A method and system for predicting the shielding effectiveness of a cable against crosstalk

Abstract

The application discloses a kind of shielded cable crosstalk suppression performance prediction method and system, belong to power electronics electromagnetic interference field.The method includes: obtaining the common-mode interference source and common-mode source impedance of inverter power supply, the common-mode electromagnetic interference equivalent circuit of inverter power supply is established, and the common-mode crosstalk model of shielded cable in inverter power supply system is constructed in combination with cable bundle equivalent circuit;Using common coupling impedance equivalence instead of the distributed parameter between cables, and updating the common-mode crosstalk model based on this common coupling impedance, obtain the shielded cable crosstalk suppression performance prediction model based on shielding structure and electromagnetic parameter;Obtain the common-mode interference current on the equivalent circuit current power cable i p , in combination with preset shielding structure and electromagnetic parameter, the common-mode crosstalk current of shielded cable is predicted by prediction model, and the shielded cable crosstalk suppression performance is evaluated.The influence of different parameters of shielded cable on common-mode crosstalk is quantified, and the shielded cable crosstalk suppression performance accurate prediction is realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of power electronic electromagnetic interference, and more particularly relates to a method and system for predicting the crosstalk suppression performance of a shielded cable. BACKGROUND

[0002] With the continuous development of traffic electrification, motor drive systems composed of inverters have been widely used in the field of transportation. The operation of inverter power supply is based on the principle of pulse width modulation (PWM). This working mode will produce large voltage jump (dv / dt) and current jump (di / dt), and the power electronic electromagnetic interference (EMI) containing rich high-frequency components generated thereby will make the electromagnetic environment inside the transportation equipment worse. The common-mode electromagnetic interference (CM EMI) generated thereby is the main component of the EMI of the inverter. Due to the limitation of narrow space, power cables and signal cables are usually tied together, so that the CM EMI on the power cable is transmitted to the signal cable through near-field coupling between the cables, causing CM cable crosstalk problem. CM cable crosstalk will hinder the effective transmission of communication signals and threaten the normal operation of sensitive equipment. In order to ensure the normal operation of the system, it is necessary to take measures to suppress CM cable crosstalk.

[0003] At present, there are two common methods to suppress cable crosstalk. The first method is to reduce the interference source, such as optimizing the modulation method and increasing the buffer circuit, or constructing a signal source to eliminate crosstalk by the method of linear combination of configuration field (LCCF) to achieve the purpose of suppressing crosstalk. The second method is to change the coupling path of crosstalk, such as increasing the distance between cables to reduce the coupling between cables, or using shielded cables to make the interference flow to a loop with smaller impedance. Among them, shielded cables are widely used as signal cables due to their ease of use. Since the ability of shielded cables to suppress CM cable crosstalk is related to the material and structure of the shielding layer, only by selecting or even designing a shielded cable with appropriate structure and parameters, can the effective suppression of CM cable crosstalk be achieved.

[0004] In order to evaluate the crosstalk suppression performance of the shielded cable, the transfer impedance, the shield attenuation and the shield effectiveness are commonly used to characterize. Among them, the research on the transfer impedance of the shielding layer is the most extensive and comprehensive, which is defined as the ratio of the induced voltage to the current between the outer shielding layer and the inner core wire when the shielding layer flows through the current. The larger the transfer impedance is, the worse the protection performance of the shielding layer is. The shield attenuation is used to characterize the crosstalk suppression performance of the shielding layer at a higher frequency band, which is defined as the ratio of the power before using the shielding layer to the power after using the shielding layer. The larger the shield attenuation value is, the better the crosstalk suppression performance of the shielding layer is. The shield effectiveness is the ratio of the electric field (magnetic field) intensity before using the shielding layer to the electric field (magnetic field) intensity after using the shielding layer, and the larger the value is, the better the crosstalk suppression performance of the shielding layer is characterized. These methods can only indirectly judge the size of the crosstalk after using the shielding layer through the impedance or the field, which is not conducive to the quantitative description of the relationship between the shielding structure and the electromagnetic parameters and the CM cable crosstalk, so it is difficult to achieve precise suppression.

[0005] In practical applications, different types of shielded cables are used in different crosstalk suppression requirements, but in existing research, the crosstalk suppression performance modeling method of the shielded cable cannot directly quantify the relationship between the CM cable crosstalk and the shielding structure and the electromagnetic parameters of the shielded cable, and cannot directly predict and evaluate the crosstalk suppression performance of the shielded cable. At present, the optimization of the crosstalk suppression performance of the shielded cable lacks relevant theoretical guidance, and it is urgent to improve the shielding cable crosstalk suppression performance modeling method which quantifies the relationship between the shielding structure and the electromagnetic parameters and the CM cable crosstalk. SUMMARY

[0006] In view of the defects of the related art, the purpose of the present application is to provide a shielded cable crosstalk suppression performance prediction method and system, which aims to solve the problem that the existing model cannot directly quantify the relationship between the shielding structure and the electromagnetic parameters and the CM cable crosstalk.

[0007] To achieve the above-mentioned purpose, in a first aspect, the present application provides a shielded cable crosstalk suppression performance prediction method, comprising:

[0008] S1, obtaining the common mode interference source and the common mode source impedance of the inverter power supply, establishing the equivalent circuit of the common mode electromagnetic interference of the inverter power supply, and based on the equivalent circuit and the cable bundle equivalent circuit, constructing the common mode crosstalk model of the shielded cable in the inverter power supply system;

[0009] S2, using the common coupling impedance to replace the distributed parameters between the cables, and updating the common mode crosstalk model of the shielded cable based on the common coupling impedance, and the shielded cable crosstalk suppression performance prediction model based on the shielding structure and the electromagnetic parameters;

[0010] S3, obtaining the common mode interference current i p, in combination with a preset shielding structure and electromagnetic parameters of the shielded cable, predicts a frequency spectrum of the common-mode crosstalk current of the shielded cable through the shielded cable crosstalk suppression performance prediction model, and evaluates the crosstalk suppression performance of the shielded cable.

[0011] Optionally, the common-mode interference source is a voltage source V CM ; and the common-mode source impedance is composed of the ground capacitance of the inverter power supply and the parasitic parameters of the filter.

[0012] Optionally, before S2, further comprising:

[0013] When the shielding layer in the cable bundle is double-ended grounded, the relationship between the ability of the shielding layer to suppress inductive coupling and the corner frequency f SH of the shielding layer is as follows:

[0014]

[0015] wherein R SH is the resistance of the shielding layer, and L SH is the self-inductance of the shielding layer.

[0016] When the predicted frequency of the crosstalk suppression performance of the shielded cable is greater than f SH , the ground loop is regarded as an open circuit to simplify the common-mode crosstalk model of the shielded cable.

[0017] Optionally, the shielded cable crosstalk suppression performance prediction model is as follows:

[0018]

[0019] wherein i p is the common-mode interference current on the power cable, is the transfer function of the common-mode interference current i p on the power cable to the common-mode crosstalk current i r on the core wire of the shielded cable, is the common coupling impedance, is the equivalent common-mode impedance of the communication device.

[0020] Optionally, the shielded cable includes a braided shielding layer shielded cable and a tubular shielding layer shielded cable.

[0021] Optionally, the common coupling impedance of the braided shielding layer shielded cable includes a scattering impedance Z d , a braided inductance M b , and a hole inductance M h , and the expression is as follows:

[0022]

[0023] wherein j is an imaginary unit, is the angular frequency, Z d M is related to the shielding structure and electromagnetic parameters, h and M b are all related to the shielding structure.

[0024] Optionally, the common coupling impedance of the tubular shielding layer shielding the cable is:

[0025]

[0026] wherein a is the outer radius, T is the thickness of the shielding layer; δ c is the skin depth of the tubular shielding layer, defined as , μ rc and σ c are the relative permeability and conductivity of the tubular shielding material, respectively.

[0027] Optionally, after S3, further comprising:

[0028] analyzing the importance of different parameters of the shielding cable on the crosstalk current i r , determining the dominant influence parameters in different frequency bands;

[0029] According to the calculated common-mode interference current i p and the corresponding common-mode crosstalk current threshold, the optimization value of the dominant influence parameters of the shielding layer of the shielding cable in different frequency bands is calculated, and the design of the shielding cable is optimized.

[0030] In a second aspect, the present application also provides a shielding cable crosstalk suppression performance prediction system, comprising:

[0031] a crosstalk model construction module, configured to obtain a common-mode interference source and a common-mode source impedance of an inverter power supply, establish an equivalent circuit of common-mode electromagnetic interference of the inverter power supply, and construct a common-mode crosstalk model of the shielding cable in the inverter power supply system based on the equivalent circuit and an equivalent circuit of the cable bundle;

[0032] a suppression performance prediction model construction module, configured to replace the distributed parameters between the cables with a common coupling impedance, and update the common-mode crosstalk model of the shielding cable based on the common coupling impedance, to obtain a shielding cable crosstalk suppression performance prediction model based on shielding structure and electromagnetic parameters;

[0033] a prediction and evaluation module, configured to obtain a common-mode interference current i p on the current power cable of the equivalent circuit, combine a preset shielding structure and electromagnetic parameters of the shielding cable, predict the common-mode crosstalk current of the shielding cable through the shielding cable crosstalk suppression performance prediction model, and evaluate the crosstalk suppression performance of the shielding cable.

[0034] Compared with the prior art, the above technical scheme conceived by the present application can achieve the following beneficial effects: the prediction method for the shielding cable crosstalk suppression performance provided by the present application creates conditions for subsequent direct characterization of the relationship between the shielding structure and electromagnetic parameters and the CM cable crosstalk by using the common coupling impedance to equivalently represent the total impedance of the distributed parameters between cables, which simplifies the complexity of the model compared with indirectly representing the shielding cable crosstalk suppression performance in the form of transfer impedance or shielding attenuation; further based on the common coupling impedance, a circuit model for the shielding cable crosstalk suppression performance considering the shielding structure and electromagnetic parameters is proposed, thereby deducing an explicit expression of the shielding structure and electromagnetic parameters and the common mode cable crosstalk, and quantifying the influence of different parameters of the shielding cable on the common mode cable crosstalk. The present application realizes accurate prediction of the shielding cable crosstalk suppression performance, and can also accurately and effectively guide the optimization design of the shielding structure and electromagnetic parameters of the shielding cable. The modeling method proposed by the present application can not only be used in inverter power supply systems, but also be applied to different types of power electronic systems such as rectifier power supply systems and direct current power supply systems, and has important practical popularization value. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 A flowchart of a prediction method for the shielding cable crosstalk suppression performance provided by the present application embodiment is shown in the figure.

[0036] Figure 2 The CM EMI equivalent circuit of the inverter power supply.

[0037] Figure 3 The equivalent circuit model of the cable bundle containing the shielding layer.

[0038] Figure 4 The common mode cable crosstalk simplified prediction model of the inverter power supply system.

[0039] Figure 5 The common coupling impedance circuit model of the common mode cable crosstalk; wherein (a) is the common mode cable crosstalk simplified prediction model with the protective ground disconnected; (b) is the common coupling impedance circuit model obtained by replacing the distributed parameters with the common coupling impedance.

[0040] Figure 6 The characteristic structure diagram of the braided shielding layer.

[0041] Figure 7 The characteristic structure diagram of the tubular shielding layer; wherein (a) is the side view of the tubular shielding layer; (b) is the front view of the tubular shielding layer.

[0042] Figure 8The common coupling impedance circuit models are for different shielding types; where (a) is the common coupling impedance circuit model with a braided shielding layer; and (b) is the common coupling impedance circuit model with a braided shielding layer.

[0043] Figure 9 This is a comparison between the model and the measured crosstalk of CM cables. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0045] Example 1

[0046] Near-field coupling occurs due to the interaction of distributed parameters between power cables and signal cables. EMI from the power cable couples to the signal cable, forming common-mode (CM) cable crosstalk, which affects signal integrity and can even threaten the reliable operation of power electronic systems. Shielded cables are typically used to suppress CM cable crosstalk. However, existing modeling methods for shielded cable crosstalk suppression performance cannot directly quantify the relationship between CM cable crosstalk and the shielding structure and electromagnetic parameters of the shielded cable, making it difficult to directly predict and evaluate the crosstalk suppression performance of shielded cables.

[0047] To address this issue, a novel method for modeling the crosstalk suppression performance of shielded cables, considering both the shielding structure and electromagnetic parameters, is proposed based on the common-mode cable crosstalk model of shielded cables in inverter power systems.

[0048] like Figure 1 As shown, this embodiment of the invention provides a method for predicting the crosstalk suppression performance of shielded cables, including:

[0049] S1. Obtain the common-mode interference source and common-mode source impedance of the inverter power supply, establish the common-mode electromagnetic interference equivalent circuit of the inverter power supply, and construct the common-mode crosstalk model of the shielded cable in the inverter power supply system based on the equivalent circuit and the cable bundle equivalent circuit.

[0050] S2. The common coupling impedance is used to replace the distributed parameters between cables, and the common-mode crosstalk model of the shielded cable is updated based on the common coupling impedance to obtain a prediction model of the crosstalk suppression performance of the shielded cable based on the shielding structure and electromagnetic parameters.

[0051] S3. Obtain the common-mode interference current i on the current power cable of the equivalent circuit. p, in combination with a preset shielding structure and electromagnetic parameter of the shielded cable, predicting a frequency spectrum of the common-mode crosstalk current of the shielded cable through the shielded cable crosstalk suppression performance prediction model, and evaluating the crosstalk suppression performance of the shielded cable.

[0052] The common-mode interference source and source impedance of the inverter power supply are obtained in a manner of actual measurement through an impedance analyzer and an oscilloscope, so as to establish an equivalent circuit of the common-mode electromagnetic interference of the inverter power supply. A cable bundle simulation model is built by using CST cable studio, which includes two single-core power cables (unshielded cables), one double-core signal cable (shielded cable) and a reference conductor, so as to obtain the distributed parameters between the cables. An initial model of the CM cable crosstalk prediction of the shielded cable in the inverter power supply system is established, and then a shielded cable crosstalk suppression performance circuit model based on the shielding structure and electromagnetic parameter is derived. The common coupling impedance of different types of shielded cables is obtained through mathematical expression calculation or actual measurement, and finally the explicit expression of the shielding structure and electromagnetic parameter and the CM cable crosstalk is obtained, that is, the final shielded cable crosstalk suppression performance prediction model.

[0053] The above scheme specifically includes the following steps:

[0054] (1) Establishing a common-mode crosstalk model of a shielded cable in an inverter power supply

[0055] The equivalent circuit of the common-mode electromagnetic interference of the inverter power supply is shown in Figure 2 The high-speed switching action of the power switch causes a large voltage jump dv / dt at the midpoint of the bridge arm, and a common-mode interference current i p is induced through the parasitic capacitance of the power module. Part of the current flows to the AC measurement through the AC cable and the filter, and flows back to the ground plane through the parasitic capacitance of the load; the other part flows to the line impedance stabilization network (LISN) through the DC cable, and finally flows back to the ground loop. The LISN functions to isolate the interference introduced by the DC power supply, and simulates the impedance of the power grid side to provide a reference for the measurement of the common-mode interference of the target device.

[0056] Based on the substitution theorem, the common-mode interference source is a voltage source V CM , as shown in formula (1), wherein U a , U b and U c are the voltages across the lower tubes of phase A, phase B and phase C, respectively. The common-mode source impedance Z CM is composed of the ground capacitance of the inverter power supply and the parasitic parameters of the filter, as shown in formula (2), wherein Z BUS is the 3C C of the upper bridge arm switch tube and the 3CE the total impedance of the AC filter inductance and its parasitic parameters, Z O is 3C O the total impedance of the AC load impedance and its ground capacitance. ACind load

[0057] (1)

[0058] (2)

[0059] Based on the multi-conductor transmission line (MTL) theory, the positive and negative lines, shielding layer of the shielded cable and the positive and negative lines of the power cable are numbered as 1~5 (i,j∈[1,5]) for the first time, and the distribution parameters between the cables are obtained by using CST cablestudio, and the corresponding cable bundle equivalent circuit model can be established, as shown in Figure 3 ii and C ii are the self-inductance and self-capacitance of each conductor, M ij(i≠j) and C ij(i≠j) are the mutual inductance and mutual capacitance between each conductor, and Z pe is the impedance of the ground plane.

[0060] Since the CM cable crosstalk mainly occurs between the power cable and the signal cable, and the CM EMI on the positive and negative lines of the power cable is the same, the CM cable crosstalk on the positive and negative lines of the signal cable is also the same, so the positive and negative lines of the power cable can be combined and equivalent to a conductor, and the positive and negative lines of the signal cable are also the same. Therefore, on the basis of the equivalent circuit of the common mode electromagnetic interference of the inverter power supply and the cable bundle equivalent circuit, the simplified model of the CM cable crosstalk in the inverter power supply system can be obtained, as shown in Figure 4 LISN / 2 is half of the LISN impedance, Z com_device is the equivalent common mode impedance of the communication equipment. L 1,1 , L 2,1 , L 3,1 are the equivalent self-inductance of the power cable core, the shielded cable core and the shielding layer, C 12,2 and M 12,2 are the mutual capacitance and mutual inductance between the power cable and the shielding layer, which are equal to the parallel values of the related parameters. M 23,2 is the equivalent mutual inductance between the shielding layer and the shielded cable core, which is equal to the parallel value of M 13 and M 23 , as shown in equation (3).

[0061] (3)​​​​

[0062] (2) Prediction model for crosstalk suppression performance of shielded cables based on shielding structure and electromagnetic parameters

[0063] Before building the predictive model, the following is also included:

[0064] When the shielding layer in the cable bundle is grounded at both ends, its ability to suppress inductive coupling is related to its inflection point frequency f. SH Related to the inflection point frequency f SH expression

[0065] As shown in equation (4):

[0066] (4)

[0067] Among them, R SH L is the resistance of the shielding layer. SH The self-inductance of the shielding layer;

[0068] When the predicted frequency of the crosstalk suppression performance of the shielded cable is greater than f SH At this time, the impedance provided by the shielding layer for the interference path is smaller than the ground loop impedance, resulting in a lower common-mode interference current i on the power cable. p The common-mode crosstalk current in the shielded cable core also flows back through the shielding layer, thus simplifying the common-mode crosstalk model of the shielded cable by treating the ground loop as an open circuit.

[0069] The electromagnetic emission and susceptibility requirements and measurements for military equipment and subsystems, specifically the power line conducted emission test item CE102, specifies electromagnetic standards for power lines in the 10kHz~10MHz frequency band. Crosstalk in CM cables focuses on frequencies above 10kHz, while the typical value of the inflection point frequency of shielded cables is around 3kHz. Therefore, the analysis of crosstalk frequencies mainly focuses on frequencies above f... SH The frequency band. When the frequency is greater than f SH At this time, the shielding layer can provide an interference flow path with a smaller impedance than the ground loop, thus reducing the common-mode interference current i on the power cable. p The current mainly returns through the shielding layer, not the ground loop, and the same applies to the CM cable crosstalk current on the signal cable. Therefore, the current on the ground loop is almost zero, and the ground loop can be considered an open circuit. The simplified CM cable crosstalk prediction model is as follows: Figure 5 As shown in (a). To more conveniently describe the characteristics of crosstalk in CM cables, the relationship between shielding structure and electromagnetic parameters and CM cable crosstalk is established. A common coupling impedance is proposed to equivalently replace the distributed parameters between cables. The distributed parameters between cables refer to the distributed parameters among the power cable core, the shielded cable core, and the shielding layer, which is expressed as: Figure 5 L in (a) 1,1 L2,1 , L 3,1 , M 12,1 , M 23,2 and C 12,2 total impedance, thus establishing a CM cable crosstalk common coupling impedance prediction model as shown in (b) of FIG. 6. Figure 5 The model is equivalent to the circuit model for measuring the shielding layer impedance, so the common coupling impedance is equal to the impedance of the shielding layer, and the impedance of the shielding layer is related to the structure and electromagnetic parameters of the shielding layer.

[0070] Further, the common coupling impedance can be mathematically expressed by the shielding structure and electromagnetic parameters, the common mode crosstalk model of the shielded cable is updated based on the common coupling impedance, and the circuit derivation can obtain a shielded cable crosstalk suppression performance prediction model related to the shielding structure and electromagnetic parameters.

[0071] The shielded cable crosstalk suppression performance prediction model is:

[0072]

[0073] wherein i p is the common mode interference current on the power cable, is the transfer function of the common mode interference current i p on the power cable to the common mode crosstalk current i r on the core of the shielded cable, is the common coupling impedance, is the equivalent common mode impedance of the communication equipment.

[0074] Further, the shielding structure and electromagnetic parameters are characteristic parameters belonging to the shielding layer of the shielded cable and are independent of each other, but the common coupling impedance can be mathematically expressed by the shielding structure and electromagnetic parameters, so the shielded cable crosstalk suppression performance prediction model constructed can intuitively express the relationship between the shielding structure and electromagnetic parameters and the common mode crosstalk.

[0075] (3) Common coupling impedance calculation for different types of shielded cables

[0076] The shielded cable includes a braided shielding layer shielded cable and a tubular shielding layer shielded cable, wherein the tubular shielding layer can be divided into two types of shielded steel pipes and shielded cables.

[0077] 1. For braided shielding layer shielded cable

[0078] The characteristic structure diagram of the braided shielding layer is as shown in FIG. 8. Figure 6As shown, the woven shield layer can be seen to be related to five structural parameters: 1) inner diameter D; 2) number of woven bands C; 3) number of woven filaments in one woven band N; 4) woven filament diameter d; 5) woven angle a. The common coupling impedance of the woven shield layer includes three parts: the first part is the scattering impedance Z d , which is used to characterize the diffusion ability of the electromagnetic field in the shield layer; the second part is the woven inductance M b , which characterizes the ability of the magnetic field coupling between the inner and outer layers of the woven bands; the third part is the hole inductance M h , which characterizes the degree of direct leakage of the electromagnetic field through the small hole. Z d is related to the shielding structure and electromagnetic parameters, M h and M b are related to the shielding structure. The expressions are as follows:

[0079] (5)

[0080] (6)

[0081] (7)

[0082] wherein μ0 is the magnetic permeability in vacuum. E(e) and K(e) are the first and second complete elliptic integrals, and K is the woven coverage. δ b , e, b and h are the skin depth of the woven layer, the eccentricity of the diamond-shaped hole, the distance between two adjacent woven bands and the distance between two intersecting woven bands, respectively, which are defined as:

[0083] (8)

[0084] (9)

[0085] (10)

[0086] (11)

[0087] μ rb and σ b in equation (8) are the relative magnetic permeability and electrical conductivity of the woven shielding material, respectively, and f is the working frequency.

[0088] A, B and D m in equation (6) are defined as

[0089] (12)

[0090] (13)

[0091] (14)

[0092] where v is the number of holes per unit length in the woven layer.

[0093] Optionally, the common coupling impedance of the shielding cable shielded by the woven shielding layer includes scattering impedance Z d , woven inductance M b and hole inductance M h , and the expression is:

[0094] (15)

[0095] where j is an imaginary unit, is an angular frequency.

[0096] 2. For a tubular shielding layer shielding cable

[0097] The characteristic diagram of the tubular shielding layer is shown in Figure 7 . As shown in Figure 7 , the tubular shielding layer structure is related to two parameters: 1) outer radius a; 2) shielding layer thickness T; since the tubular shielding layer is a complete shielding layer, there is no hole, so its common coupling impedance is only part of the composition, which is used to characterize the ability to hinder the diffusion of external electromagnetic fields to the inside.

[0098] The common coupling impedance of the tubular shielding layer shielding cable is:

[0099] (16)

[0100] where δ c is the skin depth of the tubular shielding layer, and the expression is:

[0101] (17)

[0102] where μ rc and σ c are the relative permeability and conductivity of the tubular shielding material, respectively.

[0103] In this embodiment, the common coupling impedance of the shielding layer is obtained by mathematical formula derivation method, and in another embodiment, it can also be obtained by injection line method.

[0104] (4) Constructing a shielding cable crosstalk suppression performance prediction model based on shielding structure and electromagnetic parameters

[0105] On the basis of obtaining the common coupling impedance circuit model of the shielding cable common mode crosstalk and the common coupling impedance of the shielding layer, the common mode crosstalk common coupling impedance circuit model of the shielding cable using different shielding layers can be obtained, as shown in Figure 8 . Figure 8where i rb is the CM cable crosstalk current on the shielded cable core wire. Similarly, the transfer function from i p to i p is rb

[0106] (18)

[0107] Thus, i rb can be calculated by equation (19).

[0108] (19)

[0109] Figure 8 where i rc is the CM cable crosstalk current on the shielded cable core wire. Similarly, the transfer function from i p to i rc is

[0110] (20)

[0111] Thus, i rc can be calculated by equation (21).

[0112] (21)

[0113] Through equations (19) and (21), the modeling of the crosstalk suppression performance of the shielded cable with different types of shielding layers considering the shielding structure and electromagnetic parameters can be achieved.

[0114] (5) Prediction, evaluation and optimization design of the crosstalk suppression performance of the shielded cable

[0115] The CM interference current i p is obtained through the CM electromagnetic interference model of the inverter power supply. Given the shielding structure and electromagnetic parameters of the shielded cable, the CM crosstalk current i r of the shielded cable core wire after using the shielded cable can be obtained according to equation (19) or equation (21), so as to realize the accurate prediction and evaluation of the crosstalk suppression performance of the shielded cable.

[0116] For example, the interference current i p on the current power cable of the equivalent circuit is obtained., the prediction results of the common-mode crosstalk current of the braided shielding layer shielded cable and the tubular shielding layer shielded cable are calculated according to formula (19) and formula (21) respectively, the crosstalk suppression performance of the shielded cable with different shielding structures is evaluated by comparing the values, and the shielded cable with the better shielding structure is selected.

[0117] For a determined shielding layer structure of the shielded cable, the spectrum diagram of the crosstalk current of the shielded cable is predicted for the shielding material with different electromagnetic parameters through the shielding cable crosstalk suppression performance prediction model, so as to evaluate the crosstalk suppression performance and select the optimal electromagnetic parameter.

[0118] Optionally, after S3, further comprising:

[0119] The importance of different parameters of the shielded cable on the crosstalk current i r is analyzed, and the dominant influence parameters in different frequency bands are determined.

[0120] According to the calculated crosstalk interference current i p and the corresponding common-mode crosstalk current threshold, the optimization value of the dominant influence parameter of the shielding layer of the shielded cable in different frequency bands is calculated, and the design of the shielded cable is optimized.

[0121] Specifically, based on formula (19) and formula (21), the influence of different parameters on the common-mode crosstalk current i r is analyzed, and the dominant influence parameters in different frequency bands are determined. For the braided shielded cable, the electromagnetic parameter is the dominant factor in the low frequency band, and the structural parameter is the dominant factor in the high frequency band; for the tubular shielded cable, the structure and electromagnetic parameter are the dominant factors in the whole frequency band. In the case that the current threshold of the common-mode crosstalk current i r and the common-mode interference current i p are known, the optimization value of the parameter of the shielding layer of the shielded cable in different frequency bands is calculated according to formula (19) and formula (21), so as to realize the optimization of the design of the shielded cable.

[0122] On the basis of the above embodiment, the model is verified, and in an inverter power supply system, the key parameters of the inverter power supply are as shown in Table 1. When the tubular shielded cable is used, the model prediction of the crosstalk suppression performance of the tubular shielded cable is compared with the actual measurement result, as shown in Figure 9 , the prediction error in the target frequency band is less than 6dB, and the precise modeling of the crosstalk suppression performance of the shielded cable is realized. In addition, through this model, the relationship between the shielding structure and the electromagnetic parameter and the CM cable crosstalk is quantified, so as to directly represent the influence of the shielding structure and the electromagnetic parameter on the crosstalk suppression performance of the shielded cable, provide theoretical and model guidance for the subsequent precise optimization of the crosstalk suppression performance of the shielded cable, improve the design efficiency and reduce the number of iterative designs, and effectively reduce the loss of manpower and material resources.

[0123]

[0124] In the embodiment of the present application, by adopting the common coupling impedance equivalent to the total impedance of the distributed parameters between the cables, conditions are created for subsequent direct characterization of the relationship between the shielding structure and electromagnetic parameters and the CM cable crosstalk, and compared with the indirect characterization of the shielding cable crosstalk suppression performance in the form of transfer impedance or shielding attenuation, the common coupling impedance simplifies the complexity of the model; further based on the common coupling impedance, a circuit model of the shielding cable crosstalk suppression performance considering the shielding structure and electromagnetic parameters is proposed, thereby deducing the explicit expression of the shielding structure and electromagnetic parameters and the CM cable crosstalk, and quantifying the influence of different parameters of the shielding cable on the CM cable crosstalk. The accurate prediction of the shielding cable crosstalk suppression performance is realized, and the optimization design of the shielding structure and electromagnetic parameters of the shielding cable can also be accurately and effectively guided.

[0125] Embodiment two

[0126] The present application also provides a shielding cable crosstalk suppression performance prediction system, comprising:

[0127] A crosstalk model construction module is configured to obtain the common-mode interference source and common-mode source impedance of the inverter power supply, establish an equivalent circuit of the common-mode electromagnetic interference of the inverter power supply, and construct a common-mode crosstalk model of the shielding cable in the inverter power supply system based on the equivalent circuit and the cable bundle equivalent circuit.

[0128] An suppression performance prediction model construction module is configured to replace the distributed parameters between the cables with the common coupling impedance equivalent, and update the common-mode crosstalk model of the shielding cable based on the common coupling impedance, to obtain a shielding cable crosstalk suppression performance prediction model based on the shielding structure and electromagnetic parameters.

[0129] A prediction and evaluation module is configured to obtain the common-mode interference current i p on the power cable of the equivalent circuit, combine the preset shielding structure and electromagnetic parameters of the shielding cable, predict the common-mode crosstalk current of the shielding cable through the shielding cable crosstalk suppression performance prediction model, and evaluate the crosstalk suppression performance of the shielding cable.

[0130] The shielding cable crosstalk suppression performance prediction system provided by the embodiment of the present application is used to execute the shielding cable crosstalk suppression performance prediction method in embodiment one, and has the same or similar beneficial effects.

[0131] Those skilled in the art will readily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application, and any modifications, equivalent replacements and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for predicting the crosstalk suppression performance of shielded cables, characterized in that, include: S1. Obtain the common-mode interference source and common-mode source impedance of the inverter power supply, establish the common-mode electromagnetic interference equivalent circuit of the inverter power supply, and construct the common-mode crosstalk model of the shielded cable in the inverter power supply system based on the equivalent circuit and the cable bundle equivalent circuit. S2. The common coupling impedance is used to replace the distributed parameters between cables, and the common-mode crosstalk model of the shielded cable is updated based on the common coupling impedance to obtain a prediction model of the crosstalk suppression performance of the shielded cable based on the shielding structure and electromagnetic parameters; wherein, the distributed parameters between cables refer to the distributed parameters between the power cable core, the shielded cable core, and the shielding layer. S3. Obtain the common-mode interference current on the current power cable of the equivalent circuit. i p Based on the preset shielding structure and electromagnetic parameters of the shielded cable, the crosstalk suppression performance prediction model of the shielded cable is used to predict the spectrum of the crosstalk current of the shielded cable and evaluate the crosstalk suppression performance of the shielded cable. The prediction model for the crosstalk suppression performance of the shielded cable is as follows: in, i p This refers to the common-mode interference current on the power cable. Common-mode interference current on power cables i p Common-mode crosstalk current to the shielded cable core i r The transfer function, For common coupling impedance, This is the equivalent common-mode impedance of the communication equipment.

2. The method as described in claim 1, characterized in that, The common-mode interference source is a voltage source. V CM The common-mode source impedance is composed of the inverter power supply's capacitance to ground and the parasitic parameters of the filter.

3. The method as described in claim 1, characterized in that, Before S2, it also includes: When the shielding layer in the cable bundle is grounded at both ends, its ability to suppress inductive coupling is related to its inflection point frequency. f SH The relation is: in, R SH The resistance of the shielding layer, L SH The self-inductance of the shielding layer; When the predicted frequency of the crosstalk suppression performance of the shielded cable is greater than f SH In this case, the common-mode crosstalk model of the shielded cable is simplified by treating the ground loop as an open circuit.

4. The method as described in claim 1, characterized in that, The shielded cables include braided shielded cables and tubular shielded cables.

5. The method as described in claim 4, characterized in that, The common coupling impedance of the braided shielded cable includes the scattering impedance. Z d Braided inductors M b and hole inductor M h The expression is: in, j The imaginary unit, Angular frequency, Z d It is related to the shielding structure and electromagnetic parameters. M h and M b All of these are related to the shielding structure.

6. The method as described in claim 4, characterized in that, The common coupling impedance of the tubular shielded cable is: in, a The outer radius is T The thickness of the shielding layer; δ c The skin depth of the tubular shielding layer is defined as follows: , μ rc and σ c These represent the relative magnetic permeability and electrical conductivity of the tubular shielding material, respectively.

7. The method as described in claim 1, characterized in that, Following S3, it also includes: Analyze the impact of different parameters of the shielded cable on common-mode crosstalk current. i r The importance of determining the dominant influencing parameters in different frequency bands; Based on the calculated common-mode interference current i p By calculating the optimal values ​​of the dominant influencing parameters of the shielded cable shielding layer in different frequency bands, and with the corresponding common-mode crosstalk current threshold, the design of the shielded cable can be optimized.

8. A prediction system for the crosstalk suppression performance of shielded cables, characterized in that, include: The crosstalk model construction module is used to obtain the common-mode interference source and common-mode source impedance of the inverter power supply, establish the common-mode electromagnetic interference equivalent circuit of the inverter power supply, and construct the common-mode crosstalk model of the shielded cable in the inverter power supply system based on the equivalent circuit and the cable bundle equivalent circuit. The suppression performance prediction model construction module is used to replace the distributed parameters between cables with the equivalent common coupling impedance, and update the common-mode crosstalk model of the shielded cable based on the common coupling impedance to obtain the shielded cable crosstalk suppression performance prediction model based on the shielding structure and electromagnetic parameters; wherein, the distributed parameters between cables refer to the distributed parameters between the power cable core, the shielded cable core, and the shielding layer; The prediction and evaluation module is used to obtain the common-mode interference current on the current power cable of the equivalent circuit. i p Based on the preset shielding structure and electromagnetic parameters of the shielded cable, the common-mode crosstalk current of the shielded cable is predicted by the crosstalk suppression performance prediction model of the shielded cable, and the crosstalk suppression performance of the shielded cable is evaluated. The prediction model for the crosstalk suppression performance of the shielded cable is as follows: in, i p This refers to the common-mode interference current on the power cable. Common-mode interference current on power cables i p Common-mode crosstalk current to the shielded cable core i r The transfer function, For common coupling impedance, This is the equivalent common-mode impedance of the communication equipment.

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