A design method of high-power high-frequency transformer framework using high-thermal-conductivity ceramic material

Abstract

The application provides a high-power high-frequency transformer framework design method using high-thermal-conductivity ceramic materials, the transformer comprises a primary side and a secondary side, the design method of the primary side and the secondary side is the same, and the design method of any one of the primary side and the secondary side comprises determining transformer design parameters; calculating a framework thickness minimum value wmin and setting initial values of framework geometric parameters, the framework is made of aluminum nitride material, the framework thickness minimum value wmin is calculated according to the nominal insulation strength Em of the aluminum nitride material, transformer loss is calculated; a transformer thermal circuit model is solved to calculate transformer temperature rise, and a framework design result is output.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high-power magnetic element design, and belongs to the field of electrical engineering, and particularly relates to a high-power medium-voltage high-frequency transformer framework adopting high-thermal-conductivity ceramic and a design method thereof. BACKGROUND

[0002] The transformer has the functions of electrical isolation and changing the voltage amplitude. The power electronic transformer based on the high-frequency transformer is a key device for realizing clean energy grid connection and solving the power supply demand of direct current load. With the increasing demand, the voltage level and power capacity of the high-frequency transformer have become higher and higher. The performance of the high-power medium-voltage high-frequency transformer directly determines whether the entire power electronic device can operate safely and stably, and is the core device. The limiting factor for the capacity improvement of the high-frequency transformer is the temperature rise, and the main influencing factor of the temperature rise is the transformer loss and the heat dissipation capacity of the transformer. The two factors are analyzed as follows.

[0003] The transformer loss has two types. One is the magnetic core loss, which refers to the power loss caused by the alternating or pulsating magnetic field in the magnetic material, and exists in the form of heat. The other is the winding copper loss, which refers to the copper loss caused by the current passing through the coil winding due to the existence of the ohmic resistance of the coil winding, and also exists in the form of heat. The higher the working frequency of the transformer, the more the magnetic field pulsation times in the same time, which makes the magnetic loss larger. The stronger skin effect and proximity effect caused by the high-frequency current also significantly increases the copper loss, that is, the transformer loss is proportional to the frequency. According to the Faraday's law of electromagnetic induction, the higher the frequency of the transformer, the smaller the volume of the transformer under the same capacity, which is the significance of the high-frequency transformer. The smaller the volume of the transformer, the poorer the natural heat dissipation capacity of the transformer, that is, the natural heat dissipation capacity of the transformer is inversely proportional to the frequency.

[0004] From the above analysis, for the high-power medium-voltage high-frequency transformer, firstly, compared with the same capacity power frequency transformer, the high-frequency transformer itself has the contradiction of increased iron loss and copper loss and reduced heat dissipation area, which increases the difficulty of heat dissipation; secondly, compared with the low-voltage application, the medium-voltage requires the use of a thick enough insulation material layer to ensure the insulation requirement between the coils of different potentials and the coils and the magnetic core. Based on the heat analogy theory, the thicker the insulation material layer, the higher the thermal resistance of the transformer from the inside to the outside, and the larger the temperature difference between the inside and the outside of the transformer. The above two points show that the heat cannot be effectively dissipated in the high-power medium-voltage high-frequency transformer, which further leads to high temperature rise of the transformer, and limits the further improvement of the capacity of the high-power medium-voltage high-frequency transformer. The most direct and effective way to reduce the temperature rise of the high-frequency transformer is to improve the insulation material.

[0005] Currently, the insulation of high-frequency transformers mainly relies on organic materials (such as plastics for the frame and epoxy resin for the potting material). The disadvantage of organic materials is their low thermal conductivity (only 0.2–1 W / (m·K)), which hinders the dissipation of heat from the transformer's interior. Existing technical solutions mostly focus on improving the properties of the potting material. Taking epoxy resin as an example, its thermal conductivity is typically around 0.2 W / (m·K). Improving the thermal conductivity of epoxy resin using nano- and micro-fillers has received widespread attention in recent years. Adding silica powder can increase its thermal conductivity to around 0.7 W / (m·K), and adding silica filler to the epoxy-anhydride system can increase its thermal conductivity to 1.494 W / (m·K). However, limited by the epoxy resin itself, its thermal conductivity is unlikely to exceed 1.5 W / (m·K), which is two orders of magnitude lower than the 399 W / (m·K) thermal conductivity of copper. Existing technical solutions offer limited improvement in the thermal conductivity of transformers, making it difficult to meet the heat dissipation requirements of high-power medium-voltage high-frequency transformers. Summary of the Invention

[0006] The inventors of this invention noted that the transformer bobbin, being in direct contact with the transformer's heat source (magnetic core and windings), plays a decisive role in the transformer's thermal resistance. However, existing technologies do not consider the influence of the bobbin material on the transformer's thermal conductivity. Currently, commercially available coil bobbin materials are generally made of plastic (phenolic resin) or nylon. These organic polymer materials have extremely poor thermal conductivity (not exceeding 1 W / mK), causing heat to accumulate continuously inside the transformer, leading to an increase in transformer temperature, threatening its normal operation, and limiting the improvement of transformer capacity and efficiency. Therefore, there is an urgent need for a high-voltage, high-thermal-conductivity, high-power transformer bobbin to improve the insulation and heat dissipation capabilities of high-power medium-voltage high-frequency transformers.

[0007] To address this challenge, this invention proposes a high-voltage-resistance, high-thermal-conductivity aluminum nitride ceramic skeleton for high-power medium-voltage high-frequency transformers, and also presents a design method for the aluminum nitride skeleton.

[0008] To address the shortcomings of existing technologies, this invention proposes a high-voltage, high-thermal-conductivity aluminum nitride ceramic frame for high-power medium-voltage high-frequency transformers, and presents a design method for the frame based on transformer losses and thermal circuit models. The designed frame utilizes a novel aluminum nitride ceramic material, which possesses a very high thermal conductivity (200 W / mK), approaching that of aluminum alloys; excellent insulation properties, exceeding those of ordinary insulating plastics; a low coefficient of thermal expansion; and high mechanical strength, enabling normal operation even under harsh conditions. Therefore, the transformer frame made of aluminum nitride ceramic material not only withstands high voltage but also rapidly conducts heat generated by the transformer coils and core to an external heat sink, aiding in transformer cooling and effectively solving the insulation and heat dissipation problems of transformers.

[0009] To achieve the above object, the present application provides the following technical solutions.

[0010] Specifically, the present application provides a design method of a high-power high-frequency transformer framework made of high-thermal-conductivity ceramic material, the transformer comprising a primary side and a secondary side, the design method of the primary side and the secondary side being the same, and characterized in that the design method of any one of the primary side and the secondary side comprises:

[0011] Step 1, determining transformer design parameters;

[0012] Step 2, calculating a minimum value wmin of the framework thickness and setting initial values of framework geometric parameters, the framework being made of aluminum nitride material, and the minimum value wmin of the framework thickness being calculated according to a nominal insulation strength Em of the aluminum nitride material:

[0013]

[0014] In the formula, U1 is the amplitude of the side voltage, and k is an insulation safety factor;

[0015] Step 3, calculating transformer loss;

[0016] Step 4, solving a thermal model of the transformer to calculate transformer temperature rise and output framework design results.

[0017] Preferably, the transformer design parameters comprise the amplitude U1 of the primary side voltage, the nominal insulation strength Em of the aluminum nitride material, the insulation safety factor k, the working frequency f, the magnetic flux waveform coefficient Feq, the magnetic core volume Vcore, the maximum working magnetic density of the magnetic core and the Steinmetz equation coefficients k, α, β, the winding turns N1, N2 of the primary side and the secondary side, the electrical conductivity σ and the magnetic permeability μ of copper, the diameter dr of the circular wire, the thickness w0 of the wire insulation layer, the center distance t of adjacent circular wires, the current waveform of the primary side and the secondary side winding, and the temperature rise limit Tmax.

[0018] Preferably, the set initial values of the framework geometric parameters comprise the thickness of the inner sleeve of the framework and the thickness w1 of the circular ring base, and the initial surface area A0 of the outer sleeve heat dissipation teeth.

[0019] Preferably, the transformer loss comprises the magnetic core iron loss P Fe and the winding copper loss P Cu,pri .

[0020] Preferably, the calculation process of the magnetic core iron loss P Fe comprises: calculating the iron loss Pv of the unit volume of the magnetic core, and the independent variables for the calculation are the working frequency f, the maximum working magnetic density Bm, and the Steinmetz equation coefficients k, α, β, the magnetic flux waveform coefficient Feq, and the calculation formula is as follows:

[0021]

[0022] Secondly, total core iron loss P is calculated Fe The independent variables of the calculation are core unit volume iron loss Pv and core volume Vcore, and the calculation formula is as follows:

[0023] P Fe = P v · V core

[0024] Preferably, the calculation process of copper loss P Cu,pri includes: the alternating current resistance coefficient when the frequency is f is calculated as follows:

[0025]

[0026] Wherein:

[0027]

[0028] In the formula, m is the number of winding layers, dr is the diameter of the winding round wire, t is the distance between the centers of adjacent round wires, σ is the electrical conductivity of copper, μ is the magnetic permeability of copper, ber and bei are the real part and imaginary part of the first kind 0 order Bessel function respectively, subscript 2 represents the second order, and superscript'represents derivation, and the expression of the winding copper loss PCu is as follows:

[0029]

[0030] In the formula: the alternating current resistance is embodied by the alternating current resistance coefficient, Fr,n represents the alternating current resistance coefficient of the nth harmonic current; Rdc is the direct current resistance at the operating temperature of the winding; Irms,n represents the effective value of the nth harmonic current component of the primary side.

[0031] Preferably, the process of solving the thermal circuit model of the transformer in step 4 includes:

[0032] The conduction thermal resistance is calculated, and the calculation formula of the conduction thermal resistance is as follows:

[0033]

[0034] In the formula, l represents the length of the heat flow path, S represents the cross-sectional area perpendicular to the heat flow direction, λ represents the thermal conductivity of the material,

[0035] The convection thermal resistance is calculated, and the calculation formula of the convection thermal resistance is as follows:

[0036]

[0037] In the formula, h is the convective heat transfer coefficient, A is the surface area in contact with the air, ΔT is the temperature difference of the two thermal convection,

[0038] The radiation thermal resistance is calculated, and the calculation formula of the radiation thermal resistance is as follows:

[0039]

[0040] In the formula, ε is the emissivity of the material, A is the effective area for thermal radiation, and T1 and T0 are the temperatures of the two sides of the thermal radiation, respectively.

[0041] Based on the obtained equivalent thermal circuit model and the magnitude of thermal resistance, the temperature rise at various points of the high-frequency transformer is calculated using the following set of equations:

[0042]

[0043] Solving this system of equations will yield the temperatures Tcore and T0 of the transformer core and primary winding. Cu,pri If the transformer temperature rise is too high and does not meet the temperature rise limit Tmax, then increase the surface area A0 of the heat dissipation teeth of the outer cylindrical sleeve to reduce the convective and radiative thermal resistance R between the outer cylindrical sleeve and the air. bobo,cv R bobo,rad The thermal circuit model is then resolved, and this process is iterated until an A0 is found that makes the transformer temperature rise less than Tmax. The skeleton design parameters at this point are recorded, and the skeleton design results are output.

[0044] The thermal circuit model includes: the first conductive thermal resistance R of the insulating potting compound between the magnetic core and the inner cylindrical sleeve of the frame. resini,cd The second conductive thermal resistance R of the inner cylindrical sleeve of the skeleton bobi,cd The first and second convective and radiative thermal resistance R between the circular base on the frame and the air. bobu,cv R bobu,rad The third and fourth convection and radiation thermal resistance R between the lower circular base of the skeleton and the air bobd,cv R bobd,rad The third conductive thermal resistance R of the insulating potting compound between the inner and outer cylindrical sleeves of the skeleton resino,cd The fourth conductive thermal resistance R of the outer cylindrical sleeve of the skeleton bobo,cd The fifth and sixth convection and radiation thermal resistance R between the outer cylindrical sleeve of the skeleton and the air bobo,cv R bobo,rad The fifth and sixth convective and radiative thermal resistances R bobo,cv R bobo,rad Parallel connection with the fourth thermal resistance R bobo,cd and the third thermal resistance R resino,cd The first thermal resistance branch is formed by connecting the first and second convection and radiation thermal resistances R. bobu,cv R bobu,rad The third and fourth convective and radiative thermal resistances R bobd,cv R bobd,rad After being connected in parallel, they are connected to the second thermal resistance R. bobi,cd A second thermal resistance branch is formed by connecting them in series. The branch with lower thermal resistance is connected in parallel with the second thermal resistance branch and connected to T. amb With T Cu,priBetween.

[0045] Preferably, the primary side skeleton and the secondary side skeleton have the same structure, and each comprises an inner and outer cylindrical sleeve and a circular ring base at the upper and lower ends; the inner diameter of the cylindrical sleeve of the primary side skeleton and the secondary side skeleton is larger than the diameter of the magnetic core column, and the outer diameter of the cylindrical sleeve is larger than the outer diameter of the circular ring base of the skeleton; the magnetic core column is arranged in the inner cylindrical sleeve of the primary side skeleton and the secondary side skeleton respectively, the primary side winding and the secondary side winding are wound on the primary side skeleton and the secondary side skeleton respectively, the two outer cylindrical sleeves are sleeved on the primary side skeleton and the secondary side skeleton respectively, and the gap between the inner cylindrical sleeve of the skeleton and the magnetic core column and the gap between the coil winding and the outer cylindrical sleeve are filled with high-thermal-conductivity insulating glue.

[0046] Principle

[0047] The skeleton design method of the present application firstly calculates the minimum thickness of the skeleton according to the insulation requirement, then based on the thermoelectric analogy theory, the transformer heat source and thermal resistance are solved according to the transformer loss model and the thermal model, and then the transformer temperature rise is solved, if the temperature rise is not within the allowable range, the transformer skeleton parameters are changed and the transformer thermal model is solved again, until the transformer temperature rise is within the allowable range, and the skeleton design parameters at this time are recorded as the skeleton design result output.

[0048] The outer cylindrical wall of the outer cylindrical sleeve is provided with heat dissipation teeth, so as to increase the contact area with air and improve the heat dissipation capacity.

[0049] The inner cylindrical sleeve of the primary side skeleton and the secondary side skeleton has a spiral groove on the outer side, so that the winding wire can be tightly wound on the skeleton, and the contact area between the coil and the skeleton can be increased to reduce the thermal resistance between the coil and the skeleton, facilitating winding and facilitating heat conduction.

[0050] The skeleton adopts aluminum nitride ceramic material, the heat generated by the magnetic core loss is mainly conducted to the circular ring base through the aluminum nitride skeleton for heat dissipation, and the heat generated by the coil winding is conducted to the circular ring base through the aluminum nitride skeleton for heat dissipation on one hand, and is conducted to the outer sleeve through the high-thermal-conductivity heat-conducting insulating glue for heat dissipation on the other hand.

[0051] Compared with the prior art, the present application has the following advantages:

[0052] (1) The present application is used for high-power transformers, and the heat generated by the high-power transformers is transmitted to the outside and contacted with air through the heat-conducting skeleton, so that the heat is dissipated, the aluminum nitride ceramic material has high insulation resistance, high temperature resistance, high thermal conductivity, and is a non-metallic material, and will not generate eddy current in the magnetic field, which is a revolution of the previous plastic skeleton, improves the heat dissipation capacity of the system, and improves the thermal stability of the system.

[0053] (2) The transformer skeleton design method provided by the application is based on a loss and thermal path analysis model, fully considers the heat source size inside the transformer and the heat conduction path inside the transformer, has high precision and fast calculation speed, and has practical value in high-power transformer skeleton design.

[0054] (3) The skeleton of the application adopts aluminum nitride ceramic material, which can still operate safely, reliably and stably under high-voltage working conditions, and greatly improves the insulation capacity of the transformer.

[0055] (4) The inner cylindrical sleeve of the primary and secondary skeleton has spiral grooves on the outer side, which facilitates winding and also increases the contact area of the wire and the sleeve and enhances the heat dissipation capacity. BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1 is a schematic diagram of the shape of the UY42 magnetic core in the embodiments of the application.

[0057] Figure 2 is a vertical sectional structure schematic diagram of the inner cylindrical sleeve and the upper and lower ring bases.

[0058] Figure 3 is a structure schematic diagram of the inner cylindrical sleeve and the upper and lower ring bases.

[0059] Figure 4 is a structure schematic diagram of the outer cylindrical sleeve.

[0060] Figure 5 is a schematic diagram of the overall structure of the transformer assembled with the skeleton.

[0061] Figure 6 is a flowchart of the transformer skeleton design method.

[0062] Figure 7 is the thermal conduction path and thermal path model of the primary side region.

[0063] Figure 8 、 Figure 9 The results of modeling and simulation of the primary winding are shown, and since the primary and secondary windings are independent of each other, only the primary winding is simulated and introduced here. DETAILED DESCRIPTION

[0064] The technical solutions of the application will be described in more detail below with reference to the accompanying drawings.

[0065] In order to more specifically describe the application, the technical solutions of the application and their related principles will be described in detail below with reference to the accompanying drawings and specific implementation schemes.

[0066] The large-capacity medium-voltage high-frequency transformer skeleton of the present embodiment is used on a UY-type magnetic core with a model of UY42, and the shape of the magnetic core is asFigure 1 as shown.

[0067] The transformer skeleton adopts aluminum nitride ceramic material with high heat conduction and high insulation performance, and includes a primary side skeleton and a secondary side skeleton, both of which have the same structure and include inner and outer cylindrical sleeves and upper and lower ring bases. The outer cylindrical wall of the inner cylindrical sleeve has a spiral groove, so that the winding wire can be tightly wound on the skeleton, and the contact area between the coil and the skeleton can be increased to reduce the thermal resistance between the coil and the skeleton. The vertical sectional view of the inner cylindrical sleeve and the upper and lower ring bases is as shown in Figure 2 , the cross section of the groove on the outer cylindrical wall of the inner cylindrical sleeve is a semicircle with the same radius as that of the wire, which ensures that the wire can be clamped into the groove while maximizing the contact area between the wire and the skeleton. The appearance of the inner cylindrical sleeve and the upper and lower ring bases is as shown in Figure 3 .

[0068] The inner diameter of the inner cylindrical sleeve of the primary and secondary side skeletons is greater than the diameter of the magnetic core column, and the outer diameter of the outer cylindrical sleeve is greater than the outer diameter of the ring base; the magnetic core column is arranged in the cylindrical sleeve of the primary and secondary side skeletons, and the primary and secondary side windings are wound on the primary and secondary side skeletons, respectively; the two outer sleeves are sleeved on the primary and secondary side skeletons, respectively, and the outer cylindrical wall of the outer cylindrical sleeve has heat dissipation teeth, and the structure of the outer cylindrical sleeve is as shown in Figure 4 , the heat dissipation teeth can increase the contact area between the outer sleeve and the air, effectively improving the heat dissipation capacity.

[0069] In this embodiment, the primary and secondary side windings are wound on the two side columns of the magnetic core, respectively, and the overall structure of the transformer assembled with the skeleton is as shown in Figure 5 .

[0070] Since the primary and secondary side skeletons and the windings are arranged on the two side columns of the magnetic core, respectively, the primary and secondary side skeletons do not affect each other, and can be designed independently. This embodiment takes the primary side skeleton as an example to introduce the design method, and the design method of the secondary side skeleton is the same, which will not be described here. The design method of the transformer skeleton is as shown in Figure 6 , including determining the design parameters of the transformer, calculating the minimum thickness wmin of the skeleton and setting the initial value of the geometric parameters of the skeleton, calculating the transformer loss, solving the thermal model of the transformer to calculate the temperature rise of the transformer, and outputting the design result of the skeleton.

[0071] The specific steps are as follows:

[0072] The transformer design parameters include the primary voltage amplitude U1, the nominal insulation strength Em of the aluminum nitride material, the insulation safety factor k, the working frequency f, the magnetic flux waveform coefficient Feq, the core volume Vcore, the maximum working magnetic density of the core, and the Steinmetz equation coefficients k, a, and b, the primary and secondary winding turns N1 and N2, the conductivity s and permeability m of copper, the circular wire diameter dr, the wire insulation layer thickness w0, the distance t between the centers of adjacent circular wires, the primary and secondary winding current waveforms, and the temperature rise limit Tmax.

[0073] The initial values of the skeleton geometry parameters include the inner sleeve thickness and the circular ring base thickness w1 of the skeleton, and the initial surface area A0 of the outer sleeve heat dissipation teeth. The minimum thickness wmin of the skeleton is calculated according to the nominal insulation strength Em of the aluminum nitride material:

[0074]

[0075] In the formula, U1 is the amplitude of the primary voltage, k is the insulation safety factor, which is a number less than 1, and the inner sleeve thickness and the circular ring base thickness w1 of the skeleton can be set to wmin accordingly.

[0076] The transformer losses are calculated, including the core iron loss P Fe and the winding copper loss P Cu,pri .

[0077] First, the core iron loss per unit volume Pv is calculated, and the independent variables for the calculation are the working frequency f, the maximum working magnetic density Bm, and the Steinmetz equation coefficients k, a, and b, as well as the magnetic flux waveform coefficient Feq. The calculation formula is as follows:

[0078]

[0079] Second, the total core iron loss P Fe is calculated, and the independent variables for the calculation are the core iron loss per unit volume Pv and the core volume Vcore. The calculation formula is as follows:

[0080] P Fe = P v · V core

[0081] Third, the primary winding copper loss P Cu,pri is calculated. In practical applications, the current flowing through the high-frequency transformer is often non-standard sinusoidal, and the winding current waveform should be Fourier decomposed to obtain the effective value of the current component at each frequency, and then the AC resistance of the winding at each harmonic frequency is calculated. The AC resistance coefficient at frequency f is calculated as follows:

[0082]

[0083] Where:

[0084]

[0085] where m is the number of winding layers, dr is the diameter of the winding round wire, t is the center distance of adjacent round wires, σ is the electrical conductivity of copper, μ is the magnetic permeability of copper, ber and bei are the real part and imaginary part of the 0th order Bessel function of the first kind, subscript 2 represents the second order, and superscript'represents derivation. Finally, the copper loss PCu of the winding can be obtained as follows:

[0086]

[0087] where the AC resistance is represented by the AC resistance coefficient, Fr,n represents the AC resistance coefficient of the nth harmonic current, Rdc is the DC resistance at the operating temperature of the winding, and Irms,n represents the effective value of the nth harmonic current component of the primary side.

[0088] Solving the thermal circuit model of the transformer. The heat conduction path and the thermal circuit model of the primary side region are shown in Figure 7 The meanings of the thermal resistances in the thermal circuit model are as follows: the conduction thermal resistance of the insulating pouring glue between the magnetic core and the inner cylindrical sleeve of the skeleton R resini,cd , the conduction thermal resistance of the inner cylindrical sleeve of the skeleton R bobi,cd , the convection and radiation thermal resistance between the upper circular base of the skeleton and the air R bobu,cv , R bobu,rad , the convection and radiation thermal resistance between the lower circular base of the skeleton and the air R bobd,cv , R bobd,rad , the conduction thermal resistance of the insulating pouring glue between the inner and outer cylindrical sleeves of the skeleton R resino,cd , the conduction thermal resistance of the outer cylindrical sleeve of the skeleton R bobo,cd , and the convection and radiation thermal resistance between the outer cylindrical sleeve of the skeleton and the air R bobo,cv , R bobo,rad .

[0089] P cu,pri represents the copper loss of the primary side winding, P Fe / 2 represents one half of the iron loss, because the magnetic core has two core columns and the primary side winding is only wound on one core column, so there is only one half of the iron loss. P cu,pri , P Fe / 2 are understood as current sources in the circuit, T amb represents the ambient temperature and is understood as a voltage source in the circuit, and R represents the thermal resistance and is understood as a resistance in the circuit.

[0090] The calculation formula of the conduction thermal resistance is as follows:

[0091]

[0092] where l represents the length of the heat flow path, S represents the cross-sectional area perpendicular to the heat flow direction, and λ represents the thermal conductivity of the material.

[0093] The calculation formula of the convection thermal resistance is as follows:

[0094]

[0095] In the formula, h is the convection heat transfer coefficient, A is the surface area in contact with air, and ΔT is the temperature difference of both heat convection.

[0096] The calculation formula of the radiation thermal resistance is as follows:

[0097]

[0098] In the formula, ε is the radiation coefficient of the material, A is the effective area of heat radiation, T1 and T0 are the temperatures of both heat radiation, respectively.

[0099] According to the equivalent thermal circuit model obtained and the thermal resistance size, the node voltage method and Kirchhoff's current law in the circuit theory are used to calculate the temperature rise of each part of the high-frequency transformer. Figure 7 The following equation group can be obtained:

[0100]

[0101] Solving the equation group can obtain the temperatures Tcore and T1 of the transformer magnetic core and the primary winding. Cu,pri If the temperature rise of the transformer is too high and does not meet the temperature rise limit Tmax, the surface area A0 of the outer cylindrical sleeve heat dissipation tooth is increased to reduce the convection and radiation thermal resistances Rconv and Rrad between the outer cylindrical sleeve of the framework and air. bobo,cv bobo,rad The thermal circuit model is solved again, and the iteration is performed until the temperature rise of the transformer is less than Tmax, and the framework design parameters at this time are recorded, and the framework design result is output.

[0102] The simulation process of the method of the application can be simulated in simulation software, for example, simulation and emulation can be performed in ANSYS software.

[0103] To verify the effectiveness of the transformer heat dissipation designed by the method of the application, first, the framework geometric parameters are designed according to the above framework design method, so that the temperature rise of the transformer does not exceed 70K when the framework material is aluminum nitride, and a three-dimensional thermal simulation model is built on the finite element simulation software according to the design result, as shown in Fig. Figure 8 Figure 9 (a) is the temperature distribution diagram of the transformer when the framework material is nylon, and the temperature on the winding is the highest, which is 207℃. Figure 9 ​​(b) is a temperature distribution diagram of the transformer with the skeleton material being aluminum nitride, and the temperature on the winding of the two is the same skeleton geometry parameter, and the highest temperature is 99 DEG C. By comparison, it can be found that the transformer designed by the method of the application, especially the transformer with the aluminum nitride ceramic skeleton, has a significant heat dissipation effect, greatly reduces the hot spot temperature of the transformer, and increases the thermal stability of the high-frequency transformer.

Claims

1. A design method of a high-power high-frequency transformer frame using a high-thermal-conductivity ceramic material, the transformer frame including a primary side and a secondary side, the design method of the primary side and the secondary side being the same, characterized in that, The design method of any one of the primary side and the secondary side comprises: Step 1, determining transformer design parameters; Step 2, calculating skeleton thickness minimum value w min And setting the initial value of skeleton geometry parameters, the skeleton is made of aluminum nitride material, and the skeleton thickness minimum value w min According to the nominal insulation strength Em of the aluminum nitride material: ， In the formula, U1 is the amplitude of the side voltage, and k is an insulation safety factor; Step 3, calculating transformer loss, The transformer loss includes core iron loss P Fe and winding copper loss P Cu,pri The core iron loss P Fe The calculation process includes: calculating the core unit volume iron loss P v The calculated independent variables are working frequency f, maximum working magnetic density B m and Steinmetz equation coefficients k, α, β, magnetic flux waveform coefficient F eq The calculation formula is as follows: ， Secondly, the total magnetic core iron loss P is calculated Fe The independent variables for the calculation are the iron loss P of the magnetic core per unit volume v and the volume V of the magnetic core core The calculation formula is as follows: ， Copper loss P Cu,pri The calculation process includes: calculating the AC resistance coefficient at a frequency of f as follows: ， Wherein: ， where m is the number of winding layers, dr is the diameter of the winding round wire, t is the center distance of adjacent round wires, σ is the electrical conductivity of copper, μ is the magnetic permeability of copper, ber and bei are the real part and the imaginary part of the 0th order Bessel function of the first kind, respectively, subscript 2 represents the second order, and superscript'represents derivation, to obtain the winding copper loss P Cu,pri The expression is as follows: ， wherein the AC resistance is represented by the AC resistance coefficient, F r,n represents the AC resistance coefficient of the nth harmonic current; R dc is the DC resistance at the winding operating temperature; I rms,n represents the effective value of the nth harmonic current component of the primary side, step 4, solving the transformer thermal circuit model to calculate the transformer temperature rise, outputting the skeleton design result, the process of solving the transformer thermal circuit model in step 4 includes: The calculation formula of the conduction thermal resistance is as follows: ， In the formula, l represents the length of the heat flow path, S represents the cross-sectional area perpendicular to the heat flow direction, and λ represents the thermal conductivity of the material, The calculation formula of the convection thermal resistance is as follows: ， In the formula, h is the convection heat transfer coefficient, A is the surface area in contact with the air, and ΔT is the temperature difference of the two sides of the heat convection, The calculation formula of the radiation thermal resistance is as follows: ， In the formula, ε is the radiation coefficient of the material, A is the effective area of the heat radiation, T1 and T0 are the temperatures of the two sides of the heat radiation respectively, According to the equivalent thermal circuit model obtained and the thermal resistance size, the temperature rise of the high-frequency transformer at each place is calculated as follows: ， Solving the equation set can obtain the temperature T of the transformer core and the primary winding core , Cu,pri If the temperature rise of the transformer is too high, the temperature rise limit T max is not met, the surface area A0 of the outer cylindrical sleeve heat dissipation teeth is increased to reduce the convective and radiative thermal resistance R bobo,cv , bobo,rad between the skeleton outer cylindrical sleeve and the air, and the thermal circuit model is solved again, and the iteration is continued until the A0 that makes the temperature rise of the transformer less than T max is found, and the skeleton design parameters at this time are recorded, and the skeleton design result is output, The thermal circuit model includes: the first conductive thermal resistance R of the insulating potting compound between the magnetic core and the inner cylindrical sleeve of the frame. resini,cd The second conductive thermal resistance R of the inner cylindrical sleeve of the skeleton bobi,cd The first and second convective and radiative thermal resistance R between the circular base on the frame and the air. bobu,cv R bobu,rad The third and fourth convection and radiation thermal resistance R between the lower circular base of the skeleton and the air bobd,cv R bobd,rad The third conductive thermal resistance R of the insulating potting compound between the inner and outer cylindrical sleeves of the skeleton resino,cd The fourth conductive thermal resistance R of the outer cylindrical sleeve of the skeleton bobo,cd The fifth and sixth convection and radiation thermal resistance R between the outer cylindrical sleeve of the skeleton and the air bobo,cv R bobo,rad The fifth and sixth convective and radiative thermal resistances R bobo,cv R bobo,rad Parallel connection with the fourth thermal resistance R bobo,cd and the third thermal resistance R resino,cd The first thermal resistance branch is formed by connecting the first and second convection and radiation thermal resistances R. bobu,cv R bobu,rad The third and fourth convective and radiative thermal resistances R bobd,cv R bobd,rad After being connected in parallel, they are connected to the second thermal resistance R. bobi,cd A second thermal resistance branch is formed by connecting them in series. The branch with lower thermal resistance is connected in parallel with the second thermal resistance branch and connected to T. amb With T Cu,pri between.

2. The design method of the high-power high-frequency transformer skeleton according to claim 1, characterized in that, The transformer design parameters include the primary voltage amplitude U1, the nominal insulation strength Em of the aluminum nitride material, the insulation safety factor k, the operating frequency f, the magnetic flux waveform coefficient Feq, and the core volume V. core The maximum operating magnetic flux density of the magnetic core and the coefficients k, α, β of the Steinmetz equation, the number of turns N1 and N2 of the primary and secondary windings, the conductivity σ and permeability μ of copper, the diameter dr of the round conductor, the thickness w0 of the conductor insulation layer, the center distance t between adjacent round conductors, the current waveforms of the primary and secondary windings, and the temperature rise limit T. max .

3. The design method of the high-power high-frequency transformer skeleton according to claim 1, characterized in that, The set initial values of the skeleton geometric parameters include the thickness of the inner sleeve of the skeleton and the thickness of the circular ring base w1, and the initial surface area A0 of the outer sleeve heat dissipation tooth.

4. The high-power high-frequency transformer skeleton design method according to claim 1, characterized in that, The primary side skeleton and the secondary side skeleton are the same in structure and each comprises an inner and outer cylindrical sleeve and a circular ring base at the upper and lower ends; the inner diameter of the cylindrical sleeve of the primary side skeleton and the secondary side skeleton is greater than the diameter of the magnetic core column, and the outer diameter of the outer sleeve is greater than the outer diameter of the circular ring base of the skeleton; the magnetic core column is arranged in the inner cylindrical sleeve of the primary side skeleton and the secondary side skeleton respectively, the primary side winding and the secondary side winding are wound on the primary side skeleton and the secondary side skeleton respectively, the two outer cylindrical sleeves are respectively sleeved on the primary side skeleton and the secondary side skeleton, and high-thermal-conductivity insulation glue is filled in the gap between the inner cylindrical sleeve of the skeleton and the magnetic core column and between the coil winding and the outer cylindrical sleeve.

5. A transformer skeleton designed by the method according to any one of claims 1-4.

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