A transformer structure for LLC resonant converter

Abstract

The present invention proposes a transformer structure for an LLC resonant converter, comprising a PFC rectifier circuit module, a high-frequency inverter circuit module, a resonant topology module, a rectifier circuit and a load connected in sequence, wherein the transformer, the resonant inductor and the resonant capacitor in the resonant topology module are all integrated into one component to form a capacitive-inductive integrated transformer; the capacitive-inductive integrated transformer has a multilayer thin-film capacitor integrated therein, wherein the multilayer thin-film capacitor comprises an iron-based nanocrystalline strip, and an organic insulating film is arranged between each layer of the nanocrystalline strip as a dielectric. The structure introduces iron-based nanocrystals to replace ferrite as a magnetic core, adopts a special lamination method, uses a nanocrystalline strip with high conductivity as a plate, and an organic insulating film as a dielectric on the strip base, and integrates the resonant capacitor into the magnetic core to form a capacitive-inductive integrated transformer structure, which can significantly improve the power density and economy of the LLC resonant converter.

Description

Technical Field

[0001] The invention belongs to the field of transformer structures, and in particular relates to a transformer structure for an LLC resonant converter. Background Art

[0002] In recent years, compared with traditional power frequency transformers, solid-state transformers generally use medium frequency isolation to achieve voltage conversion, so they can increase power density by reducing the size and weight of the transformer. This makes solid-state transformers widely used in fields such as DC power grid systems, high-speed rail electric traction, ships, aerospace, etc. The LLC resonant converter is the most important functional component in the solid-state transformer.

[0003] LLC resonant converters have received widespread attention in industrial applications because of their ability to adapt to wide input and load variation conditions. In traditional PWM converters, the power switch tube operates in hard switching mode, which has high switching losses and electromagnetic interference problems. In LLC resonant converters, the inverter switch tube can achieve zero voltage conduction, and the output rectifier diode can also achieve zero current shutdown, thus minimizing losses and electromagnetic interference. Based on the above characteristics, LLC resonant converters are widely used in high-frequency, high-power density power conversion systems. Especially in the conductive charging equipment of transportation vehicles operating in the hundreds of kilohertz frequency band, LLC resonant converters are the mainstream circuit topology. The transformer is one of the most important components in the LLC resonant converter. On the one hand, it can change the input / output voltage ratio, and on the other hand, it can provide electrical isolation.

[0004] However, low power density is still the main disadvantage of LLC resonant converters. Among them, the transformer is the largest component in the system, and its design has a crucial impact on the overall power density of the system. At present, ferrite cores are usually the main type of transformers. However, the magnetic saturation strength of ferrite cores is low, about 0.3T, and the magnetic loss characteristics are poor at high temperatures. These shortcomings have become the main obstacles to improving power density. On the other hand, since the LLC resonant converter mainly operates in a resonant state, the withstand voltage of its resonant capacitor often needs to reach 2kV-3kV RMS. Therefore, a large number of single capacitors are required to be connected in series and parallel to form the final resonant capacitor, which will make the overall system larger and more expensive.

[0005] Iron-based nanocrystals are a kind of metal-based soft magnetic material (Highly Efficient 11.1kW Wireless Power Transfer Utilizing Nanocrystalline Ribbon Cores) with low hysteresis loss and high magnetic saturation threshold (up to 1T), which can be used as the unsaturated magnetic core of the 22kW wireless charging system. However, the ferrite core of the same volume will experience magnetic saturation when transmitting 16kW, resulting in distortion of the system current waveform. In addition, when the operating temperature of the ferrite core is higher than 85 degrees Celsius, its core loss density increases with the increase of temperature. That is, when the operating temperature is greater than 85 degrees Celsius, the loss of the core itself gradually increases, which in turn increases the temperature, and finally causes the core to fail due to overheating. The core loss density of the iron-based nanocrystalline core remains basically stable below 120 degrees Celsius. Therefore, the use of iron-based nanocrystalline cores can effectively improve the power density of the system, and at the same time, by utilizing its high conductivity, the capacitor is integrated into the core, significantly improving the integration and economy of the system.

[0006] In the existing technology, the research on the integration of magnetic components is only at the level of excitation inductance and leakage inductance. There is also a related technology (Multilayer flexible printed circuitry planar transformer within integrated series capacitance for LLC converter) that points out the use of parasitic capacitance between different layers of coil windings as system resonant capacitance. However, this technology is often applicable to the MHz frequency band. At the same time, the magnetic component based on this technology is a two-port component, and the connection relationship between its internal inductance and capacitance is quite complicated, which is not conducive to the early setting of the resonant frequency of the system. Since the resonant capacitor required by the LLC resonant converter has a high withstand voltage value, a large number of single capacitors are required to be connected in series and parallel, which will make the resonant converter larger and more expensive. At the same time, LLC resonant converters are often used in the 10-100kHz frequency band, and the resonant capacitance value needs to be accurately calculated during the design stage. Therefore, the four-port network capacitance-inductance integrated transformer proposed in this patent provides the possibility for the integration of resonant capacitors and significantly improves the overall power density of the system. Summary of the invention

[0007] The problem to be solved by the present invention is to integrate the resonant inductor and resonant capacitor of the LLC resonant converter with the transformer, reduce the volume of the resonant converter, further improve the power density of the LLC resonant converter, and reduce its cost. To this end, an LLC resonant converter using an integrated capacitive-inductive magnetic core structure transformer composed of iron-based nanocrystalline materials and organic insulating films is proposed. Iron-based nanocrystals are introduced to replace ferrite as the magnetic core. After a special lamination method, a high-conductivity nanocrystalline strip is used as the pole plate, and the organic insulating film on the strip base is used as the dielectric. The resonant capacitor is integrated into the magnetic core to form a capacitive-inductive integrated transformer structure. The iron-based nanocrystalline transformer structure proposed in the present invention integrates the resonant compensation capacitor into the magnetic core, replacing the expensive film capacitor in the traditional resonant converter, saving the bulky capacitor space, and can significantly improve the power density and economy of the LLC resonant converter.

[0008] The purpose of the present invention can be achieved by at least one of the following technical solutions.

[0009] A transformer structure for an LLC resonant converter includes a PFC rectifier circuit module, a high-frequency inverter circuit module, a resonant topology module, a rectifier circuit and a load connected in sequence, wherein the transformer, the resonant inductor and the resonant capacitor in the resonant topology module are all integrated into one component to form a capacitor-inductor integrated transformer;

[0010] The capacitor-inductor integrated transformer has a multi-layer thin-film capacitor integrated therein, wherein the multi-layer thin-film capacitor comprises an iron-based nanocrystalline strip, and an organic insulating film is arranged between each layer of the nanocrystalline strip as a dielectric, thereby realizing capacitor-inductor integration.

[0011] Furthermore, an organic insulating film is used in combination with an iron-based nanocrystalline strip material substrate, and the two materials are wound in a stacked or wound manner.

[0012] Furthermore, the thickness of the iron-based nanocrystalline strip is 16-18 μm, and the thickness of the organic insulating film is 10-25 μm.

[0013] Furthermore, the iron-based nanocrystalline strip and the organic insulating film are bonded together by resin adhesive or electrostatic adsorption.

[0014] Furthermore, the stacking process is a stacking structure, and a vertical dislocation stacking method is adopted between adjacent nanocrystalline layers to construct a multilayer thin film capacitor, the upper protruding nanocrystalline layer is used as the positive electrode, and the lower protruding nanocrystalline layer is used as the negative electrode, and a coil winding is added to the capacitor as a transformer core.

[0015] Furthermore, the winding process is a winding structure, and there is a vertical dislocation between the two long nanocrystalline ribbons. By winding the long ribbons, a multilayer thin film capacitor is finally formed. The protruding nanocrystalline layer on the upper part of the capacitor serves as the positive electrode, and the protruding nanocrystalline layer on the lower part serves as the negative electrode. A coil winding is added to the capacitor as a transformer core.

[0016] Furthermore, during normal operation, the electric field and the magnetic field in the magnetic core are orthogonal to each other and do not interfere with each other. As a four-port network element, the transformer has no internal electrical connection between the inductor and the capacitor.

[0017] Furthermore, when the magnetic core is made by lamination, the iron-based nanocrystalline strip material is made into any suitable shape, or an air gap is introduced to meet the needs of different application scenarios.

[0018] Furthermore, the organic insulating film is a high temperature resistant material to adapt to high frequency and high power application scenarios.

[0019] Furthermore, the high-frequency inverter circuit module is a half-bridge or full-bridge circuit; and the rectifier circuit module adopts an active or passive bridge rectifier circuit.

[0020] Compared with the prior art, the present invention has the following advantages and technical effects:

[0021] The present invention utilizes the high conductivity of nanocrystalline ribbons and can be made into thin film capacitors by stacking or winding, thereby integrating all resonant elements in the LLC resonant converter into one transformer component, replacing the expensive thin film capacitors in traditional resonant converters, saving bulky capacitor space, and significantly improving the power density and economy of the LLC resonant converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the components of LLC resonant converter in an embodiment;

[0023] Figure 2 1 is a schematic diagram of an LLC resonant converter circuit based on a primary-side full-bridge inversion and a secondary-side passive rectification solution in an embodiment;

[0024] Figure 3 Schematic diagram of a capacitor-inductor integrated transformer using a stacking method in an embodiment;

[0025] Figure 4 Schematic diagram of a capacitor-inductor integrated transformer using a winding method in an embodiment. DETAILED DESCRIPTION

[0026] The specific implementation of the invention is further described below in conjunction with the accompanying drawings, but the implementation and protection of the invention are not limited thereto.

[0027] like Figure 1 As shown, an embodiment of the present invention is a transformer structure for an LLC resonant converter, including a high-frequency inverter circuit module on the primary side, a resonant topology module, a rectifier circuit module on the secondary side, and a load. The high-frequency inverter circuit module adopts an existing half-bridge or full-bridge inverter circuit; the secondary-side rectifier circuit module is a passive or active rectifier circuit. The transformer, resonant inductor, and resonant capacitor in the resonant topology module can all be integrated into one component to form a capacitive-inductive integrated transformer. The rectifier circuit module adopts a passive bridge rectifier circuit, or considers using other circuit topologies to adapt to different application scenarios. The load can be a resistive-inductive load, a pure resistive load, or a resistive-capacitive load, and can be a resistive load or a battery load.

[0028] like Figure 1 As shown in the figure, the 220V mains power is first converted into DC power by the PFC rectifier circuit module, and then converted into high-frequency AC power by the high-frequency inverter circuit. The high-frequency AC power transfers the power from the primary side to the secondary side through the resonant topology module, and finally the high-frequency AC power is converted into DC power for the load through the rectifier circuit. In the resonant topology module, all resonant passive components are integrated into a capacitor-inductor integrated transformer.

[0029] Attached Figure 2 The circuit diagram of LLC resonant converter is based on primary side full-bridge inverter and secondary side passive rectification. Figure 2 It is directly given as a DC power supply. After the PFC rectifier circuit module, the full-bridge inverter circuit converts the DC input into a square wave AC input, and the boost or buck power transmission can be achieved through the resonant topology module. The AC voltage and current induced by the secondary side of the integrated capacitor-inductor transformer pass through the rectifier circuit module and the filter capacitor connected in parallel on the output side, and finally provide DC power to the resistive load. If the DC input voltage changes, the DC input / output voltage gain of the LLC resonant converter can be changed by adjusting the operating frequency of the inverter circuit module, thereby keeping the output voltage constant.

[0030] All the passive components required for the LLC resonant cavity are integrated into a transformer. The operating frequency of the LLC resonant converter is 50-150kHz, which can change the voltage gain of the resonant converter by adjusting the operating frequency when the input voltage fluctuates, thereby keeping the output voltage constant.

[0031] By reasonably selecting the capacitance / inductance values ​​of the passive components in the resonant circuit, the total equivalent impedance is ensured to be inductive within the operating frequency band. When the upper and lower switches of the same bridge arm are added with dead time, the inverter of the LLC resonant converter is ensured to operate in a zero voltage conduction state.

[0032] The capacitor-inductor integrated transformer is formed by stacking or winding iron-based nanocrystalline (FeCuNbSiB) strips and organic insulating films, and can integrate the excitation inductance, leakage inductance and resonant capacitor in the resonant cavity into one component. The rectifier circuit module on the secondary side converts the AC power on the secondary side of the transformer into DC power to supply power to the load. During normal operation, the electric field and magnetic field in the magnetic core are orthogonal to each other and do not interfere with each other. As a four-port network element, the transformer has no internal electrical connection between the inductor and the capacitor.

[0033] Since the electrical conductivity of iron-based nanocrystals is as high as 5×10 6 S / m, and the organic insulating film (polyester film or polyimide film) is an excellent dielectric material (relative dielectric constant 3-5). The adjacent nanocrystalline layers are stacked vertically with the upper protruding nanocrystalline layer as the positive electrode and the lower protruding nanocrystalline layer as the negative electrode. The organic film is used as the dielectric to construct a multilayer film capacitor.

[0034] Iron-based nanocrystals can also be annealed through a special magnetic field process, that is, adding an external magnetic field in a specific direction during the annealing process of the FeCuNbSiB alloy from an amorphous state to a nanocrystalline state. By adjusting the direction and amplitude of the external additional magnetic field, the relative magnetic permeability of the final nanocrystalline FeCuNbSiB alloy can be reduced and its electrical conductivity can be increased, thereby effectively reducing the plate loss of the capacitor and avoiding the core from working in a saturated state.

[0035] The transformer's magnetizing inductance and leakage inductance are related to the transformer's core material, structure, number of winding turns, material and other factors. After the transformer's core is determined, the transformer's magnetizing inductance L can be controlled by a reasonable winding method (such as staggered winding of the primary and secondary windings) or by introducing an air gap. m With leakage inductance L r The ratio L n , thereby changing the gain value between the primary-side DC input voltage and the secondary-side output voltage of the LLC resonant converter. r as a resonant inductor.

[0036] As an example, Figure 3 As shown in FIG. 1 , the thickness of the iron-based nanocrystalline ribbon is 16 to 18 μm, and the thickness of the organic insulating film ribbon is 10 to 25 μm. Although the iron-based nanocrystalline ribbon has a high electrical conductivity, the iron-based nanocrystalline ribbon is made into a thickness of 16 to 18 μm and an organic insulating film is added between two adjacent nanocrystalline ribbon layers to effectively block the eddy current loop in the magnetic core, thereby reducing the eddy current loss.

[0037] Nanocrystalline strips are added with organic insulating films as substrates. The organic insulating film substrate needs to reserve some margin at the non-electrode lead-out end of the nanocrystalline strips to ensure that the capacitor formed will not short-circuit due to the strong edge leakage field of the electrode plate. The iron-based nanocrystals with a suitable number of layers (since different numbers of layers have an impact on the capacitance of the capacitor, the selected number of layers should be consistent with the size of the capacitor in the design parameters of different LLC resonant converters) are stacked alternately using vertical dislocations. In order to enhance the one-piece molding of the magnetic core after stacking, a 2-3μm resin adhesive can be attached to the organic insulating film. The iron-based nanocrystalline strips with a substrate can also be directly stacked by electrostatic adsorption. After stacking, epoxy resin is used to encapsulate and reinforce them.

[0038] Attached Figure 3 Two adjacent nanocrystal layers are separated by an organic insulating film. There is a certain distance of vertical offset between adjacent nanocrystal layers. The upper protruding nanocrystal layer serves as the positive electrode of the capacitor, the lower protruding nanocrystal layer serves as the negative electrode of the capacitor, and the organic insulating film serves as the dielectric, thereby constructing a multilayer film capacitor to achieve the purpose of integrating the resonant capacitor into the magnetic coupling mechanism. The upper and lower nanocrystal positive and negative electrodes can be bonded to the external conductive extension parts with conductive silver glue, which is convenient for connection with the external circuit during actual use.

[0039] Resonant capacitor C in LLC resonant converter r It can be provided by a transformer core, in which the nanocrystalline ribbons act as capacitor plates and the organic insulating film between the ribbon layers acts as a dielectric.

[0040] As an embodiment, the organic insulating film is made of high temperature resistant material to adapt to high frequency and high power application scenarios. The organic insulating film can be specifically a polyester film or a polyimide film.

[0041] Figure 3 Each nanocrystalline layer unit shown is a "U"-shaped structure, which can be obtained by mechanical cutting or laser cutting. Since the iron-based nanocrystals have high mechanical plasticity after being added to the organic insulating film substrate. It can also be made into a half "U"-shaped structure, the "U"-shaped nanocrystalline layer is divided into two halves, and the vertical dislocation stacking method is also used to make a capacitance-inductance integrated transformer with an air gap. This structure allows a certain air gap to exist in the magnetic core of the nanocrystalline transformer to prevent it from working in a magnetic saturation state.

[0042] Figure 4The figure shows a schematic diagram of a wound capacitive-inductive integrated nanocrystalline core. It is necessary to first lay two longer nanocrystalline ribbons with a base together and stagger them at a certain distance in the vertical position. The laid ribbons are tightly wound together using a winding machine to eventually form a transformer core. The protruding nanocrystals on the upper part of the core are the positive electrodes of the capacitor, and the protruding nanocrystals on the lower part are the negative electrodes of the capacitor, so as to achieve the purpose of integrating the resonant capacitor into the magnetic coupling mechanism. The positive and negative electrodes of the nanocrystals on the upper and lower parts can be bonded to the external conductive extension parts with conductive silver glue, which is convenient for connection with the external circuit during actual use. The advantage of this method is that the core production process is simple and efficient, and it is easy to realize machine automation.

[0043] In addition, if Figure 4 As shown, the organic insulating film substrate needs to reserve some margin at the non-electrode lead-out end of the nanocrystalline strip to ensure that the formed capacitor will not short-circuit due to the strong edge leakage field of the electrode plate.

[0044] The electric field inside the magnetic core of the integrated capacitor-inductor transformer is distributed along the radial direction of the transformer core, while the magnetic field is distributed along the circumferential direction of the core. The two are orthogonal to each other and there is no mutual interference.

[0045] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well.

Claims

1. A transformer structure for an LLC resonant converter, comprising a PFC rectifier circuit module, a high-frequency inverter circuit module, a resonant topology module, a rectifier circuit and a load connected in sequence, characterized in that: The transformer, resonant inductor and resonant capacitor in the resonant topology module are all integrated into one component to form a capacitor-inductor integrated transformer. The capacitor-inductor integrated transformer has a multilayer thin-film capacitor integrated therein, wherein the multilayer thin-film capacitor includes an iron-based nanocrystalline strip, and an organic insulating film is provided between each layer of the nanocrystalline strip as a dielectric, thereby realizing capacitor-inductor integration; The thickness of the iron-based nanocrystalline ribbon is 16~18 , the thickness of the organic insulating film is 10~25 , the iron-based nanocrystalline strip and the organic insulating film are bonded by resin adhesive or electrostatic adsorption; An organic insulating film is used as a substrate of an iron-based nanocrystalline ribbon material, and the two materials are wound in a stacked or wound manner; The stacking process is a stacking structure, and the adjacent nanocrystalline layers are stacked vertically with dislocations to construct a multilayer film capacitor. The upper protruding nanocrystalline layer is used as the positive electrode, and the lower protruding nanocrystalline layer is used as the negative electrode. A coil winding is added to the capacitor as the transformer core. When the magnetic core is made by lamination, the iron-based nanocrystalline strip material is made into any suitable shape, or an air gap is introduced to meet the needs of different application scenarios.

2. A transformer structure for LLC resonant converter according to claim 1, characterized in that: The winding process is a winding structure. There is a vertical dislocation between the two long nanocrystalline ribbons. By winding the long ribbons, a multilayer thin-film capacitor is finally formed. The protruding nanocrystalline layer on the upper part of the capacitor serves as the positive electrode, and the protruding nanocrystalline layer on the lower part serves as the negative electrode. A coil winding is added to the capacitor as the transformer core.

3. A transformer structure for LLC resonant converter according to claim 2, characterized in that: During normal operation, the electric field and magnetic field in the core are orthogonal to each other and do not interfere with each other. As a four-port network element, the transformer has no internal electrical connection between the inductor and the capacitor.

4. The transformer structure for LLC resonant converter according to claim 1, characterized in that: The organic insulating film is a high temperature resistant material to adapt to high frequency and high power application scenarios.

5. The transformer structure for LLC resonant converter according to claim 1, characterized in that: The high-frequency inverter circuit module is a half-bridge or full-bridge circuit; the rectifier circuit module adopts an active or passive bridge rectifier circuit.

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