A method for designing a magnetic integrated planar transformer with customized leakage inductance

Abstract

This invention relates to a design method for a magnetically integrated planar transformer with customized leakage inductance, comprising the following steps: S0 obtaining the target magnetizing inductance and the target leakage inductance; S1 calculating the required core air gap length to achieve the target magnetizing inductance; S2 obtaining the maximum leakage inductance L within the core window without an air gap through finite element simulation. lk0_max And the maximum leakage inductance L after opening an air gap of the stated length lk_max Then the correction coefficient k is calculated. gap S3 is based on the target leakage sensing and leakage sensing L. lk_max The optimal winding arrangement that matches the target leakage inductance is obtained by selecting a winding arrangement with smaller parasitic capacitance or by traversing all winding arrangements. This invention enables a low-cost, small-volume, and simple-layout magnetically integrated planar transformer.

Description

Technical Field

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

[0002] A key advantage of LLC resonant converters is the ease of magnetic integration in their resonant cavity structure. The resonant cavity consists of three parts: a transformer, a resonant inductor, and a resonant capacitor. In traditional designs, the magnetic components in the resonant cavity—the transformer and the resonant inductor—require separate magnetic cores, which occupy a significant area. Integrating the magnetic components onto a single core significantly reduces the circuit area and increases power density; therefore, magnetic integration is a crucial step in the design of LLC resonant converters.

[0003] Existing magnetic integration technology mainly focuses on two research directions. The first is to integrate a resonant inductor and a transformer together on a single magnetic core using a shared magnetic circuit. The second research direction utilizes the transformer's leakage inductance, adjusting its value to match the resonant inductance, thus using the transformer's leakage inductance as the resonant inductance to achieve the goal of magnetic component integration. Generally, the inherent leakage inductance of a transformer is less than the resonant inductance required by the resonant cavity; therefore, using the second magnetic integration method requires customizing the transformer's leakage inductance. One method for customizing the leakage inductance is to insert a magnetic shunt between the magnetic cores. The transformer's leakage inductance can be calculated from the energy stored within the core window: after inserting the magnetic shunt, more energy is stored within the core window. By changing the material and thickness of the magnetic shunt, the energy stored within the core window can be adjusted so that the transformer's leakage inductance equals the required resonant inductance.

[0004] All of the above methods can achieve the goal of magnetic integration, but they also have their own shortcomings. The first method, which integrates the resonant inductor and transformer by sharing a magnetic circuit, requires coils to be arranged on both the central and side columns of the magnetic core. This is different from the traditional winding arrangement and requires more complex wiring. The second method, which uses a magnetic shunt to control the leakage inductance, requires the use of a custom-made magnetic shunt, which increases manufacturing costs. At the same time, the presence of the magnetic shunt also increases 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-size, and simple-layout magnetically integrated planar transformer without the need for complex wiring design and customized magnetic shunts.

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

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

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

[0009] S2 uses finite element simulation to obtain the maximum leakage inductance L inside the transformer core window when no core air gap is opened. lk0_max And the maximum leakage inductance L within the transformer core window after opening the core air gap of the specified length. lk_max Then, the leakage inductance correction coefficient k is calculated. gap ;

[0010] S3 is based on the maximum leakage inductance L lk_max A reference range is set. If the target leakage inductance is within the reference range, the winding arrangements with smaller parasitic capacitances are traversed, and the leakage inductance L in the transformer core window after opening the core air gap is calculated for each winding arrangement. lk To obtain the optimal winding arrangement that matches the target leakage inductance, otherwise enumerate all winding arrangements to obtain the optimal winding arrangement that matches the target leakage inductance.

[0011] Furthermore, the calculation involves the maximum leakage inductance L within the transformer core window when the core air gap is not present. lk0_max And the maximum leakage inductance L within the transformer core window after opening the core air gap of the specified length. lk_max ,include:

[0012] The transformer windings are arranged to maximize leakage inductance. Finite element simulations are used to obtain the leakage inductance within the transformer core window before and after establishing the required air gap length. The maximum leakage inductance L is then determined. lk0_max and the maximum leakage inductance L lk_max .

[0013] Furthermore, prior to step S3, the following steps are also included:

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

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

[0016] Furthermore, the reference interval is

[0017] Furthermore, the leakage inductance L in the transformer core window after the core air gap is opened... lk It is obtained through the following calculation method:

[0018] Following the one-dimensional assumption, calculate the leakage inductance L within the transformer core window when the core air gap is not opened. lk0 ;

[0019] Using the leakage inductance correction coefficient k gap Regarding the leakage inductance L lk0 Make corrections to obtain the leakage inductance L within the transformer core window after opening the core air gap. lk =k gap ×L lk0 .

[0020] Furthermore, the leakage inductance LK0 within the transformer core window when the core air gap is not opened is calculated using 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 free permeability, and I p n is the current in the primary winding. p h is the number of turns in the primary winding. p I is the thickness of the primary winding. s n is the current in the secondary winding. s h is the number of turns in the secondary winding. s H is the thickness of the secondary winding, H(0) is the magnetic field strength at the surface of the winding or spacer layer, H is the magnetic field strength inside the winding or spacer layer, and h i The thickness is the spacer layer.

[0023] Furthermore, the magnetic integrated planar transformer includes a magnetic core, the four side posts of the magnetic core are connected end to end to form a magnetic core window, the central post of the magnetic core is placed in the magnetic core window, and the central post of the magnetic core is wound with windings, which form different winding arrangements depending on the winding method.

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

[0025] Beneficial effects

[0026] Due to the adoption of the above technical solution, this invention has the following advantages and positive effects compared with the prior art: This invention calculates the required core air gap length based on the target excitation inductance, and obtains the maximum leakage inductance within the transformer core window without a core air gap and after opening a core air gap of the specified length through finite element simulation, thereby calculating the correction coefficient. Since the correction coefficient remains unchanged for different winding arrangements, it can be used to correct the air gap-free leakage inductance calculated based on the one-dimensional assumption, thereby obtaining the leakage inductance of air gap transformers with different winding arrangements, and thus obtaining the optimal winding arrangement matching the target leakage inductance. This achieves the design of a magnetically integrated planar transformer with advantages such as low cost, small size, and simple layout design, which can meet the requirements of magnetic component integration in LLC resonant converters; This invention does not require winding on the core side posts, making the layout design simpler, and the leakage inductance has already been utilized in the design, so the leakage inductance does not need to be calculated again when considering parasitic parameters; This invention does not require the customization and use of magnetic shunts, reducing manufacturing costs. Attached Figure Description

[0027] Figure 1 This is a flowchart of an embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of the magnetic core window structure of the magnetically integrated planar transformer according to an embodiment of the present invention;

[0029] Figure 3 This is a schematic diagram of the magnetic field strength curve within the magnetic core window of the magnetically integrated planar transformer according to an embodiment of the present invention. Detailed Implementation

[0030] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0031] The present invention relates to a design method for a magnetically integrated planar transformer with customized leakage inductance. By adjusting the winding arrangement of the planar transformer, the energy level within the magnetic core window is controlled, 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 within the window. Adjusting the arrangement order of the primary and secondary coils on the magnetic core can change the magnetic field strength distribution within the window, thereby controlling the leakage inductance of the transformer.

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

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

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

[0036] S2 uses finite element simulation to obtain the maximum leakage inductance L inside the transformer core window when no core air gap is opened. lk0_max And the maximum leakage inductance L within the transformer core window after opening the core air gap of the aforementioned length. lk_max Then, the leakage inductance correction coefficient k is calculated. gap Determine if the target leakage inductance is greater than the maximum leakage inductance L. lk_max If the value is greater than 1, adjust the winding parameters and core specifications of the transformer and return to step S1; otherwise, proceed to step S3.

[0037] S3 sets the reference range as follows: If the target leakage inductance is within the reference range, then iterate through the winding arrangements with smaller parasitic capacitance, calculate the leakage inductance in the transformer core window after opening the core air gap for each winding arrangement, and obtain the optimal winding arrangement to match the target leakage inductance. Otherwise, enumerate all winding arrangements to obtain the optimal winding arrangement to match the target leakage inductance.

[0038] Among them, the maximum leakage inductance L in the transformer core window when the air gap is not opened and when the air gap is opened. lk0_max The maximum leakage inductance L can be calculated by: setting the transformer winding arrangement to the structure with the maximum leakage inductance, and calculating the leakage inductance within the transformer core window without and after the air gap is opened, thus obtaining the maximum leakage inductance L. lk0_max and maximum leakage inductance L lk_max .

[0039] When applied to LLC resonant converters, the design flow for a custom-designed magnetically integrated planar transformer with leakage inductance is as follows:

[0040] ① Based on the performance requirements of the LLC resonant converter, calculate the parameters of the resonant cavity: magnetizing inductance L m Resonant inductor L r Resonant capacitor C r ;

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

[0042] ③ The transformer was simulated using finite element method (FEA) software. The transformer winding arrangement was chosen so that the primary and secondary windings did not overlap at all, which is the arrangement that maximizes leakage inductance. The maximum leakage inductance L was obtained from the simulation when the magnetic core had no air gap. lk0_max Maximum leakage inductance L when the air gap is open lk_max and calculate If L r Not greater than L lk_max Then proceed with the next steps; otherwise, you need to adjust the selected transformer specifications and h. p h s h i Parameters;

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

[0044] Leakage sensation when the air gap is closed:

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

[0046] ⑤ Use computer-aided calculation to calculate the leakage inductance of transformers with different winding arrangements. If the required leakage inductance (i.e., L) is... r )exist To L lk_max In the case of L, traversal calculations can be performed only in structures with smaller parasitic capacitances: all primary (secondary) windings are arranged together and inserted into the secondary (primary) windings. This reduces the parasitic capacitance by decreasing the number of interleavings between the primary and secondary windings, and also reduces the number of traversal calculations. r Not here To L lk_max If higher design precision is required, one can try enumerating all winding arrangements.

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

[0048] Taking a 400V to 48V LLC resonant converter as an example, if the resonant frequency is selected as 500kHz, then the required excitation inductance L m The resonant inductance is 20μH. r The required leakage inductance is 4μH, meaning a leakage inductance L needs to be designed. lk It is a 4μH integrated planar transformer. We use EQ 30 / 8 / 20 type magnetic cores, with the primary winding N... p =16, secondary winding N s =2, primary and secondary winding thickness h p ,h s =70μm, inter-winding spacer thickness hi =330μm.

[0049] When the air gap is not open, the core of the transformer can be considered to follow the "one-dimensional assumption," meaning that the electromagnetic field and current distribution near the conductor only vary along the thickness of the conductor. For example... Figure 2 As shown, we assume that the magnetic field strength within the core window varies only along the thickness h of the winding. Therefore, the leakage inductance without an air gap can be calculated using 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 free permeability, and I p n is the current in the primary winding. p h is the number of turns in the primary winding. p I is the thickness of the primary winding. s n is the current in the secondary winding. s h is the number of turns in the secondary winding. s H is the thickness of the secondary winding, H(0) is the magnetic field strength at the surface of the winding or spacer layer, H is the magnetic field strength inside the winding or spacer layer, and h i The thickness is the spacer layer.

[0052] To obtain the required magnetizing inductance L m We need to add an air gap of a certain length between the two parts of the magnetic core. The formula for calculating the air gap length is as follows: Where parameter A e Parameter A L The parameter information can be found in the magnetic core's datasheet. After opening the air gap, the diffused magnetic flux at the air gap enters the magnetic core window, causing the magnetic field strength distribution within the window to no longer follow the "one-dimensional assumption." Therefore, the calculation formula for leakage inductance needs to be modified, i.e., L... lk =k gap ·L lk0 Correction factor k gap The expression is as follows:

[0053]

[0054] Where b w A is the width of the core window. w With A w 'A' represents the effective area of ​​the core window before and after the air gap is opened. cc With A c1 This represents the effective area of ​​the center and side columns of the magnetic core. 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, therefore k is obtained through FEA simulation. gapThe numerical value is a relatively convenient method.

[0055] Through simulation, we obtained the k of the designed transformer. gap =0.68. Subsequently, we performed a comprehensive calculation of the leakage inductance for different windings, and obtained a suitable winding arrangement of "2p+2s+14p", with a calculated leakage inductance value of 4.10μH. The magnetic field strength curve within the core window is shown below. Figure 3 The leakage inductance value L of the designed transformer was obtained through experimental testing. lk The value is 3.92μH, which meets the resonant inductance L required for an LLC resonant converter. r Design value requirements.

Claims

1. A method of designing a magnetic integrated planar transformer with customized leakage inductance, characterized in that, The method comprises the following steps: S0 obtaining winding parameters and core specifications of a magnetic integrated transformer, and target excitation inductance and target leakage inductance; S1 calculating a magnetic core air gap length required to reach the target excitation inductance; S2 obtains the maximum leakage inductance in the transformer core window without the magnetic core air gap by finite element simulation , and the maximum leakage inductance in the transformer core window after the magnetic core air gap with the length of the air gap is opened , and further calculates the leakage inductance correction coefficient ; S3 is based on the maximum leakage inductance A reference interval is set, if the target leakage inductance is in the reference interval, a winding arrangement with smaller stray capacitance is traversed, and the leakage inductance in the transformer core window after opening the air gap corresponding to each winding arrangement is calculated The optimal winding arrangement matching the target leakage inductance is obtained, otherwise all winding arrangements are enumerated, and the optimal winding arrangement matching the target leakage inductance is obtained; The leakage inductance in the window of the transformer core after the core gap is opened Obtained by calculation by the following method: Following the one-dimensional assumption, the leakage inductance in the transformer core window is calculated without the core air gap ; Utilizing leakage inductance correction coefficient Correcting the leakage inductance Obtaining the leakage inductance in the window of the transformer core after opening the air gap of the core ; The leakage inductance in the window of the transformer core when the core is not provided with a time-varying air gap This is calculated by the following equation: wherein, is the average width of the winding, is the average circumference of the winding, is the vacuum permeability, is the current in the primary winding, is the number of turns of the primary winding, is the thickness of the primary winding, is the current in the secondary winding, is the number of turns of the secondary winding, is the thickness of the secondary winding, is the magnetic field strength at the surface of the winding or spacer layer, is the magnetic field strength inside the winding or spacer layer, is the thickness of the spacer layer.

2. The method of claim 1, wherein, said calculation of the maximum leakage inductance in the transformer core window without a core air gap and the maximum leakage inductance in the transformer core window with a core air gap of the length of the air gap comprising: The winding arrangement of the transformer is set to a structure with maximum leakage inductance, and the leakage inductance in the window of the magnetic core of the transformer when no air gap of the magnetic core is opened and when the air gap of the magnetic core with a length is opened is obtained through finite element simulation, and the maximum leakage inductance is obtained , and the maximum leakage inductance .

3. The method of claim 1, wherein, Before step S3, further comprising: determining whether the target leakage inductance is greater than the maximum leakage inductance ; If greater, adjusting the winding parameters and core specifications of the transformer and returning to step S1, otherwise executing step S3.

4. The method of claim 1, wherein, The reference interval is .

5. The method of claim 1, wherein, The magnetic integrated planar transformer comprises a magnetic core, four edge columns of the magnetic core are connected in a head-to-tail manner to form a magnetic core window, a middle column of the magnetic core is arranged in the magnetic core window, and the middle column of the magnetic core is wound with a winding, different winding arrangements are formed according to different winding modes.

6. The method of claim 1, wherein, When the magnetic integrated planar transformer is applied to an LLC resonant converter, the excitation inductance and the resonant inductance of the LLC resonant converter are set as the target excitation inductance and the target leakage inductance of the magnetic integrated planar transformer.

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