Magnetic integration optimization design method based on LLC resonant converter

Abstract

The invention provides a magnetic integration optimization design method for an LLC resonant converter, and belongs to the technical field of power electronics. The integrated magnetic core structure comprises a magnetic core base with four winding magnetic columns and a top cover plate, and the magnetic integration method reduces the number and the size of magnetic elements and reduces the height of the magnetic elements. According to the magnetic core structure, the magnetic flux density is uniformly distributed, the magnetic core loss of the transformer is reduced, and the power density and efficiency of the transformer are improved. Primary side windings of the transformer are unevenly distributed on the four winding magnetic columns, secondary side windings of the transformer are evenly distributed on the winding magnetic columns, and leakage inductance is only generated on the primary side of the transformer due to the fact that the primary side windings of the transformer are unevenly distributed and the secondary side windings of the transformer are evenly distributed. Therefore, the generated leakage inductance is used as the resonant inductance of the LLC resonant converter, and integration of the transformer and the resonant inductance of the LLC resonant converter is realized. The magnetic integrated transformer with different transformation ratios and controllable leakage inductance can be realized by adjusting the number of turns of windings on the primary side and the secondary side of the transformer and air gaps of winding magnetic columns.

Description

Technical Field

[0001] The invention relates to a full magnetic integrated optimization design method for a transformer and a resonant inductor suitable for a high-frequency working environment, and is particularly suitable for an LLC resonant converter. Background Art

[0002] The increasing use of cloud computing and artificial intelligence technologies has led to an annual global investment of more than $200 billion in data center construction. A large part of this money is used to build infrastructure to support server operations, such as power supply systems. In response to such high costs, the industry is working hard to find ways to improve the construction and operation efficiency of data centers, such as by reducing initial construction costs or improving energy efficiency to reduce electricity costs in long-term operations. The application of wide bandgap (WBG) semiconductor devices and LLC resonant converters can significantly increase the switching frequency of power conversion systems. High switching frequencies allow the design of magnetic components (such as transformers and inductors) to shift from traditional Litz wire structures to magnetic components integrated on planar printed circuit boards (PCBs). In addition, the use of planar magnetic components can also help simplify the manufacturing process, reduce thermal resistance, improve thermal management, and further improve the overall performance of the system. The volume and loss of the magnetic components (transformers and inductors) of the DC-DC converter account for a large part of the volume and loss of the DC-DC converter. Therefore, improving the magnetic structure can help improve the overall performance of the DC-DC converter. By integrating the inductor and transformer, the performance, efficiency and power density of the power converter can be improved.

[0003] As mentioned above, the LLC circuit topology is as follows Figure 1 As shown, it includes a full-bridge inverter circuit and a full-bridge rectifier circuit composed of MOSFET switches, and a resonant network, wherein the resonant network includes a resonant capacitor, a resonant inductor, and a transformer. The resonant converter uses the characteristics of the resonant cavity to achieve zero voltage turn-on of the primary side switch and zero current turn-off of the secondary side switch, which improves the efficiency of the converter as a whole.

[0004] At the same time, the traditional LLC resonant converter requires a resonant inductor and a transformer. If two independent magnetic components are used, the LLC resonant converter will be larger in size and have lower power density. Moreover, the primary and secondary windings of the traditional transformer are wound on one magnetic column, which will cause the height of the magnetic core to be too high, limiting the application scenarios. Therefore, how to solve the problem of a large number of magnetic components, high losses, and high height in LLC circuits has become a research focus.

[0005] In existing research, a method was adopted to split the primary and secondary windings of the transformer, distribute the primary winding unevenly on the two side columns of the EI core, and evenly distribute the secondary winding on the two side columns of the EI core. The middle column of the core was used to reduce the coupling degree between the primary and secondary sides of the transformer, increase the leakage inductance of the primary side of the transformer, and use the leakage inductance as the resonant inductance of the LLC resonant converter. However, this method has a low core utilization rate, a large magnetic flux density in the middle column of the core, and a large number of winding turns on each column, resulting in a high core height. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a full magnetic integration optimization design method based on LLC resonant converter, which reduces the number, volume and loss of magnetic components in the resonant converter and further optimizes the efficiency of the converter.

[0007] like Figure 1 As shown in the figure, the integrated solution of LLC resonant converter in the existing research is to distribute the primary winding unevenly to the side column of the EI core, and evenly distribute the secondary winding to the side column of the EI core. The coupling degree of the primary and secondary windings of the transformer is reduced by using the center column of the core, and the leakage inductance of the primary side of the transformer is increased, so that the leakage inductance is used as the resonant inductance of the LLC resonant converter. Among them, "." represents the current flowing out of the paper, and "x" represents the current flowing into the paper.

[0008] Further, Figure 2 The winding direction of the primary and secondary windings of the transformer is reversed to obtain Figure 3 . Figure 3 The leakage flux of the middle column of the core and Figure 2 The leakage flux of the middle column of the middle magnetic core is equal in magnitude and opposite in direction.

[0009] Further, such as Figure 4 As shown, two EI cores are placed crosswise, and the A-type transformer is Figure 2 The winding direction of the primary and secondary windings of the B-type transformer is as shown in Figure 3 The winding direction is shown, so the magnetic flux of the middle column of the EI core can be completely offset. In order to reduce the mass and loss of the core, the middle column can be removed.

[0010] Furthermore, considering that when the areas of the magnetic columns are the same, the circumference of the circular magnetic column is the smallest and the winding loss is also the smallest, the shape of the final integrated magnetic core is as follows: Figure 5 As shown, the LLC resonant converter magnetic integration structure proposed by the present invention.

[0011] The present invention is achieved through the following technical solutions:

[0012] The present invention proposes a resonant inductor and transformer integrated structure suitable for an LLC resonant converter, wherein the LLC converter includes a primary-side inverter network, a secondary-side rectifier network and a resonant network. A resonant inductor and a transformer in the above resonant network are integrated into a magnetic element. Specifically, the primary winding of the transformer is unevenly distributed on four winding magnetic poles, while the secondary winding is evenly distributed on the winding magnetic poles. Due to the uneven distribution of the number of turns of the primary winding and the even distribution of the number of turns of the secondary winding, leakage inductance is only generated on the primary side of the transformer, so that the generated leakage inductance serves as the resonant inductor of the LLC resonant converter, thereby realizing the integration of the transformer and the resonant inductor of the LLC resonant converter.

[0013] The integrated magnetic core structure comprises a magnetic core base with four winding magnetic columns and a top cover plate.

[0014] The core base has four cylindrical magnetic columns, and magnetic columns 1, 2, 3, and 4 all have air gaps. The number of turns of the primary and secondary windings and the size of the air gaps of the four magnetic columns are changed according to different transformer ratios, leakage inductances, and transformer excitation inductances.

[0015] Furthermore, the primary winding N P Unevenly distributed on magnetic column 1, magnetic column 2, magnetic column 3, magnetic column 4, the secondary winding N of the transformer S Evenly distributed on magnetic column 1, magnetic column 2, magnetic column 3, magnetic column 4, so that the winding N on the primary side P The secondary winding N s The coupling degree is reduced, and the leakage inductance on the primary side is increased so as to act as the resonant inductor L on the primary side. r .

[0016] Furthermore, the magnetic circuit model is Figure 7 As shown, by using Ohm's law of magnetic circuit, the magnitude of the magnetic flux flowing in each magnetic circuit can be calculated:

[0017]

[0018] Where l g is the air gap length, A e is the magnetic cross-sectional area of ​​the magnetic column, μ0 is the magnetic permeability of air. g The magnetic resistance obtained by the air gaps opened by magnetic columns 1, 2, 3 and 4. At this time, since the magnetic permeability of the magnetic core is much greater than the magnetic permeability of the vacuum, the magnetic resistance of the magnetic core is ignored in all calculations of the present invention, and only the air gap magnetic resistance is considered.

[0019] N1 is the number of turns of the primary winding of the transformer on magnetic poles 1 and 4, N2 is the number of turns of the primary winding of the transformer on magnetic poles 2 and 3, and N3 is the number of turns of the secondary winding of the transformer on magnetic poles 1, 2, 3, and 4.

[0020] Furthermore, according to Faraday's law of electromagnetic induction, the transformer primary winding voltage V p , secondary winding voltage V s :

[0021]

[0022] Furthermore, the relationship between the port voltage and current can be obtained:

[0023]

[0024] Where V P 、(i p ) are the transformer primary side port voltage (current); V s (i s ) are the transformer secondary side port voltage (current); L P (L S ) is the self-inductance of the primary winding (secondary winding) of the transformer; M is the mutual inductance between the primary and secondary windings of the transformer.

[0025] Furthermore, from the above inductance matrix, the transformer primary winding self-inductance L P , Transformer secondary winding self-inductance L s The mutual inductance M between the primary and secondary windings can also be calculated and expressed as:

[0026]

[0027] Furthermore, the transformer's magnetizing inductance L m , primary side leakage inductance L kp , secondary leakage inductance L ks And the inductance K can be expressed as:

[0028]

[0029] From formula (5), we can know that the integrated magnetic core can adjust the inductance of the converter by adjusting N1 and N2 to meet the converter gain requirements, and adjust the air gap magnetic resistance R g To adjust the transformer primary leakage inductance L by the number of turns of the transformer primary winding kp The size and excitation inductance L m The size of the transformer primary leakage inductance L kpIt acts as the resonant inductor required by the LLC resonant converter without leakage inductance on the secondary side of the transformer, thus realizing the magnetic integration of the LLC resonant converter.

[0030] The beneficial effects of the present invention are as follows: the transformer and resonant inductor in the LLC resonant converter are integrated into a magnetic element, the volume and weight of the converter are reduced, the efficiency and power density are improved, the primary winding and the secondary winding of the transformer are respectively wound on four magnetic poles so that the number of winding turns on each magnetic pole is reduced, the height of the magnetic core is effectively reduced, and the central pole leakage flux of the EI magnetic core in the existing research is offset by a new winding placement method, thereby reducing the volume and loss of the magnetic core. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the principle topology diagram of LLC resonant converter;

[0032] Figure 2 This is a schematic diagram of a type A transformer;

[0033] Figure 3 It is the schematic diagram of type B transformer;

[0034] Figure 4 This is a schematic diagram of the EI core center column cancellation;

[0035] Figure 5 It is a schematic diagram of the structure of integrated magnetic components;

[0036] Figure 6 It is a three-dimensional schematic diagram of each winding of the integrated magnetic component;

[0037] Figure 7 It is the magnetic circuit equivalent model of integrated magnetic components;

[0038] Figure 8 This is a schematic diagram of magnetic simulation using Maxwell finite element software;

[0039] Fig. 9 It is a schematic diagram of the integration and promotion of n EI cores;

[0040] Fig.10 It is a schematic diagram after the integration of n EI cores; DETAILED DESCRIPTION

[0041] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in combination with the accompanying drawings and specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The accompanying drawings are only used to assist in explaining the content and purpose of the present invention, so the drawings are relatively simple and do not use precise proportions for operation.

[0042] Embodiment 1:

[0043] like Figure 1 The figure shows the principle topology diagram of the LLC resonant converter, wherein the converter includes a primary-side inverter circuit, a resonant network and a secondary-side rectifier circuit, wherein the resonant network includes a resonant inductor and a transformer. The present invention adopts magnetic integration technology to integrate a transformer and an inductor into a magnetic core.

[0044] like Figure 5 As shown, the resonant inductor and transformer integrated magnetic core structure proposed in the present invention comprises a magnetic core base with four winding magnetic columns and a top cover plate. The primary winding and the secondary winding of the transformer are both wound on the four magnetic columns.

[0045] like Figure 6 As shown, in the present invention, N1 turns of winding are wound on the magnetic columns 1 and 4 of the magnetic core base, and N2 turns of winding are wound on the magnetic columns 2 and 3, and these windings are connected in series as the primary winding of the transformer. This reduces the coupling degree between the primary winding of the transformer on the magnetic columns 1, 2, 3, and 4 and the secondary winding of the transformer, increases the leakage inductance of the primary side of the transformer, and acts as the resonant inductance L of the LLC resonant converter. r , generally N1 is not equal to N2.

[0046] Furthermore, N3 turns of windings are respectively wound on magnetic column 1, magnetic column 2, magnetic column 3, and magnetic column 4. These windings are connected in series as the secondary windings of the transformer. Since the secondary windings of the transformer are evenly distributed on magnetic column 1, magnetic column 2, magnetic column 3, and magnetic column 4, there is no leakage inductance on the secondary side of the transformer.

[0047] like Figure 7 As shown, the equivalent magnetic resistance model formed by the integrated magnetic element according to the above-mentioned new winding placement method can be used to calculate the magnetic flux flowing on each magnetic column, so as to obtain the transformer primary winding self-inductance L P and the transformer secondary winding self-inductance L S And the mutual inductance M between the primary and secondary windings.

[0048] Furthermore, in order to ensure uniform magnetic flux density in the magnetic core, the air gaps opened by magnetic pillars 1, 2, 3 and 4 are generally equal in size.

[0049] Furthermore, according to Ampere's loop law and Faraday's law of electromagnetic induction, it can be used to calculate the leakage inductance L of the primary side of the transformer. kp , the leakage inductance L of the secondary side of the transformer ks and the magnetizing inductance L m The size of the winding turns N1, N2, N3 and the size of the air gap can be determined according to the design parameter indicators.

[0050] like Figure 8As shown, the accuracy of the proposed idea is verified by the finite element simulation software Maxwell. The self-inductance and mutual inductance of the transformer winding are calculated in the simulation, and the obtained inductance matrix structure is consistent with the theoretical design.

[0051] Embodiment 2:

[0052] like Fig. 9 As shown, for the proposed integrated transformer based on 1 A-type transformer and 1 B-type transformer, it can be expanded for higher voltage and higher power applications by adding additional A(B)-type based transformers.

[0053] based on Fig. 9 The n transformers based on EI cores are shown, where the number of type A transformers is i and the number of type B transformers is (ni). The minimum value of i is 1, which means that at least one transformer must have a magnetomotive force (MMF) polarity opposite to that of the remaining transformers so that the coupling between the primary winding and the secondary winding can be adjusted and an adjustable built-in leakage inductance can be achieved. In order to achieve better flux distribution within the core board, the type A transformer and the type B transformer should be arranged in an interleaved structure, such as type A → type B → type A → type B → type A. With these new matrix integrated transformers, the flux distribution within the core board is more uniform. By reducing core loss and core volume, the utilization of the core is improved, thereby achieving higher power density.

[0054] like Fig.10 As shown, n transformers based on EI cores are connected through Fig. 9 The generalization method shown is a schematic diagram after the middle column of the EI core is offset. Considering that when the cross-sectional area of ​​the magnetic columns is the same, the circumference of the circular magnetic column is the smallest and the winding loss is also the smallest, the winding magnetic column is changed to a circular shape.

[0055] The above specific embodiments have described the principles and implementation methods of the present invention in detail, but the present invention is not limited to the above specific embodiments. Those skilled in the art can make corresponding changes in the specific implementation methods by referring to the ideas of the present invention within the scope of their knowledge.

Claims

1. A magnetic integration optimization design method based on LLC resonant converter, characterized in that: The resonant converter includes a primary-side inverter network, a resonant network and a secondary-side rectifier network, wherein the resonant inductor of the resonant network is integrated with the transformer into a magnetic element, and the magnetic core structure includes a magnetic core base with four winding magnetic columns and a top cover plate. Specifically, the magnetic core base includes four cylindrical magnetic columns, wherein the primary-side winding of the transformer is unevenly distributed on the four winding magnetic columns, and the secondary-side winding of the transformer is evenly distributed on the winding magnetic columns. Due to the uneven distribution of the turns of the primary-side winding of the transformer and the even distribution of the turns of the secondary-side winding of the transformer, leakage inductance is only generated on the primary side of the transformer, so that the leakage inductance generated on the primary side of the transformer is used as the resonant inductor of the resonant converter, realizing the integration of the transformer and the resonant inductor of the LLC resonant converter.

2. The integrated structure according to claim 1, characterized in that: The integrated magnetic core structure comprises a magnetic core base, a top cover plate and a PCB winding, wherein the magnetic core base comprises four cylindrical winding magnetic columns which are distributed in a 90° symmetrical manner in the spatial structure.

3. The integrated structure according to claim 1, characterized in that: N1 turns of winding are wound on magnetic column 1 and magnetic column 4 respectively, and N2 turns of winding are wound on magnetic column 2 and magnetic column 3. These windings are connected in series as the primary winding of the transformer. N3 turns of winding are wound on magnetic column 1, magnetic column 2, magnetic column 3, and magnetic column 4 respectively and connected in series as the secondary winding of the transformer.

4. The magnetically integrated planar transformer according to claim 1, characterized in that: The transformer primary leakage inductance L kp Acts as the resonant inductor L of the LLC resonant converter circuit r Since the transformer secondary winding is evenly distributed on four winding poles, there is no leakage inductance on the transformer secondary side.

5. The integrated structure according to claims 1, 2, 3 and 4, characterized in that: The primary windings (secondary windings) on magnetic columns 1 and 3 have the same winding direction, the primary windings (secondary windings) on magnetic columns 2 and 4 have the same winding direction, and the primary windings (secondary windings) on magnetic columns 1 and 3 are opposite to the primary windings (secondary windings) on magnetic columns 2 and 4.

6. The integrated structure according to claims 1, 2, 3, 4 and 5, characterized in that: This magnetic integration structure is not only applicable to the four-column LLC magnetic integration solution used in this example, but also to other topologies that require integrated inductors and transformers. In addition, more magnetic columns (such as six columns or eight columns) can be extended based on the magnetic core introduced this time, which is suitable for higher voltage or power.

7. The magnetically integrated planar transformer according to claims 1, 2, 3, 4, 5 and 6, characterized in that: The transformer excitation inductance L is controlled by controlling the number of turns of the transformer primary winding (secondary winding) in magnetic column 1, magnetic column 2, magnetic column 3 and magnetic column 4 and the air gap of the winding magnetic column. m , resonant inductor L r Inductance ratio K, for details, see the formula for deriving the magnetic resistance model in the instruction manual.

Images