Three-core cable space magnetic field energy collection system and design method

Abstract

A three-core cable space magnetic field energy collection system and design method, the system includes: a three-core cable, an energy collection coil, a gap ring core, a compensation network, a rectifier bridge and a load. The specific steps include: constructing a three-core cable space magnetic field energy collection model; determining a function model that relates the effective magnetic permeability of the gap arc core to the core structural parameters based on finite element simulation fitting and a mathematical model that quantifies the coil internal resistance with the side length of the central magnetic column; solving the output power; establishing an output power density description model for the three-core cable space magnetic field energy collection system; and deriving the power density description model to obtain the optimal side length of the central magnetic column. The present invention verifies through a combination of theoretical calculation and simulation that under limited volume and limited parameters, there is an optimal magnetic column side length that maximizes the system output power density, thereby effectively improving the output power density of the three-core cable space magnetic field energy collection system, and further achieving the purpose of solving the self-power supply problem of the three-core cable status monitoring sensor.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic field energy collection, and in particular to a three-core cable space magnetic field energy collection system and a design method. Background Art

[0002] As the primary carrier of power lines in urban transmission and distribution networks, three-core cables face challenges during operation, including harsh environments, insulation degradation and aging, and cable overcurrent and overheating. The stable operation of three-core cables is crucial for ensuring the normal operation of power systems. Every three-core cable incident directly or indirectly results in significant economic losses, making it imperative to improve the operational safety of three-core cables. To ensure reliable, stable, and safe operation of three-core cables, monitoring sensors are required to continuously monitor temperature, voltage, current, and other information. However, current monitoring sensors are generally battery-powered. Due to limited battery capacity, these sensors require regular replacement, which is costly and poses safety risks. Therefore, a new power supply solution is urgently needed to enable self-powered monitoring sensors.

[0003] Currently, common power supply methods include solar and wind power, vibration energy harvesting, and magnetic field energy harvesting. Solar and wind power are closely tied to local weather conditions and can be unstable. Vibration energy harvesting, on the other hand, has a narrower scope of application. In applications where vibration is less pronounced, such as with three-core cables, vibration energy harvesting cannot collect enough energy to maintain normal power supply for monitoring sensors. In contrast, magnetic field energy harvesting, with its advantages of simple structure, low production cost, and relatively stable power supply, is increasingly being used to power three-core cable wireless sensors.

[0004] Magnetic Energy Harvesting (MEH) technology is based on the law of electromagnetic induction and converts the magnetic field energy near a three-core cable into electrical energy to power the monitoring sensor. MEH is divided into invasive and non-invasive types according to whether the magnetic core is closed. The closed invasive MEH requires a ring-shaped closed magnetic core to be clipped onto the cable, and energy is obtained through the magnetic field generated inside the magnetic core by the cable current. It has been widely used in single-core cables. However, for three-core cables, because the vector sum of the three-phase current flowing through the cable is zero, the magnetic field loop integral of the closed space around it is zero, and the coupling mutual inductance values ​​of each phase conductor of the three-core cable and the energy harvesting coil are consistent, that is, the induced voltages generated by the three-phase energized conductors in the energy harvesting coil are superimposed to zero, making it impossible for the traditional closed invasive MEH to harvest energy from the three-core cable. The non-invasive MEH uses a non-closed magnetic core, which is placed around a cable carrying three-phase industrial frequency alternating current. The coupling mutual inductance between each phase of the three-phase conductor and the energy harvesting coil is different, so the induced voltage generated by each phase of the three-phase conductor in the energy harvesting coil is not zero after superposition. In theory, it can be used for multi-core cable current energy harvesting. However, the magnetic core of the non-closed space MEH is limited in the amount of magnetic field energy it can capture when the alternating magnetic fields generated by the three-phase current are superimposed and weakened. In addition, the demagnetization effect generated by the non-closed magnetic core during the magnetization process significantly reduces the effective magnetic permeability of the core, further weakening the EMH system's ability to collect magnetic field energy and further reducing its output power.

[0005] The core structures currently used for three-core cable magnetic field energy harvesting ignore the demagnetization effect of non-invasive cores during design. Most designs have the same size at both ends as the central magnetic column. The parameters of the central magnetic column closely influence the demagnetization effect of the core. Specifically, the parameters of the central magnetic column are closely related to the effective magnetic permeability of the core. A stubby central magnetic column has a strong demagnetization effect and a low effective magnetic permeability; a slender central magnetic column has a weak demagnetization effect and a high effective magnetic permeability. Core structures with greater effective magnetic permeability have higher power density for the same number of turns and device volume.

[0006] Prior art document 1 (CN117421911A) discloses a method for determining the length of a magnetic core side plate and a magnetic field energy harvesting device. Its shortcomings are that it iteratively optimizes the side plate length to increase power while maintaining the same core side plate area. It fails to consider the demagnetization effect of the core and does not provide a definitive model for describing the output power. Summary of the Invention

[0007] In order to address the deficiencies in the prior art, the present invention provides a three-core cable spatial magnetic field energy collection system and a design method thereof. That is, according to the demagnetization field theory, the effective magnetic permeability of the magnetic core is enhanced by reducing the side length of the central annular magnetic column of the gap magnetic core to weaken the demagnetization effect of the magnetic core, and reducing the side length of the central magnetic column of the gap magnetic core can effectively reduce the internal resistance of the coil, thereby improving the output power density of the three-core cable spatial magnetic field energy collection system, and achieving the purpose of solving the self-power supply problem of the three-core cable monitoring sensor through spatial magnetic field energy collection technology.

[0008] The present invention adopts the following technical solutions. In a first aspect, the present invention provides a three-core cable space magnetic field energy collection system, comprising: a three-core cable, an energy collection coil, a gap ring core, a compensation network, a rectifier bridge, and a load;

[0009] The notched annular magnetic core comprises two magnetic core side plates and an annular magnetic column, wherein the annular magnetic column comprises a complete annular magnetic core with an arc core cut off at a set angle, the two magnetic core side plates are fitted to the two ends of the annular magnetic column, and the magnetic core side plates are in contact with the magnetic field strength of the outer surface of the three-core cable;

[0010] The energy-taking coil is wound around the central magnetic column and connected in series with the compensation network to form a loop. The current of the energy-taking coil is regulated by the compensation network and enters the rectifier bridge. The output end of the compensation network is connected to the rectifier bridge. The rectifier bridge converts AC power into DC power and supplies it to the load. The output end of the rectifier bridge is connected to the load.

[0011] A second aspect of the present invention provides a design method for a three-core cable space magnetic field energy collection system, which is used to operate the above-mentioned three-core cable space magnetic field energy collection system, and the specific steps include:

[0012] Step 1: Construct a three-core cable space magnetic field energy collection model;

[0013] Step 2: Based on the three-core cable spatial magnetic field energy collection model in step 1, a functional model that relates the effective magnetic permeability of the notched arc core to the core structural parameters is determined based on finite element simulation fitting, and a mathematical model that quantifies the coil internal resistance using the side length of the central magnetic column is used;

[0014] Step 3: Calculate the output power based on the effective magnetic permeability of the core and the internal resistance of the coil in step 2.

[0015] Step 4: Using the output power obtained in step 3, establish an output power density description model for the three-core cable space magnetic field energy harvesting system;

[0016] Step 5: Derivative the power density description model in step 4 to obtain the optimal side length of the central magnetic column.

[0017] Preferably, in step 2, the effective magnetic permeability μ eff and demagnetization coefficient D MThe relationship between them is expressed as follows:

[0018]

[0019] in,

[0020] μ eff represents the effective magnetic permeability,

[0021] μ r Indicates the relative magnetic permeability of the core material,

[0022] D M represents the demagnetization coefficient;

[0023] Demagnetization coefficient D M The relationship with the core size is expressed as follows:

[0024]

[0025] in,

[0026] d represents the side length of the central magnetic column,

[0027] L represents the length of the magnetic column of the gap ring core, which is expressed by the following formula:

[0028]

[0029] Where r is the outer radius of the cable.

[0030] Preferably, the length L of the fixed gap annular core and the demagnetization coefficient D of the core are M The effective magnetic permeability μ is determined only by the side length d of the central magnetic column. eff The function model of the central magnetic column side length d is expressed as follows:

[0031] μ eff =μ eff (d) (4)

[0032] in,

[0033] μ eff represents the effective magnetic permeability,

[0034] d represents the side length of the central magnetic column.

[0035] Preferably, in step 2, the coil internal resistance R S It is quantified by the side length d of the central magnetic column and expressed by the following formula:

[0036]

[0037] in,

[0038] R S represents the internal resistance of the coil,

[0039] ρ is the resistivity of copper,

[0040] d coil Indicates the winding thickness,

[0041] d w Indicates the wire diameter,

[0042] N2 represents the number of turns of the energy taking coil,

[0043] d represents the side length of the central magnetic column.

[0044] Preferably, in step 3, the system output power P o , expressed as follows:

[0045]

[0046] in,

[0047] R S represents the internal resistance of the coil,

[0048] R o Indicates the equivalent AC load of the load and the rectifier bridge,

[0049] It represents the effective value of the equivalent induced voltage.

[0050] ω represents the angular frequency, ω=2πf, f represents the power frequency,

[0051] M A 、M B Respectively represent the mutual inductance between the three-phase conductors A, B and the energy-taking coil,

[0052] I represents three-phase industrial frequency alternating current.

[0053] Preferably, the effective value of the equivalent induced voltage The formula is expressed as follows:

[0054]

[0055] in,

[0056] They represent the equivalent induced voltages generated by the three-phase conductors A, B, and C in the energy-taking coil,

[0057] M A 、M B They represent the mutual inductance between the three-phase conductors A and B and the energy harvesting coil, respectively, and are expressed as follows:

[0058]

[0059] in,

[0060] B A 、B B Respectively represent the magnetic flux density of three-phase conductors A and B at the center of the annular magnetic column,

[0061] I represents the three-phase industrial frequency AC current, I A , I B They represent the currents passing through the three-phase conductors A and B respectively.

[0062] N2 represents the number of turns of the energy taking coil,

[0063] S is the cross-sectional area through which the magnetic flux passes, expressed as follows:

[0064] S=d 2 (12)

[0065] Where d is the side length of the central magnetic column.

[0066] Preferably, B A 、B B By solving the magnetic flux density B at the center of the annular magnetic column x It is expressed as follows:

[0067]

[0068] in,

[0069] μ eff is the effective magnetic permeability of the core,

[0070] μ0 is the magnetic permeability of vacuum,

[0071] p is the straight-line distance between the coil and the cable copper core,

[0072] I represents three-phase industrial frequency alternating current.

[0073] Preferably, in step 4, the system output power density description model is expressed by the following formula:

[0074]

[0075] in,

[0076] K represents power density,

[0077] P o Indicates the system output power,

[0078] V represents the overall volume of the three-core cable space magnetic field energy collection system, which is expressed as follows:

[0079]

[0080] in,

[0081] a represents the length of the core side plate,

[0082] b represents the width of the core side plate,

[0083] c represents the thickness of the core side plate,

[0084] L represents the length of the magnetic column of the gap ring core,

[0085] r represents the outer radius of the cable.

[0086] Preferably, in step 5, the optimal side length of the central magnetic column is obtained by taking the derivative of the system output power density with respect to the side length of the central magnetic column and setting the derivative equal to 0.

[0087] Compared with the prior art, the beneficial effect of the present invention lies in that the present invention provides a mathematical model quantification method for the association between the effective magnetic permeability of a special-shaped magnetic core and the magnetic core structural parameters, determines the function model that associates the effective magnetic permeability of a notched arc-shaped magnetic core with the magnetic core structural parameters based on finite element simulation fitting, designs the parameters of the central magnetic column of the energy-taking magnetic core based on the demagnetization theory, clarifies that there is an optimal central magnetic column side length under the same magnetic core side plate area, ensures that the magnetic flux captured by the side plate is consistent, and can effectively weaken the demagnetization effect of the non-closed magnetic core by reducing the side length of the annular central magnetic column, enhance the effective magnetic permeability of the magnetic core, and reduce the side length of the central magnetic column of the notched magnetic core to effectively reduce the internal resistance of the coil, obtains the optimal central magnetic column side length based on the derivation of the power density description model, and verifies through the combination of theoretical calculation and simulation that there is an optimal magnetic column side length under limited volume and limited parameters to maximize the system output power density, thereby effectively improving the output power density of the three-core cable space magnetic field energy harvesting system, and thus achieving the purpose of solving the self-power supply problem of the three-core cable status monitoring sensor. The present invention takes into account the demagnetization effect of arc-shaped special-shaped magnetic cores during the magnetization process. The magnetic core parameters are closely related to the demagnetization effect. Based on finite element simulation fitting, a function model that relates the effective magnetic permeability of the notched arc-shaped magnetic core to the magnetic core structural parameters is determined; the coil internal resistance description model is quantified by the magnetic core structural parameters; a description model of the output power of the three-core cable magnetic field energy harvesting system is obtained, and the influence of the magnetic core structural parameters on the output power is quantified. The optimal magnetic core structural parameters can be directly obtained without the need for tedious iterative optimization. BRIEF DESCRIPTION OF THE DRAWINGS

[0088] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0089] Figure 1Schematic diagram of the space magnetic field energy harvesting system for three-core cable monitoring sensors;

[0090] Figure 2 This is the equivalent model circuit diagram of the three-core cable space magnetic field energy harvesting system;

[0091] Figure 3 is the phase relationship diagram of the three-phase induced voltage;

[0092] Figure 4 This is a simplified equivalent circuit diagram of a three-core cable space magnetic field energy harvesting system;

[0093] Figure 5 Schematic diagram of the structure and parameters of the gap ring core;

[0094] Figure 6 Schematic diagram of the central magnetic column structure and parameters;

[0095] Figure 7 Schematic diagram of the central magnetic column structure and parameters;

[0096] Figure 8 is the degree of curve fitting;

[0097] Figure 9 Simulation results of the model describing the power density. DETAILED DESCRIPTION

[0098] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of patent protection of this invention.

[0099] Example 1

[0100] like Figure 1 As shown, Figure 1 The space magnetic field energy collection system described in this embodiment includes a three-core cable, an energy collection coil, a gap ring core, a compensation network, a rectifier bridge and a load.

[0101] The notched annular magnetic core is composed of two magnetic core side plates and an annular magnetic column. The annular magnetic column is composed of a complete annular magnetic core with a 60° arc core cut off. The two magnetic core side plates are attached to the two ends of the annular magnetic column, and the magnetic core side plates are in contact with the magnetic field strength of the outer surface of the three-core cable.

[0102] The energy-taking coil is wound around the central magnetic column and connected in series with the compensation network to form a loop. The current of the energy-taking coil is regulated by the compensation network and enters the rectifier bridge. The output end of the compensation network is connected to the rectifier bridge, which then converts the AC power into DC power and supplies it to the load. The output end of the rectifier bridge is connected to the load.

[0103] The three-core cable carries a three-phase power frequency AC current of size I, and the number of turns of each phase of the three-phase conductor is N1, usually N1=1; the number of turns of the energy taking coil is N2, and in the compensation network, the self-inductance is L S , the compensation capacitor is C S Connected in series to the circuit, the internal resistance of the coil is R S The mutual inductances between the three-phase conductors and the energy-taking coils are M A , M B , M C , the coil induced current is I2;

[0104] The gap ring core is composed of two core side plates and an annular magnetic column. The annular magnetic column is composed of a complete annular magnetic core with a 60° arc core cut off. The geometric relationship is shown in the attached Figure 5 The two core side plates are tightly fitted with the two ends of the annular magnetic column, and the core side plates are in close contact with the magnetic field strength of the outer surface of the three-core cable. The energy-taking coil is tightly wound around the central magnetic column. Figure 6 and Figure 7 In the embodiment, the gap annular magnetic core is composed of a magnetic core side plate and an annular magnetic column, wherein the side plate has a length a, a width b, and a thickness c, and the annular magnetic column has a side length d, a length L, and a cross-sectional area S;

[0105] The rectifier bridge is composed of four rectifier diodes D1, D2, D3, and D4. The equivalent AC load of the load and the rectifier bridge is R o .

[0106] Example 2

[0107] Embodiment 2 of the present invention provides a design method for a three-core cable space magnetic field energy collection system, comprising the following steps:

[0108] Step 1: Construct a three-core cable space magnetic field energy collection model;

[0109] The three-core cable carries a three-phase power frequency AC current of size I. The number of turns of each phase of the three-phase conductor is N1, N1=1, the number of turns of the energy-taking coil is N2, and the self-inductance is L s , the compensation capacitor is connected in series to the circuit, which is C s , the internal resistance is R s The mutual inductances between the three-phase conductors and the energy-taking coils are M A , M B , M CThe coil induced current is I2, the gap ring core consists of a core side plate and a ring magnetic column, the side plate length is a, the width is b, the thickness is c, the ring magnetic column side length is d, the length is L, the cross-sectional area is S; the rectifier bridge consists of four rectifier diodes D1, D2, D3, and D4. The equivalent AC load of the load and the rectifier bridge is R o .

[0110] The system output power model density description model takes into account the mutual inductance M between the three-phase conductors and the energy extraction coil A 、M B 、M C , three-phase industrial frequency AC current I, coil internal resistance R s Determine the number of turns of the energy-harvesting coil wound around the annular magnetic core, the cross-sectional area of ​​the energy-harvesting coil, and the magnetic induction intensity at the location of the energy-harvesting coil; calculate the induced voltage value at both ends of the energy-harvesting coil based on the law of electromagnetic induction; calculate the output power density of the space magnetic field energy harvesting device based on the induced voltage of the energy-harvesting coil, the internal resistance of the energy-harvesting coil, and the load resistance.

[0111] Step 2: Based on the three-core cable spatial magnetic field energy collection model in step 1, a functional model that relates the effective magnetic permeability of the notched arc core to the core structural parameters is determined based on finite element simulation fitting, and a mathematical model that quantifies the coil internal resistance using the side length of the central magnetic column is used;

[0112] Effective magnetic permeability μ eff and demagnetization coefficient D M The relationship between:

[0113]

[0114] Among them, μ r Represents the relative magnetic permeability of the core material, the demagnetization coefficient D M The relationship with the core size can be expressed as:

[0115]

[0116] According to the area with the strongest magnetic field intensity on the outer surface of the three-core cable, the length L of the magnetic column constraining the gap ring core can be expressed as:

[0117]

[0118] Where r represents the outer radius of the cable. For details on geometric constraints, see the attached Figure 5 .

[0119] Finite element simulation was used to fit a functional model linking the effective magnetic permeability of the notched arc-shaped core to the core's structural parameters. The demagnetization coefficient is determined based on the length and side length of the central magnetic column, and is directly related to the core's effective magnetic permeability. Because there's no clear expression for the effective magnetic permeability of special-shaped cores like notched ring cores, finite element simulation software was used to select coil and core structural parameters and simulate a functional model linking the effective magnetic permeability to the core's structural parameters.

[0120] Furthermore, since the length L of the gap ring core is fixed, the demagnetization coefficient D of the core is M It is only determined by the side length d of the central magnetic column, so the coil and core length parameters can be selected through finite element simulation software to simulate and fit the function model of effective magnetic permeability and the side length d of the central magnetic column. eff The function model of the side length d of the central magnetic column can be expressed as:

[0121] μ eff =μ eff (d) (4)

[0122] The mathematical model for quantifying the coil internal resistance using the side length of the central magnetic column is based on the fact that the energy coil is tightly wound around the central magnetic column, and the coil internal resistance is closely related to the side length of the central magnetic column. By quantifying the relationship between the side length parameter of the central magnetic column and the coil internal resistance, a mathematical model for quantifying the coil internal resistance using the side length of the central magnetic column is established.

[0123] On the basis of ensuring the overall structural characteristics of the gap ring core, the side length of the central magnetic column is changed to ensure that the volume of the energy extraction coil remains unchanged. Combined with the function model of the effective magnetic permeability of the gap ring core and the side length parameter of the central magnetic column, and the mathematical model of the coil internal resistance quantified by the side length of the central magnetic column, the final power density description model with respect to the side length of the central magnetic column is obtained. Based on the derivation of the power density description model, the optimal side length of the central magnetic column is obtained.

[0124] Furthermore, the steps for simulating and fitting the functional model of effective magnetic permeability and the side length d of the central magnetic column are as follows:

[0125] Step 1.1: Set simulation parameters. Based on the actual operating scenario, the space limit for installing a 10kV three-core cable determines the overall volume of the core and coil and keeps it constant. The simulation parameters are set as follows:

[0126] parameter Numerical parameter Numerical r 32mm <![CDATA[μ r ]]> 100000 a 20mm <![CDATA[d w ]]> 0.2mm b 20mm <![CDATA[d+2d coil ]]> 20mm c 2mm V <![CDATA[117cm 3 ]]>

[0127] During the control simulation process, the parameters in the table above remain unchanged, and only the side length d of the central magnetic column is changed, and the effective magnetic permeability is calculated by simulation.

[0128] Step 1.2: According to the simulation parameters set in step 1.1, calculate the effective magnetic permeability μ of the core. effThe effective magnetic permeability μ of the core is obtained by fitting the relationship with the side length d of the central magnetic column. eff Fitting relationship with the side length d of the central magnetic column. Change d to get the corresponding μ eff , as shown in the following table:

[0129] d(mm) 4 6 8 10 12 14 16 18 <![CDATA[μ eff ]]> 1026 530 332 231 173 135 109 90

[0130] Perform function fitting on the data in the table, and the effective magnetic permeability μ of the gap ring core is eff The relationship between the length d of the central magnetic column satisfies the following formula:

[0131] μ eff =B4·d 4 +B3·d 3 +B2·d 2 +B1·d 1 +B0 (5)

[0132] Among them, B0, B1, B2, B3, and B4 represent the constant term coefficient, linear term coefficient, quadratic term coefficient, cubic term coefficient, and quartic term coefficient of the fitting function respectively.

[0133] The degree of curve fitting is Figure 8 As shown, the R square is 0.99917≈1, so the fitting function is credible. It can be further expressed as follows:

[0134] μ eff =0.10298d 4 -5.44476d 3 +107.13d 2 -950.28d 1 +3431.238 (6)

[0135] Furthermore, by quantifying the relationship between the central magnetic column side length parameter and the coil internal resistance, a mathematical model for quantifying the coil internal resistance using the central magnetic column side length is established. The coil internal resistance can be quantified by the central magnetic column side length d as follows:

[0136]

[0137] Among them, R S represents the internal resistance of the coil, ρ is the copper resistivity, d coil is the winding thickness, d w represents the wire diameter, and N2 represents the number of turns in the energy extraction coil. According to the above expression, a magnetic column side length d that is too large will increase the internal resistance of the winding coil, thereby limiting the system's power output.

[0138] Step 3: Calculate the output power based on the effective magnetic permeability of the core and the internal resistance of the coil in step 2.

[0139] Based on the attached Figure 2The equivalent circuit diagram and attached Figure 3 Phase relationship diagram, calculate the equivalent induced voltage expression:

[0140]

[0141] in,

[0142] ω is the angular frequency, ω=2πf, f is the power frequency,

[0143] Respectively represent the equivalent induced voltages of the three-phase conductors A, B, and C,

[0144] M A 、M B 、M C Respectively represent the mutual inductance between the three-phase conductors A, B, and C and the energy-taking coil,

[0145] Indicates three-phase industrial frequency AC current,

[0146] I A , I B , I C Represent the currents passing through the three-phase conductors A, B, and C respectively.

[0147] Furthermore, since the three-phase induced voltages are 120° out of phase with each other, the effective value of the equivalent induced voltage is calculated as:

[0148]

[0149] in, Indicates the effective value of the equivalent induced voltage.

[0150] Furthermore, based on the Figure 4 The simplified equivalent circuit diagram of the system is used to calculate the system output power P o :

[0151]

[0152] Among them, R S Represents the internal resistance of the coil, R o Represents the equivalent AC load of the load and the rectifier bridge.

[0153] Furthermore, the relationship between mutual inductance and magnetic flux density is:

[0154]

[0155] in,

[0156] B A 、B B Respectively represent the magnetic flux density at the center of the annular magnetic column of the three-phase conductor A and B,

[0157] N2 represents the number of turns of the energy taking coil,

[0158] S is the cross-sectional area through which the magnetic flux passes, which can be expressed as:

[0159] S=d 2 (12)

[0160] The side length of the annular magnetic column is d.

[0161] Furthermore, the magnetic flux density B x expression:

[0162]

[0163] Among them, μ eff is the effective magnetic permeability of the core, μ0 is the magnetic permeability of vacuum, and p is the straight-line distance between the coil and the cable copper core. A 、B B By solving the magnetic flux density B x get.

[0164] Step 4: Using the output power obtained in step 3, establish a model describing the output power density of the three-core cable space magnetic field energy harvesting system.

[0165] Furthermore, the overall volume of the three-core cable space magnetic field energy harvesting system can be described as:

[0166]

[0167] Where r is the outer radius of the cable, a is the length of the side plate, b is the width, and c is the thickness.

[0168] Furthermore, based on the above analysis results, the system output power density description model is obtained as follows:

[0169]

[0170] Where K represents power density.

[0171] Step 5: Derivative the power density description model of step 4 to obtain the optimal side length of the central magnetic column, so that the system output power density is maximized, thereby solving the self-power supply problem of the three-core cable status monitoring sensor.

[0172] Furthermore, based on the above analysis results, the system output power density description model is obtained as follows:

[0173]

[0174] where p A and p BThey represent the straight-line distances from the A and B phase conductors to the energy harvesting coils respectively.

[0175] Based on the above description, it can be seen that when the other parameters of the system remain unchanged, the side length d of the central magnetic column has a close influence on the system power density, and its output power density is related to the effective magnetic permeability μ of the magnetic core. eff (d) is positively correlated with the internal resistance R of the coil S (d) is negatively correlated. The effective magnetic permeability μ of the magnetic core eff It is determined by the side length d of the magnetic column. That is, the smaller the side length d is, the weaker the demagnetization effect of the magnetic core is, and the effective magnetic permeability μ of the magnetic core is eff The larger d is, the larger R S Therefore, it is very necessary to optimize d, and the output power density of the three-core cable space magnetic field energy harvesting system can be improved by optimizing the side length d of the central magnetic column.

[0176] Furthermore, by taking the derivative of the function K(d) and setting dK(d) / dd=0, the steps to obtain the optimal center magnetic column side length d are as follows:

[0177] Step 5.1: Quantify R S and μ eff Substitute into the system power density expression:

[0178]

[0179] Step 5.2: By taking the derivative of the function K(d) and setting dK(d) / dd=0, the optimal side length of the central magnetic column d=6.24mm can be obtained.

[0180] Step 5.3: Verify the validity of the calculation results. The simulation software Maxwell uses the same parameters as the power density description model to perform simulation verification. The simulation results are as follows Figure 9 .

[0181] The simulation results show that the side length d of the central magnetic column has a significant impact on the output power of the system. Under the condition that the other parameters of the magnetic core and the coil volume remain unchanged, there is an optimal magnetic column side length d = 6mm, which maximizes the system output power and power density. The maximum output power reaches 24.8mW, and the maximum power density is 0.206mW / cm 3 , which proves that optimizing the side length d of the central magnetic column is effective in improving the power density of the three-core cable space magnetic field energy harvesting system.

[0182] The beneficial effect of the present invention is that the present invention provides a mathematical model quantification method for associating the effective magnetic permeability of a special-shaped magnetic core with the magnetic core structural parameters, determines the function model associating the effective magnetic permeability of a notched arc-shaped magnetic core with the magnetic core structural parameters based on finite element simulation fitting, designs the parameters of the central magnetic column of the energy-taking magnetic core based on the demagnetization theory, clarifies that there is an optimal central magnetic column side length under the same magnetic core side plate area, ensures that the magnetic flux captured by the side plate is consistent, and can effectively weaken the demagnetization effect of the non-closed magnetic core by reducing the side length of the annular central magnetic column, enhance the effective magnetic permeability of the magnetic core, and reduce the side length of the central magnetic column of the notched magnetic core to effectively reduce the internal resistance of the coil, obtains the optimal central magnetic column side length based on the derivation of the power density description model, and verifies through the combination of theoretical calculation and simulation that there is an optimal magnetic column side length under limited volume and limited parameters to maximize the system output power density, thereby effectively improving the output power density of the three-core cable space magnetic field energy harvesting system, and thus achieving the purpose of solving the self-power supply problem of the three-core cable status monitoring sensor. The present invention takes into account the demagnetization effect of arc-shaped special-shaped magnetic cores during the magnetization process. The magnetic core parameters are closely related to the demagnetization effect. Based on finite element simulation fitting, a function model that relates the effective magnetic permeability of the notched arc-shaped magnetic core to the magnetic core structural parameters is determined; the coil internal resistance description model is quantified by the magnetic core structural parameters; a description model of the output power of the three-core cable magnetic field energy harvesting system is obtained, and the influence of the magnetic core structural parameters on the output power is quantified. The optimal magnetic core structural parameters can be directly obtained without the need for tedious iterative optimization.

[0183] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A design method for a three-core cable space magnetic field energy collection system, which is used to operate a three-core cable space magnetic field energy collection system, including a three-core cable, an energy collection coil, a gap ring core, a compensation network, a rectifier bridge and a load, wherein the gap ring core comprises two core side plates and an annular magnetic column, wherein the annular magnetic column comprises a complete annular magnetic core with a 60° arc core cut off, and the core radius is set to times the outer radius of the cable, the two magnetic core side plates are fitted with the two ends of the annular magnetic column, and the magnetic core side plates are in contact with the magnetic field strength of the outer surface of the three-core cable; the energy taking coil is wound around the central magnetic column and connected in series with the compensation network to form a loop, and the current of the energy taking coil is regulated by the compensation network and enters the rectifier bridge. The output end of the compensation network is connected to the rectifier bridge, and the rectifier bridge converts AC power into DC power to supply it to the load. The output end of the rectifier bridge is connected to the load, which is characterized in that The specific steps include: Step 1: Construct a three-core cable space magnetic field energy collection model; Step 2: Based on the three-core cable spatial magnetic field energy collection model in step 1, a functional model that relates the effective magnetic permeability of the notched arc core to the core structural parameters is determined based on finite element simulation fitting, and a mathematical model that quantifies the coil internal resistance using the side length of the central magnetic column is used; Step 3: Calculate the output power based on the effective magnetic permeability of the core and the internal resistance of the coil in step 2. Step 4: Using the output power obtained in step 3, establish the output power density description model of the three-core cable space magnetic field energy harvesting system. The power density description model is as follows: in, ω is the angular frequency, ω=2πf, f is the power frequency, μ0 is the vacuum permeability, d is the side length of the annular magnetic column, N2 represents the number of turns of the energy-taking coil, μ eff (d) is the effective magnetic permeability of the core, p A and p B Represents the straight-line distance from the A and B phase conductors to the energy-taking coil, I is the three-phase power frequency AC current, ρ is the copper resistivity, and d coil is the winding thickness, d w Indicates wire diameter, R o is the equivalent AC load of the load and the rectifier bridge, r is the outer radius of the cable, a is the length of the side plate, b is the width, and c is the thickness; Step 5: Derivative the power density description model in step 4 to obtain the optimal side length of the central magnetic column.

2. The design method of the three-core cable space magnetic field energy collection system according to claim 1 is characterized by: In step 2, the effective magnetic permeability μ eff and demagnetization coefficient D M The relationship between them is expressed as follows: in, μ eff represents the effective magnetic permeability, μ r Indicates the relative magnetic permeability of the core material, D M represents the demagnetization coefficient; Demagnetization coefficient D M The relationship with the core size is expressed as follows: in, d represents the side length of the central magnetic column, L represents the length of the magnetic column of the gap ring core, which is expressed by the following formula: Where r is the outer radius of the cable.

3. The design method of the three-core cable space magnetic field energy collection system according to claim 2 is characterized by: Fixed gap ring core length L, core demagnetization coefficient D M The effective magnetic permeability μ is determined only by the side length d of the central magnetic column. eff The function model of the central magnetic column side length d is expressed as follows: m eff =μ eff (d) (4) in, μ eff represents the effective magnetic permeability, d represents the side length of the central magnetic column.

4. The design method of the three-core cable space magnetic field energy collection system according to claim 1 is characterized by: In step 2, the coil internal resistance R S It is quantified by the side length d of the central magnetic column and expressed by the following formula: in, R S represents the internal resistance of the coil, ρ is the resistivity of copper, d coil Indicates the winding thickness, d w Indicates the wire diameter, N2 represents the number of turns of the energy taking coil, d represents the side length of the central magnetic column.

5. The design method of the three-core cable space magnetic field energy collection system according to claim 1 is characterized by: In step 3, the system output power P o , expressed as follows: in, R S represents the internal resistance of the coil, R o Indicates the equivalent AC load of the load and the rectifier bridge, It represents the effective value of the equivalent induced voltage. ω represents the angular frequency, ω=2πf, f represents the power frequency, M A 、M B Respectively represent the mutual inductance between the three-phase conductors A, B and the energy-taking coil, I represents three-phase industrial frequency alternating current.

6. The design method of the three-core cable space magnetic field energy collection system according to claim 5, characterized in that: Equivalent induced voltage effective value The formula is expressed as follows: in, They represent the equivalent induced voltages generated by the three-phase conductors A, B, and C in the energy-taking coil, M A 、M B They represent the mutual inductance between the three-phase conductors A and B and the energy harvesting coil, respectively, and are expressed as follows: in, B A 、B B Respectively represent the magnetic flux density of three-phase conductors A and B at the center of the annular magnetic column, I represents the three-phase industrial frequency AC current, I A , I B They represent the currents passing through the three-phase conductors A and B respectively. N2 represents the number of turns of the energy taking coil, S is the cross-sectional area through which the magnetic flux passes, expressed as follows: S=d 2 (12) Where d is the side length of the central magnetic column.

7. The design method of the three-core cable space magnetic field energy collection system according to claim 6, characterized in that: B A 、B B By solving the magnetic flux density B at the center of the annular magnetic column x It is expressed as follows: in, μ eff is the effective magnetic permeability of the core, μ0 is the magnetic permeability of vacuum, p is the straight-line distance between the coil and the cable copper core, O represents three-phase industrial frequency alternating current.

8. The design method of the three-core cable space magnetic field energy collection system according to claim 1, characterized in that: In step 4, the system output power density description model is expressed as follows: in, K represents power density, P o Indicates the system output power, V represents the overall volume of the three-core cable space magnetic field energy collection system, which is expressed as follows: in, a represents the length of the core side plate, b represents the width of the core side plate, c represents the thickness of the core side plate, L represents the length of the magnetic column of the gap ring core, r represents the outer radius of the cable.

9. The design method of the three-core cable space magnetic field energy collection system according to claim 1, characterized in that: In step 5, the optimal side length of the central magnetic column is obtained by taking the derivative of the system output power density with respect to the side length of the central magnetic column and setting the derivative equal to 0.

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