A self-powered circuit and method for measuring line current based on magnetic field intensity inversion

Abstract

The application discloses a self-powered line current measurement circuit and method based on magnetic field intensity inversion, which comprises a vertical energy-taking and line current measurement device, a controllable rectification module, a test capacitor, a voltage follower, a hysteresis comparator module, a DC-DC module, an energy storage capacitor, a voltage step-down module and a microprocessor. The vertical energy-taking and line current measurement device converts alternating current energy into direct current energy through the controllable rectification module to charge the test capacitor. The discharge energy of the test capacitor is transmitted to the microprocessor and the energy storage capacitor through the voltage follower, the hysteresis comparator module and the DC / DC module. The time for the test capacitor to charge from a charging threshold to a discharge threshold voltage is cyclically monitored, and the line current is obtained by inversion according to the time. The test capacitor is charged in the mode of inductive magnetic field energy-taking, the line current is inversely deduced by measuring the charging time, and the working states of the controllable rectification and the microprocessor are changed through the control circuit.

Description

Technical Field

[0001] This invention relates to line current measurement technology, and in particular to a self-powered line current measurement circuit and method based on magnetic field strength inversion. Background Technology

[0002] With digital transformation driving high-quality development of power grid construction, a robust, intelligent power grid is gradually becoming a core support for modern power systems. Current measurement, as a core physical quantity for monitoring the operational status of smart grids, plays a crucial role in all aspects of power generation, transmission, distribution, and energy use. The stability and accuracy of high-current measurement technology directly impact the long-term operational safety and reliability of power systems in areas such as grid current surges, power equipment performance evaluation, and fault detection and diagnosis. It has been widely applied in various fields, including monitoring switching losses in power switching devices, current measurement in multi-core cables, and AC / DC testing in digital substations and converter stations.

[0003] Current measurement methods mainly include shunts, Hall sensors, Rogowski coils, magnetoresistive current sensors, and current transformers. The shunt method measures current by the voltage drop across a precision resistor; however, this method requires a customized measurement board for the specific measurement scenario, making it cumbersome and costly. Hall sensors offer high accuracy but are temperature-sensitive, with measurement errors significantly affected by temperature, and are difficult to install. Rogowski coils have good linearity due to the absence of core saturation issues, but their precision metal wires have poor anti-interference capabilities and demanding installation requirements. Magnetoresistive current sensors measure line current by utilizing the resistance change of a micron-sized thin-film structure caused by the magnetic field of a primary current. Their advantages include miniaturization, lightweight design, and high accuracy; however, the energy required for acquiring or outputting current signals in high-altitude or underground environments is challenging. Current transformers, as a traditional current measurement method, are prone to core saturation when the measured current is large, leading to a significant decrease in measurement accuracy.

[0004] Current current measurement technology focuses on measurement accuracy and anti-interference capabilities, but neglects the energy source of active devices for current acquisition and processing. If current measurement devices are installed at high altitudes or buried underground, the cost of regularly replacing batteries is too high, significantly reducing the operational reliability of the devices. Furthermore, most current measurement technologies require complete encapsulation of the conductor being measured, which also limits the development of non-invasive current measurement. Integrating environmental energy harvesting devices, such as solar, wind, and magnetic field energy harvesting devices, directly with current measurement devices undoubtedly increases the device size, failure rate, and installation difficulty. Moreover, the mutual constraints between environmental energy harvesting devices and current measurement application scenarios further limit the application and promotion of new current measurement devices. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a self-powered line current measurement circuit and method based on magnetic field strength inversion, which uses an induced magnetic field to extract energy to power subsequent circuits and measure line current.

[0006] Technical Solution: This invention provides a self-powered line current measurement circuit based on magnetic field strength inversion, comprising: a vertical energy harvesting and line current measurement device, a controllable rectifier module, a test capacitor, a voltage follower, a hysteresis comparator module, a DC-DC module, an energy storage capacitor, a voltage reduction module, and a microprocessor. The vertical energy harvesting and line current measurement device collects AC energy from the power line and converts it into DC energy through the controllable rectifier module to charge the test capacitor. The voltage follower collects the voltage across the parallel resistor of the test capacitor and inputs it, along with the constant output voltage of the voltage reference module, to the hysteresis comparator module. The positive and negative input terminals of the comparator module are connected to the output level signal of the hysteresis comparator module, which is then transmitted to the enable port of the DC-DC module, the voltage buck module, and the controllable rectifier module, respectively, to achieve triple function multiplexing of the level signal. The Vin of the DC-DC module is connected to one end of the test capacitor, and the Vin2 of the DC-DC module provides the power supply voltage to the hysteresis comparator module, the voltage reference module, and the voltage follower through a diode. The output of the DC-DC module is connected to the microprocessor and the energy storage capacitor, the output of the voltage buck module is connected to the microprocessor, and the output of the microprocessor is connected to the host computer.

[0007] Optionally, the parallel resistors across the test capacitor include a first resistor R1 and a second resistor R2 connected in series. By measuring the voltage change across the second resistor R2, the voltage fluctuation of the test capacitor can be obtained.

[0008] Optionally, the hysteresis comparator module includes a first sensing resistor R3 and a second sensing resistor R4, used to control the high and low level outputs of the voltage hysteresis comparator.

[0009] The discharge threshold voltage of the test capacitor corresponding to the high level output of the hysteresis comparator module is expressed as:

[0010]

[0011] Among them, U cd To test the capacitor discharge threshold voltage, U ref U is the constant output voltage of the voltage reference module. c To test the voltage across the capacitor, R1 and R2 are the first and second resistors connected in parallel across the capacitor, respectively, and R1 and R2 are connected in series.

[0012] The charging threshold voltage of the test capacitor corresponding to the low level output of the hysteresis comparator module is expressed as:

[0013]

[0014] Among them, U cc To test the capacitor charging threshold voltage, U p The voltage selection output pin Vin2 of the DC-DC module supplies power to the hysteresis comparator module, voltage reference module, and voltage follower module via a diode.

[0015] Optionally, the time-domain expression for the line current I1(t) is:

[0016] I1(t)=U oc (t) / K

[0017] Among them, U oc (t) represents the open-circuit induced voltage of the secondary winding of the vertical energy harvesting and line current measuring device, and K is U oc The proportionality coefficients of I1(t) and I1(t) can be used to realize the line current inversion measurement through the open-circuit induced voltage of the secondary winding, according to the formula.

[0018] Optionally, the effective value of the line current I1 and the capacitor voltage U c The corresponding charging time t is expressed as:

[0019]

[0020] Among them, R L R is the equivalent resistance of the load. w C is the resistance of the secondary coil of the vertical energy harvesting and line current measuring device, K is the proportionality coefficient between the open-circuit induced voltage of the secondary winding and the line current of the vertical energy harvesting and line current measuring device, and C is the resistance of the secondary coil of the vertical energy harvesting and line current measuring device. t For testing capacitors.

[0021] In one embodiment of the present invention, a method for measuring the current of a self-powered line based on magnetic field strength inversion includes the following steps:

[0022] The AC energy of the power line is obtained using a vertical energy harvesting and line current measuring device, and the test capacitor is charged.

[0023] When the test capacitor voltage first reaches the test capacitor discharge threshold voltage U cd When the hysteresis comparator module outputs a high level, the DC-DC module enters the working state, the test capacitor stops charging, and the discharge energy of the test capacitor is transferred to the microprocessor and the energy storage capacitor through the voltage follower, the hysteresis comparator module, and the DC / DC module. The microprocessor receives a high level, starts its working mode, and consumes energy. The voltage of the test capacitor drops to the test capacitor charging threshold voltage U. cc When the hysteresis comparator module outputs a low level, and the microprocessor captures the falling edge of the hysteresis comparator module output signal, the microprocessor enters sleep mode for the first time, and the test capacitor begins to charge. This moment is recorded as t0.

[0024] When the test capacitor is recharged to the discharge threshold voltage, the microprocessor is woken up by the high level of the hysteresis comparator module. At this time, the current time t1 is recorded. Therefore, the test capacitor is charged from the test capacitor charging threshold voltage U. cc Energy stored up to the test capacitor discharge threshold voltage U cd The time t is t1-t0;

[0025] When the microprocessor detects the falling edge of the hysteresis comparator module again, it re-enters sleep mode and continuously monitors the test capacitor's charging threshold voltage U. cc Energy stored up to the test capacitor discharge threshold voltage U cd The time t decreases as the line current increases, and there is a functional relationship between t and the line current. The measured time t is used to calculate the accurate inverted line current value through function calculation, and finally the inverted line current value is transmitted to the host computer.

[0026] Furthermore, the discharge threshold voltage of the test capacitor corresponding to the high level output of the hysteresis comparator module is expressed as:

[0027]

[0028] Among them, U cd To test the capacitor discharge threshold voltage, U ref U is the constant output voltage of the voltage reference module. c To test the voltage across the capacitor, R1 and R2 are the first and second resistors connected in parallel across the capacitor, respectively, and R1 and R2 are connected in series.

[0029] The charging threshold voltage of the test capacitor corresponding to the low level output of the hysteresis comparator module is expressed as:

[0030]

[0031] Among them, U cc To test the capacitor charging threshold voltage, U p Vin2 of the DC-DC module is supplied via a diode to the hysteresis comparator module, voltage reference module, and voltage follower.

[0032] Furthermore, the capacitor C was tested. t Energy storage capacitor C s Test capacitor discharge threshold voltage U cd and test capacitor charging threshold voltage U cc The following formula must be satisfied:

[0033]

[0034] Where P1 is the power required for the microprocessor to operate, P2 is the power required for the microprocessor to operate, and U... min The minimum supply voltage t required to keep the microprocessor in sleep mode w For the microprocessor's operating time, t s This refers to the microprocessor's sleep time.

[0035] Furthermore, the functional relationship between t and the effective value I1 of the line current is as follows:

[0036]

[0037] Among them, U c To test the voltage across the capacitor, R L R is the equivalent resistance of the load. w C is the resistance of the secondary coil of the vertical energy harvesting and line current measuring device, K is the proportionality coefficient between the open-circuit induced voltage of the secondary winding and the line current of the vertical energy harvesting and line current measuring device, and C is the resistance of the secondary coil of the vertical energy harvesting and line current measuring device. t For testing capacitors.

[0038] Furthermore, the comparison error between the actual current value (i.e., the clamp meter reading) and the inverted current value varies with the actual current value. The comparison error between the actual current value and the inverted current value is expressed as follows:

[0039]

[0040] Where δ represents the error between the inverted current and the actual line current; I1 is the current reading of the clamp meter, representing the effective value of the line current; and I1' is the inverted current.

[0041] Beneficial effects: Compared with the prior art, the advantages of the present invention are: it can combine energy harvesting technology and current measurement technology, which can effectively solve the power supply problem of active devices in current measurement devices. At the same time, it can effectively combine non-invasive current measurement with environmental energy harvesting devices, solving the problem of mutual constraints between the two application scenarios. Moreover, it is less affected by external interference and can achieve high-precision measurement of large current. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of a vertical energy harvesting and line current measuring device, where (a) is a schematic diagram of the device structure; and (b) is an equivalent circuit diagram of the device.

[0043] Figure 2 This is a schematic diagram of the finite element simulation model of the vertical energy harvesting and line current measuring device in an embodiment of the present invention;

[0044] Figure 3 This is a schematic diagram illustrating the changes in line current and test capacitor energy as the test capacitor reaches the charging voltage threshold in an embodiment of the present invention.

[0045] Figure 4 This is a schematic diagram illustrating the change in line current under offset conditions as the charging time required for the test capacitor to reach the charging voltage threshold in an embodiment of the present invention.

[0046] Figure 5 This is a circuit diagram for measuring line current in an embodiment of the present invention;

[0047] Figure 6 This is a flowchart of the microprocessor power management method in an embodiment of the present invention;

[0048] Figure 7 This is a voltage timing diagram in an embodiment of the present invention;

[0049] Figure 8 This is a schematic diagram of the experimental platform in an embodiment of the present invention;

[0050] Figure 9 The following are voltage experiment waveform diagrams in the embodiments of the present invention, wherein (a) is a voltage experiment waveform diagram without energy management; and (b) is a voltage experiment waveform diagram with energy management.

[0051] Figure 10 This is a schematic diagram of the line current versus the charging time of the test capacitor and its fitting curve in an embodiment of the present invention;

[0052] Figure 11 This is a schematic diagram of the error curve in an embodiment of the present invention. Detailed Implementation

[0053] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0054] This embodiment employs a vertical energy harvesting and line current measuring device, the structure of which is as follows: Figure 1 As shown in Figure (a), MFSCM refers to the vertical energy harvesting and line current measuring device, I1 is the line current, and N1 and N2 are the number of turns and layers of the secondary coil of the vertical energy harvesting and line current measuring device, respectively. and Let be the magnetic flux flowing through the air between the energy harvesting winding (i.e., the secondary coil) and the energy harvesting core of the i-th turn, j-th layer coil. Let be the magnetic flux flowing through the energy harvesting core of the i-th coil and j-th layer; m is the distance of the power line from the origin, which is the center point of the energy harvesting core of the vertical energy harvesting and line current measuring device. The selection of m is subject to the following constraints:

[0055] m≥(N1d+r+D / 2) (1)

[0056] Where D is the diameter of the power line, r is the cross-sectional radius of the cylindrical energy extraction core, and d is the diameter of the secondary coil.

[0057] Figure 1 The equivalent circuit diagram of the vertical energy extraction and line current measurement device shown in (a) is as follows Figure 1 shown in (b). In the equivalent circuit, U oc is the open-circuit voltage of the energy extraction winding (i.e., the secondary coil) of the vertical energy extraction and line current measurement device, and R L is the equivalent resistance of the load, C t is the test capacitor, and C t is the filter capacitor that converts the power frequency magnetic field into direct current, and it is also the measured component of the output voltage of the secondary coil of the vertical energy extraction and line current measurement device.

[0058] The total magnetic flux Φ ij (t) flowing through the i-th turn and j-th layer of the coil is expressed as:

[0059]

[0060] Since the coil diameter is extremely small compared to the core volume, the total magnetic flux difference between the odd layers and the adjacent even layers can be ignored. Therefore, taking the even layers of the energy extraction winding as an example, it can be respectively expressed as:

[0061]

[0062] Among them, μ0 is the vacuum magnetic permeability, μ e is the intrinsic magnetic permeability of the energy extraction core, I1(t) is the time-domain form of the power line current, y is the ordinate of the i-th turn and j-th layer of the coil, f(y) is the distance of the i-th turn and j-th layer of the coil from the central axis of the power line. When the magnetic field induction energy extraction device undergoes longitudinal or lateral displacement, in the formula, m = m ± △y, |N2 / 2 - j| = |N2 / 2 - j| ± △z, where △y and △z are the lateral and longitudinal displacement amounts of the vertical energy extraction and line current measurement device. Let the demagnetization factor calculation coefficient a = h / 2r, where h is the height of the cylindrical energy extraction core and r is the radius of the cross-sectional area of the cylindrical energy extraction core. The demagnetization factor k (0 < k < 1) corresponding to different a can be expressed as:

[0063]

[0064] μ r is the relative magnetic permeability of the energy extraction core. The relative magnetic permeability μ r of the commonly used magnetic conductive materials of the vertical energy extraction and line current measurement device is relatively large. For example, the initial relative magnetic permeability of PC40 ferrite is 2300. Further, the intrinsic magnetic permeability μ e of the vertical energy extraction and line current measurement device can be expressed as:

[0065]

[0066] From the above equation, we can see that the time-domain form of the open-circuit voltage U of the energy harvesting winding (i.e., the secondary coil) of the vertical energy harvesting and line current measuring device is... oc (t) is represented as:

[0067]

[0068] Where K is U oc Given the scaling factor between I1(t) and I1(t), the time-domain form of the line current I1(t) can be expressed as:

[0069] I1(t)=U oc (t) / K (7)

[0070] As can be seen from the above formula, the line current inversion measurement can be achieved by using the open-circuit voltage of the energy harvesting winding (i.e., the secondary coil) of the vertical energy harvesting and line current measuring device.

[0071] In the case of resonance, i.e. Where L is the inductance of the secondary coil, and C r ω is the resonant capacitor, and ω is the power frequency angular frequency.

[0072] Ignoring the additional resistance of the coil caused by eddy current effects under non-high frequency operating conditions, the resistance value R of the secondary coil is... w Represented as R w =ρl / S, where ρ is the conductivity of the copper secondary coil, with a value of 0.0172 Ω·mm. 2 / m; S is the cross-sectional area of ​​the secondary coil, and l is the total length of the secondary coil. Furthermore, based on... Figure 1 (b) Equivalent circuit of vertical energy harvesting and line current measuring device, if the test capacitor C t The initial voltage value is 0V, the effective value of the line current I1 and the voltage U across the test capacitor are... c The corresponding charging time t can be expressed as:

[0073]

[0074] Therefore, when the structural parameters of the vertical energy harvesting and line current measuring device and the number of turns of the secondary coil are fixed, the capacitor voltage U is monitored. c Alternatively, the effective value of the line current can be derived from the corresponding charging time t. Therefore, there are two methods for retrieving the line current: 1) By monitoring the voltage U across the test capacitor at a given charging time. c1) Inversely deduce the line current; 2) Inversely deduce the line current by monitoring the test charging time under a given capacitor voltage. Considering the maximum withstand voltage of power electronic devices such as rectifier bridges, the higher the line current, the higher the voltage rise of the test capacitor, which poses a risk of rectifier bridge diode breakdown. Therefore, method 1) is not appropriate. Method 2) After monitoring the test charging time t under a given capacitor voltage, further energy release and storage measures can be taken for the test capacitor, thereby opening up a power supply channel for the current data processing module.

[0075] like Figure 2 The finite element simulation model of the vertical energy harvesting and line current measuring device was built using commercial electromagnetic simulation software. The simulation compares the relationship between the charging time required for the test capacitor of the vertical energy harvesting and line current measuring device to reach a predetermined voltage and the line current at different locations.

[0076] Figure 3 To illustrate the variation of line current and test capacitor energy with the charging time required for the test capacitor to reach the charging voltage threshold, a charging voltage threshold of 5V is set. The charging time and stored energy required for the test capacitor to reach the charging voltage threshold are compared and analyzed with line current under different rectifier diode reverse resistances. The reverse resistance is calculated as the ratio of the maximum DC blocking voltage to the maximum DC reverse current. A vertical energy harvesting and line current measuring device is placed close to the line, with its center point on the same plane as the line centerline, to obtain data such as… Figure 3 The charging time required for the test capacitor to reach the charging voltage threshold and the energy stored in the test capacitor vary with the line current. The current used to calculate the energy stored in the test capacitor is fixed at 50A. Here, RD is the reverse resistance of the diode, derived from... Figure 3 It is known that, since the theoretical calculations assume the rectifier diode to be an ideal device with infinite reverse internal resistance, no conduction voltage or resistance, and no leakage current, the theoretical energy stored in the test capacitor is greater than the energy stored in the simulation. Furthermore, the theoretical time required for the test capacitor to reach a predetermined voltage under the same line current is less than the simulation time. Therefore, there are errors between the theoretical calculations and the simulation results, but the trends remain consistent. When the line current is large, the line current obtained using the reverse resistance of the two types of diodes is basically the same. When the line current is small, the charging time of the test capacitor under the same line current is significantly different. Therefore, the selection of the rectifier diode affects the accuracy of the current measurement based on magnetic field strength inversion in this invention.

[0077] Figure 4This paper analyzes the relationship between the line current and the charging time required for the test capacitor to reach the charging voltage threshold under offset conditions. Using a low forward voltage drop SS54 diode, and assuming a line current of 100A and a test capacitor charging voltage threshold of 5V, the paper examines the correspondence between the line current and the charging time required for the test capacitor to reach the charging voltage threshold under lateral and longitudinal offset conditions of a vertical energy harvesting and line current measuring device. Figure 4 It can be seen that the theoretical or simulated charging time for the test capacitor to reach the charging voltage threshold increases with the increase of the offset. This is due to the reduction in the magnetic field energy captured by the vertical energy harvesting and line current measuring device. Furthermore, under the same offset distance, the charging time of the vertical energy harvesting and line current measuring device is longer than that under the lateral Y-axis offset condition, but the capacitor charging deviation time under offset conditions is still in the second range, which can still meet the timeliness requirements for viewing current data of the vertical energy harvesting and line current measuring device.

[0078] like Figure 5 This is a self-powered high-precision line current measurement circuit based on magnetic field strength inversion. It includes a vertical energy harvesting and line current measurement device, a controllable rectifier module, a test capacitor, a voltage follower, a hysteresis comparator module, a DC-DC module, an energy storage capacitor, a voltage reduction module, and a microprocessor. The vertical energy harvesting and line current measurement device collects AC energy from the power line and converts it into DC energy through the controllable rectifier module to charge the test capacitor. The voltage follower collects the voltage across the parallel resistor on both sides of the test capacitor and inputs it, along with the constant output voltage of the voltage reference module, to the positive and negative input terminals of the hysteresis comparator module, respectively. The output level signal of the hysteresis comparator module is then transmitted to the DC-DC module. The enable port, voltage buck module, and controllable rectifier module enable triple function multiplexing of level signals. The voltage input port Vin of the DC-DC module is connected to one end of the test capacitor. The voltage selection output pin Vin2 of the DC-DC module provides power supply voltage to the hysteresis comparator module, voltage reference module, and voltage follower through a diode. The output of the DC-DC module is connected to the microprocessor and the energy storage capacitor. Considering that the high-level voltage of the hysteresis comparator output is basically consistent with the power supply and is higher than the voltage tolerance range of the microprocessor, it is necessary to step down the high-level signal of the hysteresis comparator. The output of the voltage buck module is connected to the microprocessor, and the output of the microprocessor is connected to the host computer.

[0079] In the diagram, MFSCM refers to the vertical power harvesting and line current measuring device. This device converts AC energy into DC energy to charge the test capacitor via a rectifier bridge. The rectifier bridge is a controllable rectifier; the upper arm has two rectifier diodes, and the lower arm has two switching transistors, each consisting of a MOSFET switch and a body diode. This controllable rectifier circuit, under the control of the control circuit, can control whether the power harvesting device charges the test capacitor. R1 and R2 are resistors connected in parallel across the test capacitor. By monitoring the voltage change of R2, the voltage fluctuation of the test capacitor can be obtained. A voltage follower is used to collect the voltage across resistor R2 and input it to a voltage hysteresis comparator. R3 and R4 are detection resistors that control the high and low level outputs of the voltage hysteresis comparator. U ref This is the constant output voltage of the voltage reference module connected to the negative input terminal of the voltage hysteresis comparator. By changing the values ​​of R3 and R4, the discharge threshold of the test capacitor can be changed. Furthermore, the discharge threshold voltage of the test capacitor corresponding to the high level output of the voltage hysteresis comparator is expressed as:

[0080]

[0081] Among them, U c To test the voltage across the capacitor, U cd To test the capacitor discharge threshold voltage, the capacitor charging threshold voltage corresponding to a low output level of the voltage hysteresis comparator is expressed as:

[0082]

[0083] Among them, U cc To test the capacitor charging threshold voltage, U p The voltage selection output pin Vin2, via a diode, provides the power supply voltage for devices such as the hysteresis comparator module and the voltage reference module. The output level signal of the voltage hysteresis comparator is sent to the enable port (EN) of the DC / DC converter (LTC3388-3), the voltage buck module LDO, and the controlled rectifier module MOSFET, respectively, realizing triple function multiplexing of the level signal.

[0084] When the voltage across the test capacitor U c Reaching U cd When the voltage hysteresis comparator outputs a high level, the LT-3388 energy management chip and the microprocessor enter the working state, and the test capacitor stops charging; when the voltage U across the test capacitor... c Below U cc When the voltage hysteresis comparator outputs a low level, the LT-3388 power management chip and the microprocessor enter sleep mode, and the test capacitor begins to charge.

[0085] The microprocessor consumes extremely low power in sleep mode, at the μA level, and can achieve sub-second timing. When the microprocessor detects the falling edge of the hysteresis comparator output signal (falling edges cannot be detected in sleep mode), the microprocessor enters sleep mode and records the time point t0. When the test capacitor is recharged to the discharge threshold U... cd When the microprocessor is awakened by the high level of the hysteresis comparator, it records time point t1. The time t for the test capacitor to charge from the charging threshold voltage to the discharging threshold voltage is t1-t0, and t is inversely proportional to the line current. When the microprocessor detects the falling edge of the hysteresis comparator again, it re-enters sleep mode. Combining the advantages of the two operating modes of the microprocessor, the alternating operation of the microprocessor's working mode and sleep mode is used to cyclically monitor the time t for the test capacitor to charge from the charging threshold voltage to the discharging threshold voltage. The line current can be calculated from t.

[0086] Figure 6 This is a flowchart of the microprocessor energy management method for a vertical energy harvesting and line current measurement device. It describes a self-powered, high-precision line current measurement method based on magnetic field strength inversion. The method charges a test capacitor by inducing a magnetic field and inversely calculates the line current by measuring the charging time. The control circuit changes the operating state of the controllable rectifier and the microprocessor. The specific steps are as follows:

[0087] 1) The test capacitor is charged using a vertical energy harvesting and line current measuring device. When the voltage of the test capacitor reaches the discharge threshold voltage for the first time, its discharge energy is transferred to the microprocessor and energy storage capacitor through the DC / DC module. The microprocessor is given a high level to start working mode and consumes energy. The voltage of the test capacitor drops to the charging threshold voltage. When the microprocessor captures the falling edge of the voltage hysteresis comparator output signal (the falling edge cannot be captured in the sleep state), the microprocessor enters the sleep state for the first time. This moment is recorded as t0.

[0088] 2) When the test capacitor is recharged to the discharge threshold, the microprocessor is woken up by the high level of the voltage hysteresis comparator. At this time, the current time t1 is recorded. Therefore, the test capacitor has been charged from the charging threshold voltage U. cc Energy stored up to discharge threshold voltage U cd The charging time t is t1-t0;

[0089] 3) When the microprocessor detects the falling edge of the voltage hysteresis comparator again, the microprocessor re-enters sleep mode and jumps to step 1) to continuously monitor the time it takes for the test capacitor to charge from the charging threshold voltage to the discharging threshold voltage, and transmits the line current inverted from this time to the host computer via serial communication.

[0090] As the line current increases, t decreases accordingly, and there is a functional relationship between t and the effective value of the line current I1. This function can be plotted by fitting multiple corresponding t values ​​with the line current value. The measured time t can be used to calculate the accurate effective value of the line current I1 through the function (formula (8)).

[0091] Figure 7 This is a voltage timing diagram, where U out U is the output voltage of the DC / DC module. EN The output voltage of the hysteresis comparator, t w For the microprocessor's operating time, t s For microprocessor sleep time, U min The minimum supply voltage required to keep the microprocessor in sleep mode. Therefore, the test capacitor C... t Energy storage capacitor C s Discharge threshold voltage U cd Charging threshold voltage U cc The following formula must be satisfied:

[0092]

[0093] Where P1 is the power required for the microprocessor to operate, and P2 is the power required for the microprocessor to operate.

[0094] Figure 8 This is a diagram of the experimental platform setup. In the diagram, MFSCM refers to the vertical power harvesting and line current measurement device. The power harvesting core is a PC40 with a cross-sectional diameter of 32mm and a height of 55mm. The secondary coil has a wire diameter of 0.12mm and 30,000 turns. To further improve the charging speed of the test capacitor and reduce the current data acquisition response, an nA-level voltage reference, operational amplifier, LDO, and ultra-low power DC / DC module are used to reduce the additional losses of the vertical power harvesting and line current measurement device. MOSFETs with low turn-on voltage and low turn-off voltage are used to ensure low conduction loss of the current measurement system and full turn-on characteristics under high-level drive of the hysteresis comparator output. A resonant capacitor is added to ensure that the device operates in the maximum power harvesting state.

[0095] Figure 9 These are voltage test waveforms, where (a) is without energy management and (b) is with energy management. U in The input voltage of the rectifier bridge is... Figure 9 As shown in (a), when the microprocessor does not use the power management mode, after the test capacitor discharges for the first time, the DC / DC module maintains 3.3V for a short time because the microprocessor always runs in a high-power mode. Subsequently, when the magnetic field induction power harvesting device disconnects the power supply, the DC / DC output voltage drops to 1.62V, which is insufficient to support the normal operation of the microprocessor.

[0096] Depend on Figure 9 As shown in section (b), after the microprocessor adopts the energy management method described in section 3.3, the energy storage capacitor can maintain a stable output of approximately 3.3V before the next discharge of the test capacitor, meeting the power supply requirements of the microprocessor. This also verifies the feasibility and effectiveness of the low-power energy management method proposed in this invention. Furthermore, the voltage drop rate of the test capacitor after its first discharge is faster than the drop rate after the next charging cycle. This is because the test capacitor needs to transfer energy to the energy storage capacitor during its first discharge, and the energy from subsequent discharges is then supplied to the microprocessor. It is worth noting that the initial charging time is longer than the charging time after the test capacitor discharges; the time required to recharge to the discharge threshold after the test capacitor discharges is much shorter than the initial charging time.

[0097] Figure 10 These are experimental values ​​of the charging time of the test capacitor corresponding to different currents and their fitting curves. The fitting curve of the line current changing with the charging time of the test capacitor is relatively smooth and the residual value is small, which meets the high-precision inversion requirements of line current data.

[0098] Figure 11 The error between the actual current value and the inverted current value varies with the actual current value. I1' is the inverted current calculated by the vertical energy harvesting and line current measuring device of this invention through the charging time t of the test capacitor. The error between the inverted current and the reading current of the clamp ammeter is expressed as:

[0099]

[0100] Wherein, δ represents the error between the inverted current and the effective value I1 of the line current (i.e., the current reading of the clamp ammeter). Within the line current fluctuation measurement range of 100A to 600A, the self-powered current measurement error based on magnetic field inversion proposed in this invention is within 1%, which is basically consistent with the accuracy of the current array-type magnetic field sensor and can meet the measurement accuracy requirements of 1S level for line current.

[0101] Compared to traditional ring-shaped magnetic field induction energy harvesting devices, the current measurement device used in this invention enables high-precision current measurement and signal transmission without an external power supply. The vertical magnetic field induction energy harvesting device multiplexes the dual functions of spatial magnetic field energy pickup and magnetic field strength change sensing. Its non-ring-shaped structure meets the needs of multiple application scenarios, such as buried cables and overhead lines, and offers greater freedom of installation and disassembly. It solves the problems of traditional ring-shaped magnetic field induction energy harvesting devices, such as difficult ring-shaped installation, limited installation space, high requirements for magnetic core permeability, and poor anti-saturation capability. This invention achieves line current inversion measurement by measuring the voltage rise time of the test capacitor voltage through vertical energy harvesting and the line current measurement device. Considering the issues of overcharging and continuous discharge of the test capacitor voltage, a constant voltage charging and discharging method and isolation method for the test capacitor are proposed. Based on this, an efficient and low-power energy management and parameter configuration strategy is proposed, ultimately achieving high-precision self-powered line current measurement based on magnetic field strength inversion.

Claims

1. A self-powered line current measurement circuit based on magnetic field strength inversion, characterized by, The vertical energy acquisition and line current measurement device, the controllable rectification module, the test capacitor, the voltage follower, the hysteresis comparator module, the DC-DC module, the energy storage capacitor, the voltage step-down module and the microprocessor, the upper bridge arm of the controllable rectification module is two rectifier diodes, the lower bridge arm is two switching tubes, the switching tube includes a MOSFET switch and a body diode, the DC-DC module is an energy management chip, the vertical energy acquisition and line current measurement device collects the alternating current energy of the power line, and converts the alternating current energy into direct current energy through the controllable rectification module to charge the test capacitor, the voltage follower collects the voltage of the parallel resistor between the test capacitor, and inputs the voltage and the constant output voltage of the voltage reference module into the positive input end and the negative input end of the hysteresis comparator module respectively, when the voltage between the test capacitor reaches the discharge threshold voltage, the voltage hysteresis comparator outputs high level, the energy management chip and the microprocessor enter the working state, and the test capacitor stops charging; when the voltage between the test capacitor is lower than the open circuit induced voltage of the secondary winding of the vertical energy acquisition and line current measurement device, the voltage hysteresis comparator outputs low level, the energy management chip and the microprocessor enter the sleep state, and the test capacitor starts charging; the output level signal of the hysteresis comparator module is transmitted to the DC-DC module enable port, the voltage step-down module and the controllable rectification module respectively, realizing the three functions of the level signal multiplexing; The test capacitor discharge threshold voltage corresponding to the high level output by the hysteresis comparator module is represented as: Vin of the DC-DC module is connected with one end of the test capacitor, Vin2 of the DC-DC module provides a power supply voltage for the hysteresis comparator module, the voltage reference module and the voltage follower through a diode; the output of the DC-DC module is connected with the microprocessor and the energy storage capacitor, the output of the voltage step-down module is connected with the microprocessor, and the output of the microprocessor is connected with the upper computer; the microprocessor is alternately run in the working mode and the sleep mode to cyclically monitor the time from the charging threshold to the discharging threshold voltage of the test capacitor , the line current is obtained through inverse calculation Root mean square value of line current With a capacitance voltage And its corresponding charging time Is expressed as: ， wherein, R is the equivalent resistance of the load, R is the resistance of the secondary coil of the vertical power pick-up and line current measurement device, C is the test capacitance, V is the open circuit induced voltage of the secondary winding of the vertical power pick-up and line current measurement device and the time domain form of the line current is the proportionality factor.

2. The self-powered line current measurement circuit based on magnetic field strength inversion of claim 1, wherein, The parallel resistance across the test capacitor includes a first resistance connected in series and a second resistance The voltage variation across the second resistance is acquired to obtain the voltage fluctuation of the test capacitor.

3. The self-powered line current measurement circuit based on magnetic field strength inversion of claim 1, wherein, The hysteresis comparator module includes a first detection resistor and a second detection resistor for controlling the high and low level output of the voltage hysteresis comparator; The test capacitor charging threshold voltage corresponding to the low level output by the hysteresis comparator module is represented as: ， wherein, is a test capacitor discharge threshold voltage, is a constant output voltage of the voltage reference module, is a test capacitor voltage, and are a first and second resistor connected in parallel across the test capacitor, and are connected in series; The method adopts the circuit of any one of claims 1-4, and the method comprises the following steps: ， wherein, To test the capacitor charging threshold voltage, The voltage selection output pin Vin2 of the DC-DC module provides the supply voltage for the hysteresis comparator module, the voltage reference module and the voltage follower through a diode.

4. The self-powered line current measurement circuit based on magnetic field strength inversion of claim 1, wherein, Time domain form of line current The expression for the time domain form of line current is: ， wherein, is the open-circuit induction voltage of the secondary winding of the vertical power-taking and line current measuring device, is and the proportional coefficient, according to the formula, it is known that the line current inverse measurement can be realized by the open-circuit induction voltage of the secondary winding.

5. A self-powered line current measurement method based on magnetic field strength inversion, characterized in that, The vertical energy acquisition and line current measurement device is used to acquire the alternating current energy of the power line and charge the test capacitor; The comparison error of the actual current value, i.e. the ammeter reading, and the inversion current value varies with the actual current value, and the comparison error of the actual current value and the inversion current value is represented as: When the test capacitor voltage first reaches the test capacitor discharge threshold voltage , the hysteresis comparator module outputs a high level, the DC-DC module enters the working state, the test capacitor stops charging, and the test capacitor discharge energy is transmitted to the microprocessor and the energy storage capacitor through the voltage follower, the hysteresis comparator module and the DC / DC module. The microprocessor gets a high level to start the working mode and consumes energy, and the test capacitor voltage decreases to the test capacitor charging threshold voltage , the hysteresis comparator module outputs a low level, and when the microprocessor captures the falling edge of the hysteresis comparator module output signal, the microprocessor first enters the sleep state, and the test capacitor starts charging. The time is recorded as ; When the test capacitor is again charged to the discharge threshold voltage, the microprocessor is woken up by the high level of the hysteresis comparator module, at which time the current time is recorded The test capacitor is therefore charged from the test capacitor charge threshold voltage to the test capacitor discharge threshold voltage The time is ; When the microprocessor captures the falling edge of the hysteresis comparator module again, the microprocessor re-enters the sleep state, and the test capacitor is monitored in a loop from the test capacitor charging threshold voltage to the test capacitor discharge threshold voltage The time increases as the line current increases and decreases as the line current decreases, and there is a functional relationship between the line current and the time The measured time is calculated by the function to obtain the accurate inversion line current value, and finally the inversion line current value is transmitted to the host computer.

6. The self-powered line current measurement method based on magnetic field strength inversion according to claim 5, characterized in that, test capacitor , energy storage capacitor , test capacitor discharge threshold voltage and test capacitor charge threshold voltage the following equation must be satisfied: ， wherein, Pmin is the minimum power required for the microprocessor to operate in the active state, Pmin is the minimum power required for the microprocessor to operate in the active state, Pmin is the minimum power required for the microprocessor to remain in the sleep state, Tmax is the maximum time the microprocessor can operate in the active state, Tmax is the maximum time the microprocessor can operate in the active state, 7. The self-powered line current measurement method based on magnetic field strength inversion according to claim 5, characterized in that, ​ ， wherein δ represents the error of the inversion current and the actual current of the line; is the current reading of the clamp-on ammeter, which represents the effective value of the line current; is the inversion current.

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