A low-loss transformer design method

Abstract

The application relates to a low-loss transformer design method, which comprises the following steps: constructing an application scene of a transformer, determining target parameters of the transformer; selecting core parameters of the transformer; obtaining corresponding magnetic material magnetic density-loss curves, magnetic material frequency-loss curves and loss correction coefficients corresponding to excitation waveform conversion according to the core parameters; obtaining a transformer magnetic loss equation with maximum magnetic density as a variable; obtaining primary winding copper loss and secondary winding copper loss of the transformer under the influence of skin effect respectively; obtaining a transformer copper loss equation with maximum magnetic density as a variable; obtaining a transformer total loss equation according to the transformer magnetic loss equation and the transformer copper loss equation; obtaining maximum magnetic density corresponding to a total loss minimum point of the transformer according to the transformer total loss equation; and obtaining primary winding parameters of the transformer and secondary winding parameters of the transformer according to the maximum magnetic density when the maximum magnetic density meets the core parameters, so as to complete the transformer design. The application can realize minimum loss design of the transformer.

Description

Technical Field

[0001] This invention relates to the field of transformer design technology, and more specifically, to a low-loss transformer design method. Background Technology

[0002] Photovoltaics, as a highly efficient and clean energy source, has been widely applied globally. A typical photovoltaic-storage system consists of photovoltaic modules, lithium batteries, energy storage inverters, smart meters, the power grid, grid-connected loads, and off-grid loads. To utilize clean energy more efficiently and improve the conversion efficiency of the energy storage inverters responsible for power conversion within the photovoltaic-storage system, it is necessary to minimize the overall losses of the energy storage inverters. The losses of energy storage inverters are mainly concentrated in the power conversion section, primarily including switching transistor losses and magnetic component losses. Switching transistor losses are mainly determined by the circuit topology and the performance of the switching devices. Once the circuit topology is determined, maximizing the overall conversion efficiency and designing the magnetic components to minimize their losses are crucial design objectives for the entire system.

[0003] For transformer design, the general approach is to use the area AP method to determine the magnetic core, and then calculate the turns ratio, winding diameter, and number of winding strands based on the set parameters. The maximum magnetic flux density is then checked to ensure it does not exceed the empirical value. A transformer designed in this way can meet basic electrical requirements. However, with the development of semiconductors and the increasing use of high-frequency power devices such as silicon carbide, the demand for high-frequency transformers is also growing. Therefore, transformers that meet design requirements must satisfy high density, high efficiency, and low cost. At high frequencies, losses are the main limiting factor. Therefore, finding a transformer design method with the lowest possible losses that meets these requirements is of great significance. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a low-loss transformer design method in view of the above-mentioned technical defects of the prior art.

[0005] The technical solution adopted by this invention to solve its technical problem is: to construct a low-loss transformer design method, the method comprising the following steps:

[0006] S1. Construct the application scenario of the transformer and determine the target parameters of the transformer;

[0007] S2. Select the core parameters of the transformer;

[0008] S3. Obtain the corresponding magnetic material magnetic flux density-loss curve, magnetic material frequency-loss curve, and loss correction coefficient corresponding to the excitation waveform conversion based on the magnetic core parameters, and obtain the transformer magnetic loss equation with the maximum magnetic flux density as the variable.

[0009] S4. Obtain the primary winding copper loss and secondary winding copper loss of the transformer under the influence of the skin effect, and obtain the transformer copper loss equation with the maximum magnetic flux density as the variable.

[0010] S5. Obtain the total loss equation of the transformer based on the transformer magnetic loss equation and the transformer copper loss equation;

[0011] S6. Obtain the maximum magnetic flux density corresponding to the minimum point of total transformer loss according to the total transformer loss equation, and confirm whether the maximum magnetic flux density satisfies the core parameters; if yes, proceed to step S7, otherwise proceed to step S2.

[0012] S7. Obtain the primary winding parameters and secondary winding parameters of the transformer based on the maximum magnetic flux density to complete the transformer design.

[0013] Preferably, in the low-loss transformer design method of the present invention, in step S1, the application scenarios for constructing the transformer include:

[0014] An LLC converter topology containing two transformers is constructed; the primary sides of the two transformers are connected in parallel to connect to the power input, and the secondary sides of the two transformers are connected in series to connect to the load circuit.

[0015] Preferably, in the low-loss transformer design method of the present invention, in step S1, determining the target parameters of the transformer includes: determining the input power, primary input voltage, primary input current, secondary output voltage, operating switching frequency, and core window occupancy rate of the transformer.

[0016] Preferably, in the low-loss transformer design method of the present invention, in step S2, selecting the core parameters of the transformer includes:

[0017] The magnetic core material is obtained by using the inductance area Ap method or a reference sample to obtain the core parameters.

[0018] Preferably, in the low-loss transformer design method of the present invention, in step S3, obtaining the transformer magnetic loss equation with the maximum magnetic flux density as the variable based on the core parameters, including obtaining the corresponding magnetic material flux density-loss curve, magnetic material frequency-loss curve, and loss correction coefficient corresponding to the excitation waveform conversion; includes:

[0019] S31. Interpolate and fit the magnetic flux density-loss curves of the magnetic core parameters to obtain the magnetic flux density-core loss expressions corresponding to the magnetic core parameters.

[0020] S32. Interpolate and fit the frequency-loss curve of the magnetic material corresponding to the magnetic core parameters to obtain the frequency-core loss expression corresponding to the magnetic core parameters;

[0021] S33. Obtain the ratio of eddy current loss of the transformer under square wave excitation to that under sinusoidal wave excitation, so as to obtain the loss correction coefficient of the transformer under square wave excitation.

[0022] S34. Obtain the magnetic flux density-core loss expression per unit volume based on the loss correction coefficient, the magnetic flux density-core loss expression, and the frequency-core loss expression.

[0023] S35. Transform the magnetic flux density-core loss expression corresponding to the unit volume to obtain the transformer magnetic loss equation with the maximum magnetic flux density as the variable.

[0024] Preferably, in the low-loss transformer design method of the present invention, in step S4, the step of obtaining the primary winding copper loss and secondary winding copper loss of the transformer under the influence of the skin effect, and obtaining the transformer copper loss equation with the maximum magnetic flux density as a variable, includes:

[0025] S41. Obtain the primary-to-secondary turns ratio of the transformer, and respectively obtain the primary-to-secondary turns expression and the secondary-to-secondary turns expression of the transformer with the maximum magnetic flux density as the variable;

[0026] S42. When the window area occupied by the primary side of the transformer is set to be equal to the window area occupied by the secondary side of the transformer, the window area of ​​the primary side of the transformer and the window area of ​​the secondary side of the transformer are obtained respectively.

[0027] S43. Obtain the expression for the single-turn wire diameter of the primary side of the transformer based on the expression for the number of turns on the primary side of the transformer and the window area occupied by the primary side of the transformer; obtain the expression for the single-turn wire diameter of the secondary side of the transformer based on the expression for the number of turns on the secondary side of the transformer and the window area occupied by the secondary side of the transformer.

[0028] S44. Obtain the cross-sectional area expression of the primary side single-turn wire diameter and the cross-sectional area expression of the secondary side single-turn wire diameter of the transformer according to the expression of the primary side single-turn wire diameter and the expression of the secondary side single-turn wire diameter of the transformer, respectively.

[0029] S45. Obtain the primary winding copper loss of the transformer based on the effective value of the primary current and the primary winding resistance of the transformer; obtain the secondary winding copper loss of the transformer based on the effective value of the secondary current and the secondary winding resistance of the transformer.

[0030] S46. Under the condition that the AC copper loss is equal to the DC copper loss, obtain the skin effect coefficient, and obtain the transformer copper loss equation with the maximum magnetic flux density as the variable based on the primary winding copper loss of the transformer, the secondary winding copper loss of the transformer, and the skin effect coefficient.

[0031] Preferably, in the low-loss transformer design method of the present invention, in step S5, obtaining the total transformer loss equation based on the transformer magnetic loss equation and the transformer copper loss equation includes:

[0032] The sum of the transformer magnetic loss equation and the transformer copper loss equation is the transformer total loss equation.

[0033] Preferably, in the low-loss transformer design method of the present invention, in step S6, obtaining the maximum magnetic flux density corresponding to the minimum point of total transformer loss according to the total transformer loss equation, and confirming whether the maximum magnetic flux density satisfies the core parameters; includes:

[0034] The Mathcad equation is used to solve for the maximum magnetic flux density corresponding to the point where the total loss of the transformer is minimized, which is taken as the target magnetic flux density parameter.

[0035] Preferably, in the low-loss transformer design method of the present invention, confirming whether the maximum magnetic flux density satisfies the core parameters includes:

[0036] The number of primary winding turns of the transformer is obtained according to the target magnetic flux density parameter and the expression for the number of primary winding turns of the transformer; the number of secondary winding turns of the transformer is obtained according to the target magnetic flux density parameter and the expression for the number of secondary winding turns of the transformer.

[0037] The actual magnetic flux density of the transformer is obtained according to the magnetic flux density expression of the transformer. When the actual magnetic flux density is within the core parameters, it is determined that the maximum magnetic flux density satisfies the core parameters.

[0038] Preferably, in the low-loss transformer design method of the present invention, in step S7, obtaining the primary winding parameters and the secondary winding parameters of the transformer based on the maximum magnetic flux density includes:

[0039] The primary single-turn wire diameter of the transformer is obtained based on the target magnetic flux density parameter of the transformer and the expression for the primary single-turn wire diameter of the transformer. The secondary single-turn wire diameter of the transformer is obtained based on the target magnetic flux density value of the transformer and the expression for the secondary single-turn wire diameter of the transformer.

[0040] The maximum value of the wire diameter is set according to the skin depth, so as to obtain the number of parallel strands on the primary side and the number of parallel strands on the secondary side of the transformer based on the maximum value of the wire diameter.

[0041] The low-loss transformer design method of the present invention has the following advantages: it can obtain a low-loss transformer, thereby enabling the photovoltaic energy storage inverter to achieve a higher conversion efficiency. Attached Figure Description

[0042] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0043] Figure 1 This is a flowchart of an embodiment of a low-loss transformer design method according to the present invention;

[0044] Figure 2 yes Figure 1 A circuit schematic diagram of an embodiment of the application scenario of the transformer constructed in the middle;

[0045] Figure 3 yes Figure 1 A flowchart of an embodiment corresponding to step S3;

[0046] Figure 4 Based on Figure 3 A schematic diagram showing the relationship between magnetic flux density and core loss.

[0047] Figure 5 yes Figure 1 A flowchart of an embodiment corresponding to step S4;

[0048] Figure 6 yes Figure 1 A schematic diagram of the relationship curve between the maximum magnetic flux density and the total transformer loss expression obtained in step S5;

[0049] Figure 7 yes Figure 1 A flowchart of an embodiment corresponding to step S6. Detailed Implementation

[0050] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0051] like Figure 1 The figure shows an embodiment of a low-loss transformer design method according to the present invention. Figure 1In one embodiment of the low-loss transformer design method of the present invention, the following steps are included: S1, constructing the application scenario of the transformer and determining the target parameters of the transformer; S2, selecting the core parameters of the transformer; S3, obtaining the corresponding magnetic material flux density-loss curve, magnetic material frequency-loss curve, and loss correction coefficient corresponding to the excitation waveform conversion based on the core parameters, and obtaining the transformer magnetic loss equation with the maximum flux density as the variable; S4, obtaining the primary winding copper loss and secondary winding copper loss of the transformer under the influence of the skin effect, and obtaining the transformer copper loss equation with the maximum flux density as the variable; S5, obtaining the total loss equation of the transformer based on the transformer magnetic loss equation and the transformer copper loss equation; S6, obtaining the maximum flux density corresponding to the minimum point of the total loss of the transformer based on the total loss equation of the transformer, and confirming whether the maximum flux density satisfies the core parameters; if yes, proceed to step S7, otherwise proceed to step S2; S7, obtaining the primary winding parameters and secondary winding parameters of the transformer based on the maximum flux density to complete the transformer design.

[0052] Based on step S1, in this embodiment, the transformer is designed according to the application scenario of the transformer. In a specific embodiment, such as... Figure 2 As shown, an LLC converter topology containing two transformers is constructed. The primary windings of the two transformers are connected in parallel to connect to the power input, and the secondary windings of the two transformers are connected in series to connect to the load circuit. That is, in this embodiment, the design method for the transformer in the bidirectional LLC converter of a photovoltaic energy storage inverter is introduced. In the application scenario described, the design method is presented under battery discharge conditions. This process is suitable for the design of almost all types of transformers, such as forward, flyback, half-bridge, and full-bridge transformer topologies.

[0053] Simultaneously, based on step S1, the target parameters of the transformer are determined, including: determining the transformer's input power, primary input voltage, primary input current, secondary output voltage, operating switching frequency, and core window occupancy. In a specific embodiment, specific transformer parameters are given, setting the maximum battery charging / discharging power Pin = 6000 W, the converter operating switching frequency fs = 50 kHz, and the transformer magnetizing inductance L... m = 450 μH, transformer resonant inductance L r = 2.5 μH, average value of maximum battery input current I in_max =110 A, battery input voltage Battery output voltage V out_nom = 327.273 V, Number of transformer combinations (2 transformers in parallel on the primary side and in series on the secondary side) N tranf=2; Voltage drop across a single diode in the secondary full-bridge rectifier (single-loop current flowing through 2 diodes) Vf = 1.0 V, peak value of the transformer primary current. RMS value of transformer primary current In addition, the maximum loss, cost and size requirements of the transformer, as well as the heat dissipation method of the transformer, can also be comprehensively considered.

[0054] Based on step S2, the core parameters of the transformer are initially selected. In one embodiment, this includes, but is not limited to, obtaining the core magnetic material using the inductance area Ap method or a reference sample to obtain the core parameters. In a specific embodiment, a PQ5050B core is selected, with TDK N95 magnetic material as the core material. The selected core specifications satisfy the following: core center column diameter D... PQ5050 =21mm; Core window diameter E PQ5050 =44mm; Core window area Aw PQ5050 =415.15mm 2 ; Core cross-sectional area Ae PQ5050 =363.8mm 2 ; Core volume Ve PQ5050 =41291.3mm 3 The inductance coefficient, i.e., the single-turn inductance without air gap, is AL = 8500 nH / N. 2 ; Window coefficient K of the primary and secondary sides u =0.26, here the primary and secondary sides are set to occupy the same window, the window occupancy rate generally does not exceed 0.3, here it is set to 0.26. The resistivity of copper wire at 20 degrees and standard atmospheric pressure ρ_Cu_20degC=1.724·10 -8 ·Ω·m; equivalent turn length of the winding, i.e., the length of each turn. Minimum value of magnetic flux density B min =0.1 mT; Maximum value of magnetic flux density B max =400·mT; B m =B min B min +0.01·mT...B max Define the maximum magnetic flux density B m As a variable, with a minimum increase or decrease of 0.01mT, at the minimum value B min =0.1·mT to the maximum value B max It varies between 400 mT, where mT is the unit of magnetic flux density.

[0055] Based on step S3, after selecting the core material, the magnetic flux density-loss curve, the magnetic frequency-loss curve, and the loss correction coefficient corresponding to the excitation waveform conversion are used to obtain the transformer magnetic loss equation with the maximum magnetic flux density as the variable.

[0056] In one embodiment, such as Figure 3 As shown, the specific process based on step S3 includes: S31, interpolating and fitting the magnetic flux density-loss curve corresponding to the magnetic core parameters to obtain the magnetic flux density-core loss expression corresponding to the magnetic core parameters; S32, interpolating and fitting the frequency-loss curve corresponding to the magnetic core parameters to obtain the frequency-core loss expression corresponding to the magnetic core parameters; S33, obtaining the eddy current loss ratio of the transformer under square wave excitation relative to sinusoidal wave excitation, so as to obtain the loss correction coefficient of the transformer under square wave excitation; S34, obtaining the magnetic flux density-core loss expression per unit volume based on the loss correction coefficient, the magnetic flux density-core loss expression, and the frequency-core loss expression; S35, transforming the magnetic flux density-core loss expression per unit volume to obtain the transformer magnetic loss equation with the maximum magnetic flux density as the variable.

[0057] The specific process is described using a particular embodiment. First, data is read based on the magnetic flux density-loss curve of the magnetic material provided by the manufacturer, and the following data is obtained:

[0058]

[0059] In other words, the image data is converted into a magnetic flux density-loss interpolation expression that can be used for calculation. Curve is the summary of the read data; Bmcurve (magnetic flux density data) is the extracted X-axis curve data; Ploss (core loss data) is the extracted Y-axis curve data. The magnetic flux density-core loss expression corresponding to the core parameters is obtained by interpolating and fitting the obtained data as follows:

[0060] Ploss_N95_100kHz_100degC(B m = linterp(Bmcurve, Ploss, B) m (1);

[0061] The operating conditions corresponding to the expression are set as follows: operating frequency 100kHz, operating temperature 100 degrees Celsius; the unit of Ploss_N95_100kHz_100degC is mW / cm². 3 .

[0062] Simultaneously, data was read based on the frequency-loss curve provided by the manufacturer, and the specific data obtained are as follows:

[0063]

[0064] Where Curve1 is the summary data read by the engineering software; Fscurve (operating frequency data) is the extracted X-axis curve data; and Ploss1 (core loss data) is the extracted Y-axis curve data. The frequency-core loss expression corresponding to the core parameters is obtained by interpolation and fitting of the obtained data as follows:

[0065] Ploss_N95_200mT_100degC(fs)=linterp(Fscurve,Ploss1,fs);

[0066] The operating conditions corresponding to the expression are set as follows: maximum magnetic flux density 200 mT, operating temperature 100 degrees Celsius; the unit of Ploss_N95_200mT_100degC is mW / cm². 3 The unit of fs is kHz.

[0067] Therefore, the frequency factor corresponding to the actual operating frequency in this embodiment is derived as follows:

[0068]

[0069] In actual design, the transformer operates under square wave excitation, while the curve provided by the manufacturer is based on sinusoidal excitation. Considering that for the same B value, square wave excitation produces less eddy current loss than sinusoidal excitation, for example, at an operating frequency of 50kHz, the eddy current loss ratio is <0.15. Here, we take 0.15, i.e., K... fs =0.15; thus, the eddy current loss ratios under square wave excitation and sinusoidal wave excitation are obtained as follows:

[0070]

[0071] The loss correction coefficient, considering square wave excitation and eddy current loss, satisfies:

[0072] K factor_eddy_squ_to_sin =1+(K) fs ·K squ_to_sin )-K fs =0.972;

[0073] Using equation (1), we obtain the expression for magnetic flux density and core loss per cubic centimeter, which takes into account the correction coefficient for eddy current loss under square wave excitation. This expression is obtained by correcting a sine wave to a square wave:

[0074]

[0075] With maximum magnetic flux density B m Let be the variable, and let be the expression for magnetic loss and magnetic flux density.

[0076]

[0077] Among them, P Fe_loss The unit is W.

[0078] Then one can obtain, such as Figure 4 The curve showing the relationship between magnetic flux density and core loss indicates that core loss increases with increasing magnetic flux density.

[0079] Based on step S4, the copper loss equation for the transformer is obtained. For example... Figure 5 As shown, the specific process may include: S41, obtaining the primary-to-secondary turns ratio of the transformer, and obtaining expressions for the primary-side turns and the secondary-side turns of the transformer, respectively, with the maximum magnetic flux density as a variable; S42, under the condition that the window area occupied by the primary side of the transformer is equal to the window area occupied by the secondary side of the transformer, obtaining the window area of ​​the primary side of the transformer and the window area of ​​the secondary side of the transformer, respectively; S43, obtaining the expression for the primary-side single-turn wire diameter of the transformer based on the expression for the primary-side turns and the window area occupied by the primary side of the transformer, and obtaining the expression for the secondary-side single-turn wire diameter of the transformer based on the expression for the secondary-side turns and the window area occupied by the secondary side of the transformer; S44. S45. Obtain the cross-sectional area expressions for the primary and secondary windings of the transformer based on the expressions for the primary single-turn wire diameter and the secondary single-turn wire diameter, respectively; S46. Obtain the primary winding copper loss of the transformer based on the effective value of the primary current and the primary winding resistance, and obtain the secondary winding copper loss of the transformer based on the effective value of the secondary current and the secondary winding resistance; S47. Obtain the skin effect coefficient when the AC copper loss is set to be equal to the DC copper loss, and obtain the transformer copper loss equation with the maximum magnetic flux density as the variable based on the primary winding copper loss, the secondary winding copper loss, and the skin effect coefficient.

[0080] The specific process is described using a concrete example. First, based on the principle that the copper losses on the primary and secondary sides are similar, the window areas occupied by the primary and secondary sides of the transformer are set to be the same, resulting in the following window areas for the primary and secondary sides of the transformer:

[0081]

[0082] Among them, A w_P Let A be the area of ​​the window on the original side. w_S Let be the area of ​​the secondary side window.

[0083] The turns ratio of the primary and secondary sides of the transformer is obtained as follows:

[0084]

[0085] With maximum magnetic flux density B m As a variable, the expression for the number of turns on the primary side satisfies:

[0086]

[0087] The expression for the number of turns on the secondary side satisfies:

[0088]

[0089] Referring to equation (4), the expression for the number of turns on the primary side of the transformer is obtained as follows:

[0090]

[0091] Referring to equation (5), the expression for the number of turns on the secondary side of the transformer is obtained as follows:

[0092]

[0093] By referencing equation (6), we obtain the expression for the cross-sectional area of ​​the original single-turn line:

[0094]

[0095] By referring to equation (7), we obtain the expression for the cross-sectional area of ​​a single turn on the secondary side:

[0096]

[0097] Secondary peak current:

[0098] I sec_pk =I pri_pk ·n=28.45·A;

[0099] RMS value of secondary current:

[0100]

[0101] Primary winding length:

[0102] L_Cu_P(B m ) = MPT PQ5050 ·N P (B m (10);

[0103] Secondary winding length:

[0104] L_Cu_S(B m ) = MPT PQ5050 ·N S (B m (11);

[0105] Primary wire-wound resistance:

[0106]

[0107] Secondary wire-wound resistor:

[0108]

[0109] Assume that the AC copper loss and DC copper loss under the influence of the skin effect are equal, i.e., the skin effect coefficient:

[0110] K skin =2;

[0111] Primary winding copper loss:

[0112] P Cu_P (B m ) = I pri_rms 2 ·R_Cu_100degC_P(B m (14);

[0113] Secondary winding copper loss:

[0114] P Cu_S (B m ) = I sec_rms 2 ·R_Cu_100degC_S(B m (15);

[0115] With maximum magnetic flux density B m Using variables, we obtain the expression for transformer copper loss:

[0116] P Cu_all (B m )=(P Cu_P (B m )+P Cu_S (B m ))·K skin (16);

[0117] Based on step S5, the total transformer loss equation is constructed according to the transformer magnetic loss equation and the transformer copper loss equation. Specifically, the total transformer loss equation is the sum of the transformer magnetic loss equation and the transformer copper loss equation. In a specific embodiment, referring to equations (3) and (16), the maximum magnetic flux density B is obtained. m The expression for the total transformer loss as a variable:

[0118] P loss_all (B m ) = P Fe_loss (B m )+P Cu_all (B m (17);

[0119] Then obtained Figure 6 The curve, from the maximum magnetic flux density B m The relationship curve between the total transformer loss expression and the curve clearly shows that there exists a minimum point for the total transformer loss, and the maximum magnetic flux density B corresponds to this minimum point. m That is the value we need to find.

[0120] Based on step S6, the process of obtaining the maximum magnetic flux density includes, but is not limited to, solving the Mathcad equation to obtain the maximum magnetic flux density corresponding to the point of minimum total transformer loss:

[0121] B m_need =Minimize(P loss_all B m ) = 0.191·T.

[0122] Based on the maximum magnetic flux density obtained in step S6, confirm whether this maximum magnetic flux density satisfies the selected core parameters. For example... Figure 7 As shown, the specific process is as follows: S61, obtain the number of primary winding turns of the transformer according to the target magnetic flux density parameter and the expression for the number of primary winding turns of the transformer; obtain the number of secondary winding turns of the transformer according to the target magnetic flux density parameter and the expression for the number of secondary winding turns of the transformer; S62, obtain the actual magnetic flux density value of the transformer according to the expression for the magnetic flux density of the transformer; when the actual magnetic flux density value is within the core parameters, determine that the maximum magnetic flux density satisfies the core parameters.

[0123] In one specific embodiment, referring to equation (4), the number of turns of the primary winding is obtained:

[0124]

[0125] Rounding the result, the primary winding has 4 turns, i.e., N. P =4.

[0126] Using equation (5), the number of turns of the secondary winding is obtained:

[0127]

[0128] Rounding the result, the secondary winding has 12 turns, i.e., N. s =12.

[0129] The final maximum magnetic flux density of the transformer:

[0130] Within the maximum working magnetic flux density range of magnetic material N95, the core selection requirements are met.

[0131] Based on step S7, when it is determined that the maximum magnetic flux density meets the core selection requirements, equation (6) is used to obtain the primary side single-turn wire diameter:

[0132] Using equation (7), the diameter of a single turn of the secondary side is obtained:

[0133] Considering the skin depth ε, the wire diameter should be smaller than ε, and multiple strands should be wound in parallel:

[0134] Single strand wire diameter selection: D single =0.1mm;

[0135] Number of strands wrapped around the original edge:

[0136] Secondary side and number of strands:

[0137] Transformer air gap: Where Ae is in cm 2 Lm is in mH.

[0138] If the maximum magnetic flux density obtained based on the judgment process in step S6 does not meet the core selection requirements, the core parameters can be reselected, and steps S3 to S6 can be re-executed according to the selected core parameters until the maximum magnetic flux density obtained meets the core selection requirements.

[0139] Considering that leakage inductance is affected by many factors, including the diffusion effect caused by the size of the air gap and its impact on nearby windings, the leakage inductance is generally determined by the transformer's structure and winding method. Typically, lower leakage inductance is better. In this design, the leakage inductance participates in resonance. To ensure the leakage inductance value meets design requirements, a baffle wall or a magnetic film can be added at the air gap to increase the leakage inductance.

[0140] It is understood that the above embodiments only illustrate preferred embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can freely combine the above technical features without departing from the concept of the present invention, and can also make several modifications and improvements, all of which fall within the protection scope of the present invention. Therefore, all equivalent transformations and modifications made with respect to the scope of the claims of the present invention should fall within the scope of the claims of the present invention.

Claims

1. A low-loss transformer design method, characterized in that, The method includes the following steps: S1. Construct the application scenario of the transformer and determine the target parameters of the transformer; S2. Select the core parameters of the transformer; S3. Obtain the corresponding magnetic material magnetic flux density-loss curve, magnetic material frequency-loss curve, and loss correction coefficient corresponding to the excitation waveform conversion based on the magnetic core parameters, and obtain the transformer magnetic loss equation with the maximum magnetic flux density as the variable. S4. Obtain the primary winding copper loss and secondary winding copper loss of the transformer under the influence of the skin effect, and obtain the transformer copper loss equation with the maximum magnetic flux density as the variable. S5. Obtain the total loss equation of the transformer based on the transformer magnetic loss equation and the transformer copper loss equation; S6. Obtain the maximum magnetic flux density corresponding to the minimum point of total transformer loss according to the total transformer loss equation, and confirm whether the maximum magnetic flux density satisfies the core parameters; if yes, proceed to step S7, otherwise proceed to step S2. S7. Obtain the primary winding parameters and secondary winding parameters of the transformer based on the maximum magnetic flux density to complete the transformer design.

2. The low-loss transformer design method according to claim 1, characterized in that, In step S1, the application scenarios for constructing the transformer include: Construct an LLC converter topology containing two transformers; the primary sides of the two transformers are connected in parallel to connect to the power input, and the secondary sides of the two transformers are connected in series to connect to the load circuit.

3. The low-loss transformer design method according to claim 2, characterized in that, In step S1, determining the target parameters of the transformer includes: determining the input power, primary input voltage, primary input current, secondary output voltage, operating switching frequency, and core window occupancy rate of the transformer.

4. The low-loss transformer design method according to claim 1, characterized in that, In step S2, selecting the core parameters of the transformer includes: The magnetic core material is obtained by using the inductance area Ap method or a reference sample to obtain the core parameters.

5. The low-loss transformer design method according to claim 1, characterized in that, In step S3, obtaining the transformer magnetic loss equation with the maximum magnetic flux density as the variable based on the core parameters, including obtaining the corresponding magnetic flux density-loss curve, magnetic frequency-loss curve, and loss correction coefficient corresponding to the excitation waveform conversion; includes: S31. Interpolate and fit the magnetic flux density-loss curves of the magnetic core parameters to obtain the magnetic flux density-core loss expressions corresponding to the magnetic core parameters. S32. Interpolate and fit the frequency-loss curve of the magnetic material corresponding to the magnetic core parameters to obtain the frequency-core loss expression corresponding to the magnetic core parameters; S33. Obtain the ratio of eddy current loss of the transformer under square wave excitation to that under sinusoidal wave excitation, so as to obtain the loss correction coefficient of the transformer under square wave excitation. S34. Obtain the magnetic flux density-core loss expression per unit volume based on the loss correction coefficient, the magnetic flux density-core loss expression, and the frequency-core loss expression. S35. Transform the magnetic flux density-core loss expression corresponding to the unit volume to obtain the transformer magnetic loss equation with the maximum magnetic flux density as the variable.

6. The low-loss transformer design method according to claim 1, characterized in that, In step S4, obtaining the primary winding copper loss and secondary winding copper loss of the transformer under the influence of the skin effect, and obtaining the transformer copper loss equation with the maximum magnetic flux density as the variable, includes: S41. Obtain the primary-to-secondary turns ratio of the transformer, and respectively obtain the primary-to-secondary turns expression and the secondary-to-secondary turns expression of the transformer with the maximum magnetic flux density as the variable; S42. When the window area occupied by the primary side of the transformer is set to be equal to the window area occupied by the secondary side of the transformer, the window area of ​​the primary side of the transformer and the window area of ​​the secondary side of the transformer are obtained respectively. S43. Obtain the expression for the single-turn wire diameter of the primary side of the transformer based on the expression for the number of turns on the primary side of the transformer and the window area occupied by the primary side of the transformer; obtain the expression for the single-turn wire diameter of the secondary side of the transformer based on the expression for the number of turns on the secondary side of the transformer and the window area occupied by the secondary side of the transformer. S44. Obtain the cross-sectional area expression of the primary side single-turn wire diameter and the cross-sectional area expression of the secondary side single-turn wire diameter of the transformer according to the expression of the primary side single-turn wire diameter and the expression of the secondary side single-turn wire diameter of the transformer, respectively. S45. Obtain the primary winding copper loss of the transformer based on the effective value of the primary current and the primary winding resistance of the transformer; obtain the secondary winding copper loss of the transformer based on the effective value of the secondary current and the secondary winding resistance of the transformer. S46. Under the condition that the AC copper loss is equal to the DC copper loss, obtain the skin effect coefficient, and obtain the transformer copper loss equation with the maximum magnetic flux density as the variable based on the primary winding copper loss of the transformer, the secondary winding copper loss of the transformer, and the skin effect coefficient.

7. The low-loss transformer design method according to claim 1, characterized in that, In step S5, obtaining the total transformer loss equation based on the transformer magnetic loss equation and the transformer copper loss equation includes: The sum of the transformer magnetic loss equation and the transformer copper loss equation is the transformer total loss equation.

8. The low-loss transformer design method according to claim 6, characterized in that, In step S6, obtaining the maximum magnetic flux density corresponding to the minimum point of total transformer loss according to the transformer total loss equation, and confirming whether the maximum magnetic flux density satisfies the core parameters, includes: The Mathcad equation is used to solve for the maximum magnetic flux density corresponding to the point where the total loss of the transformer is minimized, which is taken as the target magnetic flux density parameter.

9. The low-loss transformer design method according to claim 8, characterized in that, The step of confirming whether the maximum magnetic flux density meets the core parameters includes: The number of primary winding turns of the transformer is obtained according to the target magnetic flux density parameter and the expression for the number of primary winding turns of the transformer; the number of secondary winding turns of the transformer is obtained according to the target magnetic flux density parameter and the expression for the number of secondary winding turns of the transformer. The actual magnetic flux density of the transformer is obtained according to the magnetic flux density expression of the transformer. When the actual magnetic flux density is within the core parameters, it is determined that the maximum magnetic flux density satisfies the core parameters.

10. The low-loss transformer design method according to claim 9, characterized in that, In step S7, obtaining the primary winding parameters and secondary winding parameters of the transformer based on the maximum magnetic flux density includes: The primary single-turn wire diameter of the transformer is obtained based on the target magnetic flux density parameter of the transformer and the expression for the primary single-turn wire diameter of the transformer. The secondary single-turn wire diameter of the transformer is obtained based on the target magnetic flux density value of the transformer and the expression for the secondary single-turn wire diameter of the transformer. The maximum value of the wire diameter is set according to the skin depth, so as to obtain the number of parallel strands on the primary side and the number of parallel strands on the secondary side of the transformer based on the maximum value of the wire diameter.

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