Design method of magnetic integrated planar transformer with customized leakage inductance

Abstract

The invention relates to a design method of a magnetic integrated planar transformer with customized leakage inductance. The design method comprises the following steps: S0, obtaining target excitation inductance and target leakage inductance; s1, calculating the length of a magnetic core air gap required for reaching the target excitation inductance; s2, the maximum leakage inductance Llk0max in the magnetic core window when no air gap is formed and the maximum leakage inductance Llkmax after the air gap with the length is formed are obtained through finite element simulation, and then a correction coefficient kgap is calculated; and S3, according to the target leakage inductance and the leakage inductance Llkmax, selecting winding arrangement with relatively small parasitic capacitance or all winding arrangement for traversal calculation, and obtaining the optimal winding arrangement matched with the target leakage inductance. The magnetic integrated planar transformer is low in cost, small in size and simple in layout design.

Description

Technical Field

[0001] The present invention relates to, and in particular to, a design method for a magnetically integrated planar transformer with customized leakage inductance. Background Art

[0002] One of the outstanding advantages of LLC resonant converter is that the structure of its resonant cavity facilitates magnetic integration. Its resonant cavity consists of three parts: transformer, resonant inductor and resonant capacitor. In traditional designs, the magnetic components in the resonant cavity, transformer and resonant inductor, need to use a magnetic core respectively, which occupies a large area. If the magnetic components are integrated into a magnetic core, the circuit area can be significantly reduced and the power density can be improved. Therefore, magnetic integration is a very important step in the design process of LLC resonant converter.

[0003] There are two main research directions for existing magnetic integration technology. The first is to integrate the resonant inductor and the transformer on a magnetic core by sharing a magnetic circuit. The second research direction is to use the leakage inductance of the transformer, adjust the leakage inductance value of the transformer to make it equal to the resonant inductance, and use the leakage inductance of the transformer as the resonant inductance, so as to achieve the purpose of magnetic component integration. Generally speaking, the inherent leakage inductance of the transformer is smaller than the resonant inductance required by the resonant cavity, so the leakage inductance of the transformer needs to be customized when using the second magnetic integration method. One leakage inductance customization method is to insert a magnetic shunt between the magnetic cores. The leakage inductance of the transformer can be calculated by the energy stored in the core window: after inserting the magnetic shunt, more energy is stored in the core window. By changing the material and thickness of the magnetic shunt, the energy stored in the core window can be adjusted so that the leakage inductance of the transformer is equal to the required resonant inductance.

[0004] All of the above methods can achieve the purpose of magnetic integration, but they also have their own shortcomings. The first method of integrating the resonant inductor and the transformer by sharing the magnetic circuit requires arranging coils on the middle column and the side column of the magnetic core, which is different from the traditional winding arrangement and requires more complicated wiring; the second method of magnetic integration by inserting a magnetic shunt to control the leakage inductance requires the use of additional customized magnetic shunts, which increases the manufacturing cost. At the same time, the presence of the magnetic shunt will also increase the thickness of the circuit board. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a design method for a magnetically integrated planar transformer with customized leakage inductance, which can realize a low-cost, small-volume, and simple-layout magnetically integrated planar transformer without complex wiring design and customized magnetic shunts.

[0006] The technical solution adopted by the present invention to solve the technical problem is: to provide a design method of a magnetic integrated planar transformer with customized leakage inductance, comprising the following steps:

[0007] S0 obtains winding parameters and core specifications of the magnetic integrated transformer, as well as target excitation inductance and target leakage inductance;

[0008] S1 calculates the core air gap length required to achieve the target excitation inductance;

[0009] S2 obtains the maximum leakage inductance L in the transformer core window when no core air gap is opened through finite element simulation lk0_max , and the maximum leakage inductance L in the transformer core window after the core air gap of the air gap length is opened lk_max , and then calculate the leakage inductance correction coefficient k gap ;

[0010] S3 is based on the maximum leakage inductance L lk_max Set a reference interval. If the target leakage inductance is within the reference interval, traverse the winding arrangement with smaller parasitic capacitance and calculate the leakage inductance L in the transformer core window after the core air gap is opened for each winding arrangement. lk , obtain the optimal winding arrangement matching the target leakage inductance, otherwise enumerate all winding arrangements to obtain the optimal winding arrangement matching the target leakage inductance.

[0011] Furthermore, the calculation of the maximum leakage inductance L in the transformer core window when the core air gap is not provided is lk0_max , and the maximum leakage inductance L in the transformer core window after the core air gap of the air gap length is opened lk_max ,include:

[0012] The winding arrangement of the transformer is set to a structure with the largest leakage inductance, and the leakage inductance in the transformer core window is obtained by finite element simulation when the core air gap is not opened and when the core air gap with the air gap length is opened, and the maximum leakage inductance L is obtained. lk0_max , and the maximum leakage inductance L lk_max .

[0013] Furthermore, before step S3, the method further includes:

[0014] Determine whether the target leakage inductance is greater than the maximum leakage inductance L lk_max ;

[0015] If it is greater than, then adjust the winding parameters and core specifications of the transformer and return to step S1; otherwise, execute step S3.

[0016] Furthermore, the reference interval is

[0017] Furthermore, after the core air gap is opened, the leakage inductance L in the transformer core window is lk Calculated by the following method:

[0018] Following the one-dimensional assumption, calculate the leakage inductance L in the transformer core window when no core air gap is opened lk0 ;

[0019] Using the leakage inductance correction factor k gap The leakage inductance L lk0 Correction is performed to obtain the leakage inductance L in the transformer core window after the core air gap is opened. lk =k gap ×L lk0 .

[0020] Furthermore, when the core air gap is not provided, the leakage inductance LK0 in the transformer core window is calculated by the following formula:

[0021]

[0022] Where b is the average width of the winding, l is the average circumference of the winding, μ0 is the vacuum permeability, I p is the current in the primary winding, n p is the number of turns of the primary winding, h p is the thickness of the primary winding, I s is the current in the secondary winding, n s is the number of turns of the secondary winding, h s is the secondary winding thickness, H(0) is the magnetic field strength at the surface of the winding or the spacer layer, H is the magnetic field strength inside the winding or the spacer layer, and h i is the thickness of the spacer layer.

[0023] Furthermore, the magnetically integrated planar transformer includes a magnetic core, the four side columns of the magnetic core are connected end to end to form a magnetic core window, the middle column of the magnetic core is placed in the magnetic core window, and the middle column of the magnetic core is wound with a winding, forming different winding arrangements according to different winding methods.

[0024] Furthermore, when the magnetically integrated planar transformer is applied to an LLC resonant converter, the magnetizing inductance and the resonant inductance of the LLC resonant converter are set to be the target magnetizing inductance and the target leakage inductance of the magnetically integrated planar transformer, respectively.

[0025] Beneficial Effects

[0026] Due to the adoption of the above technical scheme, the present invention has the following advantages and positive effects compared with the prior art: the present invention calculates the required core air gap length according to the target excitation inductance, and obtains the maximum leakage inductance in the core window of the transformer when the core air gap is not opened and after the core air gap of the length is opened through finite element simulation, thereby calculating the correction coefficient. Since the correction coefficient for different winding arrangements remains unchanged, the correction coefficient can be used to correct the leakage inductance without air gap calculated based on the one-dimensional assumption, and the leakage inductance of the air gap transformer with different winding arrangements is obtained, and then the optimal winding arrangement matching the target leakage inductance is obtained, thereby realizing the design of a magnetic integrated planar transformer with the advantages of low cost, small size, and simple layout design, and can meet the requirements of the integration of magnetic components of LLC resonant converters; the present invention does not need to wind on the side columns of the core, the layout design is relatively simple, and the leakage inductance has been used in the design, so there is no need to calculate the leakage inductance when considering parasitic parameters; the present invention does not need to customize and use magnetic shunts, thereby reducing manufacturing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a flow chart of an embodiment of the present invention;

[0028] Figure 2 Schematic diagram of the core window structure of the magnetic integrated planar transformer according to the embodiment of the present invention;

[0029] Figure 3 It is a schematic diagram of a magnetic field intensity curve in a magnetic core window of a magnetically integrated planar transformer according to an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0031] An embodiment of the present invention relates to a design method for a magnetically integrated planar transformer with customized leakage inductance, which controls the energy in the core window by adjusting the winding arrangement of the planar transformer, thereby customizing the leakage inductance of the transformer to achieve the purpose of magnetic integration.

[0032] The leakage inductance of a planar transformer is determined by the energy stored in the core window, and the energy in the window can be calculated from the magnetic field strength in the window: Adjusting the arrangement order of the primary and secondary coils on the magnetic core can change the magnetic field intensity distribution in the window, thereby controlling the leakage inductance of the transformer.

[0033] The specific design process includes the following steps:

[0034] S0 obtains winding parameters and core specifications of the magnetic integrated transformer, as well as target excitation inductance and target leakage inductance;

[0035] S1 calculates the core air gap length required to achieve the target excitation inductance;

[0036] S2 obtains the maximum leakage inductance L in the transformer core window when no core air gap is opened through finite element simulation lk0_max , and the maximum leakage inductance L in the transformer core window after the core air gap of the above air gap length is opened lk_max , and then calculate the leakage inductance correction coefficient k gap ; Determine whether the target leakage inductance is greater than the maximum leakage inductance L lk_max If it is greater than, adjust the winding parameters and core specifications of the transformer and return to step S1, otherwise, execute step S3;

[0037] S3 sets the reference interval to If the target leakage inductance is within the reference interval, the winding arrangements with smaller parasitic capacitance are traversed, and the leakage inductance within the transformer core window after the core air gap is opened corresponding to each winding arrangement is calculated to obtain the optimal winding arrangement matching the target leakage inductance. Otherwise, all winding arrangements are enumerated to obtain the optimal winding arrangement matching the target leakage inductance.

[0038] Among them, the maximum leakage inductance L in the transformer core window when the core air gap is not opened and after the air gap is opened is lk0_max , can be calculated by the following method: Set the transformer winding arrangement to the structure with the largest leakage inductance, and calculate the leakage inductance in the transformer core window when the core air gap is not opened and after the air gap is opened, and obtain the maximum leakage inductance L lk0_max , and the maximum leakage inductance L lk_max .

[0039] When used in an LLC resonant converter, the design flow of a magnetically integrated planar transformer with customized leakage inductance is as follows:

[0040] ① According to the performance requirements of LLC resonant converter, calculate the parameters of the resonant cavity: excitation inductance L m , resonant inductor L r , resonant capacitor C r ;

[0041] ② Select the appropriate number of winding turns and transformer core specifications, the primary winding thickness h p , secondary winding thickness h s And the thickness of the spacer layer h i , calculated to obtain the excitation inductance L m Required core air gap length l g ;

[0042] ③ Use finite element (FEA) simulation software to simulate the transformer. The transformer winding arrangement method chooses the arrangement method with the largest leakage inductance, where the primary and secondary windings are completely non-interlaced. The maximum leakage inductance L obtained by simulation when the magnetic core is not gapped lk0_max The maximum leakage inductance L when the air gap is opened lk_max , and calculate If L r No more than L lk_max Then proceed to the next step, otherwise you need to adjust the selected transformer specifications and h p 、h s 、h i And other parameters;

[0043] ④ Use the following formula to calculate the leakage inductance of a transformer with a specific winding arrangement:

[0044] Leakage inductance without air gap:

[0045] Leakage inductance after air gap: L lk =k gap ·L lk0

[0046] ⑤ Use computer aid to calculate the transformer leakage inductance under different winding arrangements. r )exist To L lk_max If L is between , the traversal calculation can be performed only in the structure with smaller parasitic capacitance: all the primary (secondary) windings are arranged together and inserted into the secondary (primary) winding. The parasitic capacitance is reduced by reducing the number of interleavings of the primary and secondary windings, and the number of traversal calculations is also reduced. r Not Available To L lk_max If you need higher design accuracy, you can try to enumerate all winding arrangements;

[0047] ⑥ Select a winding arrangement with a suitable leakage inductance value to complete the design of the magnetically integrated planar transformer.

[0048] Taking the LLC resonant converter from 400V to 48V as an example, the resonant frequency is selected as 500kHz, then the required excitation inductance L m is 20μH, the resonant inductor L r 4μH, that is, the leakage inductance L needs to be designed lk The integrated planar transformer is 4μH. We use EQ 30 / 8 / 20 core, primary winding N p =16, secondary winding N s =2, thickness of primary and secondary winding h p ,h s =70μm, the thickness of the spacing layer between windings hi =330μm.

[0049] When the air gap is not opened, it can be considered that the core part of the transformer follows the "one-dimensional assumption", that is, the electromagnetic field and current distribution near the conductor only change along the thickness of the conductor. Figure 2 As shown, we assume that the magnetic field strength in the core window only changes along the thickness h of the winding, so the leakage inductance when the air gap is not opened can be calculated by the following formula:

[0050]

[0051] Where b is the average width of the winding, l is the average circumference of the winding, μ0 is the vacuum permeability, I p is the current in the primary winding, n p is the number of turns of the primary winding, h p is the thickness of the primary winding, I s is the current in the secondary winding, n s is the number of turns of the secondary winding, h s is the secondary winding thickness, H(0) is the magnetic field strength at the surface of the winding or the spacer layer, H is the magnetic field strength inside the winding or the spacer layer, and h i is the thickness of the spacer layer.

[0052] In order to obtain the required excitation inductance L m , we need to add a certain length of air gap between the two parts of the magnetic core. The calculation formula of the air gap length is as follows: The parameter A e Parameter A L You can check it in the parameter manual of the magnetic core. After the air gap is opened, the diffuse magnetic flux at the air gap enters the core window, so that the magnetic field intensity distribution in the window no longer follows the "one-dimensional assumption". Therefore, it is necessary to correct the calculation formula of leakage inductance, that is, L lk =k gap ·L lk0 , correction factor k gap The expression is as follows:

[0053]

[0054] where b w is the width of the core window, A w With A w ' are the effective areas of the core window before and after the air gap is opened, A cc With A c1 is the effective area of ​​the core center column and side column. For different winding arrangements, the correction factor k gap The values ​​of k are the same. gap Some parameters in the expression are difficult to measure accurately, so k is obtained through FEA simulation. gapThe numerical value is a more convenient method.

[0055] Through simulation, we get the k of the designed transformer gap =0.68. Then, we calculated the leakage inductance of different windings and found that a suitable winding arrangement is "2p+2s+14p", with a leakage inductance of 4.10μH. The magnetic field strength curve in the core window is as follows: Figure 3 The leakage inductance value L of the designed transformer is obtained through experimental testing. lk The resonant inductance L is 3.92μH, which meets the resonant inductance L required by the LLC resonant converter. r Design value requirements.

Claims

1. A design method for a magnetically integrated planar transformer with customized leakage inductance, characterized in that: The following steps are involved: S0 obtains winding parameters and core specifications of the magnetic integrated transformer, as well as target excitation inductance and target leakage inductance; S1 calculates the core air gap length required to achieve the target excitation inductance; S2 obtains the maximum leakage inductance L in the transformer core window when no core air gap is opened through finite element simulation lk0_max , and the maximum leakage inductance L in the transformer core window after the core air gap of the air gap length is opened lk_max , and then calculate the leakage inductance correction coefficient k gap ; S3 is based on the maximum leakage inductance L lk_max Set a reference interval. If the target leakage inductance is within the reference interval, traverse the winding arrangement with smaller parasitic capacitance and calculate the leakage inductance L in the transformer core window after the core air gap is opened for each winding arrangement. lk , obtain the optimal winding arrangement matching the target leakage inductance, otherwise enumerate all winding arrangements to obtain the optimal winding arrangement matching the target leakage inductance.

2. The method according to claim 1, characterized in that The calculation of the maximum leakage inductance L in the transformer core window when the core air gap is not set lk0_max , and the maximum leakage inductance L in the transformer core window after the core air gap of the air gap length is opened lk_max ,include: The winding arrangement of the transformer is set to a structure with the largest leakage inductance, and the leakage inductance in the transformer core window when no core air gap is provided and after the core air gap of the air gap length is provided are obtained by finite element simulation, and the maximum leakage inductance L is obtained. lk0_max , and the maximum leakage inductance L lk_max .

3. The method according to claim 1, characterized in that Before step S3, the method further includes: Determine whether the target leakage inductance is greater than the maximum leakage inductance L lk_max ; If it is greater than, then adjust the winding parameters and core specifications of the transformer and return to step S1; otherwise, execute step S3.

4. The method according to claim 1, characterized in that The reference interval is 5. The method according to claim 1, characterized in that After the core air gap is opened, the leakage inductance L in the transformer core window lk Calculated by the following method: Following the one-dimensional assumption, calculate the leakage inductance L in the transformer core window when no core air gap is opened lk0 ; Using the leakage inductance correction factor k gap The leakage inductance L lk0 Correction is performed to obtain the leakage inductance L in the transformer core window after the core air gap is opened. lk =k gap ×L lk0 .

6. The method according to claim 1, characterized in that The leakage inductance L in the transformer core window when the core air gap is not provided lk0 Calculated by the following formula: Where b is the average width of the winding, l is the average circumference of the winding, μ0 is the vacuum permeability, I p is the current in the primary winding, n p is the number of turns of the primary winding, h p is the thickness of the primary winding, I s is the current in the secondary winding, n s is the number of turns of the secondary winding, h s is the secondary winding thickness, H(0) is the magnetic field strength at the surface of the winding or the spacer layer, H is the magnetic field strength inside the winding or the spacer layer, and h i is the thickness of the spacer layer.

7. The method according to claim 1, characterized in that The magnetically integrated planar transformer comprises a magnetic core, wherein four side columns of the magnetic core are connected end to end to form a magnetic core window, a middle column of the magnetic core is placed in the magnetic core window, and a winding is wound around the middle column of the magnetic core, forming different winding arrangements according to different winding methods.

8. The method according to claim 1, characterized in that When the magnetically integrated planar transformer is applied to an LLC resonant converter, the magnetizing inductance and the resonant inductance of the LLC resonant converter are set to be the target magnetizing inductance and the target leakage inductance of the magnetically integrated planar transformer, respectively.

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