A method for constructing a large-current resonant inductor of a medium-frequency induction heating power supply

Abstract

This invention relates to a method for constructing a high-current resonant inductor for a medium-frequency induction heating power supply, belonging to the field of switching power supply design. Addressing the issues of high loss and large size of high-current single-turn wire-core resonant inductors under high-frequency, high-current conditions, this method establishes a comprehensive mathematical model incorporating inductor volume, copper loss, and magnetic loss, and optimizes parameters based on average AC magnetic flux. By selecting the inner and outer radii of the magnetic core as independent variables, expressions for loss and volume are derived, and Pareto front analysis is used to achieve dual optimization of inductor volume and converter efficiency while satisfying electrical performance requirements. This method can provide a general theoretical basis and optimization path for the design of high-power, high-current inductors, contributing to improved power density and overall efficiency of induction heating power supplies.

Description

Technical Field

[0001] This invention belongs to the field of resonant inductor design technology, and in particular, a method for constructing a high-current resonant inductor for a medium-frequency induction heating power supply. Background Technology

[0002] Induction heating power supplies, a type of special power supply, utilize the high-frequency eddy current heating effect generated by electromagnetic induction to heat objects. Compared to traditional resistance current heating and flame heating, it is a more efficient, energy-saving, environmentally friendly, safe, and controllable advanced heating method. With the advent and application of third-generation wide-bandgap semiconductors, induction heating power supplies are developing towards higher current, higher operating frequency, and higher power density. Under conditions of increased operating frequency, current, and capacity, traditional resonant inductors experience continuously increasing losses per unit volume of magnetic materials, a more pronounced skin effect in the conductor, increasingly uneven current distribution, and a larger AC resistivity, leading to increased losses. Resonant inductors have become a significant factor restricting the development of induction heating power supplies towards higher frequencies, higher efficiency, and higher power density. Therefore, it is necessary to research newer types of resonant inductors for induction heating power supplies. Furthermore, in the inductor design process, high efficiency and high power density are contradictory design goals. Establishing a comprehensive model of design variables, inductor volume, and inductor losses, and providing the basis for design parameter values ​​and optimization methods, is key to achieving comprehensive optimization of efficiency and power density. Therefore, studying the structure of resonant inductors and proposing modeling and multi-objective optimization methods has significant engineering value. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and propose a method for constructing a high-current resonant inductor for a medium-frequency induction heating power supply. For the high-current wire-core resonant inductor in a high-power medium-frequency induction heating power supply, a general loss model is established. By using a design method based on average AC magnetic flux, the Pareto front of the target magnetic design is found and the optimal magnetic design is selected, thus achieving dual optimization of inductor volume and converter efficiency.

[0004] The technical problem solved by this invention is achieved through the following technical solution: A method for constructing a high-current resonant inductor for a medium-frequency induction heating power supply includes the following steps: Step 1: Construct a volumetric model of a high-current resonant inductor; Step 2: Calculate the electrical and magnetic field characteristics based on the constructed high-current resonant inductor volume model; Step 3: Calculate the loss characteristics based on the constructed high-current resonant inductor volume model; Step 4: Calculate the loss and volume based on the electrical characteristics, magnetic field characteristics, and loss characteristics; Step 5: Parametric scanning is used to plot a scatter plot of the relationship between loss and volume to find the Pareto front of the target magnetic design.

[0005] Furthermore, the high-current resonant inductor volume model in step 1 adopts a high-power induction heating power supply topology using a voltage-type series-parallel LLC resonant circuit, wherein the wire-threaded magnetic core uses a ring-shaped open air gap structure to resist saturation. Let be the inner radius of the magnetic core. The outer radius of the magnetic core. For the depth of the magnetic core, The length of the air gap in the magnetic core. The thickness of the copper busbar is approximately [value missing], and the width of the copper busbar is approximately [value missing]. The length of the copper busbar is equal to the depth of the magnetic core, and its value is also [value missing]. The cross-sectional area of ​​the magnetic core is: The volume of the core of a high-current resonant inductor is: The overall volume of the high-current resonant inductor is: .

[0006] Furthermore, the method for calculating the electrical characteristics in step 2 is as follows: in, The peak value of the magnetic flux linkage. This represents the peak current. The method for calculating magnetic field characteristics is as follows: in, For the sensing value, The value of free permeability is 4π × 10⁻⁶. -7 H / m.

[0007] Furthermore, the method for calculating the loss characteristics in step 3 is as follows: in, This is the effective value of the rated current. For the exchange coefficient, This refers to the thickness of the copper busbar.

[0008] Furthermore, the loss calculation method in step 4 is as follows: by selecting the inner radius of the magnetic core. and the outer radius of the magnetic core Core length is the independent variable. for: in, For magnetic flux; The method for calculating magnetic loss is as follows: The method for calculating copper loss is as follows: The total loss is: in, , ; The method for calculating the volume of the magnetic core is as follows: The method for calculating the volume of an inductor is as follows: .

[0009] Furthermore, the specific implementation method of step 5 is as follows: based on the inductor volume obtained in step 4 V With independent variable and Relationship, each group of independent variables ( , Each of these has a corresponding loss data. P With volume data V volume data V The horizontal axis represents loss data. P Plot a scatter plot on the ordinate and exhaustively list the independent variables within the specified range. , By combining the results, the loss under a fixed AC magnetic flux can be plotted. P With inductor volume V A scatter plot of relational data, changing the value of the AC magnetic flux, yields the AC magnetic flux under... P - V Relational data, based on alternating magnetic flux P - V Relational data, plotting under multiple AC magnetic fluxes P - V Scatter plot, P - V The envelope in the scatter plot represents the Pareto front of the target inductor design.

[0010] The advantages and positive effects of this invention are: 1. The design optimization method based on AC flux method proposed in this invention theoretically provides the optimal trade-off between loss and volume of medium-frequency high-current resonant inductors, which can provide a reference for the application of high-power high-current inductors in other engineering projects. 2. This invention introduces design variables to achieve accurate calculation of inductor copper loss and magnetic loss under AC excitation; 3. This invention finds the Pareto front for the design of target high-current resonant inductors. Attached Figure Description

[0011] Figure 1 This is a topology diagram of the voltage-type series-parallel LLC resonant circuit of the present invention; Figure 2 This invention provides a high-current resonant inductor. Ls Conductor core structure diagram; Figure 3 This is a flowchart illustrating the design optimization of the high-current resonant inductor for this invention. Figure 4 This invention provides a diagram of equal loss lines and equal volume lines under AC magnetic flux. Figure 5 This is a scatter plot showing the loss and volume of the present invention. Detailed Implementation

[0012] The present invention will be further described in detail below with reference to the accompanying drawings.

[0013] The high-power induction heating power supply topology of the present invention using a voltage-type series-parallel LLC resonant circuit is shown in the attached figure. Figure 1 As shown in the figure. As the energy storage element of an LLC resonant circuit, reducing the volume of the resonant inductor can effectively improve the power density of the converter. The geometry of the wire-core resonant inductor used in this paper is shown in the attached figure. Figure 2 As shown, the conductor uses a copper busbar of a certain thickness, and the magnetic core uses an annular open air gap structure to resist saturation.

[0014] A method for constructing a high-current resonant inductor for a medium-frequency induction heating power supply includes the following steps: Step 1: Construct a volumetric model of a high-current resonant inductor.

[0015] High current resonant inductor L S The specific dimensions are as shown in the attached document. Figure 2 As shown in the figure, Let be the inner radius of the magnetic core. The outer radius of the magnetic core. For the depth of the magnetic core, The length of the air gap in the magnetic core. The thickness of the copper busbar is approximately [value missing], and the width of the copper busbar is approximately [value missing]. The length of the copper busbar is equal to the depth of the magnetic core, which is... The cross-sectional area of ​​the magnetic core can be expressed as: (1) The volume of the core of a high-current resonant inductor can be expressed as: (2) The overall volume of a high-current resonant inductor can be expressed as: (3) Step 2: Calculate the electrical and magnetic field characteristics based on the constructed high-current resonant inductor volume model.

[0016] The inductance of a high-current resonant inductor is related to the peak flux linkage and peak current by the following equation: (4) However, due to the high current operating conditions, the conductor is a single turn, and the magnetic flux, magnetic flux, and core cross-sectional area have the following relationship: (5) Therefore, the following relationship can be obtained: (6) Therefore, geometric parameters , , The following relation exists: (7) Analyze the magnetic circuit and the air gap length. With feeling value The following relationship exists between them: (8) in, For the sensing value, The value of free permeability is 4π × 10⁻⁶. -7 H / m.

[0017] Step 3: Calculate the loss characteristics based on the constructed high-current resonant inductor volume model.

[0018] Magnetic component losses are generally analyzed separately as copper losses and magnetic losses.

[0019] Under alternating sinusoidal excitation, the magnetic loss can be accurately described by the Steinmetz formula, and the expression for the loss per unit volume is as follows: (9) in For operating frequency, This represents the maximum magnetic flux density during operation.

[0020] At a given frequency and maximum magnetic flux density, the magnetic loss per unit volume is a fixed value, and the total magnetic loss of the magnetic core is the product of the loss per unit volume and the volume, as expressed below: (10) By combining equations (2) and (10), we can obtain the expression for the magnetic loss related to the size parameters: (11) Based on the geometry of the high-current resonant inductor, with the conductor width approximately twice the inner radius of the magnetic core, the expression for the DC resistance of the copper busbar conductor can be obtained as follows: (12) in Let be the electrical conductivity of copper.

[0021] Under alternating current excitation, due to the skin effect of the current, the AC resistance will be greater than the DC resistance, which is usually expressed as the AC coefficient. The following expression represents: (13) AC copper loss is described by the product of the square of the effective current and the AC resistance, as shown in the following expression: (14) From equations (12), (13), and (14), the AC copper loss can be described by the following expressions: (15) The total loss is the sum of magnetic loss and copper loss: (16) in, This is the effective value of the rated current. For the exchange coefficient, This refers to the thickness of the copper busbar.

[0022] Step 4: Calculate the loss and volume based on the electrical characteristics, magnetic field characteristics and loss characteristics.

[0023] Select the inner radius of the magnetic core and the outer radius of the magnetic core Core length is the independent variable. It can be described by the following expression: (17) Eliminating variables from equations (11) and (17) Magnetic loss can be expressed as: (18) Eliminating variables from equations (15) and (17) Copper loss can be expressed as: (19) From equations (16), (18), and (19), the total loss can be expressed as: (20) in , .

[0024] From equations (2) and (17), the expression for the core volume can be transformed into: (twenty one) From equations (3) and (17), the total volume of the inductor can be transformed into: (twenty two) Step 5: Parametric scanning to find the Pareto front An excessively large ratio of inner to outer radii will cause severe oversaturation on the inner side of the magnetic ring and severe undersaturation on the outer side; therefore, limiting conditions are added. Mathematical tools can be used to plot the trends of total loss and total volume as a function of two independent variables. Furthermore, these tools can be used to plot lines of equal loss and equal volume under the same alternating magnetic flux in a two-dimensional graph. Figure 4 As shown.

[0025] Based on the appendix Figure 4 loss P With independent variable and The relationship, Equation (22) expresses the inductance volume. V With independent variable and Relationship, each group of independent variables ( , Each of these has a corresponding loss data. P With volume data V volume data V The horizontal axis represents loss data. P Plot a scatter plot on the ordinate and exhaustively list the independent variables within the specified range. , The combination of these parameters can be used to plot the losses under a fixed AC magnetic flux. P With inductor volume V A scatter plot of relational data. Changing the value of the AC magnetic flux yields multiple AC magnetic flux values. P - V Relational data.

[0026] Based on multiple alternating magnetic fluxes P - V Relational data can be used to plot data under multiple AC magnetic fluxes. P - V Scatter plot attached Figure 5 As shown, the lower left envelope is the Pareto front of the target inductor design. All points on the Pareto front represent the optimal magnetic design for the target inductor. The final design is selected based on loss or size requirements.

[0027] It should be emphasized that the embodiments described in this invention are illustrative rather than limiting. Therefore, this invention includes, but is not limited to, the embodiments described in the specific implementation. Any other implementations derived by those skilled in the art based on the technical solutions of this invention are also within the scope of protection of this invention.

Claims

1. A method for constructing a high-current resonant inductor in a medium-frequency induction heating power supply, characterized in that: Includes the following steps: Step 1: Construct a volumetric model of a high-current resonant inductor; Step 2: Calculate the electrical and magnetic field characteristics based on the constructed high-current resonant inductor volume model; Step 3: Calculate the loss characteristics based on the constructed high-current resonant inductor volume model; Step 4: Calculate the loss and volume based on the electrical characteristics, magnetic field characteristics, and loss characteristics; Step 5: Parametric scanning is used to plot a scatter plot of the relationship between loss and volume to find the Pareto front of the target magnetic design.

2. The method for constructing a high-current resonant inductor for a medium-frequency induction heating power supply according to claim 1, characterized in that: In step 1, the high-current resonant inductor volume model adopts a high-power induction heating power supply topology using a voltage-type series-parallel LLC resonant circuit, wherein the wire-threaded magnetic core uses a ring-shaped open air gap structure to resist saturation. Let be the inner radius of the magnetic core. The outer radius of the magnetic core. For the depth of the magnetic core, The length of the air gap in the magnetic core. The thickness of the copper busbar is approximately [value missing], and the width of the copper busbar is approximately [value missing]. The length of the copper busbar is equal to the depth of the magnetic core, and its value is also [value missing]. The cross-sectional area of ​​the magnetic core is: ； The volume of the core of a high-current resonant inductor is: ； The overall volume of the high-current resonant inductor is: 。 3. The method for constructing a high-current resonant inductor for a medium-frequency induction heating power supply according to claim 2, characterized in that: The method for calculating the electrical characteristics in step 2 is as follows: ； in, This represents the peak flux linkage. This represents the peak current. The method for calculating magnetic field characteristics is as follows: ； in, For the sensing value, The value of free permeability is 4π × 10⁻⁶. -7 H / m.

4. The method for constructing a high-current resonant inductor for a medium-frequency induction heating power supply according to claim 1, characterized in that: The calculation method for loss characteristics in step 3 is as follows: ； ； ； in, This is the effective value of the rated current. For the exchange coefficient, This refers to the thickness of the copper busbar.

5. The method for constructing a high-current resonant inductor for a medium-frequency induction heating power supply according to claim 1, characterized in that: The loss calculation method in step 4 is as follows: by selecting the inner radius of the magnetic core. and the outer radius of the magnetic core Core length is the independent variable. for: ； in, For magnetic flux; The method for calculating magnetic loss is as follows: ； The method for calculating copper loss is as follows: ； The total loss is: ； in, , ; The method for calculating the volume of the magnetic core is as follows: ； The method for calculating the volume of an inductor is as follows: 。 6. The method for constructing a high-current resonant inductor for a medium-frequency induction heating power supply according to claim 1, characterized in that: The specific implementation method of step 5 is as follows: based on the inductor volume V and independent variable obtained in step 4... and Relationship, each group of independent variables ( , Each of these has a corresponding loss data P and volume data V. A scatter plot is drawn with volume data V on the x-axis and loss data P on the y-axis, exhaustively listing the independent variables within the specified limits. , By combining the values ​​of AC flux, a scatter plot of the relationship between loss P and inductance volume V under a fixed AC flux is plotted. By changing the value of AC flux, the PV relationship data under AC flux is obtained. Based on the PV relationship data of AC flux, a PV scatter plot under multiple AC fluxes is plotted. The envelope of the PV scatter plot is the Pareto front designed for the target inductor.

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