Optimization method for annular magnetic core of intrusive mutual inductor

Abstract

The invention belongs to the technical field of mutual inductors, and relates to an optimization method of an intrusive mutual inductor annular magnetic core, which comprises the following steps: establishing a mutual inductor equivalent model on the basis of a mutual inductor circuit model, designing a relation vector diagram of secondary side induced electromotive force and current, giving primary side current in combination with related principles, and exporting secondary side output voltage. The secondary coil output voltage is exported by setting parameters, and then the secondary side output power is exported; by analyzing the influence factors of the output voltage of the secondary coil and the output power of the secondary side, the condition for taking the maximum value of the output voltage and the output power of the secondary side coil is given, and the maximum value of the output voltage and the output power of the secondary side coil is obtained by analysis under the condition of keeping the section perimeter of a magnetic core, the resistance of the secondary coil and the current of the primary coil unchanged. The area of the cross section of the magnetic core can be increased by changing the size of the cross section of the magnetic core so as to improve parameter values of output voltage and output power of the secondary side coil to optimize the structure of the annular magnetic core.

Description

Technical Field

[0001] The invention belongs to the technical field of mutual inductors, and in particular relates to a method for optimizing a ring-shaped magnetic core of an intrusive mutual inductor. Background Art

[0002] In my country's power system, high-voltage overhead transmission lines are very important. They are responsible for transmitting electricity from power stations over long distances to various power consumption areas. However, these transmission lines are often faced with a variety of potential threats and challenges due to their exposure to the outdoor environment, such as extreme weather, external force damage, and equipment aging. Therefore, real-time monitoring of these lines is crucial to prevent accidents and ensure the stability and safety of power supply. At present, the power supply methods used for online monitoring of high-voltage transmission lines include the use of batteries, solar energy, vibration energy, and laser technologies. Although these methods have their own advantages, after in-depth analysis and comparison, it is found that they have certain limitations in meeting the needs of long-term and stable power supply, and may not be able to fully meet the development needs of online monitoring systems.

[0003] There are alternating electric and magnetic fields around high-voltage transmission lines, which provides the possibility of developing a new energy collection method. The method of using current transformers (CTs) to inductively extract power from transmission lines has become a widely adopted and increasingly valued power supply technology due to its low cost, strong environmental adaptability, simple operation, long power supply cycle and stable power output. The core of this method is the current transformer, which can sense and extract electrical energy from high-voltage transmission lines to provide the required power for monitoring equipment. Since the electromagnetic field of the transmission line is directly utilized, this method does not rely on external energy, so it has better sustainability and reliability. In addition, this method also has low maintenance costs and a long service life, which helps to reduce overall operating expenses. The method of inductively extracting power through current transformers can not only provide stable and continuous power support for the online monitoring system of high-voltage overhead transmission lines, but also because of its high efficiency and economic characteristics, it is expected to become an important direction for the development of power system monitoring technology in the future.

[0004] There is an alternating magnetic field around high-voltage transmission lines, and energy can be extracted using the principle of electromagnetic induction. The typical solution is the current transformer (CT). The specific method is to install a CT energy extraction device near the transmission line. When an alternating current flows through the transmission line, the secondary coil of the CT energy extraction device will induce a voltage, which is then processed by modules such as rectification, filtering, surge protection, and voltage stabilization to power the equipment.

[0005] CT (current transformer) is mainly classified into two types: measuring CT and power CT. Measuring transformers measure larger currents through multi-turn windings and are suitable for low-voltage and medium-voltage applications, such as power monitoring in residential and commercial buildings. Power transformers are directly mounted on high-voltage conductors and are used in high-voltage systems such as substations and transmission lines to monitor current and perform protection and control. Both are used in power systems to accurately measure current, provide overcurrent protection, and analyze and manage power supply networks.

[0006] CT energy harvesting devices can be classified into two categories, non-invasive and invasive, depending on their structure and installation location. These devices are designed to effectively harvest energy from the busbar or transmission line of the power system, and their specific implementation depends on the technical requirements and application environment to be adapted.

[0007] The non-intrusive device is characterized by the non-closed structure of its magnetic core, which allows the device to be placed directly on the surface of the high-voltage transmission line busbar without physically invading the circuit system. The advantage of this design is the easy deployment and high versatility of the device, making it particularly suitable for occasions where the installation space is limited or there are strict requirements on the invasiveness of the equipment, such as switch cabinets, substation busbars and transmission cables. In addition, the non-intrusive device has a wide range of adaptability and can be applied to busbars of various sizes and current specifications. However, due to the non-closed structure of the magnetic core, it has a low coupling efficiency, resulting in lower output power and power density than invasive devices under the same bus current conditions.

[0008] Invasive devices achieve higher coupling coefficients and input power by embedding the magnetic field source in the energy harvesting module. This structural design provides obvious advantages in energy conversion efficiency and is particularly suitable for applications that require higher power output, such as large industrial facilities or high-load equipment. Despite this, the installation process of invasive devices is relatively complicated and usually requires precise installation in specific locations, which not only increases the difficulty and cost of installation, but may also cause additional mechanical stress on the bus or transmission line due to the large size and weight of the device, thereby accelerating the aging process of the equipment and structure, affecting the overall stability and safety of the system.

[0009] In summary, when selecting a suitable CT energy harvesting device, the device's installation convenience, energy efficiency, cost, and potential long-term impact on the power system must be considered comprehensively. Through reasonable design and installation strategies, the advantages of these devices can be effectively utilized while reducing their potential risks and adverse effects. Summary of the invention

[0010] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for optimizing the annular magnetic core of an intrusive mutual inductor.

[0011] In order to achieve the purpose of the present invention, we will adopt the following technical solution to implement it:

[0012] A method for optimizing an annular magnetic core of an intrusive mutual inductor comprises the following steps:

[0013] S1. Equivalent the rectifier circuit and its subsequent circuit to resistive reactance, and establish an equivalent model of the transformer energy source based on the equivalent power source topology structure;

[0014] S2. According to the transformer energy source equivalent model established in step S1, while ignoring the secondary coil leakage inductance and the subsequent circuit line loss, the expression of the transformer energy source equivalent model is established based on the electromagnetic induction law and the full current law:

[0015]

[0016] In the formula, H m is the magnetic field strength inside the coil; l is the average magnetic circuit strength; I m is the excitation current; E2 is the secondary voltage of the coil; f is the frequency of the AC current, which is 50Hz; Φ m is the magnetic flux; S is the cross-sectional area of ​​the core; B m is the magnetic induction intensity inside the coil; μ0 is the magnetic permeability of vacuum, which is 4π×10-7H / m; μ r is the relative magnetic permeability of the core material; H m is the magnetic field strength of the primary coil; N1 and N2 are the turns of the primary and secondary coils respectively; I1 and I2 are the primary and secondary currents respectively;

[0017] S3. According to the expression in step S2, a vector diagram of the relationship between the secondary-side induced electromotive force and the current is established. Combining the principles of electromechanics and the vector relationship between the secondary-side induced electromotive force and the current in the annular magnetic core structure of the intrusive transformer, the solution is obtained:

[0018]

[0019] S4. According to the expression established in step S2 and the solution result of step S3, the secondary side output voltage E2 is derived. According to the secondary side output voltage E2, the secondary coil output voltage U2 is derived by setting parameter ɑ, and then the secondary side output power P is derived according to the secondary coil output voltage U2; wherein:

[0020] The expression of the parameter ɑ is:

[0021]

[0022] The expression of the secondary side output voltage E2 is:

[0023]

[0024] The expression of the secondary coil output voltage U2 is:

[0025]

[0026] The expression of the secondary side output power P is:

[0027]

[0028] S5. When the intrusive transformer is powered by power supply and the magnetic core is not saturated, by analyzing the factors affecting the secondary coil output voltage U2 and the secondary side output power P, it is concluded that if and only if R = αN2 2 When , the secondary coil output voltage U2 and output power P take the maximum value;

[0029] S6. According to the analysis result of step S5 and the relationship between the parameters of the ring core structure of the intrusive transformer, it is obtained through analysis that: while keeping the core cross-section perimeter L, the secondary coil resistance and the primary coil current unchanged, the core cross-section area can be increased by changing the size of the core cross-section to increase the value of the parameter ɑ of the secondary coil output voltage U2 and the output power P to optimize the structure of the ring core; wherein:

[0030] The dimension is the radial length a of the core cross section;

[0031] The relationship between the parameters is as follows:

[0032] a=(Do-Di) / 2

[0033] L=(a+W)×2

[0034] Wherein, L is the circumference of the core cross section; a is the radial length of the core cross section; W is the width of the core cross section; Do is the outer diameter of the annular core; Di is the aperture of the annular core.

[0035] As a preferred solution of the present invention, when there is no current fluctuation, reducing the magnetic path length l and increasing the core cross-sectional area S can increase the secondary side output voltage and the secondary side output power.

[0036] As a preferred solution of the present invention, the derivation process of the secondary coil output voltage U2 is as follows:

[0037]

[0038] According to the expression of secondary side output voltage E2:

[0039] set up Then the secondary coil output voltage U2 is:

[0040]

[0041] Rearranging formula (4) yields:

[0042]

[0043] As a preferred solution of the present invention, when the intrusive transformer is powered by an energy source, the secondary side output voltage is related to the primary side current of the coil, the number of turns of the secondary side coil, the magnetic permeability, size and load of the magnetic core.

[0044] As a preferred solution of the present invention, when the magnetic core is not saturated, the secondary side output power reaches a maximum value.

[0045] As a preferred solution of the present invention, the outer diameter Do and the width W of the annular magnetic core can change with the change of the radial length a.

[0046] As a preferred solution of the present invention, the secondary coil output voltage U2 and output power P can change with the change of radial length a.

[0047] Beneficial Effects

[0048] The present invention verifies through simulation experiments that, when the core cross-section perimeter L is equal and the secondary coil resistance is equal, the power-taking capacity of the mutual inductor with an elliptical cross-section core is better than that of a rectangular cross-section core;

[0049] When the input current of the primary coil is small, the magnetic core does not undergo magnetic saturation, and the maximum output power of the transformer with an elliptical cross-section core is about 34% higher than that of the transformer with a rectangular cross-section core; but the maximum output power density of the transformer with an elliptical cross-section core is only about 1.3% lower than that of the transformer with a rectangular cross-section core. It only requires a small increase in the volume of the core to improve the power supply capacity of the transformer. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is the equivalent model of the transformer energy extraction circuit;

[0051] Figure 2 The vector diagram of the relationship between the induced electromotive force and the current on the secondary side;

[0052] Figure 3 It is a structural schematic diagram of the transformer core;

[0053] Figure 4 is the graph of the induced voltage of the secondary coil changing with the radial length;

[0054] Figure 5 The graph of the output power of the secondary coil changing with the radial length;

[0055] Figure 6The figure is the variation of the induced voltage of the secondary coil of the rectangular core mutual inductor with the number of turns of the secondary coil and the equivalent load of the secondary coil;

[0056] Figure 7 The figure is the variation of the induced voltage of the secondary coil of the elliptical core mutual inductor with the number of turns of the secondary coil and the equivalent load of the secondary coil;

[0057] Figure 8 The output power of the secondary coil of the rectangular core mutual inductor varies with the number of turns of the secondary coil and the equivalent load of the secondary coil;

[0058] Fig. 9 The output power of the secondary coil of the elliptical core mutual inductor varies with the number of turns of the secondary coil and the equivalent load of the secondary coil;

[0059] Fig.10 The figure is the variation of the output power density of the rectangular core mutual inductor with the number of turns of the secondary coil and the equivalent load of the secondary coil;

[0060] Fig.11 This is a graph showing the output power density of the elliptical core transformer as a function of the number of secondary coil turns and the secondary coil equivalent load. DETAILED DESCRIPTION

[0061] The present invention will be further described below in conjunction with specific embodiments and drawings.

[0062] As an embodiment of the present invention, Figures 1 to 5 As shown, a method for optimizing an annular magnetic core of an intrusive mutual inductor comprises the following steps:

[0063] In order to analyze the factors affecting the output voltage and output power of the energy-harvesting coil, the rectifier circuit and its subsequent circuit are equivalent to resistive reactance. Based on the equivalent power supply topology, an equivalent model of the transformer energy-harvesting power supply is established, such as Figure 1 shown.

[0064] Ignoring the secondary coil leakage inductance and the subsequent circuit line loss, based on the law of electromagnetic induction and the law of full current, we can obtain:

[0065]

[0066] In the formula, H m is the magnetic field strength inside the coil; l is the average magnetic circuit strength; I m is the excitation current; E2 is the secondary voltage of the coil; Φ m is the magnetic flux; S is the cross-sectional area of ​​the core; B m is the magnetic induction intensity inside the coil; N1, N2 are the turns of the primary and secondary coils; I1, I2 are the primary and secondary currents.

[0067] Since the parameters such as coil line loss, core hysteresis loss, eddy current loss and leakage inductance voltage drop loss are small, they can be ignored when analyzing the induction energy of the transformer power supply. Therefore, this paper uses the simplified secondary side induced electromotive force and current relationship vector diagram for analysis and calculation, such as Figure 2 shown.

[0068] Combining the relevant principles of electrical engineering with Figure 3 The relationship between the induced electromotive force and the current vector on the secondary side can be solved to obtain:

[0069]

[0070] According to equations (1) and (2), the secondary side output voltage is:

[0071]

[0072] set up Then the secondary coil output voltage U2 is:

[0073]

[0074] Rearranging formula (4) yields:

[0075]

[0076] From the secondary side output voltage, the secondary side output power P is:

[0077]

[0078] If and only if R = αN2 2 When , the secondary output voltage U2 and output power P take the maximum value. It can be seen from equations (5) and (6) that when the transformer power supply is powered, the secondary output voltage is related to the primary current of the coil, the number of turns of the secondary coil, the magnetic permeability, size and load of the magnetic core; when the magnetic core is not saturated, the output power has a maximum value. In addition, when the current does not fluctuate, reducing the magnetic path length l and increasing the core cross-sectional area S can increase the secondary output voltage and output power.

[0079] When the cross-sectional perimeter L of the magnetic core is constant and the number of turns Ns of the secondary coil is also constant, the coil resistance of the secondary coil is constant. By ensuring that the cross-sectional perimeter L is constant and continuously changing the cross-sectional dimensions of the rectangular cross-sectional and elliptical cross-sectional magnetic cores, the area and area distribution of the magnetic core can be optimized, thereby improving the parameter α of formulas (5) and (6).

[0080] The dimensions of the transformer are: aperture Di = 65mm, core cross-section perimeter L = 218mm. The outer diameter Do and width W of the optimized transformer will vary with the radial length a of the core cross-section. The relationship between the dimensions is as follows: Figure 3 As shown;

[0081] The relationship between the parameters is as follows:

[0082] a=(Do-Di) / 2

[0083] L=(a+W)×2

[0084] The number of turns Ns of the secondary coil is set to 250 turns, the secondary coil load RL is 250 ohms, a is the radial length of the rectangle, and also the radial length of the elliptical cross section. Keeping the circumference of the core cross section unchanged, when the primary coil current I = 20A, the induced voltage of the secondary coil changes with the radial length as shown in Figure 4 As shown, the output power of the secondary coil varies with radial length as Figure 5 shown.

[0085] When the core diameter of the transformer is Di = 65mm, the core cross-section perimeter is L = 218mm, the number of turns of the secondary coil is Ns = 250, and the secondary coil load is RL = 250Ω, the radial length of the core cross section is 43 ± 2mm, and the transformer power supply effect is optimal. The core with an elliptical cross section has a better power supply effect than the core with a rectangular cross section.

[0086] As an embodiment of the present invention, Figure 6 and Figure 7 As shown, the radial length a of the rectangular cross-section core and the elliptical cross-section core is determined to be 43 mm. When the primary coil input current Ip = 20A, the power-taking capacity comparison of the two cores is obtained as follows:

[0087] 1. When the number of turns of the secondary coil is constant, the induced voltage of the secondary coil increases with the increase of the load of the secondary coil, and finally the induced voltage tends to saturation (the corresponding voltage is called saturation voltage);

[0088] 2. The larger the number of turns of the secondary coil, the larger the saturation voltage of the secondary coil, and the larger the minimum load corresponding to the saturation voltage;

[0089] 3. Comparing the elliptical and rectangular cores, it is found that the saturation voltage of the elliptical core is about 30% higher than that of the rectangular core under the same number of coil turns.

[0090] As an embodiment of the present invention, Figure 8 and Fig. 9 As shown in the figure, when the core is not saturated, the maximum output power of the transformer with an elliptical core is about 34% higher than that of the transformer with a rectangular core.

[0091] As an embodiment of the present invention, Fig.10 and Fig.11 As shown in the figure, when the core is not saturated, the maximum output power density of the transformer with an elliptical core is only about 10W / m lower than that of the transformer with a rectangular core. 3 , only about 1.3% lower.

[0092] The technical solution of the present invention is described in detail above in conjunction with the embodiments / drawings, but the present invention is not limited to the above technical solution. For ordinary technicians in this technical field, after knowing the contents recorded in the present invention, they can make several equivalent changes and substitutions without departing from the principle of the present invention. These equivalent changes and substitutions should also be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for optimizing an annular core of an intrusive mutual inductor, characterized in that: The steps include: S1. Equivalent the rectifier circuit and its subsequent circuit to resistive reactance, and establish a transformer energy-taking power supply circuit model based on the power supply equivalent topology structure; S2. According to the transformer energy source circuit model established in step S1, while ignoring the secondary coil leakage inductance and the subsequent circuit line loss, an equivalent model of the transformer energy source is established based on the law of electromagnetic induction and the law of full current: In the formula, H m is the magnetic field strength inside the coil; l is the average magnetic circuit strength; I m is the excitation current; E2 is the secondary voltage of the coil; f is the frequency of the AC current, which is 50Hz; Φ m is the magnetic flux; S is the cross-sectional area of ​​the magnetic core; B m is the magnetic induction intensity inside the coil; μ0 is the magnetic permeability of vacuum, which is 4π×10-7H / m; μ r is the relative magnetic permeability of the core material; H m is the magnetic field strength of the primary coil; N1 and N2 are the turns of the primary and secondary coils respectively; I1 and I2 are the primary and secondary currents respectively; S3. According to the equivalent model of the transformer energy source, a vector diagram of the relationship between the secondary side induced electromotive force and the current is established. Combining the principles of electrical machinery and the vector relationship between the secondary side induced electromotive force and the current in the ring core structure of the intrusive transformer, the solution is obtained: S4. According to the equivalent model of the transformer energy source and the solution result of step S3, the secondary side output voltage E2 is derived. According to the secondary side output voltage E2, the secondary coil output voltage U2 is derived by setting the parameter ɑ, and then the secondary side output power P is derived according to the secondary coil output voltage U2; wherein: The expression of the parameter ɑ is: The expression of the secondary side output voltage E2 is: The expression of the secondary coil output voltage U2 is: The expression of the secondary side output power P is: S5. When the intrusive transformer is powered by power supply and the magnetic core is not saturated, by analyzing the factors affecting the secondary coil output voltage U2 and the secondary side output power P, it is concluded that if and only if R = αN2 2 When , the secondary coil output voltage U2 and output power P take the maximum value; S6. By analyzing the analysis result of step S5 and the relationship between the parameters of the ring core structure of the intrusive transformer, it is obtained that: while keeping the core cross-section perimeter L, the secondary coil resistance and the primary coil current unchanged, the core cross-section area can be increased by changing the size of the core cross-section to increase the value of the parameter ɑ of the secondary coil output voltage U2 and the output power P to optimize the structure of the ring core; wherein: The dimension is the radial length a of the core cross section; The relationship between the parameters is as follows: a=(Do-Di) / 2; L = (a + W) × 2; Wherein, L is the circumference of the core cross section; a is the radial length of the core cross section; W is the width of the core cross section; Do is the outer diameter of the annular core; Di is the aperture of the annular core.

2. The optimization method of an intrusive transformer annular core according to claim 1, characterized in that: When there is no current fluctuation, reducing the magnetic circuit length l and increasing the core cross-sectional area S can increase the secondary side output voltage and secondary side output power.

3. The optimization method of an intrusive transformer annular core according to claim 1, characterized in that: The derivation process of the secondary coil output voltage U2 is as follows: According to the expression of secondary side output voltage E2: set up Then the secondary coil output voltage U2 is: Rearranging formula (4) yields:

4. The optimization method of an intrusive transformer annular core according to claim 1, characterized in that: When the intrusive transformer is powered by an energy source, the secondary output voltage is related to the primary current of the coil, the number of turns of the secondary coil, the magnetic permeability and size of the magnetic core and the load.

5. The optimization method of an intrusive transformer annular core according to claim 1, characterized in that: When the magnetic core is not saturated, the secondary side output power reaches its maximum value.

6. The optimization method of an intrusive transformer annular core according to claim 1, characterized in that: The outer diameter Do and the width W of the annular magnetic core can vary with the radial length a.

7. The optimization method of an intrusive transformer annular core according to claim 1, characterized in that: The secondary coil output voltage U2 and output power P can vary with the radial length a.

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