the induction load (Req, Leq).
    In another preferred embodiment of the invention, the induction load (Req, Leq) is coupled by means of a transformer through whose primary circulates io, in order to increase the current level.
    Another object of the present invention relates to the use of a converter according to an embodiment based on an electronic power stage of bridge type, composed of four transistors (SH.LF, SL.LF, SH, HF, SL.HF) grouped in two pairs, where fO • LF and / or fO • HF have values above the resonant frequency of the resonant tanks (C ', LF, L, .LF and C, .HF) included in the main power stage , obtaining a soft ON switching mode (ZVS) in the corresponding transistors (SH, LF, SL.LF,
    S H.HF, S L.HF).
    As will be detailed below, the main advantages of the invention over
    State-of-the-art devices are mainly: -Generation of double frequency excitation, using a single coil. -Generation of double frequency excitation by using a single
    35 converter.
    - Independent and complete control of the power and current delivered to each application frequency.
    - Optimum switching conditions across the entire range of operating powers, ensuring high efficiency and reliability.
    DESCRIPTION OF THE FIGURES
    Figure 1 shows an induction generator in bridge configuration for the generation of a single induction frequency, according to an embodiment of the state of the art based on an inverter formed by two generation branches.
    Figure 2 shows three examples of known techniques for the application of induction with several simultaneous frequencies, according to different embodiments of the prior art. Figure 2a shows an embodiment based on heating with double coil and double converter. Figure 2b shows an embodiment based on heating with single coil and double converter. Figure 2c shows an embodiment based on heating with single coil and single converter.
    Figure 3 shows a preferred embodiment of the converter of the invention, according to a preferred embodiment thereof represented by its equivalent circuit.
    Figure 4 shows a specific embodiment of the converter of Figure 3, based on a bridge inverter with two frequency generating branches fO.LFY fO.HF.
    Figure 5 shows different modes of operation of the invention, according to the preferred embodiment of Figure 4. Figure 5a shows the output voltage VO.LF and the current io when the frequency branch fO.HF is deactivated. Figure 5b shows the output voltage V O.HF and the current io when the frequency branch fO.LF is deactivated. Figure 5c shows the output voltages VO.LF and VO.HF, and the current io when both frequency branches fO.LF and fO.HF are activated, with a predominance of the frequency fO.HF. Figure 5d shows the output voltages VO.LF and VO.HF, and the current io when both frequency branches fO.LF and fO.HF are activated, with
    predominance of the frequency fO • LF.

    Figure 6 shows an example of the power control region delivered at the frequencies fO.LF and fO.HF, as well as the limits of the optimal switching zone (ZVS), in the preferred embodiment of the invention of Figure 4 .
    Figure 7 shows a specific embodiment of the converter of Figure 3, based on a bridge inverter with two frequency generating branches fO • LF and fO.HF, including a transformer stage to adapt the load impedance.
    Figure 8 shows a specific embodiment of the converter of Figure 3, based on multiple bridge inverters, for the specific case of an embodiment of the invention comprising a stage with transformer.
    Figure 9 shows a specific embodiment of the converter of Figure 3, where the induction load (Req, Leq) is coupled by means of a transformer, through which primary flows a current Io and which allows to increase the level of current in the coil.
    Detailed description of the invention
    A detailed description of the invention related to different preferred embodiments thereof, based on Figures 3-9 of this document, is set forth below. Said description is given for illustrative, but not limiting, purposes of the claimed invention.
    As shown in Figure 3, the resonant power converter proposed by the present invention allows controlling the frequency and excitation power in double frequency induction heating applications. For this, the converter of the invention preferably comprises a square voltage generating branch VO.LF of frequency fO.LF and current ÍO • LF, connected to a square voltage generating branch VO.HF of frequency fO.HF And current iO.HF where usually, the fO.LF will be designated as "low frequency", and fO • HF as Ualta frequency ".
    In said low and high frequency branches, the output of the frequency generating branch fO.LF is connected to an impedance Z LF, which comprises at least one capacitor C, .LF and a coil L, .LF. For its part, the output of the frequency generating branch fO.HF is connected to an impedance Z HF comprising at least one capacitor C, .HF.

    Likewise, and with the objective of its application to induction heating technologies, the outputs of the impedances Z LF and Z HF are connected to the input of an induction load (Req, Leq) with current io. Likewise, the output of the induction load (Req, Leq) is connected to the inputs of both branches of voltage generation VO.LF and VO.HF, so that io ;;; io.LF + io.HF. As previously mentioned, the burden of
    induction represents the coil (Leq) and the piece to be heated (Req).
    The equivalent circuit of Figure 3 generally represents the principle of operation and essential elements of the invention. However, in practice it is possible to carry out the converter proposed under different designs, depending on the specific requirements of a given application. Thus, in a preferred embodiment illustrated by Figure 4, an electronic power stage of bridge type is used consisting of four transistors (SH.LF, SL.LF, S H.HF, SL.HF) arranged in two branches . As described above, the induction load, that is, the assembly formed by the coil and the part to be heated, has been modeled as an equivalent Req resistance and Leq inductance. Additionally, there are three reactive elements, consisting of two capacitors (Cr.LF, C, .HF) and an L r.LF coil, which make up the
    Resonant tanks of the main power stage.
    The operation of said power stage can be analyzed considering the separate operation of each of the branches of the bridge (overlap) stage. The low frequency branch fO • LF excites the resonant load, where said frequency and, consequently, the design of the resonant tank elements is typically a few kHz (low frequency). In addition, the high frequency branch fO • HF also excites the resonant load, the excitation frequency being, in this case, typically several hundred kHz (high frequency).
    Figure 5 shows the main waveforms of the proposed stage, including the low frequency and high frequency branches, describing different power distributions, that is, different RRCs. Thus, Figure 5a shows the output voltage VO.LF and the current io when the frequency branch fO.HF is deactivated. Figure 5b shows the output voltage VO.HF and the current io when the frequency branch fO • LF is deactivated. Figure 5c shows the output voltages VO.LF and VO.HF, and the current io when both frequency branches fO.LF and fO.HF are activated, with a predominance of the frequency fO.HF. Figure 5d shows the output voltages VO.LF and VO.HF, and the current; 0 when both frequency branches fO.LF and fO.HF are activated,
    predominantly of the frequency fO.LF.
    Using the electronic power stage proposed, it is possible to control the frequencies of
    5 excitation selected by the switching frequency of the transistors of eachOne of the branches. In addition, the amplitude or power supplied at each frequency isYou can control by adjusting the service cycle of each of the branches or bysmall variations in the switching frequency that do not affect the process ofheating. An example of the power control region is shown in Figure 6
    10 delivered in high and low frequency (thin line in the figure), as well as the limits of the optimal switching area (thick line).
    Additionally, it should be noted that by means of the proposed stage it is possible to obtain a switching mode of soft ON switching (ZVS) in all transistors,
    15 considerably increasing the efficiency and robustness of the system. The operating region ZVS has been included in Figure 6, showing that it is operated there whenever it is operated above the resonant frequency of the low and high frequency resonant tanks, respectively.
    Alternatively to the converter proposed in the preferred embodiment shown in Figure 4, the following additional implementations of the invention are proposed:
    Figure 7 shows an embodiment of the invention based on a step comprising a transformer in the low and / or high frequency branch. This configuration allows you to adapt
    25 the impedance of the inverter load, reducing the current through the devices of the inverter branches and achieving a more efficient and safe operation.
    Figure 8 shows an embodiment of the invention based on the use of a single inverter based on one or more bridges connected to the induction load (Req, Leq). This
    The configuration allows greater control of the power delivered to said induction load (Req, Leq), and is preferably indicated for high powers.
    Figure 9 shows an embodiment of the invention based on the use of a transformer in the induction load (Req, Leq), with the aim of increasing the level of current io in the
    35 coil Leq.
    权利要求:
    Claims (6)
    [1]
    1.-Dual frequency resonant power converter, suitable for use in induction heating applications, comprising a power stage
    5 main formed by a branch of square voltage generation VO, LF of frequency fO.LF andio.LF current, connected to a square voltage VO.HF frequency generating branchfO.HF and current iO.HF,
    characterized in that: - the output of the frequency generating branch fO.LF is connected to an impedance ZLF comprising at least one capacitor C ', LF and a coil L, .LF; -the output of the frequency generating branch fO • HF is connected to an impedance Z HF comprising at least one Cr • HF capacitor; where C, .LF, L ', LF and Cr • HF form the resonant tanks of the main power stage; 15 -the outputs of the impedances Z LF and Z HF are connected to the input of an induction load (Req, Leq) with current io; and -the output of the induction load (Req, Leq) is connected to the inputs of both voltage generation branches VO.LF and VO.HF, so that io = iO • LF + iO.HF.
    2. Converter according to the preceding claim, wherein the induction load (Req, Leq) comprises a coil Leq and a piece to be heated Req.
    [3]
    3.-Converter according to any of the preceding claims, wherein the fO.LF frequency has a value of 0.1-100 kHz, and the fO.HF frequency has a value of 10025 1000 kHz.
    [4]
    4.-Converter according to any of the preceding claims, comprising an electronic power stage of bridge type, composed of four transistors (SH.LF, SL.LF, SH, HF, S L.HF) grouped in two pairs, where one of said pairs (SH, LF, SL.LF) forms the
    30 square voltage generation branch VO.LF of frequency fO.LF and current iO • LF, and another of said pairs (SH.HF, SL.HF) forms the square voltage generation branch VO.HF of frequency fO. HF and current iO.HF,
    [5]
    5.-Converter according to any of the preceding claims, wherein the main power stage 35 comprises at least one transformer in the frequency branch fO • LF and / or in the frequency branch fO • HF.
    [6]
    6.-Converter according to any of the preceding claims, comprising one or more bridge type inverters connected to the main power stage of the induction load (Req, Leq).
    5. Converter according to any of the preceding claims, wherein the loadinduction (Req, Leq) is coupled by a transformer whose primaryio current flows.
    [8]
    8. Use of a converter according to claim 4, wherein fO.LF and / or fO.HF have
    10 values above the resonant frequency of the resonant tanks (C'.LF, L, .LF, C,.,. W) including the main power stage, obtaining a switching mode of soft ON switching (ZVS ) in the corresponding transistors (SH.LF, SL.LF,
    S H.HF, S L.HF).
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    同族专利:
    公开号 | 公开日
    ES2626572B1|2018-06-14|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    WO1991015935A1|1990-04-10|1991-10-17|Elva Induksjon A.S|Method and device for surface hardening of rotation symmetrical parts through inductive heating by means of at least two different frequencies|
    JPH11288780A|1998-03-31|1999-10-19|Shinko Electric Co Ltd|Power supply circuit for double frequency power supply melting furnace|
    EP2148551A1|2008-07-21|2010-01-27|GH Electrotermia, S.A.|Inductive heating apparatus comprising a resonant circuit with simultaneous dual frequency current output and a single inverter circuit with silicon carbide|ES2762299A1|2018-11-21|2020-05-22|Gh Electrotermia S A|Synchronism method and power control for a resonant power inverter of an induction heating generator |
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