Optimization design method and device for high-frequency transformer

Abstract

The invention provides an optimal design method and device for a high-frequency transformer, and belongs to the field of high-frequency transformers. The method comprises the following steps: obtaining the value range of each design parameter of the high-frequency transformer to obtain a plurality of design schemes; under a preset constraint condition, performing multi-objective optimization on the decision variables corresponding to the plurality of design schemes to obtain optimized values of the decision variables; taking the design scheme corresponding to the optimized value of the decision variable as a target design scheme of the high-frequency transformer; wherein objective functions in the multi-objective optimization process comprise a first objective function, a second objective function and a third objective function; the first objective function is determined based on the magnetic core loss and the total loss of the litz wire winding; the second objective function is determined based on the volume of the high-frequency transformer; the third objective function is determined based on the leakage inductance value of the high-frequency transformer. According to the method, global optimization of loss, parasitic parameters, insulation design and maximum temperature rise of the high-frequency transformer can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of high-frequency transformers, and in particular to an optimization design method and device for a high-frequency transformer. Background Art

[0002] With the proposal of the "dual carbon" goal, the development of a new power system with new energy as the main body has become an inevitable trend. The access to the DC grid provides an efficient and reliable technical means to achieve the development goals of the new energy power system. Among them, the power electronic transformer (PET), which combines transformer design theory, circuit control technology and modern power electronics technology, has become the hub of DC conversion and has broad application prospects in the fields of medium and low voltage DC power distribution, electrification transportation and new energy power transmission. As the core component of the power electronic transformer, the high frequency transformer (HFT), in addition to the transformer, isolation and power transfer functions of the traditional transformer, can also cooperate with the converter to achieve power flow control and power quality regulation. Under high frequency conditions, the high frequency transformer can minimize the weight and volume of magnetic components, greatly improve the power density and efficiency, and has significant advantages in performance efficiency, manufacturing cost and installation conditions.

[0003] Although high-frequency transformers have many advantages, it is not easy to achieve high power density and high-efficiency and reliable operation in a small volume. It also brings severe challenges to accurately evaluate the transformer's loss, insulation, temperature rise, parasitic parameters and other indicators. The main performance of high-frequency transformers is: under high-frequency conditions, the eddy current loss in the core and winding will increase significantly, resulting in increased core and winding losses; parasitic parameters such as leakage inductance derived from high-frequency working conditions will cause electromagnetic interference to the external circuit and other problems, deteriorating the working characteristics of the electronic circuit; the compact structure reduces the spatial distance between the core and the winding, which threatens the insulation safety of the transformer on the one hand, and the reduction in heat dissipation area makes temperature rise evaluation more difficult on the other hand. In addition, since the optimization between each design goal is closely related to the electrical indicators and structural parameters, the design goals not only affect each other, but also conflict with each other, and it is difficult to achieve the optimal at the same time. Therefore, the design of high-frequency transformers is a multi-objective optimization problem that requires coordination of the relationship between various parameters.

[0004] At present, most of the designs of high-frequency transformers only aim to reduce or increase a certain parameter, with a relatively simple optimization goal, few constraints, and no specific control scheme, which has great limitations. For example, Swiss researcher Asier Garcia proposed an optimization design scheme for ferrite core high-frequency transformers based on genetic algorithms. However, this scheme only establishes the relationship between loss and temperature rise through a simple empirical formula, making it difficult to analyze and predict the temperature rise in detail and accurately. Researchers at the Swiss Federal Institute of Technology in Zurich also used genetic algorithms to propose a design method for a 25kW, 4kHz high-frequency transformer, but did not consider the insulation scheme of each part of the transformer. The team from Nanyang Technological University in Singapore used total loss, core size, and maximum temperature rise as optimization goals in the design process of high-frequency transformers, and assigned different weights, but did not give a theoretical explanation of the weight coefficient. Based on the intelligent optimization algorithm, the Chen Wu team from Southeast University established an optimization design scheme for a high-frequency transformer with a power of 3.52kW and 20kHz, and verified the correctness and effectiveness of the core loss prediction under non-sinusoidal excitation, but the scheme did not include the temperature rise constraint model of the transformer, so there may be certain defects in heat dissipation and reliability.

[0005] It can be seen that the significant eddy current effect and complex and compact structural layout of transformers under high-frequency conditions make it difficult to accurately analyze their electro-magnetic-thermal characteristics. In addition, multiple optimization objectives in the transformer conflict with each other and are difficult to balance, which brings severe challenges to the design and manufacture of high-frequency transformers. Summary of the invention

[0006] The embodiments of the present invention provide a method and device for optimizing the design of a high-frequency transformer, so as to solve the problem that there are limitations in the design of a high-frequency transformer at this stage.

[0007] In a first aspect, an embodiment of the present invention provides an optimization design method for a high-frequency transformer, comprising: Obtaining the value range of each design parameter of the high-frequency transformer to obtain multiple design solutions; Under the preset constraints, multi-objective optimization is performed on the decision variables corresponding to multiple design schemes to obtain the optimized values ​​of the decision variables; The design scheme corresponding to the optimized value of the decision variable is used as the target design scheme of the high-frequency transformer; Among them, the objective functions in the multi-objective optimization process include a first objective function, a second objective function and a third objective function; the first objective function is determined based on the core loss and the total loss of the Litz wire winding; the second objective function is determined based on the volume of the high-frequency transformer; and the third objective function is determined based on the leakage inductance value of the high-frequency transformer.

[0008] In a possible implementation, the first objective function is:

[0009] in, P out is the output power of the high-frequency transformer; P c is the core loss; P w is the total loss of the Litz wire winding.

[0010] In one possible implementation, the total loss of the Litz wire winding is determined according to the following formula:

[0011] in, n For the n Subharmonics; I n It is n The effective value of subharmonic current; R wn For the n AC resistance value under subharmonic; R wdc is the DC resistance value of the Litz wire winding; F Rn For the n Normalized AC resistance value under subharmonic current; m is the number of winding layers; k is the number of strands in the Litz wire; Δ str is the relative skin depth at the fundamental frequency δ w The normalized thickness value of .

[0012] In a possible implementation, the second objective function is:

[0013] in, V T is the volume of the high frequency transformer.

[0014] In a possible implementation, the third objective function is:

[0015] in, L σ ’ To meet the target leakage inductance value required by the circuit design; L σ is the leakage inductance of the high-frequency transformer.

[0016] In one possible implementation, the decision variables include the maximum current density in the winding, the number of turns per layer of the secondary winding, the number of pairs of magnetic core stacking blocks, the magnetic core thickness, the maximum magnetic flux density, the number of primary winding layers, and the number of secondary winding layers.

[0017] In a possible implementation manner, the preset constraints include decision variable constraints, temperature rise constraints, insulation distance constraints, and leakage inductance constraints.

[0018] In a possible implementation, the insulation distance constraint condition includes a leakage inductance channel length constraint condition; The length of the leakage inductance channel is calculated according to the following formula:

[0019]

[0020]

[0021]

[0022] in, k 1 , k 2 , k 3 is the calculation parameter; d ins_int1 is the thickness of the insulation layer on the outside of the winding; d ins_int2 is the thickness of the insulation layer on the outside of the winding; μ 0 is the vacuum permeability; l is the length of the winding; N l The number of turns per winding layer; I 1 and I 2 are the current values ​​flowing through the primary and secondary windings respectively; m is the number of winding layers; h w is the height of the winding; is the leakage magnetic energy of all straight line areas except the leakage inductance channel area; It is the leakage magnetic energy of all arc areas except the leakage inductance channel area.

[0023] In a possible implementation, under preset constraints, multi-objective optimization is performed on decision variables corresponding to multiple design solutions to obtain optimized values ​​of the decision variables, including: The multi-objective genetic algorithm NSGA-II is used to perform multi-objective optimization on the decision variables corresponding to multiple design schemes under preset constraints to obtain the optimized values ​​of the decision variables.

[0024] In a second aspect, an embodiment of the present invention provides an optimization design device for a high-frequency transformer, comprising: An acquisition module is used to obtain the value range of various design parameters of the high-frequency transformer to obtain multiple design solutions; An optimization module is used to perform multi-objective optimization on the decision variables corresponding to multiple design schemes under preset constraints to obtain the optimized values ​​of the decision variables; A design module, used for taking a design scheme corresponding to an optimized value of a decision variable as a target design scheme for a high-frequency transformer; Among them, the objective functions in the multi-objective optimization process include a first objective function, a second objective function and a third objective function; the first objective function is determined based on the core loss and the total loss of the Litz wire winding; the second objective function is determined based on the volume of the high-frequency transformer; and the third objective function is determined based on the leakage inductance value of the high-frequency transformer.

[0025] The embodiment of the present invention provides an optimization design method and device for a high-frequency transformer. Considering that the control scheme in the design scheme of the high-frequency transformer at this stage is unclear, only one parameter is reduced or increased, and the optimization target is relatively single, the embodiment of the present invention takes the core loss, the total loss of the Litz wire winding and the leakage magnetic energy as the optimization target, and considering that too many decision variables and how large the search range will lead to too long optimization time and increased calculation cost, too few decision variables will make it difficult to find the optimal result. Therefore, the embodiment of the present invention takes the maximum current density in the winding, the number of turns per layer of the secondary winding, the number of pairs of magnetic core stacking blocks, the thickness of the magnetic core, the maximum magnetic flux density, the number of primary winding layers and the number of secondary winding layers as decision variables. In addition, although the high-frequency condition can effectively reduce the volume and weight of the transformer, it will cause its heat dissipation area to be greatly reduced, and the heat is difficult to dissipate quickly, causing serious temperature rise. At the same time, in order to improve the probability of selecting the best in the optimization design process and avoid unreasonable design, the embodiment of the present invention takes the decision variable constraint condition, the temperature rise constraint condition, the insulation distance constraint condition and the leakage inductance value constraint condition as the constraint condition, and adds the optimization parameter to make the design of the high-frequency transformer more reasonable. It can be seen that the embodiments of the present invention can coordinate the relationship between various parameters, so that the optimization objectives considered during the design of the high-frequency transformer are more comprehensive, and global optimization of the high-frequency transformer loss, parasitic parameters, insulation design and maximum temperature rise can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 is a flow chart of an implementation of an optimization design method for a high-frequency transformer provided by an embodiment of the present invention; Figure 2 is a target optimization flow chart of the optimization design method of the high-frequency transformer provided by an embodiment of the present invention; Figure 3 It is a schematic diagram of a preset structure and parameters of a high-frequency transformer in the high-frequency transformer optimization design method provided by an embodiment of the present invention; Figure 4 It is a schematic diagram of non-sinusoidal voltage excitation and magnetic flux density waveform; Figure 5A-5C is the current density distribution diagram in different types of windings; Figure 6 1 is a graph showing the influence of the frequency and the number of winding layers on the normalized AC resistance value in the optimization design method for the high-frequency transformer provided by an embodiment of the present invention; Figure 7 is a comparison diagram of approximate and accurate calculation results of AC resistance of the optimization design method of the high-frequency transformer provided by the embodiment of the present invention; Figure 8A-8C is a magnetic field intensity distribution diagram of different winding arrangements of the high-frequency transformer optimization design method provided by an embodiment of the present invention; Fig. 9 It is the characteristic diagram of high frequency transformer winding structure; Fig.10 It is the design drawing of the insulation structure of the high-frequency transformer; Fig.11 It is a schematic diagram of the structural characteristics and basic heat transfer path of the high-frequency transformer; Fig.12 It is a thermal network model diagram of the optimization design method of the high-frequency transformer provided by the embodiment of the present invention; Fig.13 It is a schematic diagram of all results obtained by the optimization design process of the optimization design method of the high-frequency transformer provided by the embodiment of the present invention; Fig.14 It is a schematic diagram of the optimization design result of the high-frequency transformer according to the optimization design method of the high-frequency transformer provided by the embodiment of the present invention; Fig.15 It is a schematic structural diagram of a high-frequency transformer optimization design device provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0028] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present invention.

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clear, specific embodiments will be described below in conjunction with the accompanying drawings.

[0030] Figure 1 FIG. 1 is a flow chart of the implementation of the optimization design method of the high-frequency transformer provided by the embodiment of the present invention. Figure 1 As shown, the method includes: Step 110: Obtain value ranges of various design parameters of the high-frequency transformer to obtain multiple design solutions.

[0031] In this embodiment, various design parameters can be roughly divided into two categories, one is the system specification parameters, that is, the parameters that should meet the design specifications when designing the high-frequency transformer, and the other is the fixed parameters, that is, the inherent parameters determined by the selected design materials. Among them, the system specification parameters may include frequency, maximum magnetic flux density, minimum insulation distance, efficiency, high-frequency transformer capacity, primary side voltage value, secondary side voltage value, etc., which are not limited here. Fixed parameters may include core parameters, insulation parameters and material parameters, among which the core parameters may include magnetic flux density, loss parameters, etc.; insulation parameters may include the main insulation distance between the primary and secondary windings, the insulation distance between the winding and the magnetic core, the turn-to-turn insulation distance of the primary and secondary windings, the inter-layer insulation distance of the primary and secondary windings, etc., which are not limited here. Material parameters may include safety factor, short-time dielectric strength of insulating material under industrial frequency sinusoidal excitation, insulation grade, short-time industrial frequency voltage excitation borne by primary and secondary windings, high-frequency square wave voltage excitation between layers of primary or secondary windings, etc. It should be understood that the specific parameters included in the above items are only for illustration, and the corresponding other fixed parameters are also within the protection scope of the embodiments of the present invention.

[0032] Step 120: Under preset constraints, perform multi-objective optimization on the decision variables corresponding to the multiple design schemes to obtain optimized values ​​of the decision variables. The objective functions in the multi-objective optimization process include a first objective function, a second objective function, and a third objective function; the first objective function is determined based on the core loss and the total loss of the Litz wire winding; the second objective function is determined based on the volume of the high-frequency transformer; and the third objective function is determined based on the leakage magnetic energy.

[0033] In this embodiment, the preset constraints may include decision variable constraints, temperature rise constraints, insulation distance constraints, and leakage inductance constraints; the decision variables may include the maximum current density in the winding, the number of turns per layer of the secondary winding, the number of pairs of magnetic core stacking blocks, the thickness of the magnetic core, the maximum magnetic flux density, the number of primary winding layers, and the number of secondary winding layers; the objective function may include a first objective function, a second objective function, and a third objective function, wherein each objective function is as follows: Considering that the core and winding losses of the high-frequency transformer should be as small as possible to maximize efficiency, the first objective function can be:

[0034] in, P out is the output power of the high-frequency transformer; P c is the core loss; P w is the total loss of the Litz wire winding.

[0035] Considering that the volume of the high-frequency transformer is minimized and its power density is maximized, the second objective function can be:

[0036] in, V T is the volume of the high frequency transformer.

[0037] Considering that in a dual active bridge (DAB) converter, in order to meet the circuit design requirements, the designed leakage inductance of the high-frequency transformer is as close to the target leakage inductance as possible, the third objective function can be:

[0038] in, L σ ’ To meet the target leakage inductance value required by the circuit design; L σ is the leakage inductance value of the high-frequency transformer, which is calculated based on the leakage magnetic energy of the leakage inductance channel.

[0039] In this embodiment, according to the winding structure, the leakage inductance channel of the high-frequency transformer is divided into a straight line area and an arc area, and the leakage magnetic energy calculation value is determined based on the leakage inductance energy values ​​of the straight line area and the arc area. Accordingly, the leakage inductance value of the high-frequency transformer can be expressed as:

[0040]

[0041]

[0042] in, is the leakage magnetic energy stored between the primary winding layers in the straight area; is the leakage magnetic energy stored between the secondary winding layers in the straight line area; is the leakage magnetic energy stored in the primary winding conductor in the straight area; is the leakage magnetic energy stored in the secondary winding conductor in the straight area; is the leakage magnetic energy stored in the leakage inductance channel in the straight line area; The leakage magnetic energy stored between the primary winding layers in the arc area; The leakage magnetic energy stored between the secondary winding layers in the arc area; is the leakage magnetic energy stored in the primary winding conductor in the arc area; is the leakage magnetic energy stored in the secondary winding conductor in the arc area; is the leakage magnetic energy stored in the leakage inductance channel in the arc area.

[0043] In this embodiment, the focus of this embodiment is on how to perform optimization and solution, so the calculation formulas of various leakage magnetic energies are not described here.

[0044] Figure 2 is a target optimization flow chart of the optimization design method of the high frequency transformer provided by the embodiment of the present invention. Figure 2 , and the objective function, constraint conditions and decision variables given in this embodiment. The process of performing multi-objective optimization in this embodiment to obtain the optimized values ​​of the decision variables is described.

[0045] This embodiment takes into account that the NSGA-II algorithm is a typical non-dominated multi-objective genetic algorithm, and its principle is to use crossover and mutation operators to change the values ​​of decision variables, and select the next generation of population based on the Pareto front. In addition, the algorithm introduces the density of solutions around each sample on the crowding distance evaluation front, so that the population is evenly distributed on the Pareto front and the diversity of non-dominated solutions is achieved. Therefore, the multi-objective genetic algorithm NSGA-II is used to perform multi-objective optimization solutions on the decision variables corresponding to multiple design schemes under preset constraints to obtain the optimized values ​​of the decision variables. Specifically, the initial value is set, where the initial structure and initial parameters are as follows Figure 3As shown. Including insulation distance, winding height and other data. Calculate the magnetic flux density according to the initial Litz wire optimization parameters, calculate the insulation distance according to the core and winding structure parameters, calculate the leakage magnetic energy of the leakage inductance channel according to the winding parameters, and then calculate the leakage inductance value of the high-frequency transformer, and calculate the temperature rise according to the core loss and winding loss. If any of the magnetic flux density, insulation distance, leakage magnetic energy, temperature rise or the number of children in the NSGA-II algorithm does not meet the requirements, re-optimize and adjust the decision variables within the preset range, and recalculate the corresponding indicators based on the optimization adjustment results until each item meets the requirements, and output the optimized value of the decision variable at this time.

[0046] In this embodiment, the parameter settings of the NSGA-II algorithm are shown in Table 1.

[0047] Table 1 Parameter settings of NSGA-II algorithm

[0048] In Table 1, the population size is set to 200, the number of offspring is set to 500, the crossover probability is set to 0.9, the mutation probability is determined based on the number of decision variables, the number of decision variables set in this embodiment is 7, so the mutation probability is 1 / 7, the crossover distribution index is set to 20, and the mutation distribution index is set to 100.

[0049] After describing the solution process provided by this embodiment, the following describes the relevant parameters and design ideas involved in this embodiment: First, the design idea of ​​core loss is explained: This embodiment takes into account that the Improved Generalized Steinmetz Equation (IGSE) can characterize the effect of the instantaneous value and rate of change of the magnetic flux density of the magnetic material magnetization cycle on the loss, and can also reflect the magnetization history. This model is often used in the field to evaluate the core loss of high-frequency transformers under non-sinusoidal excitation due to its advantages of high calculation accuracy, simple calculation formula, few required parameters and convenient extraction. Based on this formula, the waveform of the core loss evaluation of high-frequency transformers under non-sinusoidal excitation is as follows: Figure 4 As shown, u ac ( t ) is the non-sinusoidal voltage excitation curve, B ( t ) is the magnetic flux density waveform curve. Based on this formula and Figure 4 The analysis of can obtain the expression of high frequency core loss as:

[0050] in,

[0051] in, T is the magnetization period, Δ B is the peak-to-peak value of the magnetic flux density within one magnetization cycle, k , α and β is the loss coefficient, which is determined by the inherent characteristics of the material and can be obtained by fitting according to the material test data.

[0052] To simplify the parameters k i The numerical integral term in can be α A simplified expression with a fitting error of no more than 0.15% is obtained within the relative range of:

[0053] Among them, the fitted Steinmetz loss coefficient (including k , α and β ) are: k =4.229×10 -5 , α= 1.397, β= 2.296.

[0054] After explaining the design ideas of the core loss, the design ideas of the winding loss are explained below: The winding structure design of a high-frequency transformer directly affects the electromagnetic characteristics of the transformer, and is also one of the important ways to improve its power density and efficiency. The commonly used winding types in high-frequency transformers are: copper foil winding, round conductor winding and Litz wire winding. Under high-frequency conditions, compared with copper foil and round conductor, Litz wire can effectively alleviate the skin effect and proximity effect caused by eddy currents in the winding, thereby reducing high-frequency winding losses. Figure 5A-5C is the current density distribution diagram in different types of windings, as shown in Figure 5, which is the current density distribution of different types of windings at 1MHz, where Figure 5A It is copper foil, Figure 5B is a circular conductor, Figure 5C The color depth in the figure is used to represent the current density. The maximum current density in the Litz wire winding is only 2.7065×10 7 A / m 2 , which is much lower than the maximum current density value in copper foil and round conductor windings.

[0055] While reducing the winding loss in the high-frequency transformer, in order to improve the utilization of the core window and increase the power density, it seems to be more advantageous to choose rectangular Litz wire. At a given frequency and number of winding layers, seeking the optimal Litz wire conductor size is an important part of the optimization design of high-frequency transformers. Therefore, the optimal size and minimum AC resistance value of the Litz wire winding can be determined by analyzing the loss characteristics of the Dowell model under frequency-varying conditions. Usually, the current excitation flowing through the high-frequency transformer contains multiple harmonics, and the winding loss generated by each harmonic needs to be solved and superimposed. Therefore, the primary total loss expression of the Litz wire winding can be:

[0056] Among them, the AC resistivity F R The calculation formula is:

[0057] in, ; ;

[0058] In the formula, R wn For the n AC resistance value under subharmonic, R wdc is the DC resistance of the Litz wire winding, I n It is n The effective value of subharmonic current, l w is the length of the winding, ρ w is the resistivity, f s is the frequency, μ 0 is the vacuum permeability, m is the number of winding layers, k is the number of strands in the Litz wire, d str is the strand diameter, Δ str is the relative skin depth at the fundamental frequency δ w The normalized thickness value of . η is the filling factor of Litz wire, which is expressed as η = d str / p ,in p It is the distance between the centers of adjacent strands in the same layer.

[0059] When the filling factor of the Litz wire winding η = 0.7, the number of strands is k =100, the effect of frequency and number of winding layers on the normalized AC resistance value ( F R / ( d str / δ w ) 2 ), the analysis results are as follows Figure 6 As shown. The horizontal axis is the ratio of the strand diameter to the skin depth, and the vertical axis is the AC resistance value. Figure 6 It can be seen that: (1) d str / δ w When the value is low, the winding resistance value is related to the frequency and the number of winding layers. m Not relevant.

[0060] (2) There is an optimal value for the normalized strand diameter, namely d str_opt / δ w This makes the winding AC loss reach a minimum.

[0061] (3) Affected by the proximity effect, as the number of layers increases m The increase in AC resistance R w Gradually increase.

[0062] Based on the above theory, it can be seen that within a certain frequency range (i.e. d str_opt / δ w ≤2), AC resistance coefficient in the accurate Dowell model F R Approximate expressions available F R ’ Instead, that is:

[0063] In the same range, they are F R and F R ’ Draw a change curve for comparison, as shown in the following example: Figure 7 shown. Figure 7 is a comparison diagram of the approximate and accurate calculation results of the AC resistance of the optimization design method of the high-frequency transformer provided by the embodiment of the present invention; Figure 7 The solid line is F RThe corresponding curve, the dotted line is F R ’ The corresponding curve. Figure 7 It is known that when d str_opt / δ w When ≤2, F R The approximate calculation results are basically consistent with the exact calculation results. n For subharmonic excitation, when the frequency satisfies ( n ) 1 / 2 Δ str When ≤2, the total loss expression of Litz wire winding is:

[0064] in, n For the n Subharmonics; I n It is n The effective value of subharmonic current; R wn For the n AC resistance value under subharmonic; R wdc is the DC resistance value of the Litz wire winding; F Rn For the n Normalized AC resistance value under subharmonic current; m is the number of winding layers; k is the number of strands in the Litz wire; Δ str is the relative skin depth at the fundamental frequency δ w The normalized thickness value of .

[0065] In addition, according to Figure 7 It can be seen that the Litz wire winding loss has a minimum value within a certain frequency range, so d str_opt / δ w Take the derivative and calculate the minimum value. The optimal strand diameter of the Litz wire winding is:

[0066] in, K w is the waveform factor, and its expression is:

[0067] In the formula, I Tis the effective value of the current, J max is the maximum current density in the winding.

[0068] After explaining the design ideas of winding loss, considering that the insulation distance constraint includes the length constraint of the leakage inductance channel, the design ideas of the length of the leakage inductance channel are explained below: In this embodiment, considering that leakage inductance is an important parasitic parameter in high-frequency transformers, it is often used to be integrated into power electronic converters. On the one hand, it can reduce the number of devices in the circuit, and on the other hand, it can improve the operation mode and power transmission characteristics of the converter. At present, the leakage inductance evaluation of high-frequency transformers is mainly based on the energy method. By short-circuiting the secondary winding, the magnetomotive force generated by the primary and secondary windings cancel each other out. Finally, the magnetic field energy left in the core window can be used to calculate the leakage inductance of the transformer. Therefore, the winding structure and arrangement in the core window will significantly affect the leakage inductance value of the high-frequency transformer. To this end, the magnetic field strength distributions when the windings are non-staggered, partially staggered, and fully staggered are compared. For details, please refer to . Figure 8A-8C .in, Fig. 8A is the magnetic field intensity distribution when the windings are non-staggered, Figure 8B is the magnetic field intensity distribution when the partial staggered arrangement is performed, Figure 8C is the magnetic field intensity distribution when the arrangement is completely staggered. d iso1 and d iso2 are the lengths of leakage inductance channels at different positions. HF represents the magnetic field intensity distribution at high frequency, and LF represents the magnetic field intensity distribution at low frequency.

[0069] Depend on Figure 8A-8C It can be seen that no matter how the windings are arranged, the peak value of the magnetic field strength always appears at the junction of the primary winding (P) and the secondary winding (S). Especially for non-interlaced windings, the maximum value of the magnetic field strength not only appears between the primary and secondary windings, but is also much higher than other arrangements. Therefore, for high-frequency transformers with this structure, the leakage inductance value of the high-frequency transformer can be easily controlled by properly adjusting the leakage inductance channel (also known as the main insulation distance) between the primary and secondary windings.

[0070] When determining the leakage inductance channel of a high-frequency transformer, it is necessary to divide the winding into a straight line area (L area) and an arc area (C area) according to the structural characteristics of the winding, and calculate the leakage magnetic energy in different areas respectively. Fig. 9 As shown, Fig. 9 It is the characteristic diagram of high-frequency transformer winding structure, based on Fig. 9 The structure of the high-frequency transformer is divided into a straight line area and an arc area for calculation. Specifically: The leakage magnetic energy stored between the primary and secondary winding layers in the straight line area is:

[0071]

[0072] in, N l The number of turns per winding layer, m is the number of winding layers, I 1 and I 2 are the current values ​​flowing through the primary and secondary windings respectively, h w is the height of the winding, D ins is the distance between winding layers.

[0073] The leakage magnetic energy stored in the primary and secondary winding conductors in the straight line area is:

[0074]

[0075] in,

[0076] In the formula δ w is the skin depth, d f is the side length of each winding conductor.

[0077] The leakage magnetic energy stored between the primary and secondary winding layers in the arc area can be expressed as:

[0078]

[0079] The leakage magnetic energy stored in the primary winding conductor in the arc area is:

[0080] The leakage magnetic energy stored in the secondary winding conductor in the arc area is:

[0081] Based on the above formula, the leakage magnetic energy of all straight line areas except the leakage inductance channel area can be expressed as:

[0082] The leakage magnetic energy of all arc areas except the leakage inductance channel area can be expressed as:

[0083] Accordingly, the final length of the leakage inductance channel can be calculated according to the following formula:

[0084]

[0085]

[0086]

[0087] in, k 1 , k 2 , k 3 is the calculation parameter; d ins_int1 is the thickness of the insulation layer outside the primary winding; d ins_int2 is the thickness of the insulation layer outside the secondary winding; μ 0 is the vacuum permeability; N l The number of turns per winding layer; I 1 and I 2 are the current values ​​flowing through the primary and secondary windings respectively; m is the number of winding layers; h w is the height of the winding; is the leakage magnetic energy of all straight line areas except the leakage inductance channel area; It is the leakage magnetic energy of all arc areas except the leakage inductance channel area.

[0088] After explaining the design ideas of the leakage magnetic energy of the leakage inductance channel, the design ideas of the insulation distance in the insulation distance constraint conditions are explained below: In this embodiment, the insulation design level is related to the reliable operation of power equipment. For high-frequency transformers, a small size also means a small insulation distance, and long-term operation under a voltage waveform with a short rise time, large amplitude, and high frequency increases the risk of insulation failure. Therefore, reasonable insulation structure design and accurate insulation distance assessment are particularly important for the reliable operation of high-frequency transformers. Fig.10 The basic insulation structure of the high-frequency transformer designed for the embodiment of the present invention and the insulation distance required to be evaluated are as follows: Fig.10 As shown: The insulation distance can generally include the main insulation distance and the longitudinal insulation distance. Fig.10 The various parameters and their calculations are explained below: The minimum main insulation distance between the primary and secondary windings is calculated as:

[0089] in, k saf is the safety factor, E ins It is the short-time dielectric strength of the insulating material under power frequency sinusoidal excitation. V iso The insulation level is usually considered to be twice the voltage on the high-voltage side of the converter.

[0090] The minimum insulation distance between the winding and the core is:

[0091]

[0092] in, V st1 and V st2 It is the short-time power frequency voltage excitation borne by the primary and secondary windings.

[0093] The calculation formula for the minimum insulation distance between turns of the primary and secondary windings is:

[0094] The minimum insulation distance between the primary and secondary winding layers can be expressed as:

[0095] In the formula, V l-l1,2 It is a high-frequency square wave voltage excitation between the layers of the primary or secondary winding.

[0096] The above formulas are the minimum insulation distances calculated to meet the insulation requirements and can be used to preliminarily determine the basic structure of the high-frequency transformer.

[0097] After explaining the design ideas for insulation distance, the design ideas for temperature rise assessment are explained below.

[0098] In this embodiment, considering that although high frequency conditions can effectively reduce the volume and weight of the transformer, it will cause its heat dissipation area to be greatly reduced, making it difficult for heat to dissipate quickly, causing serious temperature rise, reasonable thermal management is an important part of transformer design. Accurate temperature rise prediction can not only indirectly reflect the loss behavior of high-frequency magnetic components, but also serve as a measure of the long-term stable operation of the transformer. To this end, a 7-node centralized heating network model was established based on the structural characteristics and basic heat transfer paths of the transformer. The structural characteristics and basic heat transfer paths of the high-frequency transformer are shown in the figure. Fig.11 As shown, the thermal network model provided in this embodiment is as follows Fig.12 As shown, in Fig.12 In each block diagram, the temperature node of the part is represented. Fig.11 The dot on the high-frequency transformer is the input position of the heat source. Fig.12 The specific input heat source size depends on the loss calculation results of the magnetic core and winding. All thermal resistance values ​​in the thermal network model can be calculated by simple empirical formulas based on the inherent thermal properties of the material and the heat transfer area. Fig.12 The corresponding resistance, capacitance and corresponding node names are listed in turn, and the thermal circuit equations corresponding to each temperature node are listed: The thermal circuit differential equation at the temperature node of the core center column is:

[0099] The thermal circuit differential equation at the secondary winding temperature node is:

[0100] The thermal circuit equation at the primary winding temperature node is expressed as:

[0101] The thermal circuit equation at the outer yoke temperature node is calculated as:

[0102] The thermal circuit equations at the upper and lower yoke temperature nodes are:

[0103] The thermal circuit equation at the heat sink temperature node is:

[0104] Since the temperature rise prediction only needs to consider the steady-state temperature results, the left side of the above differential equation can be set to zero, which can be written in the following matrix form:

[0105] in A and BRepresents the thermal resistance system matrix, which can be obtained by classifying the thermal path equations corresponding to each temperature node, namely:

[0106]

[0107] in, T is the temperature node vector, U is the heat source vector. U The terms in are input heat sources, which are determined based on the core losses and winding losses.

[0108] When applied, the temperature rise is the current node temperature minus the ambient temperature.

[0109] After explaining the design ideas of temperature rise assessment, the value range and constraints of decision variables are explained below: The value range of decision variables is shown in Table 2: Table 2 Value ranges of decision variables

[0110] As shown in Table 2, the maximum current density in the winding J max The value range is: 1~5(A / mm 2 ); Number of turns per layer of the secondary winding N l2 The value range is: 3 to 10 (turns); the number of core stacking blocks n c The value range is: 1 to 5 (pairs); the core thickness A The value range is: 20~50(mm); the maximum magnetic flux density B m The value range is: 0.4~1(T); the number of primary winding layers m 1 The value range is: 1 to 3 (layers); the number of layers of the secondary winding m 2 The value range is: 1 to 3 (layers).

[0111] In order to improve the efficiency of the optimization design process and avoid unreasonable design results, some parameters need to be constrained. The maximum temperature rise of the high-frequency transformer must be lower than the maximum allowable temperature specified by the insulation material and the magnetic core; the required main insulation distance between the primary and secondary windings should meet the minimum insulation requirements; the designed leakage inductance value should be selected within a range as close to the target leakage inductance value as possible. Therefore, the optimization constraints are summarized as follows:

[0112] in,x 1 is the lower limit constraint of the decision variable, x n is the upper limit constraint of the decision variable, Δ T max It is the maximum temperature rise of high-frequency transformer.

[0113] Fig.13 Schematic diagram of all results obtained by the optimization design process of the optimization design method of the high-frequency transformer provided by the embodiment of the present invention. Fig.13 This embodiment is described.

[0114] In this embodiment, based on the objective function, constraints and decision variables, all high-frequency transformer design results that meet the constraints are obtained. Fig.13 In the figure, the x-axis represents power density, the y-axis represents efficiency, and the z-axis represents leakage inductance deviation. Each point represents the design result of a high-frequency transformer. Based on the Pareto frontier, the set of optimal design solutions is screened out. Fig.14 The schematic diagram of the overall machine optimization design results is shown in Figure 1. Fig.14 In the figure, the five-pointed star is the best solution selected in the high-frequency transformer optimization design process, that is, the optimized value of the decision variable.

[0115] Step 130: taking the design solution corresponding to the optimized value of the decision variable as the target design solution of the high-frequency transformer.

[0116] In summary, the embodiment of the present invention takes into account that the control scheme in the design scheme of the high-frequency transformer at this stage is not clear, and only aims to reduce or increase a certain parameter, and the optimization target is relatively single. The embodiment of the present invention takes the core loss, the total loss of the Litz wire winding, and the leakage magnetic energy of the leakage inductance channel as the optimization target, and considering that too many decision variables and how large the search range will lead to too long optimization time and increased calculation cost, too few decision variables will make it difficult to find the optimal result. Therefore, the embodiment of the present invention takes the maximum current density in the winding, the number of turns per layer of the secondary winding, the number of pairs of magnetic core stacking blocks, the thickness of the magnetic core, the maximum magnetic flux density, the number of primary winding layers, and the number of secondary winding layers as decision variables. In addition, although the high-frequency condition can effectively reduce the volume and weight of the transformer, it will cause its heat dissipation area to be greatly reduced, and the heat is difficult to dissipate quickly, causing serious temperature rise. At the same time, in order to improve the probability of selecting the best in the optimization design process and avoid unreasonable designs, the embodiment of the present invention takes the decision variable constraint condition, the temperature rise constraint condition, the insulation distance constraint condition, and the leakage inductance value constraint condition as the constraint condition, and adds the optimization parameters to make the design of the high-frequency transformer more reasonable. It can be seen that the embodiments of the present invention can coordinate the relationship between various parameters, so that the optimization objectives considered during the design of the high-frequency transformer are more comprehensive, and global optimization of the high-frequency transformer loss, parasitic parameters, insulation design and maximum temperature rise can be achieved.

[0117] It should be understood that the order of execution of the steps in the above embodiment does not necessarily mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present invention.

[0118] The following is an embodiment of the device of the present invention. For details not described in detail therein, reference may be made to the corresponding method embodiment described above.

[0119] Fig.15 The schematic diagram of the structure of the optimization design device of the high-frequency transformer provided by the embodiment of the present invention is shown. For the convenience of explanation, only the part related to the embodiment of the present invention is shown, which is described in detail as follows: like Fig.15 As shown, the optimization design device 15 of the high-frequency transformer includes: An acquisition module 51 is used to acquire the value range of various design parameters of the high-frequency transformer to obtain multiple design solutions; The optimization module 52 is used to perform multi-objective optimization on the decision variables corresponding to the multiple design schemes under the preset constraint conditions to obtain the optimized values ​​of the decision variables; A design module 53, used to use the design scheme corresponding to the optimized value of the decision variable as the target design scheme of the high-frequency transformer; Among them, the objective functions in the multi-objective optimization process include a first objective function, a second objective function and a third objective function; the first objective function is determined based on the core loss and the total loss of the Litz wire winding; the second objective function is determined based on the volume of the high-frequency transformer; and the third objective function is determined based on the leakage inductance value of the high-frequency transformer.

[0120] In a possible implementation, the first objective function is:

[0121] in, P out is the output power of the high-frequency transformer; P c is the core loss; P w is the total loss of the Litz wire winding.

[0122] In one possible implementation, the total loss of the Litz wire winding is determined according to the following formula:

[0123] in, n For the n Subharmonics; I n It is n The effective value of subharmonic current; R wn For the n AC resistance value under subharmonic; R wdc is the DC resistance value of the Litz wire winding; F Rn For the n Normalized AC resistance value under subharmonic current; m is the number of winding layers; k is the number of strands in the Litz wire; Δ str is the relative skin depth at the fundamental frequency δ w The normalized thickness value of .

[0124] In a possible implementation, the second objective function is:

[0125] in, V T is the volume of the high frequency transformer.

[0126] In a possible implementation, the third objective function is:

[0127] in, L σ ’ To meet the target leakage inductance value required by the circuit design; L σ is the leakage inductance of the high-frequency transformer.

[0128] In one possible implementation, the decision variables include the maximum current density in the winding, the number of turns per layer of the secondary winding, the number of pairs of magnetic core stacking blocks, the magnetic core thickness, the maximum magnetic flux density, the number of primary winding layers, and the number of secondary winding layers.

[0129] In a possible implementation manner, the preset constraints include decision variable constraints, temperature rise constraints, insulation distance constraints, and leakage inductance constraints.

[0130] In a possible implementation, the insulation distance constraint condition includes a leakage inductance channel length constraint condition; The length of the leakage inductance channel is calculated according to the following formula:

[0131]

[0132]

[0133]

[0134] in, k 1 , k 2 , k 3 is the calculation parameter; d ins_int1 is the thickness of the insulation layer on the outside of the winding; d ins_int2 is the thickness of the insulation layer on the outside of the winding; μ 0 is the vacuum permeability; N l The number of turns per winding layer; I 1 and I 2 are the current values ​​flowing through the primary and secondary windings respectively; m is the number of winding layers; h w is the height of the winding; is the leakage magnetic energy of all straight line areas except the leakage inductance channel area; It is the leakage magnetic energy of all arc areas except the leakage inductance channel area.

[0135] In a possible implementation, the design module 53 is specifically configured to: The multi-objective genetic algorithm NSGA-II is used to perform multi-objective optimization on the decision variables corresponding to multiple design schemes under preset constraints to obtain the optimized values ​​of the decision variables.

[0136] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0137] Those of ordinary skill in the art will appreciate that the templates, units, and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0138] If the module / unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by the processor, the steps of the above-mentioned optimization design method embodiments of each high-frequency transformer can be implemented. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device that can carry the computer program code, recording medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory, random access memory, electrical carrier signal, telecommunication signal and software distribution medium.

[0139] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A method for optimizing the design of a high-frequency transformer, characterized in that: include: Obtaining the value range of each design parameter of the high-frequency transformer to obtain multiple design solutions; Under the preset constraints, multi-objective optimization is performed on the decision variables corresponding to multiple design schemes to obtain the optimized values ​​of the decision variables; Using the design scheme corresponding to the optimized value of the decision variable as the target design scheme of the high-frequency transformer; Among them, the objective functions in the multi-objective optimization process include a first objective function, a second objective function and a third objective function; the first objective function is determined based on the core loss and the total loss of the Litz wire winding; the second objective function is determined based on the volume of the high-frequency transformer; the third objective function is determined based on the leakage inductance value of the high-frequency transformer.

2. The optimization design method of high-frequency transformer according to claim 1, characterized in that: The first objective function is: in, P out is the output power of the high-frequency transformer; P c is the magnetic core loss; P w is the total loss of the Litz wire winding.

3. The optimization design method of high-frequency transformer according to claim 2, characterized in that: The total losses of the Litz wire winding are determined according to the following formula: in, n For the n Subharmonics; I n It is n The effective value of subharmonic current; R wn For the n AC resistance value under subharmonic; R wdc is the DC resistance value of the Litz wire winding; F Rn For the n Normalized AC resistance value under subharmonic current; m is the number of winding layers; k is the number of strands in the Litz wire; Δ str is the relative skin depth at the fundamental frequency δ w The normalized thickness value of .

4. The optimization design method of high-frequency transformer according to claim 1, characterized in that: The second objective function is: in, V T is the volume of the high frequency transformer.

5. The optimization design method of high-frequency transformer according to claim 1, characterized in that: The third objective function is: in, L σ ’ To meet the target leakage inductance value required by the circuit design; L σ is the leakage inductance value of the high frequency transformer.

6. The optimization design method of high-frequency transformer according to claim 1, characterized in that: The decision variables include the maximum current density in the winding, the number of turns per layer of the secondary winding, the number of pairs of magnetic core stacking blocks, the thickness of the magnetic core, the maximum magnetic flux density, the number of primary winding layers, and the number of secondary winding layers.

7. The optimization design method of high frequency transformer according to claim 1, characterized in that: The preset constraints include decision variable constraints, temperature rise constraints, insulation distance constraints and leakage inductance constraints.

8. The optimization design method of high frequency transformer according to claim 7, characterized in that: The insulation distance constraint condition includes a leakage inductance channel length constraint condition; The length of the leakage inductance channel is calculated according to the following formula: in, k 1. k 2. k 3 is the calculation parameter; d ins_int1 is the thickness of the insulation layer outside the primary winding; d ins_int2 is the thickness of the insulation layer outside the secondary winding; μ 0 is the vacuum permeability; l is the length of the winding; N l The number of turns per winding layer; I 1 and I 2 are the current values ​​flowing through the primary and secondary windings respectively; m is the number of winding layers; h w is the height of the winding; is the leakage magnetic energy of all straight line areas except the leakage inductance channel area; It is the leakage magnetic energy of all arc areas except the leakage inductance channel area.

9. The optimization design method of high frequency transformer according to claim 1, characterized in that: The method of performing multi-objective optimization on the decision variables corresponding to the plurality of design schemes under the preset constraint conditions to obtain the optimized values ​​of the decision variables includes: The multi-objective genetic algorithm NSGA-II is used to perform multi-objective optimization on the decision variables corresponding to multiple design schemes under preset constraints to obtain the optimized values ​​of the decision variables.

10. An optimization design device for a high-frequency transformer, characterized in that: include: An acquisition module is used to obtain the value range of various design parameters of the high-frequency transformer to obtain multiple design solutions; An optimization module is used to perform multi-objective optimization on the decision variables corresponding to multiple design schemes under preset constraints to obtain the optimized values ​​of the decision variables; A design module, used to use the design scheme corresponding to the optimized value of the decision variable as the target design scheme of the high-frequency transformer; Among them, the objective functions in the multi-objective optimization process include a first objective function, a second objective function and a third objective function; the first objective function is determined based on the core loss and the total loss of the Litz wire winding; the second objective function is determined based on the volume of the high-frequency transformer; the third objective function is determined based on the leakage inductance value of the high-frequency transformer.

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