A method for researching frequency selectivity of carrier communication channel based on impedance analysis

Abstract

The application discloses a kind of carrier communication channel frequency selective research methods based on impedance analysis, and its technical scheme includes: step 1, power topology information survey and record such as transformer station line length, branch quantity, meter box user number range;Step 2, according to transformer station transformer specification, determine transformer equivalent impedance model;Step 3, according to the user number range information of transformer station meter box, the user load impedance model of each meter box position is randomly exported;Step 4, based on the impedance differential model of transmission line that actual transformer station transmission line parameter establishes;Step 5, the transformer equivalent impedance model of transformer station, user load impedance model, transmission line impedance differential model is substituted into two-port network transmission matrix model, and the channel frequency selection characteristic in 0.7MHz-12MHz frequency band between any two nodes of transformer station is calculated, for predicting the frequency selection characteristic between any two nodes of transformer station, can solve the problem that frequency selection characteristic between two nodes cannot be obtained by acquisition equipment due to noise or excessive attenuation.

Description

Technical Field

[0001] This invention relates to the field of low-voltage power line carrier communication technology, and in particular to a method for studying the frequency selectivity of carrier communication channels based on impedance analysis. Background Technology

[0002] HPLC communication systems utilize the 0.7MHz-12MHz frequency band for communication and are a broadband power line carrier technology for data transmission over low-voltage power lines, which has become an indispensable part of the power industry. However, due to the random connection and disconnection of power loads in low-voltage distribution networks, the complexity and diversity of electrical appliances, and impedance mismatch, the transmission environment of HPLC communication systems is not ideal, exhibiting strong frequency selectivity and time-varying characteristics. Therefore, for the further development of power line carrier communication technology, establishing an accurate power channel model to analyze the transmission characteristics of the carrier communication channel is crucial.

[0003] Currently, there are two main categories of commonly used methods for establishing channel models: top-down and bottom-up methods. The top-down method originates from multipath propagation based on transmission line theory (TL) theory, first mentioned in 1998. According to this model, the transfer function can be unified into a superposition of multiple paths, and this model can be used to fit the measured channel transfer function. However, if the detailed information of the power line link (such as topology and load) is known, the bottom-up method can be used to model it and obtain a closed-form expression for the transfer function. The bottom-up method is based on transmission line theory and applies a two-port network transmission matrix model. It can treat the power line network as a cascade of multiple two-port networks, obtaining accurate power line channel frequency selectivity characteristics. Summary of the Invention

[0004] This invention proposes a method for studying the frequency selectivity of carrier communication channels based on impedance analysis. This method clarifies that a power distribution area can be abstracted and simplified into an impedance distribution model, which consists of three models: the transformer equivalent impedance model, the transmission line impedance differential model, and the user load impedance model. Furthermore, the modeling methods for these three models are given. Based on the distribution area topology, the channel frequency selectivity characteristic curve between any two nodes is calculated using a two-port network transmission matrix model.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A method for studying the frequency selectivity of carrier communication channels based on impedance analysis includes the following steps:

[0007] Step 1: Select a pilot area for the frequency selectivity study of carrier communication channels, conduct on-site surveys and record topological information such as line length D, number of branches K, and the range of users [n,m] in the meter box. The power distribution area can be abstracted and simplified to generate an impedance distribution model, which consists of three models: transformer equivalent impedance model, user load impedance model, and transmission line impedance differential model.

[0008] Step 2: Based on the actual transformer specifications in the distribution area, the internal resistance R of the transformer can be determined. t With inductance L t This allows the transformer impedance value to be equivalent to Z0 = R. t +j2πfL t , where j is an imaginary number and f is the frequency, in the range of 0.7MHz-12MHz.

[0009] Step 3: Based on the range of the number of users in the meter box [n,m] obtained in Step 1, design the number of users in the meter box to follow a uniform distribution X~U(n,m) from n to m, and set the load of a single user to 50Ω, and obtain the load impedance of each meter box location.

[0010] Step 4: Based on the actual transmission line resistivity ρ, conductor cross-sectional area S, and the geometric mean distance D between the three phase conductors... eq Corona loss ΔP per kilometer of three-phase line g Line voltage V L Five parameters are used to establish the impedance differential model of the transmission line.

[0011] Step 5: Substitute the three models from Steps 2 to 4 into the two-port network transmission matrix model to calculate the transmission function between any two nodes in the distribution area, which is the channel frequency selection characteristic between the two nodes.

[0012] Furthermore, the method for obtaining the load impedance at the location of the i-th meter box in step 3 is to obtain the random number of users x in the meter box from the uniform distribution X~U(n,m). i Then the load impedance inside the meter box is x. i A 50Ω load is connected in parallel, meaning the load impedance of the i-th meter box is 50 / x. i .

[0013] Furthermore, in step 4, the transmission line impedance differential model analyzes the line impedance parameters by dividing them into four parts: resistance, inductance, capacitance, and conductance.

[0014] First, the resistance per unit length of a three-phase transmission line

[0015] R = ρ / S × 10 -3 (1)

[0016] The unit of R is Ω / m, and the unit of conductor resistivity ρ is Ω·mm. 2 / km, if the transmission line material is copper, then ρ=18.8; if the transmission line material is aluminum, then ρ=31.5; S is the cross-sectional area of ​​the conductor, in mm². 2 .

[0017] Secondly, the inductance per unit length of a three-phase transmission line

[0018]

[0019] The unit of H is H / m, and μ0 = 4π × 10 -4 H / km, D eq The geometric mean distance between the three phase conductors. Let r be the geometric mean distance of the cylindrical conductor, and r be the conductor radius, which can be calculated from the conductor cross-sectional area S. Then the inductive reactance per unit length Z... h =j2πfH, where f is the frequency in Hz.

[0020] Secondly, the capacitance per unit length of a three-phase transmission line.

[0021]

[0022] Where C is in F / m, D eq Let r be the geometric mean distance between the three phase conductors, and r be the conductor radius. Then the capacitive reactance per unit length Z f = 1 / (j2πfC), where f is the frequency in Hz.

[0023] Finally, the conductivity per unit length of the transmission line

[0024]

[0025] Where G is in units of S / m, ΔP g Corona loss per kilometer of three-phase line, expressed in MW / km, V L G is the line voltage, measured in kV. In low-voltage systems, because the line voltage is low, there is generally no corona phenomenon, so G is approximately 0.

[0026] The transmission parameters per unit length of the transmission line can be calculated using the four impedance parameters per unit length: resistance, inductance, capacitance, and conductance. These parameters are the transmission constant γ and the characteristic impedance Z. c The calculation method is as follows

[0027]

[0028]

[0029] Furthermore, in step 5, the two-port network transmission matrix model can physically divide the entire power grid into many cascaded two-port networks, and represent them using a transmission matrix T.

[0030]

[0031] A, B, C, and D are the T-parameters of the transmission matrix, which make the relationship between the port voltage and current of the two-port network as follows:

[0032]

[0033] Low-voltage power networks have complex and diverse structures, but they can all be decomposed into three basic components: power lines, parallel loads, and branch lines.

[0034] First, the electric field line segments can be written in matrix form as follows:

[0035]

[0036] In the formula, l is the length of the power line segment in meters, γ is the transmission constant of the power line, and Z is the transmission constant of the power line. c The characteristic impedance of the electric field line; secondly, the parallel load Z. L The two-port network transmission matrix is

[0037]

[0038] Finally, the input impedance of the branch line is obtained by the following formula.

[0039]

[0040] At this point, the branch line can be regarded as a parallel load. Therefore, according to equation (6), the branch line can be written in matrix form as follows:

[0041]

[0042] Where γ is the transmission constant of the electric field line, Z c The characteristic impedance of the power line, l is the length of the branch line in meters, and Z is the characteristic impedance of the power line. L This represents the terminal load value of the branch line.

[0043] The beneficial effects of this invention are: it provides a method for studying the frequency selectivity of carrier communication channels based on impedance analysis. This method clarifies the constituent elements of the impedance distribution model of power distribution areas and performs specific modeling, so that it can be substituted into the two-port network transmission matrix model to calculate the channel frequency selectivity characteristics between any two nodes in the distribution area. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the method flow of the present invention.

[0045] Figure 2 This is a schematic diagram of the topological structure of Jimotai District in an embodiment of the present invention.

[0046] Figure 3 This is a schematic diagram of the transmission constants of overhead lines and ground cables in an embodiment of the present invention.

[0047] Figure 4 This is a schematic diagram of the characteristic impedance of the overhead line and the ground cable in an embodiment of the present invention.

[0048] Figure 5 This is a simplified topology diagram of the Jimo area after removing irrelevant branches, as shown in this embodiment of the invention.

[0049] Figure 6 This is a simplified schematic diagram of the Jimo Tai District topology obtained in the embodiment of the present invention.

[0050] Figure 7 This is a schematic diagram illustrating the predicted channel frequency selection characteristics between nodes 2.1 and 4.4 in the Jimo station area according to an embodiment of the present invention. Detailed Implementation

[0051] 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 do not limit the scope of the invention.

[0052] Combined with appendix Figure 1 A method for studying the frequency selectivity of carrier communication channels based on impedance analysis includes the following steps:

[0053] Step 1: Taking the typical rural overhead power distribution area, Jimo distribution area, as an example, the distribution area topology is as follows: Figure 2 As shown, it contains 15 meter boxes, with each box serving 1 to 3 users.

[0054] Step 2: Based on the transformer specifications, the transformer impedance value is equivalent to Z0 = 0.001281935 + j2πf2.42645 × 10 -5 , where j is an imaginary number and f is the frequency, in the range of 0.7MHz-12MHz.

[0055] Step 3: Based on the site conditions, the number of random users in the meter box follows a uniform distribution of 1 to 3 X~U(1,3), and the load of a single user is set to 50Ω. The load impedance of each random meter box in this example is shown in Table 1.

[0056] Table 1 Random User Load Values ​​for 15 Meter Boxes

[0057]

[0058]

[0059] Step 4: From Figure 2 It can be seen that the power lines in Jimo Tai District include both overhead lines and ground cables. The transmission parameters of the two types of transmission lines are different. The parameters of the overhead lines are: aluminum transmission line, conductor cross-sectional area 100mm². 2 The geometric mean distance D between the three conductors eq =0.5m, and assuming no corona phenomenon, the overhead line impedance parameter R = 6.3 × 10⁻⁶ can be calculated according to equations (1) to (4). -4 Ω / m, conductance G=0, capacitance C=1.2354×10 -11 F / m, inductance L=1.8967×10 -6 H / m; Ground cable line parameters are: aluminum transmission line, conductor cross-sectional area 100mm². 2 The geometric mean distance D between the three conductors eq =22.4mm, and assuming no corona phenomenon, the impedance parameter R of the ground cable can be calculated according to equations (1) to (4) as 6.3×10. -4 Ω / m, conductance G=0, capacitance C=4.0029×10 -11 F / m, inductance L=6.5452×10 -7 H / m, thus the transmission constant γ and characteristic impedance Z of overhead lines and ground cables can be calculated respectively by equations (5) and (6). c γ and Z are obtained c Curves Figure 3 , Figure 4 As shown, the transmission constant γ of the ground cable is denoted as follows. g and characteristic impedance Z cg The transmission constant γ of overhead lines s and characteristic impedance Z cs .

[0060] Step 5: Substitute the three models from Steps 2 to 4 into the two-port network transmission matrix model to calculate the transmission function between any two nodes in the distribution area, which is the channel frequency selection characteristic between the two nodes.

[0061] Taking the transmission function from node 2.1 to node 4.4 in the Jimo distribution area as an example, using a two-port network transmission matrix model, irrelevant branches are equivalent to a single impedance. In this example, branch 1 of the distribution area (such as...) Figure 2The following are equivalent to Z1 (marked in the middle), Z2 is equivalent to Z2, Z3 is equivalent to Z3, and the irrelevant branches 4.1, 4.2, and 4.3 in branch 4 are equivalent to Z4. The equivalent method is as follows: taking branch 1 as an example, first, the impedance of the last node 1.4 of the branch is combined with the 15m ground cable line to obtain its input impedance by equation (11), which is set as Z1′. From Table 1, it can be seen that Z1.4 = 16.67Ω.

[0062]

[0063] Then, the input impedance Z2′ of Z1′ and the 53m overhead line branch, and the input impedance Z3′ of Z1.3 = 50Ω and the 15m ground cable branch are obtained respectively.

[0064]

[0065]

[0066] The input impedance Z4′ of Z2′ and Z3′ combined with the 49m overhead line is:

[0067]

[0068] Similarly, the input impedance Z5′ of branch 1.1 and the input impedance Z6′ of branch 1.2 are obtained. The input impedance of Z4′, Z5′, and Z6′ in parallel with the 48m overhead line is the equivalent impedance Z1 of this branch. The simplified topology of the Jimo transformer area after equivalence of all irrelevant branches is as follows: Figure 5 As shown ( Figure 5 E on the left s The power supply for the attenuation acquisition transmitter has an internal resistance of Z. s =5Ω, connected in parallel across node 2.1). Then use the same method to... Figure 5 Branch 1′ in the equation is equivalent to impedance Z1″ connected in parallel in the circuit. Then, based on the two-port network transmission matrix model, the... Figure 5 The transformation matrix is ​​converted from node 2.1 to node 4.4 in that order. Specifically, the impedance Z2.1 = 25Ω and its connected 10m ground cable are represented as matrix T1, the parallel impedance Z1″ as matrix T2, and the remaining parts as matrix T3. Taking T3 as an example, T3 = T31·T32·T33, where...

[0069]

[0070]

[0071]

[0072] Jimo Tai District can ultimately be simplified to Figure 6Where T = T1·T2·T3. Let T be...

[0073]

[0074] A, B, C, and D have been solved. The relationship between U1, U2, I1, and I2 is as follows:

[0075]

[0076] That is, U1 = A·U2 + B·I2, I1 = C·U2 + D·I2. Furthermore, from... Figure 6 It can be seen that the load voltage U2 and the power supply voltage Us can be expressed as follows:

[0077]

[0078] The transfer function H(f) from the power source to the load Z4.4 = 16.67Ω is expressed as the ratio of the load voltage to the power source voltage.

[0079]

[0080] The channel frequency selection characteristic curves predicted in this example for nodes 2.1 to 4.4 are as follows: Figure 7 As shown.

[0081] The above embodiments are descriptions of specific implementations of the present invention, and not limitations thereof. Those skilled in the art can make various modifications and changes without departing from the spirit and scope of the present invention to obtain corresponding equivalent technical solutions. Therefore, all equivalent technical solutions should be included in the patent protection scope of the present invention.

Claims

1. A method for studying the frequency selectivity of carrier communication channels based on impedance analysis, characterized in that, Includes the following steps: Step 1: Select the pilot area of ​​the power distribution station to be studied for frequency selectivity of carrier communication channel, conduct on-site survey and record the line length D, number of branches K topology information and the range of users [n,m] in the meter box of the power distribution station. Abstract and simplify the power distribution station to generate an impedance distribution model, which consists of three models: transformer equivalent impedance model, user load impedance model and transmission line impedance differential model. Step 2: Determine the internal resistance R of the transformer based on the actual transformer specifications in the distribution area. t With inductance L t This allows the transformer impedance value to be equivalent to Z0=R. t +j2πfL t j is an imaginary number, and f is the frequency, which is in the range of 0.7MHz-12MHz; Step 3: Based on the range of the number of users in the meter box [n,m] obtained in Step 1, design the number of users in the meter box to follow a uniform distribution X~U(n,m) from n to m, and set the load of a single user to 50Ω, and obtain the load impedance at each meter box location. Step 4, based on the actual transmission line resistivity ρ, conductor cross-sectional area S, and the geometric mean distance D between the three phase conductors... eq Corona loss ∆P per kilometer of three-phase line g Line voltage V L Five parameters are used to establish the impedance differential model of the transmission line; Furthermore, in step 4, the transmission line impedance differential model analyzes the line impedance parameters by dividing them into four parts: resistance, inductance, capacitance, and conductance. First, the resistance per unit length of a three-phase transmission line The unit of R is Ω / m, and the unit of conductor resistivity ρ is Ω‧mm. 2 / km, S is the cross-sectional area of ​​the conductor, in mm. 2 ; Secondly, the inductance per unit length of a three-phase transmission line The unit of H is H / m. D eq The geometric mean distance between the three phase conductors. The geometric mean distance of the cylindrical conductor is given by r, where r is the conductor radius and Z is the inductive reactance per unit length. h =j2πfH, where f is the frequency in Hz; Secondly, the capacitance per unit length of a three-phase transmission line. Where C is in F / m, D eq Let r be the geometric mean distance between the three phase conductors, and r be the conductor radius. Then the capacitive reactance per unit length Z f =1 / (j2πfC), where f is the frequency in Hz; Finally, the conductivity per unit length of the transmission line Where G is in units of S / m, ∆P g Corona loss per kilometer of three-phase line, expressed in MW / km, V L Line voltage, in kV; Based on the four impedance parameters per unit length—resistance, inductance, capacitance, and conductance—the transmission parameters per unit length of the transmission line are calculated: the transmission constant γ and the characteristic impedance Z. c The calculation method is as follows , ; Step 5: Substitute the three models from Steps 2 to 4 into the two-port network transmission matrix model to calculate the transmission function between any two nodes in the distribution area, which is the channel frequency selection characteristic between the two nodes.

2. The method for studying the frequency selectivity of carrier communication channels based on impedance analysis according to claim 1, characterized in that, The method for obtaining the load impedance of the i-th meter box location in step 3 is to obtain the random number of users x in the meter box from the uniform distribution X~U(n,m). i Then the load impedance inside the meter box is x. i A 50Ω load is connected in parallel, meaning the load impedance of the i-th meter box is 50 / x. i Ω.

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