A wideband impedance model and modeling method for analyzing LLC resonant converter

Abstract

The application belongs to the technical field of power electronics, and discloses a wide-frequency impedance model and a modeling method for analyzing an LLC resonant converter, which comprises a common-mode wide-frequency model of a full-bridge LLC resonant converter and is composed of transmission conductors, pads, terminal posts, copper traces of a PCB board, a resonant cavity, a transformer, a PCB trace-to-ground parasitic capacitance and a semiconductor switching tube MOSFET-to-ground parasitic capacitance high-frequency model; and a differential-mode wide-frequency model of the full-bridge LLC resonant converter and is composed of transmission conductors, pads, terminal posts, copper traces of a PCB board, a resonant cavity, a transformer, a PCB trace-to-ground parasitic capacitance, a semiconductor switching tube MOSFET and an input capacitance high-frequency model. The application has universality and adaptability, and different switching power supply circuit structures have certain differences, but the modeling method proposed by the application can be combined with the physical structure of an actual switching power supply circuit to accurately model the actual switching power supply.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, and in particular relates to a wideband impedance model and modeling method for analyzing LLC resonant converters. Background Technology

[0002] Currently, with the in-depth development of science and technology, the requirements for circuit modeling are becoming increasingly stringent, especially in switching power supplies. Due to the high efficiency and high power of LLC resonant converters, they have become a key focus of analysis in switching power supplies, leading to increasingly higher requirements for the switching frequency of semiconductor switching devices. Consequently, higher demands are placed on the accuracy and frequency range of wideband modeling of switching power supply circuits. Currently, commonly used modeling methods, such as those for motors and wideband gap semiconductor switching devices, are limited to impedance network analyzers within 30MHz or wideband modeling of individual devices in vector network analyzers. However, wideband equivalent circuit modeling for system circuits above 30MHz has not yet been fully established. With the increasing switching frequency of wideband gap semiconductor switching devices, it is necessary to establish system wideband models above 30MHz to understand the wideband impedance of conducted interference for the entire system.

[0003] LLC resonant converters, due to their soft-switching characteristics, can achieve high-efficiency full-load operation and are widely used in industry. However, due to the gradual increase in switching frequency under the dynamic characteristics of wide-gap devices, electromagnetic interference (EMI) of full-bridge LLC resonant converters has become a critical issue in these systems. The high dv / dt or di / dt of wide-gap semiconductor switches generate a large number of high-frequency harmonic components, thus producing common-mode and differential-mode noise signals in full-bridge LLC resonant converters. To solve the EMI problem, it is necessary to establish improved common-mode and differential-mode models to represent the wideband behavior of the converter, thereby understanding the common-mode and differential-mode noise characteristics of LLC resonant converters. Therefore, it is necessary to establish a wideband model of LLC resonant converters with higher accuracy and physical meaning based on the circuit physical structure at a higher frequency range.

[0004] Based on the above analysis, the problems and defects of the existing technology are as follows: electromagnetic interference of the full-bridge LLC resonant converter leads to the generation of common-mode and differential-mode noise signals in the full-bridge LLC resonant converter; the existing modeling methods have not yet fully established broadband equivalent circuit modeling for system circuits with frequencies above 30MHz. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a wideband impedance model and modeling method for analyzing LLC resonant converters.

[0006] This invention is implemented as follows: a broadband impedance model for analyzing LLC resonant converters includes:

[0007] The common-mode broadband model of the full-bridge LLC resonant converter consists of broadband models of transmission wires, pads, terminals, PCB traces, resonant cavity inductors and capacitors, transformers, PCB trace parasitic capacitance to ground, and MOSFET parasitic capacitance to ground. The connection relationships of each broadband model are as follows: Figure 2 As shown;

[0008] The differential-mode broadband model of a full-bridge LLC resonant converter consists of transmission wires, pads, terminals, PCB traces, resonant cavity inductors and capacitors, transformers, parasitic capacitance of PCB traces to ground, semiconductor switching transistors (MOSFETs), and input capacitor broadband models. The connection relationships between these broadband models are as follows: Figure 3 As shown.

[0009] Furthermore, in the common-mode broadband model of the full-bridge LLC resonant converter, the common-mode path represents the signal loop between the full-bridge LLC resonant converter and ground, and the common-mode lumped pre-parasitic model L... wire –L bus L wire -C wirep -R wirep These are parallel models of the parasitic inductance, parasitic capacitance, and parasitic resistance of the transmission line;

[0010] L wt -C wtp -R wtp These are parallel models of the parasitic inductance, parasitic capacitance, and parasitic resistance of the terminals;

[0011] L pad -C padp -R padp These are parallel models of the parasitic inductance, parasitic capacitance, and parasitic resistance of the pads;

[0012] L bus -C busp -R busp These are parallel models of the parasitic inductance, parasitic capacitance, and parasitic resistance of PCB traces, connected in series.

[0013] Furthermore, the resonant cavity inductance is modeled as L r -C rp -R rp L r -C rp -R rp The parasitic inductance, parasitic capacitance, and parasitic resistance are modeled in parallel, and the resonant cavity capacitance is modeled as an ideal capacitance C. r .

[0014] Furthermore, the transformer is modeled as R at both ends. pri -L priIn the series model, the primary and secondary sides are connected through the parasitic capacitance C. t Interconnected, the secondary side is modeled as R rp -L sec Series model.

[0015] Furthermore, the parasitic capacitance to ground of the full-bridge LLC resonant converter is divided into the lumped parasitic capacitance C of the semiconductor switching transistors MOSFETs through the heat sink to ground. p The lumped parasitic capacitance C on the inverter side to ground b1 and the lumped parasitic capacitance C of the rectifier side to ground b2 .

[0016] Furthermore, the differential-mode path in the differential-mode broadband model of the full-bridge LLC resonant converter represents the signal loop between the high-voltage L-line and the low-voltage N-line of the full-bridge LLC resonant converter;

[0017] The semiconductor switching transistor MOSFET is modeled as L m -C mp -R mp A high-frequency model of parasitic inductance, parasitic capacitance, and parasitic resistance in parallel;

[0018] Input capacitor C in It is a differential-mode low-impedance path, modeled as C in -L inp -R inp Series high-frequency model;

[0019] The high-impedance high-frequency model of the resonant cavity, transformer, and rectifier side lumped high impedance is simplified to Z DM1 .

[0020] Another object of the present invention is to provide a modeling method for analyzing the broadband impedance model of an LLC resonant converter, the modeling method comprising:

[0021] Step 1: Analyze the common-mode / differential-mode S obtained from the vector network analyzer. 11 Curve conversion to common mode / differential mode Z 11 The common-mode / differential-mode impedance curves of the LLC resonant converter are thus obtained from the curves.

[0022] Step 2: Observe and analyze the common-mode / differential-mode impedance curves of the converted LLC resonant converter, and determine the number of peak resonant points appearing in the amplitude-frequency curves of the common-mode / differential-mode impedance. Each peak point corresponds to a parallel RLC structure.

[0023] Step 3: Taking into account the actual connection of discrete components in the LLC resonant converter, based on the LLC resonant converter circuit model (see... Figure 1The peak resonant point of the common-mode / differential-mode impedance amplitude-frequency curve is supplemented by RLC parallel structure modeling, and its connection is matched with the actual LLC resonant converter. The number and connection relationship of RLC resonant networks in the broadband equivalent circuit of the full-bridge LLC resonant converter are determined, and the broadband modeling parameters are solved by measuring the common-mode / differential-mode impedance curve of the LLC resonant converter.

[0024] Furthermore, using the Labras transform, the s-domain impedance expression of the LCR parallel broadband model is written, and the s-domain expressions of the common-mode broadband impedance and differential-mode broadband impedance are obtained by lumping and summing the various parts.

[0025] Furthermore, the full-bridge LLC resonant converter is measured using a vector network tester, and the S-parameters are converted into Z-parameters to obtain the common-mode broadband impedance and differential-mode broadband impedance curves. The impedance amplitude and phase angle corresponding to representative frequency points are obtained. These points are then processed in Matlab, and the measured points that are equal to the parameters to be determined are substituted to obtain the parameter values.

[0026] Finally, using the parameters calculated above, an equivalent model of the full-bridge LLC resonant converter circuit is drawn in the Advanced Design System to obtain the amplitude and phase angle of the common-mode impedance and differential-mode impedance of the full-bridge LLC resonant converter. The amplitude and phase angle of the simulated common-mode impedance and differential-mode impedance are compared with the amplitude and phase angle of the actual measured common-mode impedance and differential-mode impedance in Matlab. Based on the difference between the two, the above parameters are finely adjusted to obtain the optimal differential-mode broadband model and common-mode broadband model of the full-bridge LLC resonant converter.

[0027] Furthermore, since the amplitude-frequency curve of the wideband common-mode impedance has four distinct peaks, the wideband equivalent circuit of the full-bridge LLC resonant converter has at least four RLC resonant networks.

[0028] If the amplitude-frequency curve of the wideband differential mode impedance has five distinct peaks, then the high-frequency equivalent circuit of the full-bridge LLC resonant converter has at least five RLC resonant networks.

[0029] Based on the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solution to be protected by this invention are as follows:

[0030] First, addressing the technical problems existing in the prior art and the difficulty in solving them, this paper closely analyzes, in conjunction with the technical solution to be protected by this invention and the results and data obtained during the research and development process, how the technical solution of this invention solves the technical problems, and the inventive technical effects brought about by solving these problems. The specific description is as follows:

[0031] This invention provides a wideband equivalent model and modeling method for a full-bridge LLC resonant converter. It utilizes a vector network analyzer to measure the wideband impedance of the full-bridge LLC resonant converter. Considering the topological relationships of the discrete components in the actual full-bridge LLC resonant converter and their connection to the wideband common-mode / differential-mode impedance loops, it organically combines the physical structure of the full-bridge LLC resonant converter with mathematical methods for solving engineering problems. Based on the topology of the full-bridge LLC resonant converter, it supplements the model with a parallel RLC structure for the measured wideband common-mode and wideband differential-mode impedances. The resulting wideband common-mode and wideband differential-mode model impedances of the full-bridge LLC resonant converter are approximately consistent with the actual measured wideband common-mode and wideband differential-mode impedances. The model itself has physical meaning and provides guidance for engineering and switching power supply modeling. The modeling method for the wideband full-bridge LLC resonant converter provided by this invention has universality and applicability. Different switching power supply circuit structures have certain differences, but the modeling method proposed in this invention, combined with the physical structure of the actual switching power supply circuit, can accurately model actual switching power supplies.

[0032] Second, considering the technical solution as a whole or from a product perspective, the technical effects and advantages of the technical solution to be protected by this invention are specifically described as follows:

[0033] This invention provides a method for analyzing and modeling the high-frequency equivalent circuit of LLC resonant converters from the perspective of wideband common-mode impedance and wideband differential-mode impedance models. Based on the current modeling methods of impedance network analyzers with wideband impedance up to 30MHz and vector network analyzers with wideband impedance up to 30MHz and above, a novel wideband modeling method for LLC resonant converters with high accuracy up to 500MHz is proposed, which makes a significant contribution to the modeling of general circuits in engineering and switching power supplies.

[0034] Third, as supplementary evidence of the inventive step of the claims of this invention, it is also reflected in the following important aspects:

[0035] Does the technical solution of this invention solve a technical problem that people have long desired to solve but have never been able to achieve: accurate wideband modeling technology for switching power supply converters, a novel wideband modeling method for LLC resonant converters with high accuracy up to 500MHz? Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a measured model of a full-bridge LLC resonant converter provided in an embodiment of the present invention;

[0037] Figure 2 This is a simplified circuit diagram of the wideband common-mode impedance model of the full-bridge LLC resonant converter provided in Embodiment 1 of the present invention;

[0038] Figure 3 This is a simplified circuit diagram of the wideband differential mode impedance model of the full-bridge LLC resonant converter provided in Embodiment 1 of the present invention;

[0039] Figure 4 A comparison chart showing the common-mode impedance amplitude and phase angle curves simulated in the Advanced Design System in Matlab with the actual measured common-mode impedance amplitude and phase angle curves;

[0040] Figure 5 This is a comparison chart of the common-mode impedance amplitude and phase angle curves simulated in the Advanced Design System in Matlab with the actual measured common-mode impedance amplitude and phase angle curves. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0042] To enable those skilled in the art to fully understand how the present invention is specifically implemented, this section provides an explanatory description of the embodiments that expand upon the technical solutions of the claims.

[0043] In the modeling method for analyzing the broadband impedance model of an LLC resonant converter provided in this embodiment of the invention, the common-mode impedance S obtained by the vector network analyzer is used. 11 Curve converted to common mode Z 11 The common-mode impedance curve of the circuit system is obtained from the curve. Observing and analyzing the transformed common-mode impedance curve, we can find that the phase angle curve of the common-mode impedance shows four obvious peaks, indicating that there are at least four RLC resonant networks in the high-frequency equivalent circuit of the full-bridge LLC resonant converter. Considering the physical structure of the transmission wires, terminals, PCB traces, pads, semiconductor switches, and heat sinks in the circuit, a broadband common-mode model of the full-bridge LLC resonant converter is given. At the same time, the differential-mode S obtained by the vector network analyzer is also used to obtain the common-mode impedance curve. 11 Curve converted to differential mode Z 11 The differential-mode impedance curve of the circuit system is obtained from the curve. By observing and analyzing the converted common-mode impedance curve, we can find that the phase angle curve of the common-mode impedance has five obvious peaks, indicating that there are at least five RLC resonant networks in the high-frequency equivalent circuit of the full-bridge LLC resonant converter. Considering the physical structure of the circuit, such as transmission wires, terminals, PCB traces, pads, semiconductor switching transistors MOSFETs and input capacitors, a differential-mode broadband model of the full-bridge LLC resonant converter is given.

[0044] Measured model of full-bridge LLC resonant converter (e.g.) Figure 1 (As shown) includes DC source V DC LISN and full-bridge LLC resonant converters, the LISN includes an R1-C1-R2-C2 DC source high-frequency filter circuit, an L1-L2 isolation circuit, and a C L -R L -C N -R N The converter has a high-frequency filter circuit, while the full-bridge LLC resonant converter includes an input capacitor C. in Semiconductor switches Q1-Q4, resonant cavity C r -L r Transformer L m Diodes D1-D4, Output capacitor C out and output resistance R load Meanwhile, C pg This is the lumped parasitic capacitance to ground of the full-bridge LLC resonant converter.

[0045] Full-bridge LLC resonant converter common-mode wideband model (e.g.) Figure 2 The model shown consists of circuit wires, pads, terminals, PCB traces, resonant cavity, transformer, parasitic capacitance of PCB traces to ground, and high-frequency model of parasitic capacitance of MOSFETs to ground. The common-mode path represents the parasitic loop between the full-bridge LLC resonant converter and ground. The common-mode lumped pre-parasitic model L... wire -L bus It exists due to the necessity of layout and connection, including L wire -C wirep -R wirep These are parallel models of the parasitic inductance, parasitic capacitance, and parasitic resistance of the transmission line, L. wt -C wtp -R wtp These are parallel models of the parasitic inductance, parasitic capacitance, and parasitic resistance of the terminals, L. pad -C padp -R padp These are the parallel models of the parasitic inductance, parasitic capacitance, and parasitic resistance of the pads, and L... bus -C busp -R busp These are parallel models of the parasitic inductance, parasitic capacitance, and parasitic resistance of the copper traces on a PCB board, and then connected in series. Due to the resonant cavity capacitance C during operation... r The voltage across the terminals has no higher harmonics, C r It is considered to be the ideal capacitor of the resonant cavity, while the resonant cavity inductance L is actually in operation. r The voltage across the terminals contains higher harmonics, therefore it is modeled as L r -C rp -R rpParasitic inductance, parasitic capacitance, and parasitic resistance are modeled in parallel. Due to the symmetry of the upper and lower ports of the transformer primary side, they are modeled as R at the upper and lower ends. pri -L pri In the series model, the primary and secondary sides are connected through the parasitic capacitance C. t Interconnected, the secondary side is modeled as R rp -L sec Series model. Additionally, the parasitic capacitance to ground of the full-bridge LLC resonant converter is divided into the lumped parasitic capacitance C of the semiconductor switching transistors (MOSFETs) through the heat sink to ground. p The lumped parasitic capacitance C on the inverter side to ground b1 and the lumped parasitic capacitance C of the rectifier side to ground b2 .

[0046] Differential-mode wideband model of full-bridge LLC resonant converter (e.g.) Figure 3 The model shown consists of circuit wires, pads, terminals, PCB traces, resonant cavity, transformer, parasitic capacitance of PCB traces to ground, MOSFET semiconductor switching transistors, and input capacitors in a high-frequency model. The differential-mode path represents the parasitic loop between the high-voltage L-line and the low-voltage N-line of the full-bridge LLC resonant converter, while the common-mode lumped pre-parasitic model L... wire -L b Due to the inherent limitations of its layout, it is the same as the common-mode model. However, the semiconductor switching transistor MOSFET will generate a series-parallel resonant point in the differential-mode mid-frequency band. Therefore, the semiconductor switching transistor MOSFET is modeled as L... m -C mp -R mp A high-frequency model of parasitic inductance, parasitic capacitance, and parasitic resistance in parallel. Input capacitance C. in It is a differential-mode low-impedance circuit, therefore it is modeled as C. in -L inp -R inp The series high-frequency model, and the corresponding simplified high-frequency model Z of the resonant cavity, transformer, and rectifier side lumped high impedance. DM1 .

[0047] Furthermore, using the Labras transform, the s-domain impedance expression of the RLC parallel broadband model is written, and the lumped sum of each part is used to obtain the s-domain expressions for the common-mode broadband impedance and the differential-mode broadband impedance.

[0048] Furthermore, the full-bridge LLC resonant converter is measured using a vector network tester, and the S-parameters are converted into Z-parameters to obtain wideband common-mode impedance and wideband differential-mode impedance curves. Representative frequency points (the inflection points of amplitude and phase angle on the main impedance curves) are obtained, and the impedance amplitude and phase angle corresponding to these points are processed in Matlab. The measured points are then substituted with the same measurement points as the parameters to be determined to obtain the parameter values.

[0049] Finally, using the parameters calculated above, an equivalent model of the full-bridge LLC resonant converter circuit is drawn in Advanced Design System, obtaining the amplitude and phase angle of the wideband common-mode impedance and wideband differential-mode impedance of the full-bridge LLC resonant converter. The amplitude and phase angle of the simulated wideband common-mode impedance and wideband differential-mode impedance are compared with the actual measured amplitude and phase angle of the common-mode impedance and differential-mode impedance in Matlab. Based on the difference between the two, the above parameters are finely adjusted to obtain the optimal wideband differential-mode model and wideband common-mode model of the full-bridge LLC resonant converter.

[0050] To demonstrate the inventiveness and technical value of the technical solution of this invention, this section provides specific product or related technology application examples of the technical solution claimed.

[0051] The present invention provides a method for analyzing and modeling the high-frequency equivalent circuit of LLC resonant converters from the perspective of wideband common-mode impedance and wideband differential-mode impedance models. This method can accurately model the wideband common-mode impedance and wideband differential-mode impedance of PCB-based switching power converter circuits. After accurate modeling, it can provide important references for determining key factors of common-mode and differential-mode impedance, LISN-based EMI noise measurement, and filter design.

[0052] The embodiments of the present invention have achieved some positive results during the research and development or use process, and have indeed great advantages compared with the prior art. The following content describes them in conjunction with the data, charts and other information of the experimental process.

[0053] Example 1

[0054] The impedance curve measured in this embodiment was obtained in the laboratory using a vector network analyzer on a 1kW full-bridge LLC resonant converter. Firstly, the impedance curve was measured... Figure 1 The full-bridge LLC resonant converter shown measures the wideband common-mode impedance and wideband differential-mode impedance S-parameters. 11 Transform into Z-parameters Z 11 :

[0055]

[0056] Taking into account the actual discrete device connection situation of LLC resonant converter, based on the LLC resonant converter circuit model (see...) Figure 1 For the impedance Z parameter Z 11 The peak resonance point is supplemented by RLC parallel structure modeling, and its connection is matched with the actual LLC resonant converter. The number and connection relationship of RLC resonant networks in the broadband equivalent circuit of the full-bridge LLC resonant converter are determined. The broadband modeling parameters are solved by the measured common-mode / differential-mode impedance curve of the LLC resonant converter.

[0057] Based on broadband common-mode impedance and broadband differential-mode impedance models, the values ​​of each parameter in the proposed model are determined. Due to the multi-stage series and parallel connection, it is difficult to determine the precise influence of the series resonant point on each parameter. Therefore, considering only a parallel structure of inductor L, capacitor C, and resistor R, we can obtain:

[0058]

[0059] Converting to jw yields:

[0060]

[0061] Therefore, the formulas for phase angle and magnitude are:

[0062]

[0063] like Figure 2 As shown, the resonant cavity, transformer, and rectifier side form a common-mode high-resistance circuit; therefore, the influence of this secondary factor is ignored in the calculation. Thus, the common-mode impedance can be obtained:

[0064]

[0065] Simultaneously, four precise formulas for parallel resonant points can be used to verify the solution of the parametric equations:

[0066]

[0067] like Figure 3 As shown, similarly, the resonant cavity, transformer, and rectifier side form a differential-mode high-resistivity circuit, therefore the influence of this secondary factor is ignored in the calculation. Thus, the differential-mode impedance can be obtained:

[0068]

[0069] Simultaneously, five precise formulas for parallel resonant points can be used to verify the solution of the parametric equations:

[0070]

[0071]

[0072] Solving equations (1) to (8) simultaneously yields the parameters of the wideband differential-mode impedance model and the wideband common-mode impedance model of the full-bridge LLC resonant converter. The parameter values ​​are obtained by calculating the transfer function using Matlab. A comparison of the amplitude and phase angle curves of the common-mode impedance simulated using the Advanced Design System with the amplitude and phase angle curves of the actually measured wideband common-mode impedance is shown in the figure below. Figure 4 The figure shown is a comparison of the amplitude and phase angle curves of the wideband differential mode impedance. Figure 5As shown, we can see that the two curves completely overlap, indicating that the fitting accuracy is high.

[0073] In summary, this invention provides a wideband common-mode and differential-mode model of a full-bridge LLC resonant converter with a bandwidth of up to 500MHz, suitable for analyzing conducted interference. It achieves wideband modeling of circuit systems based on the physical structure of switching power supply converters, offering high accuracy. This solves the problem that high-precision models within the 30MHz band, while accurate, often fail to meet practical engineering needs or fail to consider the actual circuit physical structure. Wideband converter models, while accurate, lack guidance for engineering and converter modeling. This invention achieves accurate modeling of full-bridge LLC resonant converters. Furthermore, the wideband modeling method provided by this invention represents a significant improvement over previous wideband circuit modeling methods, achieving highly satisfactory results and representing a major breakthrough in the field of switching power supply converter modeling. This invention is not limited to this embodiment and is particularly applicable to modeling various switching power supply converter topologies used in experiments.

[0074] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A broadband impedance analysis device for LLC resonant converters, characterized in that, The broadband impedance analysis device for LLC resonant converters includes: The common-mode high-frequency module of the full-bridge LLC resonant converter consists of circuit wires, pads, terminals, PCB copper traces, resonant cavity, transformer, PCB trace parasitic capacitance to ground, and a high-frequency model of MOSFET parasitic capacitance to ground. The differential-mode high-frequency module of the full-bridge LLC resonant converter consists of circuit wires, pads, terminals, PCB copper traces, resonant cavity, transformer, PCB trace parasitic capacitance to ground, semiconductor switching transistors MOSFETs, and a high-frequency model of the input capacitor. The common-mode path in the common-mode high-frequency module of a full-bridge LLC resonant converter represents the parasitic loop between the full-bridge LLC resonant converter and ground. The common-mode lumped pre-parasitic model L... wire –L bus including L wire -C wirep -R wirep These are parallel models of the parasitic inductance, parasitic capacitance, and parasitic resistance of the transmission line; L wt -C wtp -R wtp These are parallel models of the parasitic inductance, parasitic capacitance, and parasitic resistance of the terminals; L pad -C padp -R padp These are parallel models of the parasitic inductance, parasitic capacitance, and parasitic resistance of the pads; L bus -C busp -R busp These are parallel models of the parasitic inductance, parasitic capacitance, and parasitic resistance of the copper traces on a PCB board, connected in series. The resonant cavity is modeled as L r -C rp -R rp L r -C rp -R rp These are parallel models of parasitic inductance, parasitic capacitance, and parasitic resistance, respectively.

2. The broadband impedance analysis device for LLC resonant converters as described in claim 1, characterized in that, The transformer is modeled as R at both ends. pri -L pri In the series model, the primary and secondary sides are connected through the parasitic capacitance C. t Interconnected, the secondary side is modeled as R sec -L sec Series model.

3. The broadband impedance analysis device for LLC resonant converters as described in claim 1, characterized in that, The parasitic capacitance to ground of a full-bridge LLC resonant converter is divided into the lumped parasitic capacitance C of the semiconductor switching transistors (MOSFETs) through the heat sink to ground. p The lumped parasitic capacitance C on the inverter side to ground b1 and the lumped parasitic capacitance C of the rectifier side to ground b2 .

4. The broadband impedance analysis device for LLC resonant converters as described in claim 1, characterized in that, The differential-mode path in the differential-mode high-frequency module of a full-bridge LLC resonant converter represents the parasitic loop between the high-voltage L-line and the low-voltage N-line of the full-bridge LLC resonant converter. The semiconductor switching transistor MOSFET is modeled as L m -C mp -R mp A high-frequency model of parasitic inductance, parasitic capacitance, and parasitic resistance in parallel; Input capacitor C in It is a differential-mode low-impedance circuit, modeled as C. in -L inp -R inp Series high-frequency model; Simplified high-impedance high-frequency model of resonant cavity, transformer and rectifier side lumped high impedance ZDM1.

5. A method for constructing a broadband impedance device for analyzing LLC resonant converters as described in any one of claims 1 to 4, characterized in that, The method for analyzing the broadband impedance device of an LLC resonant converter includes: Step 1: Convert the common-mode / differential-mode S11 curve obtained from the vector network analyzer into a common-mode / differential-mode Z11 curve to obtain the common-mode / differential-mode impedance curve of the circuit system; Step 2: Observe and analyze the common-mode / differential-mode impedance curves of the system obtained by conversion, and determine the number of peaks appearing in the phase angle curves of the common-mode / differential-mode impedance. Step 3: Considering the actual connection of discrete components in the LLC resonant converter, based on the LLC resonant converter circuit model, the peak resonant point of the amplitude-frequency curve of the common-mode / differential-mode impedance is supplemented by RLC parallel structure modeling, and its connection is matched with the actual LLC resonant converter. The number and connection relationship of RLC resonant networks in the broadband equivalent circuit of the full-bridge LLC resonant converter are determined, and the broadband modeling parameters are solved by measuring the common-mode / differential-mode impedance curve of the LLC resonant converter.

6. The method for analyzing the broadband impedance of an LLC resonant converter as described in claim 5, characterized in that, Using the Labras transform, the s-domain impedance expression of the LCR parallel broadband model is written. By lumping and summing the various parts, the s-domain expressions of the common-mode broadband impedance and differential-mode broadband impedance are obtained.

7. The method for analyzing the broadband impedance of an LLC resonant converter as described in claim 5, characterized in that, The common-mode broadband impedance and differential-mode broadband impedance curves of the full-bridge LLC resonant converter are obtained by measuring the S-parameters and converting them into Z-parameters using a vector network tester. The impedance amplitude and phase angle corresponding to representative frequency points are obtained. These points are then processed in Matlab, and the measured points that are equal to the parameters to be determined are substituted to obtain the parameter values. Finally, using the parameters calculated above, an equivalent model of the full-bridge LLC resonant converter circuit is drawn in the Advanced Design System to obtain the amplitude and phase angle of the common-mode impedance and differential-mode impedance of the full-bridge LLC resonant converter. The amplitude and phase angle of the simulated common-mode impedance and differential-mode impedance are compared with the amplitude and phase angle of the actual measured common-mode impedance and differential-mode impedance in Matlab. Based on the difference between the two, the above parameters are finely adjusted to obtain the optimal differential-mode broadband model and common-mode broadband model of the full-bridge LLC resonant converter.

8. The method for analyzing the broadband impedance of an LLC resonant converter as described in claim 5, characterized in that, If the phase angle curve of the common-mode impedance has four distinct peaks, then the high-frequency equivalent circuit of the full-bridge LLC resonant converter has at least four RLC resonant networks. If the phase angle curve of the differential mode impedance has five distinct peaks, then the high-frequency equivalent circuit of the full-bridge LLC resonant converter has at least five RLC resonant networks.

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