A magnetically integrated planar transformer for bidirectional CLLC resonant converter

Abstract

The present invention discloses a magnetically integrated planar transformer for a bidirectional CLLC resonant converter. The transformer comprises an EI-type magnetic core, wherein the E-type magnetic core comprises a core center column and core side columns. A g1 air gap is provided between the E-type core center column and an I-type magnetic core, and a g2 air gap is provided between the core side columns and the I-type magnetic core. Primary and secondary windings are asymmetrically distributed on the side columns of the EI core. The I-type magnetic core has a narrow and long g3 air gap extending front to back and up to down on both sides of the core centerline. By asymmetrically distributing the primary and secondary windings and adjusting the air gap, leakage inductance is increased, and when the leakage inductance of the planar transformer is used as the resonant inductance of the CLLC resonant converter, the resonant inductance is adjustable, while reducing the edge loss caused by the large air gap.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic power conversion, and in particular to a magnetically integrated planar transformer applied to a bidirectional CLLC resonant converter. Background Art

[0002] With the advancement of power electronics technology, high-power density and high-efficiency converters are widely used in automotive, aerospace, and energy storage systems. The soft-switching properties of bidirectional CLLC resonant converters can achieve zero-voltage switching (ZVS) for the primary-side switches and zero-current switching (ZCS) for the secondary-side switches. As magnetic components in a CLLC resonant converter, the resonant inductor and transformer occupy a significant portion of the converter's volume. To reduce the converter's size and achieve miniaturization, magnetic integration solutions can be employed.

[0003] The bidirectional CLLC resonant converter includes a primary-side connected energy storage battery and a secondary-side connected DC bus, which are connected to two full-bridge circuits. Each full-bridge consists of four MOSFETs, namely S1-S4 and S5-S8. The bridge arm formed by S1-S4 is connected to the resonant cavity. The primary resonant cavity is connected by the resonant inductor L r1 , resonant capacitor C r1 The secondary resonant cavity is composed of L r2 and C r2 The bridge arm composed of S5-S8 is connected to the resonant cavity in front. The primary and secondary resonant cavities are connected by a high-frequency transformer T with a transformation ratio of n:1.

[0004] For example, the patent with publication number CN114268226A discloses a magnetically integrated planar transformer for a bidirectional CLLC circuit, using an EE core. The transformer primary winding T1 and secondary winding T2 are wound around the core center column V3; the primary inductor winding Lp1 and the primary inductor winding Lp2 with the same number of turns are wound around the core side columns V1 and V2 respectively; the secondary inductor winding Ls1 and the secondary inductor winding Ls2 with the same number of turns are also wound around the core side columns V1 and V2 respectively. The present invention realizes the decoupling integration of the two resonant inductors and the transformer in the CLLC in a pair of magnetic cores, reducing the volume of the power converter. At the same time, by utilizing the coupling characteristics of the two resonant inductors in this structure, the number of turns of the resonant inductor is reduced while ensuring that the resonant frequency and inductance ratio of the CLLC circuit remain unchanged, reducing the winding loss and improving the power density and efficiency of the CLLC converter.

[0005] For example, the patent with publication number CN112019053A discloses a resonant converter, including an EI-type magnetic integrated transformer, which includes: a magnetic core having a center column and a first side column and a second side column respectively located on both sides of the center column; a primary winding and a secondary winding wound on the center column; and a first inductor winding and a second inductor winding respectively wound on the first side column and the second side column, wherein the first inductor winding, the primary winding and the second inductor winding are connected in series to form an integral winding wound sequentially on the first side column, the center column and the second side column, wherein the first inductor winding and the second inductor winding are arranged to generate an induced electromotive force at the first side column and the second side column through self-inductance.

[0006] In actual operation, the above patents and existing technologies have the following deficiencies: There are mainly the following ways to implement magnetic integration of bidirectional CLLC resonant converters: In order to increase the leakage inductance of the planar transformer, a magnetic shunt device is added in the middle of the original EE core, but this structure increases the AC loss; the asymmetric horizontal air gap structure reduces the AC loss to a certain extent, but is not suitable for symmetrical CLLC topology; the planar transformer design with adjustable inductance distributes the primary and secondary windings asymmetrically on the side columns, and adjusts the inductance by adjusting the air gap, but this will increase the edge loss. Summary of the Invention

[0007] In view of the deficiencies in the prior art, the present invention provides a magnetically integrated planar transformer for use in a bidirectional CLLC resonant converter to solve the above problems.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0009] A magnetically integrated planar transformer for a bidirectional CLLC resonant converter comprises an E-type magnetic core and an I-type magnetic core, wherein the E-type magnetic core comprises a core C center column, a core L side column, and a core R side column, wherein the I-type magnetic core is arranged at the open end of the E-type magnetic core and the center lines of the two cores coincide with each other, a g1 air gap is provided between the core C center column and the I-type magnetic core, a g2 air gap is provided between the core L side column and the core R side column and the I-type magnetic core, a primary P1 winding and a secondary S1 winding are wound on the core L side column, a primary P2 winding and a secondary S2 winding are wound on the core R side column, and a narrow g3 air gap is provided on both sides of the core center line, which is through front to back and up to down, and the primary leakage inductance of the transformer is L. lkp , the secondary leakage inductance of the transformer is L lks , the primary self-inductance of the transformer is L pp , the secondary self-inductance of the transformer is L ss .

[0010] Preferably, the primary winding P1 and the secondary winding S1 on the side column of the magnetic core L are asymmetrically distributed.

[0011] Preferably, the primary winding P2 and the secondary winding S2 on the R side column of the magnetic core are asymmetrically distributed.

[0012] Preferably, the primary leakage inductance L of the transformer lkp As the resonant inductor L of the bidirectional CLLC resonant converter circuit r1 The resonant inductor L designed by the circuit is used r1 Sure.

[0013] Preferably, the secondary leakage inductance L of the transformer lks As the resonant inductor L of the bidirectional CLLC resonant converter circuit r2 The resonant inductor L designed by the circuit is used r2 Sure.

[0014] Preferably, the distance from the inner edge of the g3 air gap to the core centerline (7) is d, and the length of the g1 air gap is l g1 , the length of the g2 air gap is l g2 , the length of the g3 air gap is l g3 , the magnetic resistance of each magnetic circuit of the transformer is R x , x=1, 2, 3, 4, 5, g1, g2, g3, the cross-sectional area of each magnetic circuit of the transformer is A x , x=1, 2, 3, 4, 5, g1, g2, g3, the equivalent magnetic resistance of the transformer side column is R a , the equivalent magnetic resistance of the transformer column is R b The magnetic flux of the left column of the transformer is φ1, the magnetic flux of the middle column of the transformer is φ2, the magnetic flux of the right column of the transformer is φ3, and the magnetic permeability of the transformer core is μ r , the vacuum magnetic permeability is μ0, and the number of turns of the primary P1 winding (31) is N p1 The number of turns of the primary P2 winding (32) is N p2 The number of turns of the secondary side S1 winding (41) is N s1 The number of turns of the secondary side S2 winding (42) is N s2 , n is the primary-to-secondary turns ratio, M is the mutual inductance coefficient, the transformer's magnetizing inductance is L m , the length of the g1 air gap l g1 and the length of the g2 air gap and the g3 air gap and l g2 +l g3 Determined by the following formula:

[0015] L m =n·M

[0016]

[0017]

[0018] Φ1=Φ2+Φ3

[0019] R a =R1+R2+R g2 +R4+R g3 +R5

[0020] R b =R3+R g1

[0021]

[0022] Preferably, the length l of the g2 air gap g2 and the length l of the air gap g3 g3 The optimal value is determined by loss simulation using finite element analysis software.

[0023] Preferably, the distance d from the inner edge of the g3 air gap to the center line of the magnetic core is determined to have an optimal value by performing loss simulation using finite element analysis software.

[0024] In summary, compared with the prior art, the present invention has the following advantages: the resonant inductance of the bidirectional CLLC resonant converter is similar to the leakage inductance model of the transformer, so magnetic integration technology can be used to convert the leakage inductance L of the transformer into a lkp and L lks As the resonant inductor L r1 and L r2 The use of asymmetrically distributed windings reduces parasitic capacitance between the primary and secondary windings, reduces EMI crosstalk between the primary and secondary windings, reduces the number of magnetic components in the converter, reduces the size of the converter, improves the power density and efficiency of the converter, reduces costs, improves reliability, and makes the output current purer. The asymmetrical distribution of the primary and secondary windings on the side columns of the magnetic core reduces coupling between the primary and secondary windings and increases leakage inductance. The g1 air gap, g2 air gap, and g3 air gap can be used to adjust the excitation inductance and leakage inductance of the transformer. Based on the improvement of the asymmetrically distributed winding, two vertical g3 air gaps are added to the I-type core in the EI core. By adjusting the distribution position and length of the g3 air gaps, the edge loss caused by the edge effect caused by the large air gap between the EI cores is reduced, achieving controllable inductance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the circuit topology diagram of the bidirectional CLLC resonant converter;

[0026] Figure 2 It is a schematic diagram of the structure of a planar transformer with a vertical air gap;

[0027] Figure 3This is the equivalent reluctance model diagram of the planar transformer;

[0028] Figure 4 It is the loss curve under different air gap length distribution;

[0029] Figure 5 It is the loss curve diagram under different air gap position distribution;

[0030] Figure 6 It is the magnetic density cloud diagram of the core when the design is optimized;

[0031] Among them, 1-E-type magnetic core, 11-core C middle column, 12-core L side column, 13-core R side column, 2-I-type magnetic core, 21-g3 air gap, 3-primary winding, 31-primary P1 winding, 32-primary P2 winding, 4-secondary winding, 41-secondary S1 winding, 42-secondary S2 winding, 5-g1 air gap, 6-g2 air gap, 7-core center line. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0033] This embodiment provides a technical solution: a magnetically integrated planar transformer for a bidirectional CLLC resonant converter of the present invention, wherein a g1 air gap 5 and a g2 air gap 6 are added between EI, a vertical g3 air gap 21 is opened on the I magnetic core, the primary winding 3 is composed of a primary P1 winding 31 and a primary P2 winding 32, and the secondary winding 4 is composed of a secondary S1 winding 41 and a secondary S2 winding 42. The magnetic resistance model of the magnetic core is established according to the structure proposed in this solution.

[0034] like Figure 3 , the magnetic resistance of a certain path (x=1,2,3,4,5) is:

[0035]

[0036] The magnetic flux is:

[0037]

[0038] Φ1=Φ2+Φ3

[0039] R a =R1+R2+R g2 +R4+R g3 +R5 (3)

[0040] R b =R3+R g1 (4)

[0041] Transformer self-inductance L pp 、L ss and mutual inductance M are:

[0042]

[0043] Transformer leakage inductance L lkp 、L lks and the magnetizing inductance L m It can be obtained from the following formula:

[0044] L pp =L lkp +n·M (8)

[0045]

[0046] L m =n·M (10)

[0047] Among them, n is the primary-to-secondary turns ratio, M is the mutual inductance coefficient, that is, the preliminary design of the bidirectional CLLC resonant converter, the excitation inductance L of the converter is obtained m and resonant inductor L r1 and L r2 In this embodiment, according to

[0048]

[0049] U inmax is the maximum value of the input voltage, D is the duty cycle of the converter, f min is the minimum switching frequency of the converter, B m is the saturation magnetic field strength of the core, A e is the cross-sectional area of the core C column 11. The number of turns N of the primary winding 3 can be calculated. p =4, secondary winding 4 turns N s =8, where N p1 、N p2 and N s1 、N s2 The value of N is reasonably distributed according to the value of the resonant inductance and excitation inductance in the converter. p1 =3,N p2 =1, N s1 =2, N s2 =6. Get the primary magnetizing inductance L m is 12.9μH, the resonant inductor L r1 4.3μH, L r2 is 17.2μH. lkp and L lks Replace the resonant inductor L r1 and L r2, calculate the air gap l according to formulas (1)-(10) g1 and l g2 +l g3 The value of l g2 and l g3 Repeated adjustments are made to obtain the lowest edge loss.

[0050] In this embodiment, Maxwell finite element analysis and simulation were used, and the planar EI58 core from Ferromagnetics was selected. The core specifications were drawn or generated using a script, and the windings were drawn after calculating the effective current value and current density. The primary and secondary windings were distributed on the side columns in a ratio of 3:2 and 1:6 respectively. After the windings were reasonably distributed, the windings were excited and optimized. According to the excitation inductance L m and the resonant inductance value L r1 and L r2 , use formula (1)-(10) to obtain l g1 =0.3mm, l g2 +l g3 =0.4mm, where g2 +l g3 After confirmation, when l g2 Each time a value is taken, l g3 A corresponding value is obtained. For the air gap at a distance d from the center line of the core and l g2 、l g3 The edge loss at different size distributions is simulated to obtain Figure 4 and Figure 5 The loss curve shown in FIG. 1 , thereby obtaining the length l of the g2 air gap 6 and the g3 air gap 21 g2 and l g3 The optimal design of Figure 4 It can be seen that the best l g2 The value is 0.15mm, then the best l g3 The value is 0.25mm, the optimal d value is 21mm, and the l g2 and l g3 After the value is calculated according to l g2 Then adjust the length of l2.

[0051] According to simulation analysis, compared with the distribution mode of I-type magnetic core 2 without vertical g3 air gap 21, the edge loss of the transformer of I-type magnetic core 2 without g3 air gap 21 is 9.6W, while the minimum edge loss of the transformer of optimized I-type magnetic core 2 with g3 air gap 21 is 2.1W. Obviously, the edge loss of the transformer with vertical g3 air gap 21 is lower. The magnetic flux B value under the optimized air gap distribution is simulated and obtained. Figure 6 The magnetic flux density cloud diagram of the magnetic core during the optimal design shown has a maximum value of 0.2T, which is less than the saturation magnetic flux density of the selected magnetic core.

[0052] Compared with a planar transformer with an I-type magnetic core without a vertical g3 air gap 21, the present invention achieves the following beneficial technical results: the vertical air gap is added, the loss caused by the edge effect is reduced, and the efficiency of the converter is effectively improved.

[0053] In the description of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0054] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A magnetic integrated planar transformer for a bidirectional CLLC resonant converter, comprising an E-type magnetic core (1) and an I-type magnetic core (2), wherein the E-type magnetic core (1) comprises a core C middle column (11), a core L side column (12), and a core R side column (13), and the I-type magnetic core (2) is arranged at an open end of the E-type magnetic core (1) and the center lines (7) of the two cores coincide with each other, and is characterized in that: A g1 air gap (5) is provided between the core C center column (11) and the I-type core (2); a g2 air gap (6) is provided between the core L side column (12) and the core R side column (13) and the I-type core (2); a primary P1 winding (31) and a secondary S1 winding (41) are wound on the core L side column (12); a primary P2 winding (32) and a secondary S2 winding (42) are wound on the core R side column (13); the I-type core (2) has a narrow g3 air gap (21) extending from front to back and from top to bottom on both sides of the core center line (7); the primary leakage inductance of the transformer is L lkp , the secondary leakage inductance of the transformer is L lks , the primary self-inductance of the transformer is L pp , the secondary self-inductance of the transformer is L ss .

2. The magnetically integrated planar transformer for a bidirectional CLLC resonant converter according to claim 1, wherein: The primary P1 winding (31) and the secondary S1 winding (41) on the L-side column (12) of the magnetic core are asymmetrically distributed.

3. The magnetically integrated planar transformer for a bidirectional CLLC resonant converter according to claim 2, wherein: The primary P2 winding (32) and the secondary S2 winding (42) on the magnetic core R side column (13) are asymmetrically distributed.

4. The magnetically integrated planar transformer for a bidirectional CLLC resonant converter according to claim 1, wherein: The primary leakage inductance L of the transformer lkp As the resonant inductor L of the bidirectional CLLC resonant converter circuit r1 The resonant inductor L designed by the circuit is used r1 Sure.

5. The magnetically integrated planar transformer for a bidirectional CLLC resonant converter according to claim 1, wherein: The secondary leakage inductance L of the transformer lks As the resonant inductor L of the bidirectional CLLC resonant converter circuit r2 The resonant inductor L designed by the circuit is used r2 Sure.

6. The magnetically integrated planar transformer for a bidirectional CLLC resonant converter according to claim 1, characterized in that: The distance from the inner edge of the g3 air gap to the core centerline (7) is d, and the length of the g1 air gap is l g1 , the length of the g2 air gap is l g2 , the length of the g3 air gap is l g3 , the magnetic resistance of each magnetic circuit of the transformer is R x , x=1, 2, 3, 4, 5, g1, g2, g3, the cross-sectional area of each magnetic circuit of the transformer is A x , x=1, 2, 3, 4, 5, g1, g2, g3, the equivalent magnetic resistance of the transformer side column is R a , the equivalent magnetic resistance of the transformer column is R b The magnetic flux of the left column of the transformer is φ1, the magnetic flux of the middle column of the transformer is φ2, the magnetic flux of the right column of the transformer is φ3, and the magnetic permeability of the transformer core is μ r , the vacuum magnetic permeability is μ0, and the number of turns of the primary P1 winding (31) is N p1 The number of turns of the primary P2 winding (32) is N p2 The number of turns of the secondary side S1 winding (41) is N s1 The number of turns of the secondary side S2 winding (42) is N s2 , n is the primary-to-secondary turns ratio, M is the mutual inductance coefficient, the transformer's magnetizing inductance is L m , the length of the g1 air gap l g1 and the length of the g2 air gap and the g3 air gap and l g2 +l g3 Determined by the following formula: L m =n·M Φ1=Φ2+Φ3 R a =R1+R2+R g2 +R4+R g3 +R5 R b =R3+R g1 7. The magnetically integrated planar transformer for a bidirectional CLLC resonant converter according to claim 6, characterized in that: The length l of the g2 air gap g2 and the length l of the air gap g3 g3 The optimal value is determined by loss simulation using finite element analysis software.

8. The magnetically integrated planar transformer for a bidirectional CLLC resonant converter according to claim 6, characterized in that: The distance d from the inner edge of the g3 air gap to the center line (7) of the magnetic core is determined to have an optimal value by performing loss simulation using finite element analysis software.

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