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

Abstract

The invention discloses a three-core cable space magnetic field energy collection system and a design method. The system comprises a three-core cable, an energy taking coil, a notch annular magnetic core, a compensation network, a rectifier bridge and a load. The method comprises the following specific steps: constructing a three-core cable space magnetic field energy collection model; on the basis of finite element simulation fitting, determining a function model in which the effective magnetic conductivity of the notch arc-shaped magnetic core is associated with magnetic core structure parameters and a mathematical model in which the coil internal resistance is quantized by the side length of a central magnetic column; solving the output power; establishing an output power density description model of the three-core cable space magnetic field energy collection system; and performing model description and derivation on the power density to obtain the optimal side length of the central magnetic column. Theoretical calculation and simulation are combined to verify that the optimal magnetic column side length exists under limited volume and limited parameters, so that the output power density of the system is maximum, the output power density of the three-core cable space magnetic field energy taking system is effectively improved, and the purpose of solving the self-power supply problem of the three-core cable state monitoring sensor is achieved.

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 main carrier of the power supply line of the urban transmission and distribution network, the three-core cable faces problems such as harsh environment, insulation shedding and aging, and cable overcurrent and overheating during use. The stable operation of the three-core cable is one of the important factors to ensure the normal operation of the power system. Every three-core cable accident will directly or indirectly cause huge economic losses. Therefore, it is urgent to improve the operation safety of the three-core cable. In order to ensure the reliable, stable and safe operation of the three-core cable, it is necessary to use monitoring sensors to continuously monitor its temperature, voltage, current and other information. However, the current monitoring sensors are generally powered by batteries. Due to the limitation of battery capacity, such sensors require special personnel to replace the batteries regularly, which is costly and has safety hazards. Therefore, there is an urgent need for a new power supply solution to achieve self-powering of monitoring sensors.

[0003] At present, common power supply methods include solar and wind power supply, vibration energy supply and magnetic field energy collection. Among them, solar and wind power supply is closely related to local weather conditions and has the problem of unstable power supply; the actual application range of vibration energy supply is relatively narrow. For application scenarios such as three-core cables where vibration phenomena are not obvious, vibration energy collection cannot collect enough energy to maintain the normal power supply of monitoring sensors; in contrast, magnetic field energy collection has been gradually applied to the power supply of three-core cable wireless sensors due to its advantages such as simple equipment structure, low production cost and relatively stable power supply.

[0004] Magnetic Energy Harvesting (MEH) technology is based on the law of electromagnetic induction, which converts the magnetic field energy near the 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 the annular closed magnetic core to be buckled on the cable, and energy is obtained through the magnetic field generated by the cable current inside the magnetic core. 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 integral of the magnetic field loop in 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 collection coil are consistent, that is, the superposition of the induced voltages generated by the three-phase energized conductors in the energy collection coil is zero, making it impossible for the traditional closed invasive MEH to collect energy from the three-core cable. The non-invasive MEH uses a non-closed magnetic core, which is placed around a cable with three-phase industrial frequency alternating current. The coupling mutual inductance between each phase in the three-phase conductor and the energy collection coil is different, so the induced voltage generated by each phase of the three-phase conductor in the energy collection coil is not zero after superposition. In theory, it can be used for multi-core cable current energy collection. However, the magnetic core of the non-closed space MEH has limited magnetic field energy captured when the alternating magnetic field generated by the three-phase current is superimposed and weakened. In addition, the demagnetization effect generated by the non-closed magnetic core during the magnetization process greatly reduces the effective magnetic permeability of the magnetic core, further weakening the ability of the EMH system to collect magnetic field energy, and further reducing its output power.

[0005] The core structure currently used for three-core cable magnetic field energy extraction ignores the demagnetization effect of non-invasive cores during design. Most of them are designed to be equal in size to the center magnetic column at both ends. The parameters of the center magnetic column closely affect the demagnetization effect of the core, that is, the parameters of the center magnetic column are closely related to the effective magnetic permeability of the core. The demagnetization effect of the thick and short center magnetic column is strong, and the effective magnetic permeability of the core is small; the demagnetization effect of the slender center magnetic column is weak, and the effective magnetic permeability of the core is large. The core structure with a larger effective magnetic permeability has a higher power density under the same number of turns and the same 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 collection device. Its shortcomings are that the side plate length is iteratively optimized to increase power while keeping the area of ​​the magnetic core side plate unchanged, without considering the demagnetization effect of the magnetic core, and without obtaining an exact description model of the output power. Summary of the invention

[0007] In order to solve the deficiencies in the prior art, the present invention provides a three-core cable space 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 notched magnetic core to weaken the demagnetization effect of the magnetic core, and reducing the side length of the central magnetic column of the notched magnetic core can effectively reduce the internal resistance of the coil, thereby improving the output power density of the three-core cable space magnetic field energy collection system, and achieving the purpose of solving the self-power supply problem of the three-core cable monitoring sensor through the space 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, the annular magnetic column comprises a complete annular magnetic core with a circular arc magnetic 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 extraction 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 extraction 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: According to the three-core cable space magnetic field energy collection model in step 1, the function model that relates the effective magnetic permeability of the notched arc core to the core structure parameters is determined based on finite element simulation fitting, and the mathematical model of the coil internal resistance is quantified by the side length of the central magnetic column;

[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 of the three-core cable space magnetic field energy collection 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 Represents 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 is 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 magnetic core and the demagnetization coefficient D of the magnetic core 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 side length d of the central magnetic column 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] N 2 Indicates 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 They represent the mutual inductance between the three-phase conductors A and B and the energy-taking coil,

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

[0053] Preferably, the equivalent induced voltage effective value 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, and are expressed by the following formula:

[0058]

[0059] in,

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

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

[0062] N 2 Indicates 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 the following formula:

[0067]

[0068] in,

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

[0070] μ 0 is the vacuum permeability,

[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 by the following formula:

[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 system output power density is differentiated with respect to the side length of the central magnetic column, and the derivative is set equal to 0 to obtain the optimal side length of the central magnetic column.

[0087] Compared with the prior art, the beneficial effect of the present invention lies in that the present invention provides a method for quantifying a mathematical model of the association between the effective magnetic permeability of a special-shaped magnetic core and the magnetic core structural parameters, determines a 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-harvesting 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 further 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 implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

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

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

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

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

[0093] Figure 5 It is a schematic diagram of the structure and parameters of the gap ring core;

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

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

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

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

[0098] The following will be combined with the 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 described embodiments 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 creative work are within the scope of patent protection of the present 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 notched 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 magnetic core cut off. 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.

[0102] The energy extraction 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 extraction 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 industrial frequency alternating current of magnitude I, and the number of turns of each phase of the three-phase conductor is N. 1 , usually N 1 =1; the number of turns of the energy taking coil is N 2 , in the compensation network, the self-inductance is L S , the compensation capacitor is C S Connected in series to the loop, the internal resistance of the coil is R S The mutual inductance between the three-phase conductor and the energy-taking coil is M A , M B , M C , the coil induced current is I 2 ;

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

[0105] The rectifier bridge consists of D 1 , D 2 , D 3 , D 4 The load is composed of four rectifier diodes, and 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 industrial frequency AC current of magnitude I, and the number of turns of each phase of the three-phase conductor is N. 1 , N 1 =1, the number of turns of the energy taking coil is N 2 , self-sensitivity 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 inductance between the three-phase conductor and the energy-taking coil is M A , M B , M C , the coil induced current is I 2 The gap annular magnetic core is composed of a magnetic core side plate and an annular magnetic column, the side plate length is a, the width is b, the thickness is c, the annular magnetic column side length is d, the length is L, and the cross-sectional area is S; the rectifier bridge is composed of D 1 , D 2 , D 3 , D 4 The load is composed of four rectifier diodes, and 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-collecting coil wound around the annular magnetic core, the cross-sectional area of ​​the energy-collecting coil, and the magnetic induction intensity at the location of the energy-collecting coil; calculate the induced voltage value at both ends of the energy-collecting coil based on the law of electromagnetic induction; calculate the output power density of the space magnetic field energy collection device based on the induced voltage of the energy-collecting coil, the internal resistance of the energy-collecting coil, and the load resistance.

[0111] Step 2: According to the three-core cable space magnetic field energy collection model in step 1, the function model that relates the effective magnetic permeability of the notched arc core to the core structure parameters is determined based on finite element simulation fitting, and the mathematical model of the coil internal resistance is quantified by the side length of the central magnetic column;

[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 strength 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] Based on the finite element simulation fitting, the function model that links the effective magnetic permeability of the gap arc core with the core structure parameters is determined. The demagnetization coefficient is determined according to the length of the central magnetic column and the side length of the central magnetic column. The demagnetization coefficient is directly related to the effective magnetic permeability of the core. Since there is no clear expression for the effective magnetic permeability of special-shaped magnetic cores such as gap ring cores, the coil and core structure parameters are selected through finite element simulation software, and the function model of the effective magnetic permeability and core structure parameters is simulated and fitted.

[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 internal resistance of the coil using the side length of the central magnetic column is that the energy-taking coil is tightly wound around the central magnetic column, and the internal resistance of the coil 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 internal resistance of the coil, a mathematical model for quantifying the internal resistance of the coil using the side length of the central magnetic column is established.

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

[0124] Furthermore, the steps of 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. According to the actual operation scenario, the overall volume of the core and coil is determined and kept unchanged based on the installation space limit margin of the 10kV three-core cable. The simulation parameters are set as follows:

[0126] parameter Numeric parameter Numeric 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] The parameters in the table above are kept unchanged during the control simulation process, 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 magnetic core. eff The effective magnetic permeability μ of the magnetic 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. Changing d, we 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 of the central magnetic column and the side length d satisfies the following formula:

[0131] μ eff =B 4 ·d 4 +B 3 ·d 3 +B 2 ·d 2 +B 1 ·d 1 +B 0 (5)

[0132] Among them, B 0 , B 1 , B 2 , B 3 , B 4 They represent respectively: constant term coefficient, linear term coefficient, quadratic term coefficient, cubic term coefficient and quartic term coefficient of the fitting function.

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

[0136]

[0137] Among them, R S represents the internal resistance of the coil, ρ is the resistivity of copper, d coil is the winding thickness, d w Indicates wire diameter, N 2 Indicates the number of turns of the energy extraction coil. According to the above expression, if the side length d of the magnetic column is too large, the internal resistance of the winding coil will increase, thereby limiting the power output of the system.

[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 2 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] They represent the equivalent induced voltages of the three-phase conductors A, B, and C respectively.

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

[0145] Represents three-phase industrial frequency alternating current,

[0146] I A ,I B ,I C They represent the current passing through the three-phase wires A, B, and C respectively.

[0147] Furthermore, since the three-phase induced voltages are in a 120° phase relationship 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] Further, the relationship between mutual inductance and magnetic flux density is:

[0154]

[0155] in,

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

[0157] N 2 Indicates 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] Among them, 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, μ 0 is the vacuum magnetic permeability, 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 the output power density description model of the three-core cable space magnetic field energy collection system

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

[0166]

[0167] Among them, 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 B They 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 necessary to optimize d, and the output power density of the three-core cable space magnetic field energy collection system can be increased 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 can be obtained as d=6.24 mm.

[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: Fig. 9 .

[0181] The simulation results show that the 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 length d = 6mm, which makes the system output power and power density the highest. 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 lies in that the present invention provides a method for quantifying a mathematical model of the association between the effective magnetic permeability of a special-shaped magnetic core and the magnetic core structural parameters, determines a 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-harvesting 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 further 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 relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A three-core cable space magnetic field energy collection system, comprising: Three-core cable, energy taking coil, notched ring core, compensation network, rectifier bridge and load, characterized by: The notched annular magnetic core comprises two magnetic core side plates and an annular magnetic column, the annular magnetic column comprises a complete annular magnetic core with a circular arc magnetic 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; The energy extraction 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 extraction 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.

2. A design method for a three-core cable space magnetic field energy collection system, used to operate a three-core cable space magnetic field energy collection system according to claim 1, characterized in that: The specific steps include: Step 1: Construct a three-core cable space magnetic field energy collection model; Step 2: According to the three-core cable space magnetic field energy collection model in step 1, the function model that relates the effective magnetic permeability of the notched arc core to the core structure parameters is determined based on finite element simulation fitting, and the mathematical model of the coil internal resistance is quantified by the side length of the central magnetic column; 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 an output power density description model of the three-core cable space magnetic field energy collection system; Step 5: Derivative the power density description model in step 4 to obtain the optimal side length of the central magnetic column.

3. The design method of the three-core cable space magnetic field energy collection system according to claim 2 is characterized in that: 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 Represents 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 is 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.

4. The design method of the three-core cable space magnetic field energy collection system according to claim 3 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 side length d of the central magnetic column 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.

5. The design method of the three-core cable space magnetic field energy collection system according to claim 2 is characterized in that: 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.

6. The design method of the three-core cable space magnetic field energy collection system according to claim 2 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 They represent the mutual inductance between the three-phase conductors A and B and the energy-taking coil, I represents three-phase industrial frequency alternating current.

7. The design method of the three-core cable space magnetic field energy collection system according to claim 6 is characterized by: 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, and are expressed by the following formula: in, B A , B B They represent the magnetic flux density of the three-phase conductors A and B at the center of the annular magnetic column, I represents the three-phase industrial frequency alternating 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.

8. The design method of the three-core cable space magnetic field energy collection system according to claim 7 is characterized by: B A , B B By solving the magnetic flux density B at the center of the annular magnetic column x It is expressed as the following formula: 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, I represents three-phase industrial frequency alternating current.

9. The design method of the three-core cable space magnetic field energy collection system according to claim 2 is characterized by: 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 by the following formula: 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.

10. The design method of the three-core cable space magnetic field energy collection system according to claim 2 is characterized by: 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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