High-voltage cable terminal energy taking device and method

Abstract

The invention discloses a high-voltage cable terminal energy taking device and method, and belongs to the technical field of power equipment.The method comprises the steps that firstly, the CT power taking principle is analyzed, modeling is conducted on an induction power taking CT, the relation between output power and the number of turns on the secondary side and the relation between output power and resistive loads are deduced from the two aspects of load current continuity and discontinuity, the number of turns is optimized according to the specific resistance value, and the power taking current is obtained; the CT is enabled to work in a high output power state, so that the energy-taking power supply efficiency is improved. Secondly, analyzing the influence degree of the saturation magnetic induction intensity of the iron core on the power taking output power, and considering that the induction electromotive force waveform is distorted when the iron core enters a saturation state to cause heating of the iron core to influence energy extraction, so that how to select a proper magnetic core material is determined under the condition that the utilization rate of the magnetic core is improved as much as possible; and determining the effective magnetic path length of the magnetic core, the cross section area of the magnetic core and the parameters of the secondary coil to avoid the saturation phenomenon of the magnetic core.

Description

Technical Field

[0001] The present invention belongs to the technical field of electric power equipment, and in particular to a high-voltage cable terminal energy extraction device and method. Background Art

[0002] The safe operation of the power system is related to the country's economic development and the normal life of the people. As the main artery for transmitting electric energy, the normal operation of high-voltage transmission lines is an important prerequisite for maintaining the safety and stability of the power system. The insulation characteristics and cable joint resistance of power cables and their accessories under high-voltage and high-current conditions will change during long-term operation. These characteristics will endanger the safe operation of the cable to a certain extent. In order to ensure the safe operation of high-voltage lines, it is necessary to discover potential problems in a timely manner and take preventive measures to avoid power outages. Therefore, it is necessary to monitor the operation status of the line in real time. With the development of my country's smart grid, more and more online monitoring equipment has been applied to the power system, and higher requirements have been put forward for online monitoring technology of transmission lines. However, online monitoring equipment has extremely high requirements for power supply. At present, the more commonly used power supply methods include solar cell power supply, current transformer power supply, capacitor voltage divider power supply, laser power supply, etc. The power supply of solar cells will be affected by the weather and needs to be configured with batteries, but the life of batteries is limited. Due to the stable voltage on the high-voltage line, the output power of the capacitor voltage divider power supply is stable, but its output power is small. The output power of the laser power supply is stable, but the output power is limited, and the power semiconductor laser has a short life and high cost. Current transformer energy extraction, or CT energy extraction, has a basic working mechanism of converting the magnetic field energy generated by the high-voltage line current into electrical energy using electromagnetic induction. Since it uses electromagnetic induction, it has its own isolation effect, so it solves the problem of electrical insulation of high-voltage lines. It is economical and has a large output power. It is currently a more commonly used power supply method with development prospects. However, CT energy extraction also has some problems, such as the output power is affected by the line current, there is a power supply dead zone, and when the line current is large, the iron core is prone to over-saturation. The existing solutions to the CT energy extraction problem mainly focus on the following aspects: improving the efficiency of the CT energy extraction power supply, suppressing the saturation of the iron core and reducing the starting current, energy storage methods, and energy discharge. Summary of the invention

[0003] The technical solution of the present invention is as follows: a high-voltage cable terminal energy extraction device and method, comprising the following steps:

[0004] S1 establishes the load working model of the power taking coil and output power analysis: the relationship between the output power and the secondary side turns and the resistance load is derived from the continuous and intermittent load current to achieve the best power taking efficiency;

[0005] S2 power CT parameter design: Analyze the influence of the core saturation magnetic induction intensity on the power output power, clarify the method of determining the core material, the effective magnetic path length of the core, the cross-sectional area of ​​the core and the secondary coil parameters, so as to avoid core saturation while improving the core utilization rate;

[0006] S3 induction power supply design: designed a power management solution based on BQ25505 + super capacitor.

[0007] Furthermore, in the power coil load working model, the primary and secondary coils are N1 and N2 respectively, N1 = 1 turn, i1 and i2 are the high voltage side sinusoidal current and the current actually flowing to the load respectively, i m is the excitation current, according to the law of electromagnetic induction and the transformer magnetomotive force balance equation: N1i1=N2i2+N2i m .

[0008] Furthermore, the relationship between the output power, the number of secondary turns and the resistive load is derived as follows:

[0009] When the load current is continuous, according to the law of electromagnetic induction, the induced voltage across the power coil is

[0010]

[0011] Where S is the cross-sectional area of ​​the core, B c It is the magnetic induction intensity when the magnetic core is working.

[0012] Integrating equation (1) within an AC current cycle T, the absolute value of the square wave voltage across the coil is obtained as follows:

[0013]

[0014] At the same time, u=L m d m / dt, combined with equation (2), we get:

[0015]

[0016] In the formula, A=4(t-kT) / T, k=0,1,2,…,

[0017] Assume the peak value of the primary sinusoidal current is I 1m , the primary current is ω=100π, when t=0, i2=0, i1 / N2 all flows through L m Branch, then:

[0018]

[0019] Considering only the fundamental component of the excitation current, from KCL, the expression of i2 is:

[0020]

[0021] The average current flowing through the load R in a time period T is

[0022]

[0023] Ignoring the voltage drop of the rectifier bridge, the average power flowing through the load R is

[0024]

[0025] According to the formula for determining the inductance of the magnetic ring, we have:

[0026]

[0027] In the formula, μ is the magnetic permeability, l is the effective magnetic path length of the magnetic core,

[0028] Combining equations (2), (7) and (8), we can get the maximum output power P max Time

[0029]

[0030] When the load is continuous, P max It has nothing to do with N2, but only with μ, l, and S; P max The corresponding u and μ, l, S, N2, I 1m About P max The corresponding R is related to μ, l, S, N2, and I 1m Not relevant;

[0031] When the load current is intermittent, i2 = 0; when t = 0, i2 = 0, i1 / N2 and i m Tangent, then:

[0032]

[0033] Combining equations (4) and (10), we can obtain the critical voltage U c for

[0034]

[0035] U c The value determines the state of the circuit. c There will be intermittent phenomenon, otherwise it will be continuous. At time t0, i1 / N2=i m ,but:

[0036]

[0037] As with the continuous analysis, the average current flowing through the load R is

[0038]

[0039] By solving equations (12) and (13) by numerical calculation method, when the load current is intermittent and i2 is zero, the capacitor C discharges to the load R, so the output voltage ripple increases and the output power decreases.

[0040] Furthermore, the design method of the power coil parameters is as follows: analyzing the influence of the saturation magnetic induction intensity of the iron core on the power output power. The design of the power coil needs to improve the utilization of the magnetic core while avoiding the saturation of the magnetic core. The design steps include the selection of the magnetic core material and the determination of l, S, and N2, as follows:

[0041] Determine the power supply parameters, including the range of primary current I 1min ~I 1max , period T, output voltage u and output power P;

[0042] A higher initial magnetic permeability μ can make the high-voltage cable obtain a larger power when the current is small, and a larger saturation magnetic induction intensity B sat The core can adapt to higher u and have a longer service life. Usually the core can be made of laminated silicon steel sheets to obtain a larger μ.

[0043] Set the required P and starting current I 1min Substituting T into equation (9) we can obtain (S / l) min ;

[0044] From formula (9), we can see that when P is the largest, u is related to N2 and I 1m Proportional, u is the preset value of the subsequent circuit, select a voltage stabilization value u, so that the high-voltage cable current is I 1min To obtain sufficient power, we need to set T, u, S / l, μ and I 1min Substitute into formula (9) to calculate the corresponding N2;

[0045] When u is at its maximum value, the core should be prevented from entering oversaturation. sat Substitute into formula (2) to obtain S, and finally obtain l from the value of S / l;

[0046] The inner and outer diameters of the core are denoted as D i , D o , D i is greater than the line diameter D, take Di = 1.1D, and calculate πl = (D i +D o ) / 2, substitute l, D i , find D o ;

[0047] According to I 1max / N2, select the appropriate wire diameter of the power coil winding, combined with D i , D o , l, calculate whether N2 turns of coil can be wound evenly on the core. If so, wind the coil evenly and complete the design; if not, reselect S / l or D i The value of is used to optimize the design parameters of the power taking coil.

[0048] Furthermore, S / l is greater than (S / l) min , S / l=1.5(S / l) min .

[0049] Furthermore, the power management solution is specifically as follows: the power management circuit consists of a Schottky diode rectifier bridge, a diode clamp voltage limiting circuit, a MOS tube overvoltage protection circuit, a BQ25505 low-power energy collection management and supercapacitor charging management. Among them, the Schottky diode rectifier bridge converts AC into DC, the diode clamp voltage limiting circuit is used as the input protection of the BQ25505 to prevent the input voltage from being too high and the iron core from entering deep saturation, the MOS tube overvoltage protection circuit is used to protect the supercapacitor to prevent the capacitor from overcharging, and the BQ25505 is a low-power boost DC / DC charging management that realizes energy collection from an input voltage as low as 130mV. To improve charging efficiency, the supercapacitor charging adopts a pumping method, that is, a hysteresis comparator is used to control a fast, low-loss load switch to transfer the electricity stored in a small capacitor to a supercapacitor.

[0050] The beneficial effects of the present invention are:

[0051] The problems existing in the prior art, such as the output power being affected by the line current, the dead zone of power supply, and the easy over-saturation of the core when the line current is large, are solved. By analyzing the principle of CT power supply, the inductive power supply CT is modeled, and the relationship between the output power and the secondary side turns and the resistive load is derived from the two aspects of continuous and intermittent load current. The factors affecting the power output efficiency and the influence of the saturation magnetic induction intensity of the core on the power output power are analyzed to ensure that the energy-taking device achieves the best power efficiency. Considering that the induced electromotive force waveform will be distorted when the core enters the saturation state, causing the core to heat up and affect the energy extraction, it is necessary to clarify how to select the appropriate core material, the effective magnetic path length of the core, the cross-sectional area of ​​the core, and the secondary coil parameters while maximizing the utilization rate of the core to avoid the occurrence of core saturation. Finally, the inductive power supply is designed under the premise of realizing small current startup and large current protection to provide stable voltage and sufficient power for the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is the power-taking CT load working model of the present invention;

[0053] Figure 2 The current and voltage waveform diagram of the present invention when the load is continuous;

[0054] Figure 3 The waveform diagram of i1 / N2 and im when the load current is critically discontinuous in the present invention;

[0055] Figure 4 The waveform diagram of i1 / N2 and im when the load current is intermittent in the present invention;

[0056] Figure 5 This is a power management solution diagram based on BQ25505+SC of the present invention;

[0057] Figure 6 This is the bq25505+SC energy collection management diagram of the present invention;

[0058] Figure 7 This is the hysteresis comparator and hysteresis characteristic of the present invention. DETAILED DESCRIPTION

[0059] It should be noted that in the description of the present invention, the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", "clockwise", "counterclockwise", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction.

[0060] In the present invention, unless otherwise clearly specified and limited, the terms "set", "install", "connect", "connect" and the like should be understood in a broad sense. For example, "fixed" can be a fixed connection, a detachable connection, or an integral connection; the connection can be a mechanical connection or an electrical connection; the connection can be a direct connection or an indirect connection through an intermediate medium, and can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0061] See also Figures 1 to 6As shown, the present invention is applicable to a high-voltage cable terminal energy extraction device and method. First, the principle of CT power extraction is analyzed, and the inductive power extraction CT is modeled. From the two aspects of continuous and intermittent load current, the relationship between output power and the number of turns on the secondary side and the resistive load is derived. The number of turns is optimized for a specific resistance value, so that the CT works in a state of higher output power, thereby improving the efficiency of the energy extraction power supply. Secondly, the influence of the saturation magnetic induction intensity of the iron core on the output power of power extraction is analyzed. Considering that when the iron core enters the saturation state, the induced electromotive force waveform will be distorted, causing the iron core to heat up and affect the energy extraction, so under the condition of maximizing the utilization rate of the magnetic core, it is clear how to select a suitable magnetic core material, clarify the effective magnetic path length of the magnetic core, the cross-sectional area of ​​the magnetic core, and the secondary coil parameters to avoid the occurrence of magnetic core saturation. Finally, under the premise of realizing small current startup and large current protection, an inductive power supply is designed to provide a stable voltage and sufficient power for the sensor.

[0062] 1. Derivation of the relationship between output power, secondary side turns and resistive load

[0063] Assume that the primary and secondary coils are N1 and N2 respectively, N1 = 1 turn, i1 and i2 are the high voltage side sinusoidal current and the current actually flowing to the load respectively. m is the excitation current. According to the law of electromagnetic induction and the transformer magnetomotive force balance equation: N1i1=N2i2+N2i m , due to the current source nature of the primary line, the primary leakage impedance is ignored. For the power-taking CT, the secondary leakage impedance is much smaller than the excitation impedance and can be ignored. Considering the tube voltage drop of the rectifier bridge, the actual output power can be approximated by the measured load voltage plus the diode voltage drop in the actual power calculation, so it can be ignored in the model. In the excitation impedance, the excitation inductance is much larger than the excitation resistance, so R is ignored. m In summary, the load working model of the power coil is established as follows: Figure 1 .

[0064] The following analyzes the factors affecting the power output from the two aspects of continuous and intermittent load current, derives the relationship between the output power and the secondary side turns and resistive load, and achieves the best power efficiency.

[0065] 1) Load current continuous

[0066] When C is large enough, i2 is continuous, that is, i2 is greater than zero except at the diode reversal point. m The waveform is as Figure 2 .

[0067] According to the law of electromagnetic induction, the induced voltage across the power coil is

[0068]

[0069] Where S is the cross-sectional area of ​​the core, B c It is the magnetic induction intensity when the magnetic core is working.

[0070] By integrating equation (1) within an AC current cycle T, the absolute value of the square wave voltage across the coil is obtained as follows:

[0071]

[0072] At the same time, u=L m d m / dt, combined with equation (2), we can get:

[0073]

[0074] In the formula, A=4(t-kT) / T, k=0,1,2,….

[0075] Assume the peak value of the primary sinusoidal current is I 1m , when Figure 2 At the waveform moment, the primary current is ω=100π, when t=0, i2=0, i1 / N2 all flows through L m Branch road, then:

[0076]

[0077] Considering only the fundamental component of the excitation current, from KCL, the expression of i2 can be approximated as

[0078]

[0079] The average current flowing through the load R in a time period T is

[0080]

[0081] Ignoring the voltage drop of the rectifier bridge, the average power flowing through the load R is

[0082]

[0083] According to the formula for determining the inductance of the magnetic ring, we have:

[0084]

[0085] Where μ is the magnetic permeability and l is the effective magnetic path length of the core.

[0086] Combining equations (2), (7) and (8), we can get the maximum output power P max Time

[0087]

[0088] It can be seen from the above formula that when the load is continuous, P max It has nothing to do with N2, but only with μ, l, and S; P max The corresponding u and μ, l, S, N2, I 1m About P max The corresponding R is related to μ, l, S, N2, and I 1m Not relevant.

[0089] 2) Load current is intermittent

[0090] Considering the critical discontinuous situation, i2=0, i1 / N2 and i m satisfy Figure 3 When t=0, i2=0, i1 / N2 and i m Tangent, then:

[0091]

[0092] Combining equations (4) and (10), we can obtain the critical voltage U c for

[0093]

[0094] U c The value determines the state of the circuit. c There will be a discontinuous phenomenon, otherwise it will be continuous. m Relationship Figure 4 shown.

[0095] At t0, i1 / N2=i m , then:

[0096]

[0097] As with the continuous analysis, the average current flowing through the load R is

[0098]

[0099] Equations (12) and (13) are solved by numerical calculation method. When the load current is intermittent and i2 is zero, the capacitor C discharges to the load R, so the output voltage ripple increases and the output power decreases.

[0100] 2. Method for determining core material, effective magnetic path length, cross-sectional area of ​​core and secondary coil parameters

[0101] In order to simplify the analysis, it is assumed that before the core material enters the saturation state, the magnetic induction intensity B changes linearly with the magnetic field intensity. The magnetic saturation characteristics will cause the induced electromotive force waveform to be distorted. The larger the wire current, the higher the ratio of the core in the saturation zone to the linear zone, the more serious the distortion, and the induced electromotive force will have spike distortion. When the secondary side is connected to the rectifier bridge and energy storage capacitor, the output spike pulse of the secondary voltage u is reduced due to the voltage stabilization effect of the capacitor, and the actual waveform is close to a trapezoidal wave. As the wire current increases, the secondary induced electromotive force waveform gradually tends to a rectangular wave.

[0102] Since the peak value of the induced electromotive force of the secondary winding is the voltage across the capacitor, it can be seen from formula (1) that the slope of the magnetic induction intensity is inversely proportional to the number of turns of the secondary winding, that is, the fewer the number of turns, the greater the slope of the magnetic induction intensity in the peak area.

[0103] The following three working states are discussed.

[0104] ① State 1: The number of turns of the secondary winding is small. Because the maximum induced electromotive force of the secondary winding is a constant value (capacitor voltage). Because N2 is relatively small, the rate of change of the magnetic induction intensity of the iron core is relatively large. Limited by the saturation magnetic induction intensity of the iron core, the excessive magnetic induction intensity slope causes the iron core to enter the magnetic saturation zone early, causing the induced electromotive force waveform to become narrower. At this time, since the energy is concentrated in a short time, the charging current pulsates greatly. In this state, the iron core works in the magnetic saturation zone for a long time, which easily causes the iron core to heat up and the power extraction efficiency to decrease.

[0105] ② State 2: The secondary winding has more turns. The corresponding change rate of the magnetic induction intensity of the core is small, resulting in the core magnetic induction intensity not having enough time to enter the magnetic saturation zone. Therefore, the core always works in the non-saturation zone, and the induced electromotive force presents a triangular wave. Because the induced voltage is small, the efficiency of energy extraction from the wire is relatively low.

[0106] ③ State 3: On the basis of state 2, the number of turns of the secondary winding is gradually reduced, and the fluctuation range of the magnetic induction intensity will gradually increase. When the fluctuation amplitude of the magnetic induction intensity reaches the saturation magnetic induction intensity, the induced electromotive force waveform presents a relatively large triangle wave with a waveform width of the power frequency cycle. At this time, the amplitude of the induced electromotive force becomes larger than that of state 2. Since there is no spike pulse phenomenon in state 1, the charging current fluctuation is smaller than that of state 1, and the charging efficiency is relatively high, and the iron core works in the non-saturated zone, and the heat generated by the iron core is small. Therefore, this state is called the optimal charging state.

[0107] The design of the power coil should maximize the utilization of the core while avoiding core saturation. The design steps include the selection of core materials and the determination of l, S, and N2, as follows:

[0108] ① Determine the power supply parameters, including the range of primary current I1min ~I 1max , period T, output voltage u and output power P;

[0109] ② A higher initial magnetic permeability μ can make the high-voltage cable obtain greater power when the current is small, and a larger saturation magnetic induction intensity B sat It can make the core adapt to higher u and have longer service life. Usually the core can be made of laminated silicon steel sheets to obtain a larger μ;

[0110] ③ Set the required P and starting current I 1min Substituting T into formula (9) we can obtain (S / l) min In actual design, S / l should be greater than (S / l) min , take S / l = 1.5(S / l) min ;

[0111] ④ From formula (9), we can see that when P is the largest, u is related to N2 and I 1m In addition, u is also the preset value of the subsequent circuit. A voltage stabilization value u can be selected to make the high-voltage cable current I 1min When sufficient power is obtained, T, u, S / l, μ and I 1min Substitute into formula (9) to calculate the corresponding N2;

[0112] ⑤ When u is at its maximum value, the core should be prevented from entering oversaturation. Substitute T, u, N2 and Bsat into formula (2) to obtain S, and finally l can be obtained from the value of S / l;

[0113] ⑥The inner and outer diameters of the core are denoted as D i , D o Considering the space required for coil winding, D i It should be slightly larger than the line diameter D, and D i =1.1D. Rough calculation: let πl = (D i +D o ) / 2. Substitute l and D i , we can get D o ;

[0114] ⑦According to I 1max / N2, select the appropriate wire diameter of the power coil winding, and then combine D i , D o , l, estimate whether the N2 turns of coil can be wound evenly on the magnetic core. If it can, the coil is wound evenly and the design is completed; if it cannot, that is, the winding wire diameter is too large, then you can reselect S / l in step ③ or D in step ⑥. i The value of is used to optimize the design parameters of the power taking coil.

[0115] 3. Design of induction power supply management solution

[0116] The principle of CT power supply is to use current transformer to obtain electric energy. The output power of the power supply changes with the primary current. Since the primary current range is large, CT power supply must be able to adapt to a wide current working range, have a low starting current and withstand large impact current. In order to achieve a starting current of 2A, a power management solution based on BQ25505 + super capacitor (SC) is designed. Figure 5 As shown. The power management circuit is mainly composed of Schottky diode rectifier bridge, diode clamp voltage limiting circuit, MOS tube overvoltage protection circuit, BQ25505 low-power energy collection management, supercapacitor charging management, etc. Among them, the Schottky diode rectifier bridge converts AC to DC. The diode clamp voltage limiting circuit is used as the input protection of BQ25505 to prevent the input voltage from being too high and the core from entering deep saturation. The MOS tube overvoltage protection circuit is used to protect the SC and prevent the capacitor from overcharging. BQ25505 is a low-power boost DC / DC charging management that can realize energy collection from an input voltage as low as 130mV. In order to improve the charging efficiency, the SC charging adopts the pumping method, that is, the hysteresis comparator is used to control the fast and low-loss load switch to transfer the electricity stored in the small capacitor to the SC.

[0117] 1) Rectification and input limiting circuit

[0118] like Figure 5 As shown in the figure, the diode rectifier bridge uses a low voltage drop 3A Schottky diode SS34. The input limiter circuit uses three 3A rectifier diodes S3M connected in series, which are connected in parallel on the DC side to limit the input voltage to 2.1V.

[0119] 2) Boost DC / DC circuit based on bq25505

[0120] BQ25505 is a micropower collection solution designed by Ti that is particularly suitable for ultra-low power applications. It can collect power in the μW to mW range from high output impedance DC sources (such as thermoelectric generators, photovoltaic cells) or AC-DC rectifier bridges and piezoelectric generators. BQ5505 integrates a high-efficiency, pulse-width frequency modulated boost / charge DC-DC, which can continuously collect energy at input voltages as low as 130mV.

[0121] This solution uses the energy collection method of BQ25505+SC. The application circuit schematic is as follows Figure 6 As shown. Among them, select R6 = 3MΩ and R7 = 18MΩ, set the maximum power tracking point to 0.85; R1 = 1.8MΩ and R2 = 1.8MΩ, set the overvoltage action threshold to 5.08V; R3 = 300kΩ, R4 = 2.2MΩ and R5 = 1.3MΩ, set the battery voltage VBAT_SEC normal operating range to 3.26V ~ 3.54V, used to charge SC.

[0122] 3) Voltage monitoring and hysteresis comparator parameter calculation

[0123] In order to improve the SC charging efficiency and prevent the capacitor from overcharging and over-discharging, as well as provide a stable 3.3V power rail to the sensor, three sets of voltage monitoring circuits based on hysteresis comparators are used, and the corresponding load switches are controlled to achieve power path management. Figure 7 As shown. TLV3012 has a built-in 1.242V reference voltage output. The first group of voltage monitoring circuits monitors the BQ25505 output pin VBAT_SEC, controls the load switch RT9701, and implements SC charging management. The second group of voltage monitoring circuits monitors the SC voltage VCC, controls the DC side MOS tube, and prevents the capacitor from overcharging. The third group of voltage monitoring still monitors VCC, controls another load switch RT9701 to output VOUT, and VOUT then supplies power to the load through a 3.3V LDO to prevent the capacitor from over-discharging.

[0124] Hysteresis comparator voltage upper limit V th1 and the lower limit V th2 The calculation formulas are as follows:

[0125]

[0126] The hysteresis parameters of the three voltage monitoring circuits are shown in Table 2.

[0127] Table 2 Parameters and action thresholds of three groups of hysteresis comparators

[0128]

[0129] The above is only a specific implementation of the present invention, but the protection scope of the present invention is not limited thereto. Any modification, equivalent replacement and improvement made by any person skilled in the art within the technical scope disclosed by the present invention and within the spirit and principle of the present invention shall be covered within the protection scope of the present invention. At the same time, the contents not described in detail in this specification belong to the prior art known to those skilled in the art.

[0130] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

Claims

1. A high voltage cable terminal energy extraction device and method, characterized in that: The following steps are involved: S1 establishes the load working model of the power taking coil and the output power analysis: the relationship between the output power and the secondary side turns and the resistance load is derived through the continuous and intermittent load current to achieve the best power taking efficiency; S2 power CT parameter design: Analyze the influence of the core saturation magnetic induction intensity on the power output power, clarify the method of determining the core material, the effective magnetic path length of the core, the core cross-sectional area and the secondary coil parameters, so as to avoid core saturation while improving the core utilization rate; S3 induction power supply design: designed a power management solution based on BQ25505 + super capacitor.

2. A high-voltage cable terminal energy extraction device and method according to claim 1, characterized in that: In the load working model of the power coil, the primary and secondary coils are N1 and N2 respectively, N1 = 1 turn, i1 and i2 are the high voltage side sinusoidal current and the current actually flowing to the load respectively, i m is the excitation current, according to the law of electromagnetic induction and the transformer magnetomotive force balance equation: N1i1=N2i2+N2i m .

3. A high-voltage cable terminal energy extraction device and method according to claim 1, characterized in that: In step S1, the relationship between the output power, the secondary side turns and the resistance load is derived as follows: When the load current is continuous, according to the law of electromagnetic induction, the induced voltage across the power coil is Where S is the cross-sectional area of ​​the core, B c is the magnetic induction intensity when the core is working, Integrating equation (1) within an AC current cycle T, the absolute value of the square wave voltage across the coil is obtained as follows: At the same time, u=L m d m / dt, combined with equation (2), we get: In the formula, A=4(t-kT) / T, k=0,1,2,…, Assume the peak value of the primary sinusoidal current is I 1m , the primary current is ω=100π, when t=0, i2=0, i1 / N2 all flows through L m Branch, then: Considering only the fundamental component of the excitation current, from KCL, the expression of i2 is: The average current flowing through the load R in a time period T is Ignoring the voltage drop of the rectifier bridge, the average power flowing through the load R is According to the formula for determining the inductance of the magnetic ring, we have: In the formula, μ is the magnetic permeability, l is the effective magnetic path length of the magnetic core, Combining equations (2), (7) and (8), we can get the maximum output power P max Time When the load is continuous, P max It has nothing to do with N2, but only with μ, l, and S; P max The corresponding u and μ, l, S, N2, I 1m About P max The corresponding R is related to μ, l, S, N2, and I 1m Not relevant; When the load current is intermittent, i2 = 0; when t = 0, i2 = 0, i1 / N2 and i m Tangent, then: Combining equations (4) and (10), we can obtain the critical voltage U c for U c The value determines the state of the circuit. If the output voltage is higher than U c There will be intermittent phenomenon, otherwise it will be continuous. At time t0, i1 / N2=i m ,but: As with the continuous analysis, the average current flowing through the load R is By solving equations (12) and (13) by numerical calculation method, when the load current is intermittent and i2 is zero, the capacitor C discharges to the load R, so the output voltage ripple increases and the output power decreases.

4. A high-voltage cable terminal energy extraction device and method according to claim 1, characterized in that: The specific method for designing the parameters of the power taking coil is as follows: analyzing the influence of the saturation magnetic induction intensity of the iron core on the power taking output power. The design of the power taking coil needs to improve the utilization of the magnetic core while avoiding the saturation of the magnetic core. The design steps include the selection of the magnetic core material and the determination of l, S, and N2, as follows: Determine the power supply parameters, including the range of primary current I 1min ~I 1max , period T, output voltage u and output power P; A higher initial magnetic permeability μ can make the high-voltage cable obtain a larger power when the current is small, and a larger saturation magnetic induction intensity B sat The core can adapt to higher u and have a longer service life. Usually, the core can be made of laminated silicon steel sheets to obtain a larger μ. Set the required P and starting current I 1min Substituting T into equation (9) we can obtain (S / l) min ; From formula (9), we can see that when P is the largest, u is related to N2 and I 1m Proportional, u is the preset value of the subsequent circuit, select a voltage stabilization value u, so that the high-voltage cable current is I 1min To obtain sufficient power, we need to set T, u, S / l, μ and I 1min Substitute into formula (9) to calculate the corresponding N2; When u is at its maximum value, the core should be prevented from entering oversaturation. sat Substitute into formula (2) to obtain S, and finally obtain l from the value of S / l; The inner and outer diameters of the core are denoted as D i , D o , D i is greater than the line diameter D, take Di = 1.1D, and calculate πl = (D i +D o ) / 2, substitute l, D i , find D o ; According to I 1max / N2, select the appropriate wire diameter of the power coil winding, combined with D i , D o , l, calculate whether N2 turns of coil can be wound evenly on the core. If so, wind the coil evenly and complete the design; if not, reselect S / l or D i The value of is used to optimize the design parameters of the power taking coil.

5. A high-voltage cable terminal energy extraction device and method according to claim 4, characterized in that: S / l is greater than (S / l) min , S / l=1.5(S / l) min .

6. A high-voltage cable terminal energy extraction device and method according to claim 1, characterized in that: The specific power management solution is as follows: the power management circuit consists of a Schottky diode rectifier bridge, a diode clamp voltage limiting circuit, a MOS tube overvoltage protection circuit, a BQ25505 low-power energy collection management and supercapacitor charging management. Among them, the Schottky diode rectifier bridge converts AC into DC, and the diode clamp voltage limiting circuit is used as the input protection of the BQ25505 to prevent the input voltage from being too high and the core from entering deep saturation. The MOS tube overvoltage protection circuit is used to protect the supercapacitor and prevent the capacitor from overcharging. The BQ25505 is a low-power boost DC / DC charging management that realizes energy collection from an input voltage as low as 130mV. To improve charging efficiency, the supercapacitor charging adopts the pumping method, that is, the hysteresis comparator is used to control the fast, low-loss load switch to transfer the electricity stored in the small capacitor to the supercapacitor.

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