Magnetic integrated transformer and electric vehicle charging system

Abstract

The invention discloses a magnetic integrated transformer and an electric vehicle charging system.The magnetic integrated transformer comprises a magnetic column, a first winding, a second winding and a third winding and is characterized in that the second winding is wound in the middle of the magnetic column, and the first winding comprises a first part and a second part which are wound on the two sides of the second winding; the third winding is wound by a copper bar, and the third winding and the second winding are wound in a laminated manner; the inner side wall of the third winding is coated with at least one magnetic sheet used for reducing eddy current loss caused by magnetic leakage and improving the leakage inductance value. Compared with the prior art, the problem that leakage flux of a magnetic integrated transformer in an electric vehicle charging system generates high eddy current loss on a metal conductor can be solved, meanwhile, the leakage inductance of the transformer is improved, and the working efficiency of a vehicle-mounted charger is improved under the condition that the multifunctional application requirement of the vehicle-mounted charger is met.

Description

Technical Field

[0001] The invention relates to the field of electric vehicle charging, in particular to a magnetic integrated transformer and an electric vehicle charging system. Background Art

[0002] The on-board charger (OBC) is an important part of the electric vehicle charging system. It usually has a two-stage structure: a power factor correction (PFC) stage cascaded with a DC-DC stage (DC-DC) to charge the high-voltage battery (HVB). ​​For safety reasons, the DC-DC is implemented by an isolated topology, such as a resonant converter or a dual active bridge converter. In addition, there is a low-voltage battery (LVB) in the electric vehicle to power the vehicle's low-voltage equipment, so an additional isolated DC-DC converter is required. Due to the limited installation space of the on-board charger in the electric vehicle, and the large volume and weight of magnetic components such as resonant inductors and transformers in the OBC, the power density of the OBC is severely limited, and the cost of the OBC is increased.

[0003] Magnetic integration is an effective way to reduce the total volume of magnetic components. In order to improve the power density of OBC, in recent years, some literatures have studied the integration of OBC and low-voltage DC-DC. Considering magnetic integration and battery voltage range, the three-port converter topology is a very attractive choice for OBC. The isolation between the three ports can be achieved by a dual transformer or a three-winding transformer.

[0004] Due to the application scenario requirements of OBC, the secondary side of the magnetic integrated transformer has two parts: high-voltage winding and low-voltage winding. When the low-voltage DC / DC output power is large, it has the characteristics of low voltage and high current. Copper bar windings are often used to ensure current density. In the three-port converter topology, the power inductor of OBC is integrated into the transformer in the form of leakage inductance, which can further improve the power density of OBC. However, the leakage flux generated by the leakage inductance induces eddy currents on the low-voltage winding and the casing, resulting in reduced OBC efficiency. Secondly, when the transformer leakage inductance is large, it is not conducive to the transformer size design and further limits the switching frequency of OBC. When the transformer leakage inductance is small, it will make the soft switching of OBC difficult, making the OBC inefficient. Summary of the invention

[0005] In view of the problem in the prior art that the leakage magnetic field of the magnetic integrated transformer generates high eddy current loss on the metal conductor, resulting in reduced OBC efficiency, the present invention proposes a magnetic integrated transformer and an electric vehicle charging system.

[0006] The technical solution of the present invention is to propose a magnetic integrated transformer, comprising a magnetic column, a first winding, a second winding, and a third winding, wherein the second winding is wound in the middle of the magnetic column, the first winding comprises a first part and a second part wound on both sides of the second winding, and the third winding is wound with a copper bar and is stacked with the second winding;

[0007] At least one magnetic sheet is attached to the inner wall of the third winding to reduce eddy current loss caused by magnetic leakage and increase leakage inductance.

[0008] Furthermore, the magnetic sheet is made of a magnetic material with high magnetic permeability and low electrical conductivity.

[0009] Furthermore, the magnetic sheet is doped with magnetic core particles and / or high thermal conductivity particles.

[0010] Furthermore, the bonding method of the magnetic sheet and the third winding is at least one of gluing, inlaying, and overmolding.

[0011] Furthermore, the magnetic integrated transformer arranges a plurality of magnetic sheets in a combination mode so that the magnetic permeability of the plurality of magnetic sheets changes continuously or in stages.

[0012] Furthermore, the multiple layers of magnetic sheets are arranged in order according to the magnitude of the magnetic permeability of the magnetic sheets.

[0013] Furthermore, the multi-layer magnetic sheet is designed to meet the following requirements:

[0014] B shield <B sat

[0015] Among them, B shield is the magnetic flux density of the area covered by the magnetic sheet, B sat is the saturation flux of the magnetic piece.

[0016] Furthermore, the magnetic integrated transformer achieves coordinated control of leakage inductance and eddy current loss by adjusting the coverage area ratio of the magnetic sheet, the magnetic permeability of the magnetic sheet, and the thickness of the magnetic sheet.

[0017] Furthermore, the leakage inductance and eddy current loss of the magnetic integrated transformer satisfy the calculation model:

[0018]

[0019] Among them, L leak_old is the leakage inductance without adding the magnetic sheet, P eddy_old is the eddy current loss without adding the magnetic sheet, L leak_new is the leakage inductance after adding the magnetic sheet, P eddy_newis the eddy current loss after adding the magnetic sheet, α is the coverage area ratio of the magnetic sheet, ξ is the leakage inductance additional correction factor, λ is the leakage magnetic flux shunt efficiency, μ r is the magnetic permeability of the magnetic sheet.

[0020] Further, the charging circuit has the above-mentioned magnetic integrated transformer;

[0021] The charging circuit adopts at least one of a DAB converter topology, a resonant converter topology, and a three-port converter topology.

[0022] Compared with the prior art, the present invention has at least the following beneficial effects:

[0023] The present invention covers the third winding of the magnetic integrated transformer with a magnetic sheet, shields the leakage flux of the magnetic integrated transformer in the form of a magnetic sheet combination, and uses the magnetic permeability of the magnetic sheet to reconstruct the leakage flux path, so as to achieve the purpose of improving the leakage inductance of the transformer leakage flux, thereby suppressing the eddy current loss caused by leakage flux in the OBC, and effectively solving the problem of low efficiency of the magnetic integrated transformer. Due to the improved leakage inductance, the switching frequency of the OBC can be reduced without affecting the size of the magnetic integrated transformer, and EMI can be suppressed, providing a feasible solution for the OBC with small volume, high power density and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0025] Figure 1 It is a structural schematic diagram of the magnetic integrated transformer in the present invention;

[0026] Figure 2 It is a schematic diagram of magnetic field distribution when the magnetic integrated transformer of the present invention is not covered with magnetic sheets;

[0027] Figure 3 It is a schematic diagram of magnetic flux distribution when the magnetic integrated transformer of the present invention is not covered with magnetic sheets;

[0028] Figure 4 Schematic diagram of copper busbar current density when the magnetic integrated transformer is not covered with magnetic sheets in the present invention;

[0029] Figure 5 It is a schematic diagram of the magnetic field distribution when the magnetic integrated transformer of the present invention is covered with magnetic sheets;

[0030] Figure 6 It is a schematic diagram of magnetic flux distribution when the magnetic integrated transformer of the present invention is covered with magnetic sheets;

[0031] Figure 7 It is a schematic diagram of the copper busbar current density when the magnetic integrated transformer is covered with magnetic sheets in the present invention;

[0032] Among them, 10 is the first magnetic core, 20 is the second magnetic core, 30 is the magnetic sheet, W1a is the first part of the first winding, W1b is the second part of the first winding, W2 is the second winding, and W3 is the third winding. DETAILED DESCRIPTION

[0033] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0034] Thus, a feature indicated in this specification will be used to illustrate one of the features of an embodiment of the present invention, rather than implying that each embodiment of the present invention must have the described feature. In addition, it should be noted that this specification describes many features. Although some features can be combined together to illustrate possible system designs, these features can also be used in other combinations that are not explicitly described. Thus, unless otherwise stated, the described combinations are not intended to be limiting.

[0035] The principle and structure of the present invention are described in detail below with reference to the accompanying drawings and embodiments.

[0036] In the three-port converter topology, the power inductance of the OBC is integrated into the transformer in the form of leakage inductance, which can further improve the power density of the OBC. However, the leakage flux generated by the leakage inductance induces eddy currents on the low-voltage winding and the casing, resulting in reduced OBC efficiency. Secondly, when the transformer leakage inductance is large, it is not conducive to the transformer size design and further limits the switching frequency of the OBC. When the transformer leakage inductance is small, it will make the soft switching of the OBC difficult, resulting in low OBC efficiency.

[0037] Based on the above problems, the present invention proposes an optimization design method for a magnetic integrated transformer, which is used to solve the problem of high eddy current loss caused by leakage magnetic field of the magnetic integrated transformer on the metal conductor in the electric vehicle charging system, and at the same time improve the leakage inductance of the transformer, so as to optimize and improve the working efficiency of the OBC while meeting the multi-functional application requirements of the OBC. The specific optimization design method of the magnetic integrated transformer includes an eddy current loss suppression method of magnetic shielding of magnetic sheets, a magnetic permeability gradient configuration method, a leakage inductance and eddy current loss coordinated control method and a magnetic integrated transformer.

[0038] Specifically, the magnetic integrated transformer proposed in the present invention includes a magnetic column, a first winding, a second winding W2, and a third winding W3, the second winding W2 is wound in the middle of the magnetic column, the first winding includes a first part W1a and a second part W1b wound on both sides of the second winding W2, and the third winding W3 is wound with a copper bar and is stacked with the second winding W2;

[0039] At least one magnetic sheet 30 is attached to the inner wall of the third winding W3 to reduce eddy current loss caused by magnetic leakage and increase leakage inductance.

[0040] In one embodiment, the first winding is wound around the first part W1a and the second part W1b on both sides of the second winding W2, and the first part W1a of the first winding, the second winding W2 and the second part W1b of the first winding present a symmetrical structure, and the magnetic field at the center of the copper bar is offset, and eddy current loss occurs on both sides of the copper bar, which is also the place where the leakage magnetic flux is concentrated;

[0041] In one embodiment, the first winding is connected to the primary circuit, the second winding W2 is connected to the first secondary circuit, and the third winding W3 is connected to the second secondary circuit.

[0042] Figure 1 Schematic diagram of the structure of the magnetic integrated transformer in the present invention. The first magnetic core 10 and the second magnetic core 20 are connected to form a magnetic column. When setting, the second winding W2 is first passed through the magnetic core window and wound on the center of the magnetic column. Then, the first winding is evenly divided into a first part W1a and a second part W1b according to the number of turns, and passed through the magnetic core window and symmetrically wound on both sides of the second winding W2. Finally, the third winding W3 is passed through the magnetic core window and wound on the center of the magnetic column, and the second winding W2 and the third winding W3 are stacked and wound, so as to ensure the close coupling between the second winding W2 and the third winding W3.

[0043] After adopting the above setting method, according to the principle of magnetic field superposition, the leakage flux of the magnetic integrated transformer is modeled as:

[0044] φ leak =φ left +φ right -φ coupling

[0045] Among them, φ left is the leakage flux of the left winding located at the center of the magnetic column, φ right is the leakage flux of the right winding located at the center of the magnetic column, φ coupling is the coupling component of the magnetic field at both ends in the copper busbar area, k v and k v' is the equivalent coupling coefficient, and its relationship with the leakage flux is as follows:

[0046]

[0047] Among them, I p is the current flowing through the first part W1a of the first winding or the second part W1b of the first winding, I s is the current flowing through the second winding W2, k v is the coupling coefficient between the first part W1a of the first winding and the second winding W2, k v' is the coupling coefficient between the second part W1b of the first winding and the second winding W2, N p left is the number of turns of the first part W1a of the first winding, N p right is the number of turns of winding W1b, N s is the number of turns of the second winding W2.

[0048] The magnetomotive force (MMF) of the windings on both sides of the primary side is distributed in a reverse gradient, forming a transverse leakage flux in the core window. The leakage flux energy through the closed copper bar is:

[0049]

[0050] Among them, μ 0 is the vacuum permeability, W leak is the leakage magnetic energy, H leak is the magnetic flux leakage intensity, V is the space volume, L k is the leakage inductance, and I is the current flowing through the leakage inductance.

[0051] The transverse magnetic field intensity Hcu at the copper bar (the third winding here uses a copper bar) is negatively correlated with the winding layer spacing d, which can be expressed as:

[0052]

[0053] Among them, N p is the total number of turns of the first part W1a of the first winding and the second part W1b of the first winding, N s is the number of turns of the second winding W2, I p is the current flowing through the first part W1a of the first winding or the second part W1b of the first winding, I s is the current flowing through the second winding W2, and d is the distance between winding layers.

[0054] The eddy current density in a metal conductor is:

[0055]

[0056] By integration, the expression of eddy current loss can be derived

[0057]

[0058] Among them, σ is the conductivity, ω is the angular frequency, which reflects the rate of the alternating magnetic field and is proportional to the induced electromotive force. Cu and l Cu are the width and length of the copper bar, B leak_pk is the peak value of leakage flux density, t cu is the copper busbar thickness.

[0059] According to the above formula, it can be analyzed that in the magnetic integrated transformer, since the first part W1a of the first winding, the second winding W2 and the winding W1b present a symmetrical structure, the magnetic field at the center of the copper bar is offset, and eddy current losses appear on both sides of the copper bar, which is also the place where the leakage magnetic field is concentrated.

[0060] Due to the integrated leakage inductance of the magnetic integrated transformer, leakage magnetic flux is generated between the first part W1a of the first winding and the second winding W2, and between the second part W1b of the first winding and the second winding W2. The copper busbar has a large conductive area and high conductivity. When the leakage magnetic flux passes through the copper busbar, eddy currents are induced inside it, resulting in large eddy current losses. When the OBC adopts converter topologies such as the DAB converter topology and the resonant converter topology, the operating frequency is tens of kHz to hundreds of kHz, resulting in a high alternating frequency of the magnetic field. The eddy current losses will increase significantly, causing heat and reduced efficiency.

[0061] In this regard, the present invention covers the inner wall of the third winding W3 with at least one magnetic sheet 30 for reducing eddy current loss caused by magnetic leakage and increasing leakage inductance, so as to solve the above problem.

[0062] The magnetic sheet 30 is made of a magnetic material with high magnetic permeability and low electrical conductivity, which may be one or more of a ferrite sheet, a nanocrystalline alloy sheet, an iron powder core magnetic sheet, and an amorphous alloy sheet. The magnetic sheet 30 is selected to be attached to the inner wall of the third winding W3. By utilizing the magnetic shielding effect of the magnetic sheet 30, when the magnetic sheet 30 is attached to the copper busbar, the leakage magnetic flux tends to be closed through the path of the magnetic sheet 30 with higher magnetic permeability, rather than passing through the copper busbar.

[0063] Since the eddy current loss is proportional to the square of the alternating magnetic field, the eddy current loss can be greatly reduced by significantly reducing the magnetic field strength at the copper busbar. By adopting the method of coating the magnetic sheet 30, the leakage magnetic penetration in the copper busbar area can be reduced. At the same time, the low electrical conductivity of the magnetic sheet 30 can avoid the introduction of additional eddy current loss in the magnetic sheet 30. The present invention takes a ferrite sheet as an example, and the relationship between the magnetic induction strength inside and outside the ferrite satisfies:

[0064]

[0065] Among them, B outside is the magnetic flux density in the external area, such as air or the non-magnetic area around the copper busbar, B inside is the magnetic flux density in the internal area, such as the inside of a ferrite magnetic sheet, μ 0 is the vacuum magnetic permeability, μr is the magnetic permeability of the magnetic sheet 30, H outside is the external magnetic field strength of the ferrite magnetic sheet, H inside is the magnetic field strength in the inner area of ​​the magnetic sheet 30.

[0066] According to the magnetic field continuity condition:

[0067]

[0068] It can be concluded that the high magnetic permeability of ferrite leads to the magnetic field strength H inside the copper bar. inside Greatly reduce, thereby reducing the magnetic field source H in the copper busbar area outside Therefore, the ferrite magnetic sheet has a shielding effect of absorbing leakage magnetic field. Assume that the surface area of ​​the ferrite coverage area is A shield , the uncovered area is A air , the total leakage flux is:

[0069] Φ leak =B shield ·A shield +B air ·A air

[0070] Among them, Φ leak Represents the total leakage flux, B shield represents the magnetic flux density of the area covered by the magnetic sheet 30, B air It represents the magnetic flux density of the area not covered by the magnetic sheet 30.

[0071] According to the magnetoresistance model, the magnetoresistance R of the area covered by the magnetic sheet 30 is shield and the magnetic resistance R of the uncovered area air It is expressed as:

[0072]

[0073] Among them, l shield represents the magnetic path length of the area covered by the magnetic sheet 30, l air represents the magnetic path length of the area not covered by the magnetic sheet 30, μ 0 is the vacuum magnetic permeability, μ r is the magnetic permeability of the magnetic sheet 30, A shield is the surface area of ​​the magnetic sheet 30, A air It is the area not covered by the magnetic sheet 30.

[0074] The total flux distribution ratio is:

[0075]

[0076] Among them, Φ leak Represents the total leakage flux, Φ shield It represents the leakage flux of the area covered by the magnetic sheet 30.

[0077] The eddy current loss is proportional to the square of the magnetic flux density, so the suppression ratio of the eddy current loss is:

[0078]

[0079] Among them, P eddyshield is the eddy current loss in the area covered by the magnetic sheet 30, P eddy0 is the original eddy current loss of the copper bar without the magnetic sheet 30, Φ leak Represents the total leakage flux, Φ air Represents the leakage flux in the air.

[0080] When the magnetic path length of the magnetic sheet 30 is the same as that of the air, the distribution relationship of the leakage flux is:

[0081]

[0082] The leakage magnetic shielding efficiency is expressed as:

[0083]

[0084] This is the calculation model of the shielding efficiency of the magnetic sheet 30 against the leakage flux mentioned above, Ф leak is the total leakage flux of the magnetic integrated transformer, Ф air is the leakage flux in the air, A shield is the surface area of ​​the magnetic sheet 30, A air is the surface area of ​​the uncovered area of ​​the magnetic sheet 30, μ r is the magnetic permeability of the magnetic sheet 30.

[0085] It can be seen from the above formula that when the magnetic sheet 30 is not applied, the total leakage flux all passes through the air, while when the magnetic sheet 30 is applied, part of the leakage flux is passed through the high magnetic permeability (μ r >>1) Magnetic material diversion, the area of ​​the coating area A shield The larger the magnetic permeability μ r The higher the leakage flux Φ in the air air The smaller it is, the magnetic flux of the remaining air path is reduced, resulting in lower eddy current losses.

[0086] The above-mentioned method of reducing leakage inductance by pasting the magnetic sheet 30 is also the eddy current loss suppression method based on the magnetic shielding of the magnetic sheet 30 in the present invention. In addition, in order to optimize the magnetic field distribution and reduce the eddy current loss, the present invention also proposes a magnetic permeability gradient configuration method. At this time, the magnetic integrated transformer sets a multi-layer magnetic sheet 30 combination to make the magnetic permeability change continuously or in stages. The present invention takes a double-layer magnetic sheet 30 as an example, assuming that the thickness of the first magnetic sheet (here the first magnetic sheet is the inner magnetic sheet) is t 1 , the magnetic permeability is μ r1 , the thickness of the second magnetic sheet (here the second magnetic sheet is the outer magnetic sheet) is t2 , the magnetic permeability is μ r2 , then according to the magnetic flux continuity between layers, the equivalent magnetic permeability μ of the magnetic sheet 30 is derived eff for:

[0087]

[0088] Simplifying it, we can get:

[0089]

[0090] That is, in the above text, when the magnetic sheet 30 is set as two layers, the calculation model of the equivalent magnetic permeability of the magnetic sheet 30 is, here, t 1 ,t 2 is the thickness of the two layers of magnetic sheets 30, μ r1 and μ r1 is the magnetic permeability of the two layers of magnetic sheets 30, μ 0 is the magnetic permeability of vacuum.

[0091] In this embodiment, when the magnetic sheet 30 is provided as two layers, the magnetic permeability of the inner magnetic sheet 30 is set to be greater than 1000, and the magnetic permeability of the outer magnetic sheet 30 is set to be less than 1000;

[0092] The thickness of the inner magnetic sheet 30 and the outer magnetic sheet 30 are both set to 1 mm.

[0093] It can be seen from the above formula that the gradient configuration of the magnetic sheet 30 can be achieved by adjusting the thickness of the two layers of magnetic sheets 30 and their corresponding magnetic permeabilities. r1 ≥1000 As the inner layer of the magnetic sheet, it preferentially absorbs high-frequency leakage magnetic field, μ r2 ≤1000 as the outer layer of the magnetic sheet, used to delay magnetic saturation, the thickness of the two layers of magnetic sheet 30 is t 1 and t 2 If both are 1 mm, then:

[0094]

[0095] The higher the magnetic permeability, the greater the thickness, the larger the magnetic conductive area or volume, and the better the magnetic shielding effect provided. However, different magnetic permeabilities also have different saturation flux densities, and it is necessary to ensure that the material will not saturate under the applied field strength. sat Constraints on the upper limit of high frequency applications, maximum allowable magnetic field B max for:

[0096]

[0097] Among them, f sw is the operating frequency, f crossover is the frequency inflection point determined by the magnetic permeability and electrical conductivity of the magnetic sheet 30, and the expression is:

[0098]

[0099] Wherein, σ is the conductivity of the magnetic sheet 30, μ r is the magnetic permeability of the magnetic sheet 30.

[0100] Based on the above design, the multi-layer magnetic sheet 30 should be designed to meet the following requirements:

[0101] B shield <B sat

[0102] Among them, B shield is the magnetic flux density of the area covered by the magnetic sheet 30, B sat is the saturation magnetic flux of the magnetic piece 30.

[0103] Furthermore, the magnetic permeability gradient configuration method can be a multi-layer structure, such as the outer layer uses a magnetic sheet 30 with a magnetic permeability of 1500, the middle layer uses a magnetic sheet 30 with a magnetic permeability of 1000, and the inner layer uses a magnetic sheet 30 with a magnetic permeability of 500.

[0104] Alternatively, the outer layer may be a magnetic sheet 30 with a magnetic permeability of 500, the middle layer may be a magnetic sheet 30 with a magnetic permeability of 1000, and the inner layer may be a magnetic sheet 30 with a magnetic permeability of 1500.

[0105] Here, the multilayer magnetic sheets 30 mentioned above are arranged in order of magnetic permeability. It should be pointed out that the above-mentioned magnetic permeability 1500, magnetic permeability 1000, and magnetic permeability 500 are all settings under one embodiment of the present invention, and the present invention is not limited to the above-mentioned magnetic permeability.

[0106] In the present invention, the outer layer may be a magnetic sheet 30 made of ferrite material, the middle layer may be a magnetic sheet 30 made of nanocrystalline alloy, and the inner layer may be a magnetic sheet 30 made of amorphous alloy.

[0107] In addition, the gradient direction of the magnetic permeability can be a radial gradient, such as the cross-sectional area of ​​the magnetic core, or a longitudinal gradient, such as the axial direction of the winding.

[0108] Optionally, the selected magnetic sheet 30 may be in array form, that is, magnetic sheet materials with different cross-sectional sizes and different magnetic permeabilities may be attached to the same area of ​​the copper busbar.

[0109] Assuming eddy current losses:

[0110]

[0111] For gradient materials, there are:

[0112]

[0113] Where B represents the magnetic flux density, μ(z) represents the position-related magnetic permeability, z represents the thickness direction of the copper bar, and H represents the magnetic field intensity. Based on the above formula, the gradient of μ can be reasonably designed to reduce the alternating gradient of the magnetic field inside the material, thereby reducing eddy currents.

[0114] The above setting method, that is, the magnetic permeability gradient configuration method in the present invention, is to simultaneously realize the coordinated control of leakage inductance and eddy current loss, so that the leakage inductance can be improved while reducing the eddy current loss. The present invention also proposes a method for coordinated control of leakage inductance and eddy current loss, which realizes the coordinated control of leakage inductance and eddy current loss by adjusting the coverage area ratio of the magnetic sheet 30, the magnetic permeability of the magnetic sheet 30, and the thickness of the magnetic sheet 30.

[0115] When the magnetic sheet 30 is used to cover the copper busbar, the magnetic sheet 30 changes the leakage flux path and reconstructs the magnetic circuit of the transformer. The leakage flux originally dispersed in the air is concentrated and guided by the ferrite. Since the magnetic resistance of ferrite is much lower than that of air, the leakage flux increases, and the stored magnetic energy also increases, making the equivalent leakage inductance L leak improve.

[0116] The magnetic energy formula of leakage inductance is:

[0117]

[0118] Among them, μ 0 is the vacuum permeability, W leak is the leakage magnetic energy, H is the leakage magnetic intensity, v is the space volume, L k is the leakage inductance, and I is the current flowing through the leakage inductance. The calculation of leakage inductance is inversely proportional to magnetic resistance. The low magnetic resistance path provided by ferrite increases the total leakage inductance. According to the design structure of the magnetic integrated transformer, the leakage inductance is determined by the mutual magnetic flux linkage between the primary and secondary sides:

[0119]

[0120] Among them, N p is the total number of turns of the first part W1a of the first winding and the second part W1b of the first winding, h is the height of the core window, A coupling A is the effective cross-sectional area of ​​the first part W1a of the first winding / the second part W1b of the first winding coupled with the second winding W2, core is the effective cross-sectional area of ​​the core.

[0121] After the magnetic sheet 30 is applied, according to the effective magnetic permeability μ eff , the leakage inductance expression is corrected to get

[0122]

[0123] Among them, A shild A is the cross-sectional area of ​​the ferrite covered path,leak is the cross-sectional area of ​​the initial magnetic flux leakage path. The coverage area ratio of the magnetic sheet 30 is defined as α=A shield / A leak By adjusting α and the magnetic permeability μ of the magnetic sheet 30 efff and the thickness t of the magnetic sheet 30, the leakage inductance can be adjusted and the eddy current loss can be controlled at the same time. According to the magnetic integrated transformer structure proposed by the present invention, it is approximately considered that the length of the magnetic sheet 30 and the air path is similar, that is, l leak ≈l air , leakage inductance and eddy current loss can be fitted according to the experiment, and the empirical formula is:

[0124]

[0125] That is, the leakage inductance and eddy current loss of the magnetic integrated transformer mentioned above satisfy the calculation model, where L leak_old is the leakage inductance without adding the magnetic sheet 30, P eddy_old is the eddy current loss without adding the magnetic sheet 30, L leak_new is the leakage inductance after adding the magnetic sheet 30, P eddy_new is the eddy current loss after adding the magnetic sheet 30, α is the coverage area ratio of the magnetic sheet 30, ξ is the additional correction factor of leakage inductance, and λ is the leakage magnetic flux shunt efficiency.

[0126] Due to the non-uniformity of magnetic field distribution, an additional correction factor ξ=0.15 is added to the leakage inductance increase in the above formula. The exponent of magnetic permeability 0.5 is determined by the shunt effect of the actual leakage magnetic path. λ=0.8 means that the efficiency of leakage magnetic shunt is 80% of the theoretical value. The remaining 20% ​​may come from factors such as nonlinear magnetic permeability of the shielding material, incomplete magnetic field coupling between the magnetic sheet 30 and the air path, and additional losses caused by high-frequency skin effect.

[0127] Furthermore, the magnetic sheet 30 in the present invention can be a combination of at least one of a ferrite sheet, a nanocrystalline alloy sheet, an iron powder core magnetic sheet, and an amorphous alloy sheet, that is, one of the materials can be used, or a combination of two or more materials can be used, such as a ferrite sheet + an iron powder core magnetic sheet;

[0128] The magnetic sheet 30 in the present invention may have different magnetic permeabilities, such as 180, 200, 500, 1000, 1500, etc.;

[0129] Meanwhile, the magnetic sheet 30 may have different thicknesses, such as 0.5 mm, 1 mm, 2 mm, etc.;

[0130] The magnetic sheet 30 in the present invention can be a multi-layer structure, such as an outer layer using a magnetic sheet 30 with a magnetic permeability of 1000, a middle layer using a magnetic sheet 30 with a magnetic permeability of 500, and an inner layer using a magnetic sheet 30 with a magnetic permeability of 200. It can be in an array form, such as an arrangement of magnetic permeabilities of 1000, 500 and 200, and the sizes of the magnetic sheets 30 can be different.

[0131] Furthermore, the magnetic sheet 30 in the present invention may also be a composite material, and magnetic particles and / or high thermal conductivity particles may be doped into the magnetic material, so that the magnetic sheet 30 has a magnetic-thermal synergistic function.

[0132] The bonding method of the magnetic sheet 30 and the third winding W3 (ie, the copper busbar) is at least one of gluing, inlaying, and overmolding.

[0133] Figure 2 Schematic diagram of magnetic field distribution when the magnetic integrated transformer of the present invention is not covered with magnetic sheet 30. Figure 2 It can be seen that the copper busbar of the magnetic integrated transformer is not covered with the magnetic sheet 30. Due to the leakage inductance of the magnetic integrated transformer, a higher magnetic field strength is generated between the first part W1a of the first winding and the second winding W2, and between the second part W1b of the first winding and the second winding W2. The leakage magnetic flux directly contacts the third winding W3, causing the leakage magnetic flux to generate eddy current loss on the copper busbar. Figure 5 Schematic diagram of magnetic field distribution when the magnetic integrated transformer of the present invention is covered with magnetic sheet 30, from Figure 5 It can be seen that after the copper busbar of the magnetic integrated transformer is covered with the magnetic sheet 30, the magnetic field strength near the leakage flux is still very high, but the magnetic field strength is shielded by the magnetic sheet 30, and the leakage flux area does not directly contact the copper busbar of the magnetic integrated transformer, so that the eddy current loss of the leakage flux on the copper busbar is reduced.

[0134] Figure 3 Schematic diagram of magnetic flux distribution when the magnetic integrated transformer of the present invention is not covered with magnetic sheet 30, Figure 6 The magnetic flux distribution diagram of the magnetic integrated transformer in the present invention when the magnetic sheet 30 is attached can be seen from Figure 3 and Figure 6 By comparison, it can be seen that for the magnetic integrated transformer not coated with the magnetic sheet 30, the magnetic flux vector is in the leakage magnetic area and its direction is toward the copper busbar, while for the transformer coated with the magnetic sheet 30, the path of the magnetic flux vector changes, and the third winding W3 is directly isolated from the first part W1a of the first winding, the second winding W2 and the second part W1b of the first winding by the magnetic sheet 30, and the magnetic sheet 30 plays a role in absorbing the leakage magnetic field.

[0135] Figure 4 Schematic diagram of the copper busbar current density when the magnetic integrated transformer is not covered with the magnetic sheet 30 in the present invention. The current density reacts violently on the copper busbar. Since the current density reflects the eddy current loss of the copper busbar, Figure 4It can be seen that the current density in most areas of the copper busbar exceeds 20A / mm 2 , Figure 7 This is a schematic diagram of the current density of the copper busbar when the magnetic integrated transformer in the present invention is covered with the magnetic sheet 30. It can be seen that under the action of the magnetic sheet 30, there is almost no current density on the copper busbar. The magnetic permeability of the magnetic sheet 30 set in the simulation of the present invention is 1000. Under higher magnetic permeability, the magnetic sheet 30 has a very good attenuation effect on the eddy current loss of the copper busbar.

[0136] The present invention applies the eddy current loss suppression method of the magnetic sheet magnetic shield, the magnetic permeability gradient configuration method, and the leakage inductance and eddy current loss coordinated control method to the magnetic integrated transformer, that is, proposes a magnetic integrated transformer that can effectively attenuate eddy current losses and improve the leakage inductance of the transformer.

[0137] The optimization design method proposed in the present invention is universally applicable to the DAB converter topology, resonant converter topology and three-port converter topology widely used in electric vehicle charging systems. For the magnetic integrated transformer adopting the leakage inductance integrated design, leakage magnetic flux will inevitably be generated in the leakage inductance formation area, and the leakage magnetic flux will generate eddy current loss on the nearby metal conductor. Through the optimization design method described in the present invention, the eddy current loss generated by the transformer leakage magnetic flux can be effectively suppressed, a higher integrated transformer design can be achieved, the volume of the magnetic components in the charger is effectively reduced, and the power density of the charger is improved.

[0138] Based on this, the present invention also proposes an electric vehicle charging system, including a charging circuit, the charging circuit having the above-mentioned magnetic integrated transformer;

[0139] The charging circuit adopts at least one of a DAB converter topology, a resonant converter topology, and a three-port converter topology.

[0140] In summary, compared with the prior art, the present invention has at least the following beneficial effects:

[0141] The present invention covers the third winding of the magnetic integrated transformer with a magnetic sheet, shields the leakage flux of the magnetic integrated transformer in the form of a magnetic sheet combination, and uses the magnetic permeability of the magnetic sheet to reconstruct the leakage flux path, so as to achieve the purpose of improving the leakage inductance of the transformer leakage flux, thereby suppressing the eddy current loss caused by leakage flux in the OBC, and effectively solving the problem of low efficiency of the magnetic integrated transformer. Due to the improved leakage inductance, the switching frequency of the OBC can be reduced without affecting the size of the magnetic integrated transformer, and EMI can be suppressed, providing a feasible solution for the OBC with small volume, high power density and low cost.

[0142] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A magnetic integrated transformer, comprising a magnetic column, a first winding, a second winding, and a third winding, characterized in that: The second winding is wound on the middle part of the magnetic column, the first winding includes a first part and a second part wound on both sides of the second winding, and the third winding is wound with a copper bar and is stacked with the second winding; At least one magnetic sheet is attached to the inner wall of the third winding to reduce eddy current loss caused by magnetic leakage and increase leakage inductance.

2. The magnetic integrated transformer according to claim 1, characterized in that: The magnetic sheet is made of magnetic material with high magnetic permeability and low electrical conductivity.

3. The magnetic integrated transformer according to claim 1, characterized in that: The magnetic sheet is doped with magnetic core particles and / or high thermal conductivity particles.

4. The magnetic integrated transformer according to claim 1, characterized in that: The bonding method of the magnetic sheet and the third winding is at least one of gluing, inlaying, and overmolding.

5. The magnetic integrated transformer according to claim 1, characterized in that: The magnetic integrated transformer arranges a plurality of magnetic sheets in a combination mode so that the magnetic permeability of the plurality of magnetic sheets changes continuously or in stages.

6. The magnetic integrated transformer according to claim 5, characterized in that: The multiple layers of magnetic sheets are arranged in order according to the magnitude of the magnetic permeability of the magnetic sheets.

7. The magnetic integrated transformer according to claim 5, characterized in that: The multi-layer magnetic sheet is designed to meet the following requirements: B shield <B sat Among them, B shield is the magnetic flux density of the area covered by the magnetic sheet, B sat is the saturation flux of the magnetic piece.

8. The magnetic integrated transformer according to claim 1, characterized in that: The magnetic integrated transformer realizes coordinated control of leakage inductance and eddy current loss by adjusting the coverage area ratio of the magnetic sheet, the magnetic permeability of the magnetic sheet, and the thickness of the magnetic sheet.

9. The magnetic integrated transformer according to claim 8, characterized in that: The leakage inductance and eddy current loss of the magnetic integrated transformer meet the calculation model: Among them, L leak_old is the leakage inductance without adding the magnetic sheet, P eddy_old is the eddy current loss without adding the magnetic sheet, L leak_new is the leakage inductance after adding the magnetic sheet, P eddy_new is the eddy current loss after adding the magnetic sheet, α is the coverage area ratio of the magnetic sheet, ξ is the leakage inductance additional correction factor, λ is the leakage magnetic flux shunt efficiency, μ r is the magnetic permeability of the magnetic sheet.

10. An electric vehicle charging system, characterized in that: A charging circuit comprising a magnetic integrated transformer as claimed in any one of claims 1 to 9; The charging circuit adopts at least one of a DAB converter topology, a resonant converter topology, and a three-port converter topology.

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