Fractional turn winding structure applied to boost planar transformer and design method

Abstract

The invention discloses a fractional-turn winding structure applied to a boost planar transformer and a design method, and relates to a fractional-turn winding structure and a design method. The planar transformer aims to solve the problems that an existing planar transformer is large in stray capacitance and large in work loss. The fractional turn winding structure applied to the boost type planar transformer comprises three winding units, and the three winding units are sequentially arranged between a first magnetic core and a second magnetic core of the boost type planar transformer in an overlapped mode from top to bottom. The invention belongs to the technical field of power conversion.

Description

Technical Field

[0001] The invention relates to a fractional-turn winding structure and a design method, belonging to the technical field of power conversion. Background Art

[0002] Planar transformers (PTs) are often used in LLC resonant converters due to their unique advantages. Modern switching power supplies typically require miniaturized and lightweight power conversion systems, and research on planar transformers can provide ideal solutions for these applications, improving efficiency and saving costs. Compared with wound transformers, the characteristics of planar transformers make them more competitive in modern power electronics equipment, miniaturization, high frequency, and high-efficiency applications. Their main advantages include: increased power density and volumetric efficiency, optimized performance under high-frequency conditions, smaller parasitic capacitance and leakage inductance, better thermal management and heat dissipation, high manufacturing process and automation level, flexibility and design freedom, and suitability for smart grids. In summary, the application of planar transformers has gradually become a research hotspot, especially in the context of the new energy era.

[0003] With the development of wide-bandgap devices, particularly the breakthroughs in GaN (gallium nitride) and SiC (silicon carbide) devices, the operating frequency of switching power supplies has leapt from the kHz level to the MHz level. At high frequencies, planar transformer winding losses (affected by skin effect, proximity effect, and edge effect) and core losses significantly increase. Furthermore, parasitic parameters such as parasitic capacitance and leakage inductance within the primary winding interact with the resonant components in the LLC resonant converter, affecting the zero-voltage switching (ZVS) performance of the primary switching transistor. Although the theory of fractional-turn transformers has been proposed for a long time, research literature is limited and has primarily focused on the secondary windings of step-down planar transformers. Therefore, research on a fractional-turn winding structure that minimizes system losses and parasitics for step-up planar transformers is of great practical significance. This fractional-turn winding structure should comprehensively consider both losses and parasitics, optimizing the layout and connection of the multilayer PCB windings to further improve the performance and reliability of the planar transformer and achieve efficient system operation. Summary of the Invention

[0004] The present invention aims to solve the problem of large parasitic capacitance and large loss during operation of existing planar transformers, and further proposes a fractional-turn winding structure and design method for a step-up planar transformer.

[0005] The technical solution adopted by the present invention to solve the above problems is: the fractional-turn winding structure applied to the boost planar transformer described in the present invention includes three winding units, and the three winding units are stacked in sequence from top to bottom and arranged between the first magnetic core and the second magnetic core of the boost planar transformer.

[0006] Furthermore, each winding unit is composed of a first secondary winding S, a first primary winding P, a second primary winding P and a second secondary winding S;

[0007] The first secondary winding S is connected in series with the second secondary winding S through via 1 to form a 2-turn winding, and the first primary winding P is connected with half of the second primary winding P through via 2 to form a 1.5-turn winding.

[0008] The present invention provides a method for designing a fractional-turn winding structure for a step-up planar transformer, comprising the following steps:

[0009] Step 1: Select the core structure and size by AP method;

[0010] Step 2: Select the number of primary turns and obtain the excitation inductance L through ANSYS simulation. m ;

[0011] Step 3: Simulate and obtain the primary current I p , and judge the primary current I p Check whether the requirements are met. If yes, proceed to step 4. If not, change the excitation inductance value and return to step 2.

[0012] Step 4: Verify whether the core is magnetically saturated. If so, adjust the core size and return to step 1. If not, determine the parameters and winding structure.

[0013] Furthermore, when the magnetic field is uniformly distributed, the relationship between the number of winding turns and the primary self-inductance is:

[0014]

[0015] In formula (1), L m Indicates the excitation inductance, N p Indicates the number of primary turns, μ r represents relative magnetic permeability, μ0 represents magnetic permeability in vacuum, A e Indicates the effective core cross-sectional area, L e Indicates the effective magnetic circuit length, R m represents magnetic resistance;

[0016] Primary side self-inductance L p and the excitation inductance L m and leakage inductance L E The relationship is:

[0017] L p =L m +L E (2),

[0018] Primary winding current I p and the excitation current I LmThe relationship between the load current I1 is:

[0019] I p =I Lm +I1(3).

[0020] The beneficial effects of the present invention are as follows: the present invention is applicable to an LLC resonant converter system based on a boost-type planar transformer. Without changing the LLC converter topology, the integer-turn primary winding structure is replaced by a fractional-turn primary winding junction. While reducing the number of PCB winding layers, the parasitic capacitance can be reduced without much change in leakage inductance. At the same time, the fractional-turn winding structure effectively reduces the transformer loss by reducing resistance, thereby improving the overall operating efficiency of the system. Compared with the traditional integer-turn transformer, the "pseudo-fractional-turn" winding structure proposed in the present invention can effectively reduce system losses and improve system efficiency. This is mainly due to the characteristic of the fractional-turn structure that can reduce winding resistance, thereby effectively reducing winding losses and improving system efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the overall system diagram of the LLC resonant converter;

[0022] Figure 2 It is the overall system diagram;

[0023] Figure 2 (a) is a schematic diagram of the overall structure of the planar transformer;

[0024] Figure 2 (b) is a schematic diagram of the 0.5-turn winding structure;

[0025] Figure 3 is the primary winding current I p The excitation inductance changes with L m Change relationship diagram;

[0026] Figure 4 This is a flow chart for designing the fractional-turn winding structure of a step-up planar transformer;

[0027] Figure 5 It is a schematic diagram of the fractional-turn winding structure;

[0028] Figure 5 (a) is a schematic diagram of the secondary winding structure of the first layer;

[0029] Figure 5 (b) is a schematic diagram of the primary winding structure of the second layer;

[0030] Figure 5 (c) is a schematic diagram of the primary winding structure of the third layer;

[0031] Figure 5 (d) is a schematic diagram of the secondary winding structure of the 4th layer;

[0032] Figure 6 is the leakage excitation ratio of the two transformers;

[0033] Figure 6 (a) is an integer-turn transformer;

[0034] Figure 6 (b) is a fractional-turn transformer;

[0035] Figure 7 This is a schematic diagram comparing the losses of two transformers;

[0036] Figure 7 (a) is an integer-turn transformer;

[0037] Figure 7 (b) is a fractional-turn transformer. DETAILED DESCRIPTION

[0038] Specific implementation method 1: Figure 1 and Figure 2 As shown, a fractional-turn winding structure applied to a boost planar transformer includes three winding units, which are stacked sequentially from top to bottom and arranged between a first magnetic core 1 and a second magnetic core 2 of the boost planar transformer.

[0039] Among them, such as Figure 5 As shown, each winding unit consists of a first secondary winding S, a first primary winding P, a second primary winding P and a second secondary winding S;

[0040] The first secondary winding S is connected in series with the second secondary winding S through via 1 to form a 2-turn winding, and the first primary winding P is connected with half of the second primary winding P through via 2 to form a 1.5-turn winding.

[0041] The fractional-turn winding structure has four fewer layers than the integer-turn structure, significantly saving planar transformer window space and PCB manufacturing costs. The saved space allows for the use of PCBs with thicker insulation layers. The parasitic capacitance formula shows that the value of parasitic capacitance is inversely proportional to the distance between windings. Therefore, the fractional-turn transformer structure can effectively reduce parasitic capacitance. At the same time, the leakage excitation ratio of the fractional-turn transformer increases slightly, but the impact is minimal due to the high transformer coupling coefficient.

[0042] According to the Ampere ring law, the magnetic field strength in the core of the integer-turn transformer is higher. Therefore, in order to obtain the same magnetic induction intensity, the integer-turn transformer needs to open a longer air gap. Under the condition of ensuring that the core is not saturated, the losses of the two transformers at different air gaps are as follows: Figure 7As shown in the figure, under the same magnetic core and magnetic induction intensity, the core loss of the two transformers is basically the same, but the winding loss of the fractional-turn transformer is 2.05W, and the winding loss of the integer-turn transformer is 2.85W, which can reduce the transformer winding loss by 28% and the total loss by 7.3%.

[0043] Specific implementation method 2: Figure 4 As shown, a method for designing a fractional winding structure for a step-up planar transformer includes the following steps:

[0044] Step 1: Select the core structure and size by AP method;

[0045] Step 2: Select the number of primary turns and obtain the excitation inductance L through ANSYS simulation. m ;

[0046] Step 3: Simulate and obtain the primary current I p , and judge the primary current I p Whether the requirements are met, if yes, go to step 4, if not, change the excitation inductance value and return to step 2;

[0047] Step 4: Verify whether the core is magnetically saturated. If so, adjust the core size and return to step 1. If not, determine the parameters and winding structure.

[0048] Among them, when the magnetic field is uniformly distributed, the relationship between the number of winding turns and the primary self-inductance is:

[0049]

[0050] In formula (1), L m Indicates the excitation inductance, N p Indicates the number of primary turns, μ r represents relative magnetic permeability, μ0 represents magnetic permeability in vacuum, A e Indicates the effective core cross-sectional area, L e Indicates the effective magnetic circuit length, R m represents magnetic resistance;

[0051] Primary side self-inductance L p and the excitation inductance L m and leakage inductance L E The relationship is:

[0052] L p =L m +L E (2),

[0053] Primary winding current I p and the excitation current I Lm The relationship between the load current I1 is:

[0054] I p =I Lm +I1(3).

[0055] How it works

[0056] like Figure 1 As shown, Figure 1 The dotted box in the middle is the position of the planar transformer in the LLC system, and the excitation inductance L m Provided by the primary winding of the transformer, the value of the excitation inductance will affect the excitation current I Lm , which in turn affects the total current I of the primary winding p Therefore, when designing the fractional-turn winding, the effect of the number of turns on the excitation inductance must be taken into account.

[0057] like Figure 2 As shown, Figure 2 This is the overall structural diagram of the planar transformer and the 0.5-turn winding structure. The principle of the fractional-turn transformer is that windings P1 and P2 are turned on at the same time and generate a magnetic flux equal to that of a classic single-turn winding. As long as the symmetry of the winding is guaranteed, the magnetic flux in the two side legs of the ferrite core is equal, which is equivalent to changing the number of winding turns from one turn to two 0.5 turns.

[0058] like Figure 3 As shown, Figure 3 is the excitation inductance L obtained by simulating the circuit m The total current of the primary winding I p The relationship between the excitation inductance L m The total current of the primary winding I p The relationship is inversely proportional, and as the excitation inductance increases, the primary winding current decreases gradually and approaches a negative current. Therefore, when the excitation inductance is large, continuing to increase the inductance value has little effect on reducing the primary current. The best choice is an excitation inductance of 3 to 5 μH.

[0059] The turns ratio of a planar transformer is 1:4. If the traditional 0.5-turn fractional-turn technology used for the secondary winding of a step-down planar transformer is applied to the primary winding, the secondary winding will have 2 turns. Through ANSYS Maxwell finite element simulation, the parameters of the secondary winding at different air gaps are shown in Table 1:

[0060] Table 1 Parameters of half-turn transformer

[0061] Air gap length (mm) Excitation self-inductance (μH) Secondary side self-inductance (μH) Is the core magnetically saturated? 0.03 0.556 8.894 yes 0.04 0.448 7.171 no 0.05 0.376 6.022 no 0.06 0.326 5.220 no 0.07 0.287 4.600 no 0.1 0.214 3.418 no

[0062] Depend on Figure 2It can be seen that when the primary self-inductance is 0.5μH, the total effective value of the primary current reaches 81A, and its peak value has exceeded the limit that the switching tube and transformer winding can withstand. In addition, excessive current will lead to a sharp increase in losses and system overheating. Therefore, for step-up transformers, using fractional turns less than 1, such as 0.5 turns or 0.25 turns, is obviously not advisable. Therefore, a "pseudo-fractional" winding structure with an equivalent number of turns of 1.5 turns is proposed. In this case, the secondary winding has 6 turns, and the parameters obtained by simulation are shown in Table 2:

[0063] Table 2 Parameters of 1.5-turn transformer

[0064]

[0065]

[0066] When the primary self-inductance is 3μH, the total primary current is approximately 23A, which is fully sustainable for the switch and transformer windings. Substituting the current excitation values into the ANSYS simulation reveals that the core is not saturated, meeting the requirements.

[0067] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the present profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical content disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent replacement and improvement of the above embodiments made according to the technical essence of the present invention, within the spirit and principles of the present invention, without departing from the content of the technical solution of the present invention, shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A fractional-turn winding structure for a step-up planar transformer, characterized in that: The invention comprises three winding units, which are sequentially stacked from top to bottom and arranged between a first magnetic core (1) and a second magnetic core (2) of a boost-type planar transformer.

2. The fractional-turn winding structure for a step-up planar transformer according to claim 1, wherein: Each winding unit consists of a first secondary winding S, a first primary winding P, a second primary winding P and a second secondary winding S; The first secondary winding S is connected in series with the second secondary winding S through via 1 to form a 2-turn winding, and the first primary winding P is connected with half of the second primary winding P through via 2 to form a 1.5-turn winding.

3. A method for designing a fractional winding structure for a step-up planar transformer, characterized in that: The specific steps include: Step 1: Select the core structure and size by AP method; Step 2: Select the number of primary turns and obtain the excitation inductance L through ANSYS simulation. m ; Step 3: Simulate and obtain the primary current I p , and judge the primary current I p Check whether the requirements are met. If yes, proceed to step 4. If not, change the excitation inductance value and return to step 2. Step 4: Verify whether the core is magnetically saturated. If so, adjust the core size and return to step 1. If not, determine the parameters and winding structure.

4. The method for designing a fractional winding structure for a step-up planar transformer according to claim 3, wherein: When the magnetic field is uniformly distributed, the relationship between the number of winding turns and the primary self-inductance is: In formula (1), L m Indicates the excitation inductance, N p Indicates the number of primary turns, μ r represents relative magnetic permeability, μ0 represents magnetic permeability in vacuum, A e Indicates the effective core cross-sectional area, L e Indicates the effective magnetic circuit length, R m represents magnetic resistance; Primary side self-inductance L p and the excitation inductance L m and leakage inductance L E The relationship is: L p =L m +L E (2), Primary winding current I p and the excitation current I Lm The relationship between the load current I1 is: I p =I Lm +I1 (3).

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