A magnetic integration device for a three-phase LCL grid-connected inverter based on equal magnetic flux

Abstract

The application discloses a three-phase LCL grid-connected inverter magnetic integration structure based on equal magnetic flux technology, relates to the field of power electronics, and aims to solve the problems of the asymmetric magnetic circuit, large volume, high loss and low power density of a traditional three-phase LCL filter. The structure comprises a Y-shaped equal magnetic flux magnetic core main body, an inverter side winding, a grid side winding and a filter capacitor. The Y-shaped equal magnetic flux magnetic core main body is composed of three magnetic columns symmetrically distributed at 120 degrees and a central triangular magnetic concentrator, and an air gap is arranged at the connection between the magnetic column and the central magnetic concentrator. The inverter side winding and the grid side winding are respectively wound on the upper and lower sections of the magnetic column, and the number of turns and the number of layers of the two groups of windings are determined through a multi-objective optimization algorithm. The application realizes equal length and uniform distribution of three-phase magnetic flux paths, and the maximum deviation of three-phase inductance is less than or equal to 0.21%. Compared with a traditional discrete structure, the weight and volume are reduced by 33% and 24% respectively, the efficiency at a rated power point reaches 96.5%, the total harmonic distortion at the grid side is less than or equal to 1.69%, and the application is suitable for a high-power-density new energy grid-connected inverter system.

Description

Technical Field

[0001] This invention belongs to the field of motor control technology and provides a magnetic integration device for a three-phase LCL grid-connected inverter based on equal magnetic flux. Background Technology

[0002] With the rapid development of new energy grid-connected technologies, improving system power density has become an important industry goal, and optimizing the size and weight of LCL filters is a key challenge in achieving this goal. Traditional designs rely on multiple independent filter components, making it difficult to effectively reduce size and weight, which severely restricts the system's compactness and efficiency.

[0003] Three-phase inductors are an important component of three-phase power systems. In current technologies, an increasing number of three-phase systems utilize three-phase coupled inductors or magnetically integrated inductors to reduce the size of magnetic components. However, traditional E-type three-phase coupled inductors often introduce magnetic circuit asymmetry, leading to three-phase inductance imbalance and affecting the power quality of three-phase inverters. The E-type core structure also easily causes deviations in the self-inductance and mutual inductance parameters of the three-phase inductors, which can trigger voltage and current imbalances in three-phase systems such as power grids or motor drive systems, ultimately affecting the stability and overall performance of the system.

[0004] Furthermore, while breakthroughs have been made in addressing the imbalance problem in three-phase magnetic core circuits, several challenges and limitations remain. Complex fabrication processes hinder large-scale production; insufficient adaptability to high-performance soft magnetic materials such as amorphous alloys and nanocrystals limits performance potential; and the lack of flexible parameter adjustment standards makes optimized design according to actual needs difficult. Looking ahead, researchers need to achieve breakthroughs in core structure, winding methods, and material adaptability to develop more efficient, flexible, and easily fabricated three-phase magnetic core structures, providing a solid technological foundation for the high performance and miniaturization of power electronic devices.

[0005] Meanwhile, the development of soft magnetic materials has provided new pathways for core optimization. Ferrite materials have consistently held a crucial position throughout the long history of inductor design. With their excellent high-frequency performance, good temperature stability, and relatively low cost, they have long been the preferred material for magnetic component design. Especially in applications such as high-frequency switching power supplies and communication equipment, the low-loss characteristics and stable magnetic properties of ferrite materials make them ideal for inductor design. However, as power electronics technology moves towards higher frequencies and smaller sizes, the limitations of ferrite materials are becoming increasingly apparent: their relative permeability (typically in the range of 1000-5000) and saturation flux density (approximately 0.3-0.5T) are relatively low, which severely restricts the miniaturization process of magnetic components. In high-power-density applications, ferrite cores often require larger volumes to meet performance requirements, which contradicts the design trend of miniaturization and lightweighting in modern electronic devices.

[0006] To address these issues, existing technologies have proposed an E-type three-phase coupled filter structure, using two EE magnetic cores to integrate the three-phase inductors onto a single core. Each magnetic post is wound with one phase winding, and through reasonable parameter design, the filter size is significantly reduced. To further reduce the size of LCL filters in grid-connected inverters, research on magnetic integration of LCL filters has gradually unfolded. Some scholars have proposed magnetic integration of LCL filters, using EIE-type magnetic cores to integrate the inverter's magnetic inductance and the grid-side filter inductance together. The core windings use E-type magnetic cores, and the two filters are integrated onto a single core via an I-type common magnetic core, greatly reducing the filter size. This magnetically integrated filter is suitable not only for single-phase systems but also for three-phase systems. However, due to magnetic circuit asymmetry, three-phase inductor imbalance can occur during three-phase winding.

[0007] In recent years, planar magnetic integration technology has made breakthrough progress in the field of EMI filters. Through precise PCB winding layout and multi-layer magnetic circuit coupling, it has achieved high common-mode rejection ratios and millimeter-thin packaging. E-type planar magnetic integration adopts a planar core structure, improving flux distribution uniformity and space utilization through optimized magnetic circuit layout, innovatively achieving dual-function integration of EMI and LCL filtering. The LCL-EMI hybrid filter design achieved a 35% volume reduction in GaN inverter applications, with conducted EMI attenuation reaching 65 dBμV and power density increased to 5.8 kW / dm³, meeting grid connection standards. However, when this application is extended to industrial-grade high-power scenarios, the limitations of the planar structure lead to increased interlayer distributed capacitance at high frequencies, resonant frequency shift, limited current carrying capacity, and easy core saturation, making it difficult to maintain sufficient design margin. Although EMI filters have made significant progress in low- and medium-power applications, research progress in high-power harmonic filter integration remains relatively slow. While LCL filters, also aimed at harmonic suppression, possess theoretically wide-bandgap attenuation characteristics, their magnetic integration research lags significantly behind technological development needs. Current mainstream solutions still employ discrete magnetic component combinations, resulting in an excessively large volume proportion in the inverter system. Current research on magnetic integration of LCL filters faces three main challenges: First, traditional E-type integration schemes are limited by asymmetrical magnetic circuits, leading to three-phase inductor deviations; second, while planar magnetic integration technology can achieve high-frequency, low-loss operation, its winding current density exceeding 7.2 A / mm² in high-power applications causes severe heat accumulation; third, existing magnetoelectric coupling models fail to effectively quantify the cross-coupling effect between inverter-side and grid-side inductors, and so on. Despite these bottlenecks, achieving deep magnetic integration of LCL filters has become a core research area for breaking through power density limitations in high-density grid-connected new energy scenarios, thus its research has profound significance. Summary of the Invention

[0008] To address the aforementioned unresolved technical problems, the main objective of this invention is to provide a magnetic integration device for a three-phase LCL grid-connected inverter based on equal magnetic flux, aiming to solve the problems of magnetic circuit asymmetry, large size, high loss, and low power density of existing three-phase LCL filters.

[0009] To achieve the above objectives, the present invention provides a magnetic integration device for a three-phase LCL grid-connected inverter based on equal flux, comprising: a Y-type equal flux magnetic core body, an inverter-side winding, and a grid-side winding.

[0010] It should be noted that the Y-shaped shape of the constant flux magnetic core provided in this application is from a top-down or bottom-up view.

[0011] Furthermore, the Y-type flux-equal magnetic core body includes: three magnetic pillars and a central triangular magnet collector integrally formed, with the three magnetic pillars symmetrically distributed at 120° with the geometric center of the central triangular magnet collector as the origin.

[0012] It should be noted that in LCL filter design, the core concept of the Y-shaped magnetic core is to integrate both the inverter-side and grid-side three-phase inductors into this Y-shaped magnetic circuit, forming the overall architecture of the three-phase LCL magnetic device, as shown in the diagram. Figure 1 As shown, this structure is called "Y-type" because, from a top-view perspective, its three magnetic fluxes are uniformly distributed at 120° on the plane. Therefore, thanks to its unique connection method, it has broad material adaptability and is easy to manufacture. The Y-type constant flux core is geometrically closer to an equilateral distribution, making the three-phase flux path length and cross-sectional area nearly identical, fundamentally reducing inductance imbalance. The inverter-side and grid-side windings can be rationally arranged on the same Y-type frame, making it easier to achieve low coupling compared to the EIE structure, avoiding interference from unnecessary parasitic resonances or leakage flux. Because the Y-type core combines compactness and symmetry, it has better design potential in high-power grid-connected applications. The coupling between the three-phase fluxes is easier to manage uniformly; the flux linkage, inductance, and losses of each phase winding can evolve in a consistent direction, helping to reduce harmonic distortion and current imbalance in grid-connected inverters. In addition, the Y-type magnetic core design is more flexible in terms of thermal management and heat dissipation design. It can further improve heat dissipation efficiency by reserving specific airflow channels between the central yoke or the three-phase magnetic columns.

[0013] Furthermore, the inverter-side winding and the grid-side winding are respectively wound with conductors on the upper and lower sections of each magnetic column, and the winding directions of the conductors of the inverter-side winding and the grid-side winding on the same magnetic column are opposite.

[0014] It should be noted that the reason for winding the inverter-side winding and the grid-side winding into two sections, upper and lower, on the magnetic column is to reduce the high-frequency circulating current loss caused by asymmetry.

[0015] Furthermore, the total number of turns of the inverter-side winding The total number of turns of the grid-side winding satisfy The value of K ranges from 0.2 to 0.3.

[0016] It should also be noted that the selection of the grid-side inductor Lgrid needs to be designed in conjunction with Linv, and usually follows the principle of proportional allocation, i.e. In the formula, K is the proportionality coefficient, which is usually taken as 0.2-0.3. Based on this, the total number of turns of the transformer-side winding is... Total number of turns of the grid-side winding It also follows the principle of proportional distribution, so In this context, the value of K ranges from 0.2 to 0.3.

[0017] Furthermore, an air gap is provided at the connection between each magnetic column and the central triangular magnet collector. The air gap is made of ceramic sheet pad and is located at the upper and lower ends of the magnetic column. The length of the air gap is 0.3-3.0mm.

[0018] It should be noted that an air gap is provided at the connection between each phase magnetic column and the central yoke to precisely adjust the inductance value and suppress magnetic saturation.

[0019] Furthermore, the central triangular magnet collector has an equilateral triangular structure, and its side length is equal to the side length of the cross-section of the magnetic column; the cross-section of the magnetic column is rectangular.

[0020] It should be noted that the triangular magnet collector has an equilateral triangular structure. The side length of the central triangular magnet collector is equal to the side length of the cross-section of the magnetic column. This is to ensure that all magnetic flux in the three phases can pass completely through all surfaces of the magnetic column.

[0021] Furthermore, the Y-type constant flux magnetic core body is made of amorphous alloy or nanocrystalline alloy; while the inverter-side winding and the grid-side winding are made of copper conductor or aluminum conductor.

[0022] It should be noted that amorphous alloys and nanocrystalline alloys are used as the main materials for Y-type flux cores because amorphous alloys with high magnetic saturation density are chosen to demonstrate the magnetic flux distribution without easily causing saturation, making it easier to observe the magnetic flux density of the core under high current conditions.

[0023] Furthermore, the number of lateral layers of the inverter-side winding Number of turns per layer in the longitudinal direction satisfy The number of transverse layers of the grid-side winding Number of turns per layer in the longitudinal direction satisfy ;in , The value range is 1-10 layers. , The value range is 1-100 turns.

[0024] It should be noted that, Given the theoretical cross-sectional area of ​​the conductor, it is normalized using wire gauge standardization functions. roundWG(a) Mapped to the actual wire diameter. This represents the theoretical number of turns of the inverter-side inductor, which is then integerized to obtain the actual number of turns. N=round (N Winding layout parameters Nw1 and N d1 These represent the number of layers in the lateral and longitudinal windings of the inverter side, respectively, and must satisfy the following constraints. N 1 ≤ N w1 ×N d1 Number of turns in the winding N The range is determined based on the system voltage level (650V) and switching frequency (50kHz) to balance magnetic flux density and winding losses. The specific calculations are based on:

[0025] In the formula, V rms For effective voltage, ω The angular frequency is denoted by ω. Too many turns increase winding resistance, leading to decreased efficiency; too few turns result in excessively high magnetic flux density, potentially causing core saturation. Therefore, the selection of the number of turns balances theoretical constraints with practical engineering requirements.

[0026] Furthermore, the three-phase LCL grid-connected inverter magnetic integration device also includes a filter capacitor and a damping resistor.

[0027] Furthermore, the filter capacitor adopts a star connection, with one end connected to the output terminal of the power grid winding and the other end grounded through a damping resistor.

[0028] It should be noted that imbalances among the three-phase inductors or improper magnetic circuit coupling design can lead to three-phase output imbalances, affecting power quality and increasing control complexity. Excessive capacitance values ​​can lower the resonant frequency and increase the risk of system instability; therefore, resonance suppression requires the use of a damping resistor Rd or an active damping strategy. The damping resistor is an aluminum-cased non-inductive resistor (3.9Ω / 50W), connected in a star configuration to the midpoint of the capacitor, effectively suppressing resonant peak values.

[0029] As can be seen from the above, the Y-type constant flux magnetic core body designed in this application, through the 120° distributed magnetic columns and the central magnet collector, divides the inverter-side winding and the grid-side winding into upper and lower sections wound on the magnetic columns. Compared with the traditional discrete structure, the weight and volume are reduced by 33% and 24% respectively. The rated power point efficiency reaches 96.5%, the magnetic core loss is reduced by 7.19%, the long-term operating energy consumption is significantly reduced, and under load change and overload conditions, the THD is always ≤1.85%, and the dynamic response is fast and oscillation-free. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a perspective view of the Y-type three-phase equal flux LCL magnetic integrated device provided in an embodiment of the present invention; Figure 2 This is a top view of the Y-type three-phase equal flux LCL magnetic integrated device provided in an embodiment of the present invention; Figure 3 This is a top view of the Y-type three-phase equal flux LCL magnetic integrated core provided in an embodiment of the present invention; Figure 4 This is a three-dimensional dimension diagram of the three-phase equal flux LCL magnetic integrated core provided in the embodiment of the present invention; Figure 5 This is a comparison chart of the weight and volume of three types of magnetic cores provided in the embodiments of the present invention; Figure 6 These are efficiency curves of three filters provided in this embodiment of the invention at different power levels. Detailed Implementation

[0032] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0033] It should be understood that, when used in this specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0034] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0035] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0036] As used in this specification and the appended claims, the term "if" may be interpreted, depending on the context, as "when," "once," "in response to determination," or "in response to detection." Similarly, the phrases "if determined" or "if detected [the described condition or event]" may be interpreted, depending on the context, as meaning "once determined," "in response to determination," "once detected [the described condition or event]," or "in response to detection [the described condition or event]."

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0039] To better understand the embodiments of this application, the magnetic integration device of a three-phase LCL grid-connected inverter based on equal magnetic flux, its parameter optimization, and magnetic circuit analysis are described below.

[0040] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0041] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the above device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this invention. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0042] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0043] [Example 1] Improved Three-Phase Equal Flux Path Coupled Inductor Structure like Figure 1 As shown, this application further improves the basic Y-shaped magnetic core to adapt to the practical application requirements of magnetic cores in medium-to-high power or high-current applications, enhancing the practicality of the material. The three magnetic pillars of the new architecture are still distributed symmetrically in a Y-shape at 120°, with a triangular central magnetic yoke added at the center position. Its function is to act as a central magnet collector to ensure that the three-phase magnetic flux can be efficiently exchanged at the center. By setting a uniform and controllable air gap g at the center, the total magnetic reluctance of the three-phase inductor can be dominated to a certain extent, making it easier to achieve consistency between the magnetic circuit length and air gap ratio of each phase winding during winding. For laminated iron cores, as long as the stacking direction and dimensional accuracy of each lamination are strictly maintained during the manufacturing process, the magnetic flux can be guided towards the center of the Y-shaped architecture, thereby effectively reducing unnecessary eddy current circulation. At high frequencies, this design concept of reducing eddy current circulation and leakage flux is crucial for reducing additional iron losses and improving inductor efficiency.

[0044] The magnetic flux coupling between the three-phase magnetic column and the central yoke can be described by the following equation:

[0045] in Ni For the first i Number of turns of phase, I i This is the phase current. R m This represents the equivalent magnetic reluctance formed by the magnetic pillars and the central yoke. When the three phases... A, B, C The magnetic column and the central collector have the same or similar magnetic circuit length. l c and cross-sectional area A e And ensure air gap g When arranged properly, it can achieve the desired effect to a large extent:

[0046] This allows for a more balanced distribution of magnetic flux across the three phases, achieving the design goal of equal flux paths on a macroscopic scale. Compared to traditional E-type or EI-type magnetic cores, the improved Y-shaped magnetic core not only has a more symmetrical shape but also provides sufficient design space at the central collector, allowing for flexible adjustment of the air gap size and shape according to application requirements. This results in more stable high power density and high efficiency in three-phase filter inductors.

[0047] Furthermore, similar to other symmetrical magnetic cores, the improved Y-type structure can also employ segmented windings in layers and regions during the actual winding process to further balance the leakage flux and distributed capacitance of each phase winding. This results in a more uniform distribution of parasitic parameters and reduces high-frequency circulating current losses caused by asymmetry.

[0048] [Example 2] Analysis of Three-Phase Equal Flux and Permeability Path like Figure 2 and Figure 3 As shown, the Y-type constant flux core has a geometry closer to an equilateral distribution, making the three-phase flux path length and cross-sectional area nearly identical, thus fundamentally reducing inductance imbalance. By setting a uniform and controllable air gap at the central yoke, the inductance values ​​on both the inverter side and the grid side can be adjusted simultaneously, and leakage flux outflow can be suppressed to a great extent. The inverter-side and grid-side windings can be rationally arranged on the same Y-type frame, making it easier to achieve low coupling compared to the EIE structure, avoiding interference from unnecessary parasitic resonances or leakage flux.

[0049] Because of its compactness and symmetry, the Y-type magnetic core offers greater design potential for high-power grid-connected applications. The coupling between the three-phase fluxes is easier to manage uniformly, and the flux linkage, inductance, and losses of each phase winding can evolve in a more consistent manner, helping to reduce harmonic distortion and current imbalance in grid-connected inverters. Furthermore, the Y-type magnetic core design offers greater flexibility in thermal management and heat dissipation, allowing for further improvements in heat dissipation efficiency by reserving specific airflow channels between the central yoke or the three-phase columns.

[0050] Based on the dimensions of the three-phase integrated inductor, define the dimension designations and leakage flux paths for each component, such as... Figure 3 As shown, the thickness of each phase magnetic column is defined as l c , w b Remove the width at the connection point for each phase column. w s The width of each phase column to the center yoke (i.e., the width of the winding slot opening). w e The thickness of the central magnetic yoke, w w and d w These represent the width and height of the winding plane, respectively, and there are two sets, upper and lower. d s1 and d s2 This refers to the maximum winding height of the inverter-side and grid-side magnetic cores. Finally, the air gap is defined as... g The vacuum permeability is μ 0.

[0051] The central magnetic collector (central yoke) is a device with a side length of... An equilateral triangle This represents the distance from the center point of the triangle to the side. For ease of analysis, the central yoke of the triangle will be divided into three equal parts. Based on the triangle's relationships... With core thickness The following relationship exists:

[0052] After establishing the three-phase LCL symmetrical integrated magnetic core, we began to analyze the magnetic permeability of the air gap and edge regions.

[0053] First, there's path 1 through the air gap. This is equivalent to considering the central cross-section of the magnetic column and the main air gap between the central magnetic collector as a simple magnetic flux path on a parallel plate. This is the most direct and core air gap path, and the corresponding magnetic permeability can be expressed by the following formula:

[0054] Path 2 is the main edge path from the top of the core pillar across the air gap into the central core, including both the real and virtual cores. Its permeability can be expressed by the following formula:

[0055] in It is the vacuum permeability. ln(...) is a logarithmic term that characterizes the scattering effect of magnetic flux in the air gap region and is closely related to the geometry of the air gap.

[0056] Path 3 is somewhat similar to Path 2, but it captures the bypass path at or below the lower edge of the air gap (see Path 3 in the figure). Its magnetic permeability can be expressed by the following formula:

[0057] Path 4 represents the edge flux that passes through the air gap edge from one side (front / back) of the magnetic core. Similar to the air gap pathways at the left and right ends of the core, because the core is not infinitely wide, there will be leakage flux at the air gap edge, producing additional edge effects. Its permeability can be expressed by the following formula:

[0058] Path 5 corresponds to a path further down. It represents the edge magnetic flux around the top of the core generated in the region where the three-phase cores are relatively close to each other. This region includes the connection between the core and the central core, and can also be described as the pathway between phases through the upper edge of the air gap. Its permeability can be expressed by the following formula:

[0059] Mode There is a coefficient of 3 and 2. π The factor is due to treating the three-phase structure as three symmetrical "Y"-shaped magnetic core pillars, resulting in a 3-fold relationship during coordinate transformations or "Δ→Y circuit" transformations. The total permeability of the effective air gap can be expressed by the formula... This indicates that the air gap region's ability to conduct magnetic flux directly affects the inductance value and energy storage characteristics.

[0060]

[0061] Path 6 is similar to path 5, also a type of edge flux bypassing the top air gap "phase-to-phase", but it occurs where the core column does not connect to the central core. w s The path 5 primarily corresponds to the area where the magnetic pillar and the central core connect, while path 6 addresses the width of the area providing the winding. w b , d s1 and d s2 The region, in the end, is similarly obtained as follows:

[0062] Due to symmetry, the wire-winding area on the side of the mesh corresponds to d s2 Part of the leakage flux path can be represented by path 7, which is consistent with path 6, the only difference being that the flux travels through the inverter side. d s1 Change to d s2 Its magnetic permeability can be expressed by the following formula:

[0063] At this point, the edge permeability of the virtual magnetic core can be expressed by the formula... This value indicates that it reflects the conduction characteristics of the virtual magnetic core to the edge magnetic flux, affecting the symmetry and coupling effect of the magnetic field.

[0064]

[0065] Paths 8 and 9 represent the inter-slot leakage magnetic permeability in the vertical direction of the upper and lower windings, which can be expressed by the following formula:

[0066] Paths 10 and 11 represent the horizontal inter-slot leakage permeability of the upper and lower windings. The horizontal slot leakage permeability is dominated by the transverse magnetic field distribution, and a modified model is used.

[53] It can be expressed as follows:

[0067] The total permeability of the leakage flux path can be expressed by the following formula:

[0068] Finally, the magnetic permeation paths of all MECs have been defined, and the effectiveness of the multi-objective optimization model can be improved through refined magnetic flux analysis.

[0069] [Example 3] Introduction to the functions of inverter-side inductors and grid-side inductors 1. Inverter-side inductor The design of the inverter-side inductor Linv needs to balance current ripple suppression and system dynamic performance. Based on the switching frequency fsw and the allowable peak ripple current ΔIpp, its inductance value can be calculated using the following formula:

[0070] Mode China V dcThe DC bus voltage, ΔI pp Typically, the inductance value is set to 10%-20% of the rated current. To verify the filtering effect of the integrated filter under severe operating conditions, this article selects 20%. An excessively large inductance value will reduce the system's dynamic response speed and increase manufacturing costs, while an excessively small inductance value will lead to increased current ripple and exacerbate losses in switching devices. In engineering practice, the fundamental voltage drop of the Linv needs to be controlled within 5% of the rated voltage to achieve a balance between efficiency and performance.

[0071] 2. Grid-side inductance The selection of the grid-side inductor Lgrid needs to be coordinated with the Linv design, and usually follows the principle of proportional allocation, i.e.

[0072] Mode In this context, k is a proportionality coefficient, typically ranging from 0.2 to 0.3; this paper selects 0.29. A smaller Lgrid is beneficial for reducing filter size and cost, but it is necessary to ensure that the total inductance (Linv + Lgrid) meets grid-connected harmonic standards (such as IEEE 519). Furthermore, the resonant frequency fres of the total inductance and filter capacitor Cf must satisfy the following constraints:

[0073] To avoid low-frequency oscillations and high-frequency switching interference, the resonant frequency should meet the following requirements:

[0074]

[0075] Mode In this context, fgrid represents the power grid frequency. This constraint plays a crucial role in suppressing the resonance peak of the LCL filter.

[0076] [Example 4] Material Selection for Filter Capacitors Filter capacitor C f The capacity selection needs to balance reactive power compensation requirements and system stability. Its value can be determined by:

[0077] in Q c The reactive power of the capacitor is generally limited to 3%-5% of the rated power. ω This is the angular frequency of the power grid.

[0078] An excessively large capacitance value will lower the resonant frequency and increase the risk of system instability; therefore, a damping resistor must be used in conjunction. Alternatively, an active damping strategy can be used to suppress resonance. Damping resistor. The value of must satisfy:

[0079] Angular frequency in the formula ω r =2πf res .

[0080] Meanwhile, parasitic parameters such as the equivalent series resistance (ESR) and equivalent series inductance (ESL) of the actual capacitor will significantly affect the high-frequency characteristics, so thin film capacitors with low ESR / ESL should be preferred.

[0081] To ensure system stability, the resonant frequency of the system must be verified.

[0082] In the formula L total The total inductance value satisfies the equation The requirements are 500 Hz < 5.1 kHz < 25 kHz to ensure stable operation of the LCL filter.

[0083] [Example 5] Simulation Analysis of a Three-Phase Equal Flux LCL Filter like Figure 4 The figure shows the three-dimensional dimensions of the three-phase equal flux LCL integrated magnetic core after rounding. This structure is made of amorphous alloy material and consists of three magnetic pillars evenly distributed at 120° intervals and a central triangular yoke, forming a geometrically symmetrical "Y"-shaped structure. The three magnetic pillars are connected to the central yoke to form the flux exchange region. The figure shows the detailed dimensional parameters of one phase magnetic pillar; the other two phase magnetic pillars have identical structures, ensuring the geometric consistency of the three-phase inductance. Each magnetic pillar has two sets of coils wound on it: the upper coil is for the inverter side, and the lower coil is for the grid side. The coil spacing is rationally designed to reduce mutual inductance effects. Three 0.5mm air gaps are provided at the connection between each phase magnetic pillar and the central yoke for precise adjustment of the inductance value and suppression of magnetic saturation.

[0084] The electromagnetic performance advantages of the Y-type equal flux structure proposed in this application are demonstrated by the accurate electromagnetic field model established using Ansys Maxwell three-dimensional finite element analysis software. The simulation setup employs tetrahedral mesh generation (minimum mesh size 0.2 mm) and utilizes a nonlinear transient solver to capture eddy current effects and hysteresis characteristics. The control group uses the currently mainstream EIE-type three-phase magnetic integrated structure. Both models maintain consistent inverter-side and grid-side winding column dimensions; the main differences lie in the yoke layout and air gap distribution.

[0085] [Example 6] Performance Analysis of a Three-Phase Equal Flux LCL Magnetic Integrated Filter Three different LCL filter designs were used as parallel comparisons: a traditional discrete LCL filter, the Y-type equal-flux core integrated LCL filter proposed in this paper, and an LCL filter using a traditional E-type integrated core. Two of the integrated cores used the same core material (amorphous alloy) and winding configuration, with ceramic sheet pads used in the air gap region. In terms of size, the discrete filter structure is relatively large, while both integrated LCL filters achieve structural compactness through core integration design.

[0086] like Figure 5 As shown in the experiment, the comparison test of weight and volume shows that, compared with discrete filters, the optimized E-type integrated magnetic core filter reduces weight and volume by about 22% and 12% respectively, while the Y-type constant flux magnetic core scheme reduces weight and volume by about 33% and 24% respectively. It not only achieves the goal of significant weight and volume reduction, but its symmetrical structure also provides a more ideal design basis for subsequent system integration and high power density applications.

[0087] like Figure 6 As shown, further, the power curves under light load, medium load and rated load conditions were measured using a power analyzer. Based on the experimental test data of the three filter structures, the efficiency of Y-type equal flux integrated core, E-type magnetic integrated core and traditional discrete LCL filter under different power levels is compared and analyzed below.

[0088] Experimental results show that under light load conditions (360W, approximately 20% of rated power), the efficiency of the Y-type constant flux structure is 94.22%, the E-type integrated structure is 93.71%, and the discrete structure is the lowest at 93.41%. When the power is increased to 900W (50% of rated power), the efficiency of all three structures improves significantly: the Y-type constant flux structure reaches 95.88%, the E-type integrated structure reaches 95.32%, and the discrete structure reaches 94.34%. Under 1800W (rated power) conditions, the efficiency of the Y-type structure reaches a peak of 96.5%, the E-type structure reaches 96.1%, and the discrete structure reaches 94.9%.

[0089] Comparative experimental data shows that the Y-type flux-equalizing structure maintains the highest efficiency across the entire load range, exceeding the discrete structure by 1.6 percentage points at rated power and the E-type structure by 0.4 percentage points. The Y-type structure not only leads in absolute efficiency but also exhibits a steeper efficiency curve, indicating a more significant efficiency improvement in the low-to-medium load range. This is of great importance for power electronic systems that frequently operate under partial loads.

[0090] Both integrated magnetic core designs exhibit significantly higher efficiency than discrete components at the rated power point (1800W). This difference is primarily attributed to the amorphous alloy material structure used in the integrated magnetic cores. The amorphous alloy core, with its unique structure and high resistivity, significantly reduces losses in the mid-to-high frequency range. Combined with the integrated design of Y-type and other flux structures, it achieves uniform flux distribution and suppression of local saturation, resulting in a substantial improvement in overall efficiency compared to traditional discrete components.

[0091] For three-phase LCL filters, the new equal flux integrated inductor achieves a 1.6% efficiency improvement. Considering the long-term operation characteristics of power electronic systems and the cumulative efficiency effect of multi-stage power conversion, this improvement will bring significant energy savings and reduced heat dissipation burden to practical applications, thereby improving the reliability and service life of the system.

[0092] The performance advantages of the Y-type three-phase equal flux LCL magnetic integrated filter were comprehensively evaluated. Simulation results show that the proposed Y-type equal flux structure not only achieves high consistency in the three-phase inductance values ​​but also makes the flux distribution more uniform, avoiding local saturation. In terms of experimental verification, compared with traditional discrete structures and E-type integrated structures, the Y-type magnetic integrated filter reduces weight and volume by 33% and 24%, respectively, while maintaining lower harmonic distortion and higher system efficiency. Closed-loop control experiments further confirm the excellent dynamic response characteristics of this structure under sudden load changes; even under a 5% overload condition, the output current THD remains at a low level of 1.85%. The comprehensive test results demonstrate that the proposed three-phase LCL magnetic integrated scheme based on equal flux technology achieves the expected design goals in terms of overall performance, stability, and dynamic characteristics, providing a reliable technical solution for high power density grid-connected inverter systems.

[0093] In the embodiments provided by this invention, it should be understood that the disclosed apparatus / terminal devices and methods can be implemented in other ways. For example, the apparatus / terminal device embodiments described above are merely illustrative. For instance, the division of the above modules or units is merely a logical functional division, and in actual implementation, it can be divided in other ways. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed.

[0094] If the integrated modules / units described above are implemented as software functional units and sold or used as independent products, they can be stored in a computer storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. This computer program can be stored in a computer storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer-readable medium may include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc. It should be noted that the content included in the computer storage medium may be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction.

[0095] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions are not in essence a departure from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A magnetic integration device for a three-phase LCL grid-connected inverter based on equal magnetic flux, characterized in that, include: Y-type constant flux magnetic core body, inverter-side winding, grid-side winding.

2. The magnetic integration device for a three-phase LCL grid-connected inverter based on equal magnetic flux as described in claim 1, characterized in that, The Y-type constant flux magnetic core body includes: three magnetic pillars and a central triangular magnet collector. The three magnetic pillars are symmetrically distributed at 120° with the geometric center of the central triangular magnet collector as the origin.

3. The magnetic integration device for a three-phase LCL grid-connected inverter based on equal magnetic flux as described in claim 2, characterized in that, The inverter-side winding and the grid-side winding are respectively wound with conductors on the upper and lower sections of each magnetic column, and the winding directions of the conductors of the inverter-side winding and the grid-side winding on the same magnetic column are opposite.

4. The magnetic integration device for a three-phase LCL grid-connected inverter based on equal magnetic flux as described in claim 3, characterized in that, The total number of turns of the inverter-side winding The total number of turns of the grid-side winding satisfy The value of K ranges from 0.2 to 0.

3.

5. The magnetic integration device for a three-phase LCL grid-connected inverter based on equal magnetic flux as described in claim 2, characterized in that, An air gap is provided at the connection between each magnetic column and the central triangular magnet collector. The air gap is made of ceramic sheet pad, and there are two air gaps at the connection between each magnetic column and the central triangular magnet collector. The air gaps are located at the upper and lower ends of the magnetic column, and the length of the air gap is 0.3-3.0mm.

6. The magnetic integration device for a three-phase LCL grid-connected inverter based on equal magnetic flux as described in claim 2, characterized in that, The central triangular magnet collector has an equilateral triangular structure, and the side length of the central triangular magnet collector is equal to the side length of the cross-section of the magnetic column, which has a rectangular cross-section.

7. The magnetic integration device for a three-phase LCL grid-connected inverter based on equal magnetic flux as described in claim 2, characterized in that, The Y-type constant flux magnetic core is made of amorphous alloy or nanocrystalline alloy material, and the inverter-side winding and the grid-side winding are made of copper or aluminum conductors.

8. The magnetic integration device for a three-phase LCL grid-connected inverter based on equal magnetic flux as described in claim 2, characterized in that, The number of lateral layers of the inverter-side winding Number of turns per layer in the longitudinal direction satisfy The number of transverse layers of the grid-side winding Number of turns per layer in the longitudinal direction satisfy ;in , The value range is 1-10 layers. , The value range is 1-100 turns.

9. The magnetic integration device for a three-phase LCL grid-connected inverter based on equal magnetic flux as described in claims 1-8, characterized in that, The three-phase LCL grid-connected inverter magnetic integration device also includes a filter capacitor and a damping resistor.

10. The magnetic integration device for a three-phase LCL grid-connected inverter based on equal magnetic flux as described in claim 9, characterized in that, The filter capacitor is connected in a star configuration, with one end connected to the output terminal of the power grid winding and the other end grounded through a damping resistor.

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