Transformer structure for LLC resonant converter

Abstract

Provided in the present invention is a transformer structure for an LLC resonant converter. The transformer structure comprises a PFC rectifier circuit module, a high-frequency inverter circuit module, a resonant topology module, a rectifier circuit and a load, which are sequentially connected, wherein a transformer, a resonant inductor and a resonant capacitor in the resonant topology module are all integrated in one component to form a capacitor-inductor integrated transformer; and a multilayer thin-film capacitor is integrated inside the capacitor-inductor integrated transformer, the multilayer thin-film capacitor comprises an iron-based nanocrystalline strip, and an organic insulating thin film is disposed between nanocrystalline strip layers to serve as a dielectric. In the structure, iron-based nanocrystalline is introduced to replace ferrite to serve as a magnetic core, after a special lamination method is used, a nanocrystalline strip with high conductivity is used as an electrode plate, a substrate, i.e., an organic insulating thin film, of the strip is used as a dielectric, and a resonant capacitor is integrated in the magnetic core, so as to form a capacitor-inductor integrated transformer structure, such that the power density and economic efficiency of an LLC resonant converter can be significantly improved.

Description

A transformer structure for LLC resonant converter Technical Field

[0001] The present 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, solid-state transformers (SSTs), compared to traditional power-frequency transformers, have generally adopted medium-frequency isolation for voltage conversion. This reduces the size and weight of the transformer, thereby increasing power density. This has led to widespread application of SSTs in areas such as DC grid systems, high-speed rail electric traction, ships, and aerospace. The LLC resonant converter is the most important functional component in a SST.

[0003] LLC resonant converters have garnered widespread attention in industrial applications due to their ability to adapt to wide input and load variations. In traditional PWM converters, the power switches operate in hard-switching mode, resulting in high switching losses and electromagnetic interference. In an LLC resonant converter, the inverter switches can achieve zero-voltage turn-on, and the output rectifier diodes can achieve zero-current turn-off, thereby minimizing losses and electromagnetic interference. Based on these characteristics, LLC resonant converters are widely used in high-frequency, high-power-density power conversion systems. In particular, LLC resonant converters are the mainstream circuit topology for conductive charging devices used in transportation vehicles operating in the hundreds of kilohertz frequency band. The transformer is one of the most important components in an LLC resonant converter, altering the input / output voltage ratio and providing electrical isolation.

[0004] However, low power density remains the main disadvantage of the LLC resonant converter. As the largest component in the system, the transformer's design has a crucial impact on the overall power density of the system. Currently, transformers are typically made of ferrite cores. However, ferrite cores have a low magnetic saturation strength of approximately 0.3T, and poor magnetic loss characteristics at high temperatures. These shortcomings have become the main obstacles to improving power density. On the other hand, since the LLC resonant converter primarily operates in a resonant state, the withstand voltage of its resonant capacitor often needs to reach 2 kV-3 kV 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 metal-based soft magnetic material (Highly Efficient 11.1 kW Wireless Power Transfer Utilizing Nanocrystalline Ribbon Cores) with low hysteresis losses and a high magnetic saturation threshold (up to 1T). They can be used as the core of a 22kW wireless charging system without saturation. Ferrite cores of the same volume, however, experience magnetic saturation at 16kW, resulting in distortion of the system's current waveform. Furthermore, the core loss density of ferrite cores increases with operating temperatures above 85°C. Specifically, when the operating temperature exceeds 85°C, the core loss gradually increases, further increasing the temperature and ultimately leading to core failure due to overheating. Iron-based nanocrystalline cores, on the other hand, maintain a relatively stable core loss density below 120°C. Therefore, the use of iron-based nanocrystalline cores can effectively increase system power density. Furthermore, their high electrical conductivity allows capacitors to be integrated into the core, significantly improving system integration and cost-effectiveness.

[0006] In existing technologies, research on magnetic component integration has limited focus on the magnetizing inductance and leakage inductance. A related technology (Multilayer Flexible Printed Circuitry Planar Transformer with Integrated Series Capacitance for LLC Converters) utilizes the parasitic capacitance between different layers of the coil winding as the system's resonant capacitor. However, this technology is typically applicable to frequencies in the MHz range. Furthermore, the magnetic component underlying this technology is a two-port device, and the internal connections between the inductor and capacitor are quite complex, making it difficult to initially set the system's resonant frequency. Because the resonant capacitor required for LLC resonant converters requires a high withstand voltage, a large number of individual capacitors are connected in series and parallel, resulting in a larger and more expensive resonant converter. LLC resonant converters are often used in the 10-100kHz frequency range, and precise calculation of the resonant capacitance is required during the design phase. Therefore, the four-port network capacitor-inductor integrated transformer proposed in this patent facilitates the integration of resonant capacitors, significantly improving the overall system power density. 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 capacitance-inductance 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 adopting a special lamination method, high-conductivity nanocrystalline strips are used as pole plates, 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 capacitance-inductance 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, which are connected in sequence. The transformer, resonant inductor, and resonant capacitor in the resonant topology module are all integrated into one component to form an integrated capacitor-inductor transformer.

[0010] The capacitor-inductor integrated transformer has a multi-layer thin film capacitor integrated therein. The multi-layer thin film capacitor includes an iron-based nanocrystalline strip. An organic insulating film is provided between each layer of the nanocrystalline strip as a dielectric to achieve 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 ribbon 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. A coil winding is added to the capacitor as the 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 the transformer core.

[0016] Furthermore, 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 component, 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 ribbon 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 electrical 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 a 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] FIG1 is a schematic diagram of the components of an LLC resonant converter according to an embodiment;

[0023] FIG2 is a schematic diagram of an LLC resonant converter circuit based on a primary-side full-bridge inverter and a secondary-side passive rectification scheme according to an embodiment;

[0024] FIG3 is a schematic diagram of a capacitor-inductor integrated transformer using a stacking method according to an embodiment;

[0025] FIG4 is a schematic diagram of a capacitor-inductor integrated transformer using a winding method according to an embodiment. Modes for Carrying Out the Invention

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

[0027] As shown in Figure 1, 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 purely resistive load, or a resistive-capacitive load, and can be a resistive load or a battery load.

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

[0029] Figure 2 shows a circuit diagram of an LLC resonant converter based on primary-side full-bridge inverter and secondary-side passive rectification. Because the front-end PFC rectifier circuit module is relatively complex, it is directly shown as a DC power supply in Figure 2. Following the PFC rectifier circuit module, the full-bridge inverter circuit converts the DC input into a square-wave AC input, which can be boosted or bucked through the resonant topology module. The AC voltage and current sensed on 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, ultimately providing DC power to the resistive load. If the DC input voltage fluctuates, 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 maintaining a constant output voltage.

[0030] All the passive components required for the LLC resonant cavity are integrated into a single transformer. The LLC resonant converter operates at a frequency of 50-150kHz. This allows the converter to maintain a constant output voltage by adjusting the operating frequency to vary the voltage gain of the resonant converter when the input voltage fluctuates.

[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 dead time is added to the upper and lower switches of the same bridge arm, 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, which can integrate the excitation inductance, leakage inductance and resonant capacitance 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 the load. During normal operation, the electric and magnetic fields in the magnetic core are mutually positive and do not interfere with each other. As a four-port network component, the transformer has no internal electrical connection between the inductor and 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, an external magnetic field in a specific direction is added during the annealing process of the FeCuNbSiB alloy from the amorphous state to the 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 preventing the magnetic core from operating in a saturated state.

[0035] The magnetizing inductance and leakage inductance of the transformer are related to the transformer core material, structure, number of winding turns, material and other factors. After the transformer core is determined, the magnetizing inductance L of the transformer 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 and 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, as shown in Figure 3, the thickness of the iron-based nanocrystalline ribbon is 16-18 μm, and the thickness of the organic insulating film ribbon is 10-25 μm. Although the iron-based nanocrystalline ribbon has high electrical conductivity, making the iron-based nanocrystalline ribbon 16-18 μm thick and adding an organic insulating film between two adjacent nanocrystalline ribbon layers can effectively block the eddy current loops in the magnetic core, thereby reducing eddy current losses.

[0037] Nanocrystalline ribbons are bonded to an organic insulating film as a substrate. This organic insulating film substrate requires some margin at the non-electrode leads of the nanocrystalline ribbons to ensure that the resulting capacitor does not short-circuit due to strong edge leakage fields from the electrode plates. An appropriate number of layers of iron-based nanocrystalline substrates (the number of layers affects the capacitance value, so the selected number of layers should be consistent with the capacitance requirements of different LLC resonant converter design parameters) are laminated using a vertically dislocated alternating method. To enhance the integral molding of the magnetic core after lamination, a 2-2μm thick resin adhesive can be applied to the organic insulating film. Alternatively, the iron-based nanocrystalline ribbons with substrates can be laminated directly using electrostatic adsorption. After lamination, the laminate is then encapsulated and reinforced with epoxy resin.

[0038] In Figure 3, two adjacent nanocrystalline layers are separated by an organic insulating film. There is a certain distance of vertical offset between adjacent nanocrystalline layers. The upper protruding nanocrystalline layer serves as the positive electrode of the capacitor, the lower protruding nanocrystalline layer serves as the negative electrode of the capacitor, and the organic insulating film serves as the dielectric. In this way, a multilayer thin-film capacitor is constructed, achieving the purpose of integrating the resonant capacitor into the magnetic coupling mechanism. The upper and lower nanocrystalline positive and negative electrodes can be bonded to the external conductive extension component using conductive silver glue, which is convenient for connection to the external circuit during actual use.

[0039] Resonant capacitor C in LLC resonant converter r This 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 the dielectric.

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

[0041] Each nanocrystal layer unit shown in Figure 3 has a U-shaped structure, which can be obtained by mechanical or laser cutting. Because iron-based nanocrystals exhibit high mechanical plasticity after being added to an organic insulating film substrate, they can also be made into a half-U-shaped structure. By splitting the U-shaped nanocrystal layer in half and similarly using vertical dislocation stacking, a capacitive-inductive integrated transformer with an air gap can be created. This structure allows for a certain air gap in the nanocrystal transformer's magnetic core, preventing it from operating in a state of magnetic saturation.

[0042] Figure 4 shows a schematic diagram of a wound, capacitive-inductive integrated nanocrystalline core. This requires first stacking two longer nanocrystalline ribbons with a base material and vertically staggering them a certain distance apart. The stacked ribbons are then tightly wound together using a winding machine to form the transformer core. The nanocrystals protruding from the top of the core serve as the positive electrode of the capacitor, while the nanocrystals protruding from the bottom serve as the negative electrode, integrating the resonant capacitor into the magnetic coupling mechanism. The positive and negative electrodes of the nanocrystals at the top and bottom can be bonded to external conductive extension components using conductive silver glue, making them convenient for connection to external circuits during actual use. The advantage of this method is that the core production process is simple and efficient, and machine automation is easily achieved.

[0043] In addition, as shown in FIG4 , 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 capacitor formed 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 intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, numerous modifications and variations are possible based on the contents of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, so that those skilled in the art can better understand and utilize the present invention.

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 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.

2. A transformer structure for LLC resonant converter according to claim 1, characterized in that: 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.

3. The transformer structure for LLC resonant converter according to claim 1, characterized in that: The thickness of the iron-based nanocrystalline ribbon is 16~18μm, and the thickness of the organic insulating film is 10~25μm.

4. The transformer structure for LLC resonant converter according to claim 1, characterized in that: The iron-based nanocrystalline strip and the organic insulating film are bonded by resin adhesive or electrostatic adsorption.

5. The transformer structure for LLC resonant converter according to claim 2, characterized in that: The stacking process is a stacking structure, and vertical dislocation stacking is used 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. A coil winding is added to the capacitor as the transformer core.

6. A transformer structure for LLC resonant converter according to claim 2, 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.

7. A transformer structure for LLC resonant converter according to claim 5 or 6, 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.

8. The transformer structure for LLC resonant converter according to claim 5, characterized in that: 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.

9. 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.

10. 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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