Design method of low-loss transformer

Abstract

The invention relates to a low-loss transformer design method which comprises the following steps: constructing an application scene of a transformer, and determining target parameters of the transformer; selecting magnetic core parameters of the transformer; a corresponding magnetic material flux density-loss curve and a magnetic material frequency-loss curve are obtained according to the magnetic core parameters, and a transformer magnetic loss equation with the maximum flux density as a variable is obtained according to a loss correction coefficient corresponding to excitation waveform conversion; respectively acquiring primary winding copper loss and secondary winding copper loss of the transformer under the influence of the skin effect, and acquiring a transformer copper loss equation taking the maximum flux density as a variable; obtaining a transformer total loss equation according to the transformer magnetic loss equation and the transformer copper loss equation; obtaining the maximum flux density corresponding to the lowest point of the total loss of the transformer according to the total loss equation of the transformer, and obtaining the primary winding parameter and the secondary winding parameter of the transformer according to the maximum flux density when the maximum flux density meets the magnetic core parameter, so as to complete the design of the transformer. According to the invention, the minimum loss design of the transformer can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of transformer design, and more particularly to a low-loss transformer design method. Background Art

[0002] Photovoltaics, as a highly efficient clean energy, has been widely used around the world. Photovoltaic storage systems are usually composed of photovoltaic modules, lithium batteries, energy storage inverters, smart meters, power grids, grid-connected loads and off-grid loads. In order to more efficiently utilize clean energy and improve the conversion efficiency of the energy storage inverter that performs power conversion in the photovoltaic storage system, it is necessary to reduce the overall loss of the energy storage inverter as much as possible. The loss of the energy storage inverter is mainly concentrated in the power conversion part, which mainly includes the loss of the switch tube and the loss of the magnetic device. The loss of the switch tube is mainly determined by the circuit topology and the performance of the switching device. After the circuit topology is determined, how to maximize the conversion efficiency of the whole machine and how to design the magnetic device to minimize the loss of the magnetic device are important goals of the whole machine design.

[0003] For transformer design, the general practice is to confirm the magnetic core using the area AP method, and then calculate the turns ratio, winding wire diameter, and number of winding strands based on the set parameters. The maximum magnetic flux density is calculated to be no greater than the empirical value. The transformer after preliminary design can meet basic electrical requirements. However, with the development of semiconductors, the high-frequency application of power devices such as silicon carbide is increasing, and the demand for high-frequency transformers is also increasing. Therefore, transformers that meet the design requirements must meet high density, high efficiency, and low cost. At high frequencies, loss is the main limiting factor. Therefore, it is of great significance to find a transformer design method with the lowest loss that meets the requirements. 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 the present invention to solve the technical problem is: constructing a low-loss transformer design method, the method comprising the following steps:

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

[0007] S2, selecting the core parameters of the transformer;

[0008] S3, obtaining the corresponding magnetic material flux density-loss curve, the magnetic material frequency-loss curve and the loss correction coefficient corresponding to the excitation waveform conversion according to the magnetic core parameters to obtain the transformer magnetic loss equation with the maximum flux density as a variable;

[0009] S4. Obtaining the primary winding copper loss and the secondary winding copper loss of the transformer under the influence of the skin effect, respectively, and obtaining a transformer copper loss equation with the maximum magnetic flux density as a variable;

[0010] S5. Obtaining the transformer total loss equation according to the transformer magnetic loss equation and the transformer copper loss equation;

[0011] S6, obtaining the maximum magnetic flux density corresponding to the lowest point of the total loss of the transformer according to the total loss equation of the transformer, and confirming whether the maximum magnetic flux density meets the magnetic core parameters; if so, executing step S7, otherwise executing step S2;

[0012] S7. Obtain primary winding parameters of the transformer and secondary winding parameters of the transformer according to 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 scenario of constructing the transformer includes:

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

[0015] Preferably, in the low-loss transformer design method described in the present invention, in the 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 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 core magnetic material is obtained according to the inductance area product Ap method or reference samples to obtain the core parameters.

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

[0019] S31, performing interpolation fitting on the magnetic material magnetic density-loss curve corresponding to the magnetic core parameters to obtain a magnetic density-core loss expression corresponding to the magnetic core parameters;

[0020] S32, performing interpolation fitting on the magnetic material frequency-loss curve corresponding to the magnetic core parameters to obtain a frequency-core loss expression corresponding to the magnetic core parameters;

[0021] S33, obtaining the eddy current loss ratio of the transformer under square wave excitation relative to that under sine wave excitation to obtain a loss correction coefficient of the transformer under square wave excitation;

[0022] S34, obtaining a magnetic flux density-core loss expression corresponding to a unit volume according to 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 a transformer magnetic loss equation with the maximum magnetic flux density as a variable.

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

[0025] S41, obtaining the primary-to-secondary turns ratio of the transformer, and respectively obtaining an expression for the primary turns of the transformer and an expression for the secondary turns of the transformer with the maximum magnetic density as a variable;

[0026] S42, respectively obtaining the primary side window area of ​​the transformer and the secondary side window area of ​​the transformer under the condition that 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;

[0027] S43, obtaining a primary single-turn wire diameter expression of the transformer according to an expression of the number of primary turns of the transformer and an area of ​​the window occupied by the primary side of the transformer, and obtaining a secondary single-turn wire diameter expression of the transformer according to an expression of the number of secondary turns of the transformer and an area of ​​the window occupied by the secondary side of the transformer;

[0028] S44, obtaining an expression for the cross-sectional area of ​​a single turn of wire on the primary side of the transformer and an expression for the cross-sectional area of ​​a single turn of wire on the secondary side of the transformer respectively according to an expression for the diameter of a single turn of wire on the primary side of the transformer and an expression for the diameter of a single turn of wire on the secondary side of the transformer;

[0029] S45, obtaining the primary winding copper loss of the transformer according to the effective value of the primary current of the transformer and the primary winding resistance of the transformer, and obtaining the secondary winding copper loss of the transformer according to the effective value of the secondary current of the transformer and the secondary winding resistance of the transformer;

[0030] S46. 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 a variable according to 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 the step S5, the step of obtaining the transformer total loss equation according to the transformer magnetic loss equation and the transformer copper loss equation comprises:

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

[0033] Preferably, in the low-loss transformer design method of the present invention, in the step S6, the maximum magnetic flux density corresponding to the lowest point of the total loss of the transformer is obtained according to the total loss equation of the transformer, and it is confirmed whether the maximum magnetic flux density satisfies the magnetic core parameters; including:

[0034] The Mathcad equation is used to solve the maximum magnetic flux density corresponding to the lowest point of the total loss of the transformer, and the target magnetic flux density parameter is obtained.

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

[0036] The primary winding turns of the transformer are obtained according to the target magnetic flux density parameter and the expression of the primary winding turns of the transformer, and the secondary winding turns of the transformer are obtained according to the target magnetic flux density parameter and the expression of the secondary winding turns of the transformer;

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

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

[0039] Obtaining the primary single-turn wire diameter of the transformer according to the target magnetic density parameter of the transformer and the primary single-turn wire diameter expression of the transformer, and obtaining the secondary single-turn wire diameter of the transformer according to the target magnetic density value of the transformer and the secondary single-turn wire diameter expression 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 winding strands of the primary side of the transformer and the number of parallel winding strands of the secondary side of the transformer according to the maximum value of the wire diameter.

[0041] The implementation of a low-loss transformer design method of the present invention has the following beneficial effects: a low-loss transformer can be obtained, thereby enabling the photovoltaic energy storage inverter to achieve a higher conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0043] Figure 1 It is a program flow chart of an embodiment of a low-loss transformer design method of the present invention;

[0044] Figure 2 yes Figure 1 A circuit schematic diagram of an embodiment of an application scenario 1 of a transformer constructed in FIG.

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

[0046] Figure 4 is based on Figure 3 Schematic diagram of the relationship between magnetic flux density and core loss obtained;

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

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

[0049] Figure 7 yes Figure 1 A program flow chart of an embodiment corresponding to step S6 in FIG. DETAILED DESCRIPTION

[0050] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0051] like Figure 1 FIG. 1 is a diagram showing an embodiment of a method for designing a low-loss transformer according to the present invention. Figure 1In one embodiment of a low-loss transformer design method of the present invention, the following steps are included: S1, constructing an 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 according to the core parameters to obtain the transformer magnetic loss equation with the maximum flux density as the variable; S4, respectively obtaining the primary winding copper loss and the 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 transformer total loss equation according to the transformer magnetic loss equation and the transformer copper loss equation; S6, obtaining the maximum flux density corresponding to the lowest point of the total loss of the transformer according to the transformer total loss equation, and confirming whether the maximum flux density meets the core parameters; if so, executing step S7, otherwise executing step S2; S7, obtaining the primary winding parameters of the transformer and the secondary winding parameters of the transformer according to 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. Figure 2 As shown, an LLC converter topology structure including 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. That is, in this embodiment, the design method is introduced for the voltage transformation in the bidirectional LLC converter in the photovoltaic energy storage inverter. In the constructed application scenario, the battery discharge state is selected to introduce the design method. This process is suitable for the design of almost all types of transformers, such as transformers of various types of topologies such as forward, flyback, half-bridge, full-bridge, etc.

[0053] At the same time, based on step S1, the target parameters of the transformer are determined, including: determining the input power, primary input voltage, primary input current, secondary output voltage, working switching frequency and core window occupancy of the transformer. In a specific embodiment, the specific parameters of the transformer are given, and the maximum battery charge and discharge power Pin = 6000·W, the converter working switching frequency fs = 50·kHz, and the transformer excitation inductance L m =450·μH, transformer resonant inductance L r =2.5·μH, the average value of the 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 (two transformers connected in parallel on the primary side and in series on the secondary side) N tranf=2; the voltage drop of a single diode in the secondary full-bridge rectifier (a single loop current flows through two diodes) Vf = 1.0 V, the peak current of the primary side of the transformer Transformer primary current effective value Among them, the maximum loss, cost and volume 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 preliminarily selected. In one embodiment, the core parameters are obtained by obtaining the core magnetic material according to the inductance area product Ap method or reference samples. In a specific embodiment, a PQ5050B core is selected, and the core material is TDK's N95 magnetic material. The core specification parameters are selected to meet the following requirements: The 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 ; Inductance coefficient, i.e. single turn inductance without air gap, AL = 8500·nH / N 2 ; The window coefficient K of the original secondary side u =0.26, here the occupancy window of the original and secondary sides is set the same, the window occupancy rate is generally not more than 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 winding, i.e. the length of each turn Magnetic density B value minimum value B min =0.1·mT; maximum value of magnetic density B value B max =400·mT; B m =B min ,B min +0.01·mT...B max , define the maximum magnetic density B m is a variable, with 0.01mT as the minimum increase or decrease, at the minimum value B min =0.1·mT to maximum value B max =400·mT, where mT is the unit of magnetic density.

[0055] Based on step S3, after the core material is selected, the magnetic material flux density-loss curve, the magnetic material 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 flux density as the variable.

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

[0057] The specific process is described with a specific embodiment. First, data is read according to the magnetic material magnetic density-loss curve provided by the manufacturer, and the following data is obtained:

[0058]

[0059] That is, the tool converts the image data information into a magnetic flux density-loss interpolation expression that can be used for calculation. Curve is a summary of the read data; Bmcurve (magnetic flux density data) is the extracted X-axis data of the curve; Ploss (core loss data) is the extracted Y-axis data of the curve. The obtained data is interpolated and fitted to obtain the magnetic flux density-core loss expression corresponding to the core parameters as follows:

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

[0061] And set the working conditions corresponding to the expression as: working frequency 100kHz, working temperature 100 degrees Celsius; the unit of Ploss_N95_100kHz_100degC is mW / cm 3 .

[0062] At the same time, data is read according to the frequency-loss curve provided by the manufacturer, and the specific data obtained are as follows:

[0063]

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

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

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

[0067] Then, the frequency factor corresponding to the actual operating frequency in this embodiment is deduced as:

[0068]

[0069] Because in the actual design process, the working environment of the transformer is square wave excitation, and the curve provided by the manufacturer is the result under sine wave excitation. Considering the same B value, the eddy current loss generated by square wave excitation is smaller than that of sine wave. For example, when the operating frequency is 50kHz, the eddy current loss ratio is <0.15, so 0.15 is taken here, that is, K fs =0.15; thus the eddy current loss ratio under square wave excitation and sine wave excitation is as follows:

[0070]

[0071] The loss correction factor after 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] By quoting formula (1), we can obtain the expression of magnetic flux density and core loss per unit volume of 1 cubic centimeter, that is, the correction coefficient of eddy current loss under square wave excitation is taken into account, which is the expression obtained by correcting the sine wave to the square wave:

[0074]

[0075] With maximum magnetic density B m is a variable, the expression of magnetic loss and magnetic density;

[0076]

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

[0078] Then we can get Figure 4 The relationship curve between magnetic flux density and core loss is shown. From this curve, it can be seen that as the magnetic flux density increases, the core loss also increases.

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

[0080] The specific process is described with a specific embodiment. First, based on the principle that the copper loss of the primary and secondary sides is similar, the window area occupied by the primary and secondary sides of the transformer is set to be the same, and the window area of ​​the primary and secondary sides of the transformer is obtained as follows:

[0081]

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

[0083] Get the turns ratio of the primary and secondary sides of the transformer:

[0084]

[0085] With maximum magnetic density B m is a variable, and the expression of the number of turns of the primary side satisfies:

[0086]

[0087] The expression of secondary turns satisfies:

[0088]

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

[0090]

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

[0092]

[0093] By quoting formula (6), we can get the expression of the cross-sectional area of ​​the original single-turn wire:

[0094]

[0095] By referring to formula (7), we can get the expression of cross-sectional area of ​​single turn wire on the secondary side:

[0096]

[0097] Secondary peak current:

[0098] I sec_pk =I pri_pk n = 28.45 A;

[0099] Secondary current effective value:

[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 winding resistance:

[0106]

[0107] Secondary winding resistance:

[0108]

[0109] Assume that the AC copper loss and DC copper loss under the influence of skin effect are equal, that is, 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 density B m As variables, the transformer copper loss expression is obtained:

[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 transformer total loss equation is constructed according to the transformer magnetic loss equation and the transformer copper loss equation. Specifically, the sum of the transformer magnetic loss equation and the transformer copper loss equation is taken as the transformer total loss equation. In a specific embodiment, citing equations (3) and (16), the maximum magnetic density B is obtained. m The total transformer loss expression with variable is:

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

[0119] Then get Figure 6 Curve, from the maximum magnetic density B m The relationship curve corresponding to the total loss expression of the transformer can be intuitively seen that there is a minimum point in the total loss of the transformer, and the maximum magnetic flux density B corresponding to the minimum point m This is the value we need to find.

[0120] Based on step S6, the maximum magnetic flux density acquisition process includes but is not limited to solving the Mathcad equation, and the maximum magnetic flux density corresponding to the lowest point of the transformer total loss can be obtained:

[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, it is confirmed whether the maximum magnetic flux density meets the selected magnetic core parameters. Figure 7 As shown, the specific process is: S61, obtaining the primary winding turns of the transformer according to the target magnetic density parameter and the primary turns expression of the transformer, and obtaining the secondary winding turns of the transformer according to the target magnetic density parameter and the secondary turns expression of the transformer; S62, obtaining the actual magnetic density value of the transformer according to the magnetic density expression of the transformer, and when the actual magnetic density value is within the core parameters, determining that the maximum magnetic density satisfies the core parameters.

[0123] In a specific embodiment, the number of turns of the primary winding is obtained by citing formula (4):

[0124]

[0125] Round the result, the number of turns of the primary winding is 4, that is, N P =4.

[0126] By quoting formula (5), we can get the number of winding turns of the secondary side:

[0127]

[0128] Round the result, the secondary winding number of turns is 12, that is, N s =12.

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

[0130] Within the maximum working magnetic flux density range of magnetic material N95, the requirements for core selection 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 quoted to obtain the primary single-turn wire diameter:

[0132] Using formula (7), we can get the diameter of a single turn of the secondary side:

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

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

[0135] Number of original side windings:

[0136] Number of secondary winding strands:

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

[0138] If the maximum magnetic density obtained based on the judgment process of 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 density obtained meets the core selection requirements.

[0139] Considering that leakage inductance is affected by many factors, such as the diffusion effect caused by the size of the air gap and the impact on nearby windings, in summary, leakage inductance is determined by the structure and winding method of the transformer. Generally speaking, the smaller the leakage inductance, the better. In this design, leakage inductance participates in resonance. In order to make the leakage inductance value meet the design requirements, a retaining wall or a magnetic film can be added at the air gap to increase the leakage inductance.

[0140] It can be understood that the above embodiments only express the preferred implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the patent scope of the present invention. It should be pointed out that, for ordinary technicians in this field, the above technical features can be freely combined without departing from the concept of the present invention, and several deformations and improvements can be made, which all belong to the protection scope of the present invention. Therefore, all equivalent changes and modifications made to the scope of the claims of the present invention should belong to the coverage of the claims of the present invention.

Claims

1. A low-loss transformer design method, characterized in that: The method comprises the following steps: S1. Construct an application scenario of a transformer and determine target parameters of the transformer; S2, selecting the core parameters of the transformer; S3, obtaining the corresponding magnetic material flux density-loss curve, the magnetic material frequency-loss curve and the loss correction coefficient corresponding to the excitation waveform conversion according to the magnetic core parameters to obtain the transformer magnetic loss equation with the maximum flux density as a variable; S4. Obtaining the primary winding copper loss and the secondary winding copper loss of the transformer under the influence of the skin effect, respectively, and obtaining a transformer copper loss equation with the maximum magnetic flux density as a variable; S5. Obtaining the transformer total loss equation according to the transformer magnetic loss equation and the transformer copper loss equation; S6, obtaining the maximum magnetic flux density corresponding to the lowest point of the total loss of the transformer according to the total loss equation of the transformer, and confirming whether the maximum magnetic flux density meets the magnetic core parameters; if so, executing step S7, otherwise executing step S2; S7. Obtain primary winding parameters of the transformer and secondary winding parameters of the transformer according to 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 of constructing the transformer include: An LLC converter topology structure including two transformers is constructed; the primary sides of the two transformers are connected in parallel for connecting to a power input, and the secondary sides of the two transformers are connected in series for connecting to a load circuit.

3. The low-loss transformer design method according to claim 2, characterized in that: In the 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 of the transformer.

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

5. The low-loss transformer design method according to claim 1, characterized in that: In the step S3, the step of obtaining the corresponding magnetic material flux density-loss curve, the magnetic material frequency-loss curve and the loss correction coefficient corresponding to the excitation waveform conversion according to the magnetic core parameters to obtain the transformer magnetic loss equation with the maximum flux density as a variable includes: S31, performing interpolation fitting on the magnetic material magnetic density-loss curve corresponding to the magnetic core parameters to obtain a magnetic density-core loss expression corresponding to the magnetic core parameters; S32, performing interpolation fitting on the magnetic material frequency-loss curve corresponding to the magnetic core parameters to obtain a 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 that under sine wave excitation to obtain a loss correction coefficient of the transformer under square wave excitation; S34, obtaining a magnetic flux density-core loss expression corresponding to a unit volume according to 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 a transformer magnetic loss equation with the maximum magnetic flux density as a variable.

6. The low-loss transformer design method according to claim 1, characterized in that: In the step S4, the primary winding copper loss and the secondary winding copper loss of the transformer under the influence of the skin effect are respectively obtained, and the transformer copper loss equation with the maximum magnetic flux density as a variable is obtained; including: S41, obtaining the primary-to-secondary turns ratio of the transformer, and respectively obtaining an expression for the primary turns of the transformer and an expression for the secondary turns of the transformer with the maximum magnetic density as a variable; S42, respectively obtaining the primary side window area of ​​the transformer and the secondary side window area of ​​the transformer under the condition that 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; S43, obtaining a primary single-turn wire diameter expression of the transformer according to an expression of the number of primary turns of the transformer and an area of ​​the window occupied by the primary side of the transformer, and obtaining a secondary single-turn wire diameter expression of the transformer according to an expression of the number of secondary turns of the transformer and an area of ​​the window occupied by the secondary side of the transformer; S44, obtaining an expression for the cross-sectional area of ​​a single turn of wire on the primary side of the transformer and an expression for the cross-sectional area of ​​a single turn of wire on the secondary side of the transformer respectively according to an expression for the diameter of a single turn of wire on the primary side of the transformer and an expression for the diameter of a single turn of wire on the secondary side of the transformer; S45, obtaining the primary winding copper loss of the transformer according to the effective value of the primary current of the transformer and the primary winding resistance of the transformer, and obtaining the secondary winding copper loss of the transformer according to the effective value of the secondary current of the transformer and the secondary winding resistance of the transformer; S46. 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 a variable according to 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 the step S5, the transformer total loss equation is obtained according to the transformer magnetic loss equation and the transformer copper loss equation; comprising: The sum of the transformer magnetic loss equation and the transformer copper loss equation is obtained as the transformer total loss equation.

8. The low-loss transformer design method according to claim 6, characterized in that: In the step S6, the maximum magnetic flux density corresponding to the lowest point of the total loss of the transformer is obtained according to the total loss equation of the transformer, and it is confirmed whether the maximum magnetic flux density satisfies the magnetic core parameters; including: The Mathcad equation is used to solve the maximum magnetic flux density corresponding to the lowest point of the total loss of the transformer, and the target magnetic flux density parameter is obtained.

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

10. The low-loss transformer design method according to claim 9, characterized in that: In the step S7, the step of obtaining the primary winding parameters of the transformer and the secondary winding parameters of the transformer according to the maximum magnetic flux density comprises: Obtaining the primary single-turn wire diameter of the transformer according to the target magnetic density parameter of the transformer and the expression for the primary single-turn wire diameter of the transformer, and obtaining the secondary single-turn wire diameter of the transformer according to the target magnetic 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 winding strands of the primary side of the transformer and the number of parallel winding strands of the secondary side of the transformer according to the maximum value of the wire diameter.

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