A loosely coupled transformer device and circuit for wireless charging of electric vehicles

Abstract

The present invention discloses a loosely coupled transformer device and circuit for wireless charging of electric vehicles, wherein the transformer device includes two shielded metal plates and mutually coupled transmitting side module and receiving side module, the transmitting side module is placed at the ground end, and the receiving side module is placed at the bottom of the vehicle body; the transmitting side module and the receiving side module are both embedded in the corresponding shielded metal plates, and the transmitting side module and the receiving side module both include an insulating plate, a magnetic core, a transformer coil and an inductor coil; the transformer coil is fixed on one side surface of the magnetic core, and the transformer coil of the transmitting side module is arranged opposite to the transformer coil of the receiving side module; the inductor coil is spirally wound on the magnetic core, and the winding direction of the inductor coil of the transmitting side module is perpendicular to the winding direction of the inductor coil of the receiving side module; the transformer coil and the inductor coil on the same magnetic core are perpendicular to each other at the overlap. The present invention also includes a circuit for charging an electric vehicle using the above-mentioned transformer device.

Description

Technical Field

[0001] The present invention relates to the field of wireless power transmission, and in particular to a loosely coupled transformer device and a circuit for wireless charging of electric vehicles. Background Art

[0002] Inductive wireless power transmission technology mainly uses the principle of magnetic field coupling to achieve power transmission. This wireless charging method does not require physical line connection, which can effectively avoid the danger of short circuit and disconnection caused by environmental factors. It is also suitable for some harsh charging environments, such as mining operations, underwater charging, rainy and snowy weather, etc., and has a higher safety factor. Wireless charging technology can overcome many problems of existing contact charging, and can reduce the size of vehicle batteries, making it cleaner, more efficient and safer, so it has good development prospects.

[0003] However, the loosely magnetically coupled transformer has a large leakage inductance, and the coupling coefficient is not high when the primary and secondary sides are facing each other. In particular, when the on-board secondary coil is offset, the coupling coefficient of the transformer drops rapidly. In order to compensate for the large transformer leakage inductance and transfer energy as efficiently as possible, it is necessary to compensate the primary and secondary coil inductance at the transmitting and receiving ends, that is, to increase the resonant inductance or resonant capacitance to improve the transmission power and efficiency of the system and reduce the stress of the power device. The traditional resonant compensation scheme has the advantages of simple structure and easy control of the tuning characteristic curve, but it also has the disadvantages of low freedom in system parameter design. For the circuit compensation scheme, the development of a higher-order compensation network with better performance can obtain better impedance characteristics and higher design freedom, which has become one of the main solutions for wireless power transmission applications in electric vehicles.

[0004] When a wireless power transmission system uses a high-order compensation network, the resonant inductor becomes the key to the design of system components. The volume of the magnetic core required for a traditional discrete inductor is proportional to the inductance of the resonant inductor and the energy that needs to be stored. For a wireless power transmission system, the inductance of the resonant inductor is large, and the peak value of the resonant current is high. When the system offset is considered, the resonant current will further increase, which results in the AC resonant inductor used in the high-order resonant network requiring the use of a larger magnetic core, thereby significantly reducing the power density of the system.

[0005] On the other hand, loosely coupled transformers usually use large-area ferrite cores to enhance coupling, and due to the wide air gap, the magnetic induction intensity in the ferrite core is low, and the corresponding core loss is low; while the magnetic induction intensity in the discrete inductor core is designed to be high, and the corresponding core loss is high. This flux imbalance in the same system leads to core redundancy and magnetic loss matching within the system.

[0006] In response to the above problems, the prior art provides a variety of design solutions that integrate resonant inductors with loose magnetic coupling transformer decoupling: including a planar stacked structure, that is, the transformer coils on the transmitting side and the receiving side adopt a square symmetrical structure, and the magnetic flux generated by them is non-directional; while the inductor coils on the transmitting side and the receiving side adopt a double D-type structure, and the magnetic flux generated by them is directional. Since the inductor coil is placed at the center of the transformer coil, the inductor coil and the transformer coil are decoupled due to the principle of magnetic flux symmetry; and the magnetic flux directions of the two inductor coils are orthogonal, so that the inductor coils are decoupled when facing each other.

[0007] However, this solution can achieve good magnetic integration effect under normal conditions, but when lateral and longitudinal offsets occur, the power transmission characteristics of the system will be affected due to the existence of cross-coupling. Summary of the invention

[0008] In order to solve the problems existing in the prior art, the present invention provides a loosely coupled transformer device and circuit for wireless charging of electric vehicles. The device can maintain low cross-coupling when the primary and secondary sides of the transformer are facing each other or when a large offset (including lateral and longitudinal) occurs, thereby maintaining a high system transmission efficiency while greatly improving the power density of the system.

[0009] A loosely coupled transformer device for wireless charging of electric vehicles, comprising two shielding metal plates and a mutually coupled transmitting side module and a receiving side module, wherein the transmitting side module is placed at the ground end and the receiving side module is placed at the bottom of the vehicle body; the transmitting side module and the receiving side module are both embedded in the corresponding shielding metal plates, and the transmitting side module and the receiving side module both include an insulating plate, a magnetic core, a transformer coil and an inductor coil;

[0010] The transformer coil is wound on one end face of the magnetic core, and the transformer coil of the transmitting side module is arranged opposite to the transformer coil of the receiving side module;

[0011] The inductor coil is spirally wound on the magnetic core, and the winding direction of the inductor coil of the transmitting side module and the winding direction of the inductor coil of the receiving side module are perpendicular to each other;

[0012] The transformer coil and the inductor coil wound on the same magnetic core are perpendicular to each other at the overlap.

[0013] Specifically, the insulating plate is arranged between the shielding metal plate and the magnetic core; the transmitting side module is the primary side of the transformer, and the receiving side module is the secondary side of the transformer;

[0014] When wirelessly charging electric vehicles, the primary side of the loose magnetic coupling transformer is generally placed in a relatively fixed position, such as buried under the road surface or under a parking space, while the secondary side, i.e. the receiving side, is generally placed on the chassis of the electric vehicle as an energy interface between the on-board battery and the external power injection. For the design of the loose magnetic coupling transformer, the operating frequency is generally selected to be 85kHz. In practical applications, the operating frequency can be fine-tuned to optimize the resonant state of the system. Under the excitation of the alternating current at this frequency, an alternating magnetic field will be induced near the coil of the primary side of the transformer. According to the principle of electromagnetic induction, the alternating magnetic field will induce a voltage signal on the secondary side of the loose magnetic coupling transformer. The specific action law is determined by Faraday's law of electromagnetic induction. The voltage signal will act on the secondary side of the transformer to generate a high-frequency current signal, and then pass through the secondary rectifier to realize the entire wireless power transmission "electric energy-magnetic field-electric energy" conversion process.

[0015] In the process of energy conversion, the coils on the primary and secondary sides of the transformer act as energy carriers. In order to improve the coupling between the primary and secondary sides of the transformer, it is necessary to add a magnetic core with high magnetic permeability as a magnetic conductive medium to the primary and secondary sides. At this time, the magnetic field generated by the coil is mainly dissipated to the external environment through the magnetic core, and the receiving side module also reduces the magnetic resistance through the magnetic core, thereby shortening the magnetic flux path and improving the coupling coefficient.

[0016] The magnetic flux generated by the transformer coil of the loosely coupled transformer device provided by the present invention is perpendicularly interlaced with the magnetic flux generated by the inductor coil, so the transformer coil and the inductor coil are orthogonally decoupled in the face-to-face and different offset conditions.

[0017] In addition, the insulating board is a bakelite board, an epoxy resin board, an organic glass board, or a tempered glass board.

[0018] The magnetic core is made of at least one of the following materials: ferrite, amorphous, microcrystalline, Permalloy, and magnetic powder core.

[0019] Preferably, the magnetic core is a symmetrical block structure with a through hole at the center; the inductor coil passes through the through hole of the magnetic core and is spirally wound on the magnetic core; and the winding shape of the transformer coil is adapted to the shape of the magnetism.

[0020] Specifically, compared with a magnetic core without a through hole, the inductor coil on the magnetic core with a through hole can pass through the through hole and be wound around the magnetic core. This winding method concentrates the magnetic flux generated by the inductor coil inside the magnetic core, thereby effectively reducing the leakage magnetic flux in the space.

[0021] Preferably, two inductance coils arranged opposite to each other are wound around the magnetic core of the transmitting side module; and two inductance coils arranged opposite to each other are wound around the magnetic core of the receiving side module.

[0022] Specifically, the two inductance coils on the same magnetic core play the role of coupled inductance, and the same-name ends of the two inductance coils are the same, so that the magnetic fluxes generated by the two inductance coils play a superposition role.

[0023] Preferably, the magnetic core is an integral block structure, an air gap is provided on the magnetic core, and the air gap is adapted to the position of the inductor coil.

[0024] Specifically, the air gap can be used for inductive energy storage, and by adjusting the length of the air gap, the required inductance value of the inductor coil can be accurately returned.

[0025] Preferably, the magnetic core is a spliced ​​structure, and at least one air gap is provided on the magnetic core, and the air gap is adapted to the position of the inductor coil.

[0026] Specifically, for a spliced ​​magnetic core, an air gap is provided at the splicing position, and for a splicing position without an air gap, a crimping method is used to reduce the width of the gap as much as possible.

[0027] Preferably, the transformer coil and the inductor coil are both formed by winding single or multiple Litz wires or copper strips or copper tubes in parallel.

[0028] Specifically, when high-frequency current passes through a conductor, due to the influence of skin effect and proximity effect, the high-frequency current tends to flow on the surface of the conductor, which increases the AC resistance of the line and the loss on the wire, affecting the system efficiency. The use of coils wound with single or multiple strands of Litz wire or copper strip or copper tube can reduce the influence of skin effect accordingly due to the small diameter of the wire, and the coil formed by winding multiple strands of Litz wire or copper strip or copper tube in parallel can further reduce the loss of the coil. The parallel connection is determined by the current and power level of the primary and secondary sides of the transformer.

[0029] Preferably, the metal shielding plate is made of a metal with good electrical conductivity but no magnetic conductivity, such as aluminum, copper, silver, etc.

[0030] Specifically, since the rated coupling coefficient between the transmitting side module and the receiving side module is low, a large part of the magnetic field generated by the transmitting side module will dissipate into the surrounding environment. This part of the leakage magnetic field will cause electromagnetic interference to other circuits and electronic equipment, and will generate electromagnetic radiation to pedestrians passing by the car and people in the car. Therefore, a metal shielding plate is required to isolate the magnetic field.

[0031] A circuit for wireless charging of an electric vehicle, using the loosely coupled transformer device for wireless charging of an electric vehicle as described in any one of the above items, further comprising a DC power supply, an inverter module, and a transmitting side impedance matching circuit electrically connected in sequence, wherein the transmitting side impedance matching circuit is electrically connected to the transmitting side module;

[0032] It also includes a load, a DC conversion module, a rectifier module, and a receiving-side impedance matching circuit that are electrically connected in sequence, and the receiving-side impedance matching circuit is electrically connected to the receiving-side module.

[0033] Preferably, the transmitting side impedance matching circuit and the receiving side impedance matching circuit adopt compensation circuits containing resonant inductors.

[0034] Preferably, the resonant inductor of the compensation circuit is an inductor coil of a transformer device.

[0035] Compared with the prior art, the present invention is beneficial in that:

[0036] The structure of the loose magnetic coupling transformer device provided by the present invention can not only reduce the volume of multiple resonant inductors and improve the power density of the system, but also eliminate the influence of cross-coupling. Moreover, this structure does not affect the power transmission of the system and has good application prospects in the wireless power transmission system of electric vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A schematic structural diagram of an embodiment of a loosely coupled transformer device provided by the present invention;

[0038] Figure 2 A schematic structural diagram of another embodiment of a loosely coupled transformer device provided by the present invention;

[0039] Figure 3 A schematic diagram of an embodiment of a magnetic core of a loosely coupled transformer device provided by the present invention;

[0040] Figure 4 Schematic diagram of another embodiment of the magnetic core of the loosely coupled transformer device provided by the present invention

[0041] Figure 5 A schematic diagram of a system module when the loosely coupled transformer device provided by the present invention is applied to a circuit;

[0042] Figure 6 A schematic diagram of circuit connection when the loosely coupled transformer device provided by the present invention has two inductance coils on the primary and secondary sides and is applied in a circuit;

[0043] Figure 7 A schematic diagram of the structure of a loosely coupled transformer device provided by the present invention when the primary and secondary sides each have an inductor coil and are applied in a circuit;

[0044] Figure 8 A measurement diagram of the coupling coefficient of the loosely coupled transformer device provided by the present invention when the X-axis is offset;

[0045] Fig. 9A measurement diagram of the coupling coefficient of the loosely coupled transformer device provided by the present invention when the Y axis is offset;

[0046] Fig.10 A measurement diagram of the coupling coefficient of a loosely coupled transformer device provided by the present invention when it is rotated and offset along an axis. DETAILED DESCRIPTION

[0047] The scheme of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0048] like Figure 1 As shown, the shielding metal plate 100 is arranged at the outermost side, and the transmitting side module 200 and the receiving side module 300 both include an insulating plate 410, a magnetic core 420, a transformer coil 430, and an inductor coil 440. The magnetic core 420 adopts a rectangular block structure with a through hole in the center; the transformer coil 430 and the inductor coil 440 are both formed by winding multiple strands of Litz wire in parallel; the shielding metal plate 100 is made of aluminum material for shielding electromagnetic radiation; the magnetic core 420 is a magnetic core of ferrite material.

[0049] The transformer coil 430 on the transmitting side is surrounded in a rectangular shape and attached to one side surface of the magnetic core 120 on the transmitting side. The two inductor coils 440 on the transmitting side pass through the through holes of the magnetic core 420 on the transmitting side and are spirally wound on the magnetic core 420 on the transmitting side. The two inductor coils 440 on the transmitting side are positioned opposite to each other, and the magnetic flux generated by the transformer coil 430 on the transmitting side and the magnetic flux generated by the inductor coil 440 on the transmitting side are perpendicular to each other.

[0050] The winding method of the transformer coil 430 and the inductor coil 440 on the receiving side is the same as that of the transformer coil 430 and the inductor coil 440 on the transmitting side, and the transformer coil 430 on the transmitting side is arranged opposite to the transformer coil 430 on the receiving side, and the winding direction of the inductor coil 440 on the transmitting side is perpendicular to the winding direction of the inductor coil 440 on the receiving side.

[0051] In addition, the two inductance coils 440 wound on the same magnetic core 420 can play the role of coupled inductance. The same-named ends of the two inductance coils 440 are the same, so the magnetic flux generated plays a superposition role, resulting in the overall resonant compensation inductance being the self-inductance of the two inductance coils 440 plus twice the mutual inductance of the inductance coils 440, that is:

[0052] L p '=L p1 +L p2 +2M p1p2

[0053] L s '=L s1 +L s2 +2M s1s2

[0054] Among them, L p ' and L s ' is the equivalent primary-secondary resonant compensation inductance, L p1 and L p2 is the self-inductance of the transmitting side inductor 440, M p1p2 is the mutual inductance of the transmitting side inductor 440, L s1 and L s2 is the self-inductance of the receiving-side inductor 440, M s1s2 is the mutual inductance of the receiving-side inductor 440 .

[0055] like Figure 2 As shown, the magnetic core 420 may also adopt a circular block structure. When the magnetic core 420 is circular, the surrounding shape of the transformer coil 430 is also circular.

[0056] like Figure 3 As shown, the magnetic core 420 may adopt an integrated structure, and the magnetic core 420 adopting the integrated structure is provided with only one air gap 500, and the position of the air gap 500 is adapted to the position of an inductor 440. Figure 4 As shown, the magnetic core 420 can adopt a splicing structure. The magnetic core 420 adopting the splicing structure is provided with air gaps 500 at the splicing positions. The number and distance of the air gaps 500 can be adjusted according to the required inductance value. In addition, the winding orientation of the inductor coil 440 is adapted to the air gaps 500.

[0057] Will Figure 1 or Figure 2 The transformer unit provided is connected to the Figure 5 In the circuit shown, the transmitting side module 200 is electrically connected to one side of the transmitting side impedance matching circuit 630, the other side of the transmitting side impedance matching circuit 630 is electrically connected to one side of the inverter module 620, and the other side of the inverter module 620 is electrically connected to the DC power supply 610; the receiving side module 300 is electrically connected to one side of the receiving side impedance matching circuit 640, the other side of the receiving side impedance matching circuit 640 is electrically connected to one side of the rectifier module 650, the other side of the rectifier module 650 is electrically connected to one side of the DC conversion module 660, and the other side of the DC conversion module 660 is connected to the load 670; the transmitting side module 200 and the receiving side module 300 are coupled to each other.

[0058] Figure 6 for Figure 5The specific structure of the circuit shown in the figure is that the transmitting side impedance matching circuit 630 and the receiving side impedance matching circuit 640 are both LCC type resonant networks. In order to suppress the common mode current of the system, the resonant inductor and the resonant capacitor in the resonant network both adopt a vertically symmetrical structure. Therefore, the transmitting side impedance matching circuit 630 in the system has two resonant inductors L p1 and L p2 The receiving side impedance matching circuit 640 has two resonant inductors L s1 and L s2 , L p is the transmitting coil on the transmitting side, L s is the receiving coil on the receiving side, and the two resonant inductors L of the transmitting side impedance matching circuit 630 p1 and L p2 That is, the two inductor coils 440 of the transmitting side module 200 and the two resonant inductors L in the receiving side impedance matching circuit 640 s1 and L s2 That is, the two inductor coils 440 of the receiving side module 300 .

[0059] When only one inductor 440 is wound around each of the magnetic core 420 on the transmitting side and the magnetic core 420 on the receiving side, the transformer is connected to the circuit, and the circuit structure is as follows: Figure 7 As shown, each of the transmitting side impedance matching circuit 630 and the receiving side impedance matching circuit 640 has only one resonant inductor.

[0060] Below Figure 1 Taking the loose magnetic coupling transformer structure shown in the figure as an example, the transmitting side module 200 and the receiving side module 300 are the primary and secondary sides of the transformer respectively, and the finite element simulation software Ansoft Maxwell 3D is used for simulation analysis to specifically describe the effect of this structure on improving the coupling coefficient when the primary and secondary sides are facing and offset.

[0061] The test conditions of the simulation are as follows: the outer dimensions of the primary and secondary transformers are 420 mm*420 mm, the spacing between the primary and secondary sides is 160 mm, the transformer coil 430 and the inductor coil 440 use single-turn thick wire and set their type to stranded wire winding, the material is copper, and the material of the magnetic core 420 is selected to have a relative magnetic permeability μ r The ferrite material is equal to 3000, the shielding metal plate 100 is an aluminum plate with a thickness of 10 mm, and the excitation current is selected to apply a current of 20 A to each coil. When exploring the coupling coefficient of the primary and secondary sides, the value of the current excitation has almost no effect on it, which is mainly related to the physical structure of the primary and secondary coils and the size and position of the magnetic core.

[0062] By optimizing the parameters such as the width of the coil and the width of the magnetic core 420, the approximate peak value of the primary-secondary coupling coefficient under the existing size can be obtained. Under the optimized conditions, the coupling coefficient between the primary and secondary coils is 0.235, which can achieve a higher coupling coefficient value under the corresponding size.

[0063] Secondly, the coupling coefficient between different coils of the coupling transformer is measured under X-axis, Y-axis and rotation offset along the axis.

[0064] The measurement results are as follows Figure 8 , 9 As shown in Figures 10, the highest cross-coupling coefficient at different offsets is 0.02, which indicates that the magnetic integration solution of the loose magnetic coupling transformer structure provided in this embodiment can achieve decoupling at different offsets, thereby eliminating the influence of cross-coupling.

[0065] Depend on Figure 8 , 9 , 10 It can be seen that when the primary and secondary sides of the transformer are offset by a large amount, the cross coupling can still be kept relatively low.

[0066] Therefore, the magnetic integration solution of the loose magnetic coupling transformer structure provided in this embodiment can not only reduce the volume of multiple resonant inductors and improve the power density of the system, but also eliminate the influence of cross coupling, and the magnetic integration solution does not affect the power transmission of the system. Therefore, the solution of the present invention has a good application prospect for the wireless power transmission system of electric vehicles.

Claims

1. A loosely coupled transformer device for wireless charging of electric vehicles, comprising two shielding metal plates and a mutually coupled transmitting side module and a receiving side module, wherein the transmitting side module is placed on the ground end and the receiving side module is placed on the bottom of the vehicle body; the transmitting side module and the receiving side module are both embedded in the corresponding shielding metal plates, characterized in that: The transmitting side module and the receiving side module both include an insulating plate, a magnetic core, a transformer coil and an inductor coil; The magnetic core is a symmetrical block structure with a through hole in the center; the inductor passes through the through hole of the magnetic core and is spirally wound on the magnetic core; the winding shape of the transformer coil is adapted to the shape of the magnetic core, and two inductors arranged oppositely are wound on the magnetic core of the transmitting side module; and two inductors arranged oppositely are wound on the magnetic core of the receiving side module; The transformer coil on the transmitting side is surrounded in a rectangular shape and attached to one side surface of the magnetic core on the transmitting side. The two inductance coils on the transmitting side pass through the through holes of the magnetic core on the transmitting side and are spirally wound on the magnetic core on the transmitting side. The two inductance coils on the transmitting side are located opposite to each other. The magnetic flux generated by the transformer coil on the transmitting side and the magnetic flux generated by the inductance coil on the transmitting side are perpendicular to each other. The winding mode of the transformer coil and the inductor coil on the receiving side is the same as that of the transformer coil and the inductor coil on the transmitting side, and the transformer coil on the transmitting side is arranged opposite to the transformer coil on the receiving side, and the winding direction of the inductor coil on the transmitting side is perpendicular to the winding direction of the inductor coil on the receiving side; The transformer coil is fixed on one side surface of the magnetic core, and the transformer coil of the transmitting side module is arranged opposite to the transformer coil of the receiving side module; The inductor coil is spirally wound on the magnetic core, and the winding direction of the inductor coil of the transmitting side module and the winding direction of the inductor coil of the receiving side module are perpendicular to each other; The transformer coil and the inductor coil wound on the same magnetic core are perpendicular to each other at the overlap; The insulating plate is arranged between the shielding metal plate and the magnetic core; the transmitting side module is the primary side of the transformer, and the receiving side module is the secondary side of the transformer.

2. The loosely coupled transformer device for wireless charging of electric vehicles according to claim 1, characterized in that: The magnetic core is an integral block structure, and an air gap is provided on the magnetic core, and the air gap is adapted to the position of the inductor coil.

3. The loosely coupled transformer device for wireless charging of electric vehicles according to claim 1, characterized in that: The magnetic core is a spliced ​​structure, and at least one air gap is provided on the magnetic core, and the air gap is adapted to the position of the inductor coil.

4. The loosely coupled transformer device for wireless charging of electric vehicles according to claim 1, characterized in that: The transformer coil and the inductor coil are both formed by winding single or multiple Litz wires or copper strips or copper tubes in parallel.

5. The loosely coupled transformer device for wireless charging of electric vehicles according to claim 1, characterized in that: The shielding metal plate is made of metal with good electrical conductivity but no magnetic conductivity.

6. A circuit for wireless charging of electric vehicles, characterized in that: A loosely coupled transformer device for wireless charging of an electric vehicle as claimed in any one of claims 1 to 5, comprising a DC power supply, an inverter module, and a transmitting side impedance matching circuit electrically connected in sequence, wherein the transmitting side impedance matching circuit is electrically connected to the transmitting side module; It also includes a load, a DC conversion module, a rectifier module, and a receiving-side impedance matching circuit that are electrically connected in sequence, and the receiving-side impedance matching circuit is electrically connected to the receiving-side module.

7. The circuit for wireless charging of electric vehicles according to claim 6, characterized in that: The transmitting side impedance matching circuit and the receiving side impedance matching circuit are compensation circuits containing resonant inductors.

8. The circuit for wireless charging of electric vehicles according to claim 7, characterized in that: The resonant inductor of the compensation circuit is the inductor coil of the transformer device.

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