A polarity identification method for measuring DC current with dual iron core symmetrical nonlinear magnetic modulation

Abstract

This invention discloses a polarity identification method for measuring DC current using a dual-core symmetrical nonlinear magnetic modulation. Utilizing the differences in effective values ​​and polarity characteristics of signals on two measuring resistors under different polarity conditions, the method calculates and compares the effective values ​​of the two voltages in real time. Combined with polarity detection logic, it achieves automatic identification of the primary current direction and determination of the diode connection status. This hardware-based effective value discrimination and absolute value output mechanism, while fully retaining the core advantages of magnetic modulation high-current measurement devices such as simple structure, high reliability, and strong anti-interference capability, fundamentally overcomes the inherent defect of magnetic modulation high-current measurement devices' inability to autonomously identify current polarity. This significantly improves the measurement reliability, response speed, and system adaptability of the device under complex dynamic conditions such as polarity reversal.

Description

Technical Field

[0001] This invention relates to the field of DC high current measurement, and in particular to a polarity identification method for measuring DC current using a dual-core symmetrical nonlinear magnetic modulation. Background Technology

[0002] In high-voltage direct current transmission systems, when it is necessary to achieve bidirectional power flow regulation, switching of operating states, or rapid handling of transient faults, the direction of primary current flow is changed by altering the operation of the converter, i.e., triggering polarity reversal. This is the core operating mode for the system to achieve flexible regulation.

[0003] During the polarity reversal process, the converter stations at both ends switch operating modes synchronously. The direction of the primary current reverses rapidly and is accompanied by an amplitude oscillation of at least twice the rated current. This places extremely high demands on the polarity identification speed and accuracy of the DC measuring device, as well as the DC insulation safety.

[0004] If the polarity is incorrectly identified, it will lead to misjudgment by the control system, maloperation or failure of the relay protection, seriously threatening the safety of main equipment such as converter transformers; in addition, the strong electromagnetic interference of the converter station can easily cause distortion of measurement signals, further aggravating the risk of misjudgment.

[0005] Therefore, DC measuring devices must have the ability to quickly and accurately identify polarity, strong resistance to electromagnetic interference, and signal self-correction function to provide reliable measurement data for DC transmission systems, which is of key significance for ensuring the safe and stable operation of the system.

[0006] The disclosure of the above background technical content is only for the purpose of assisting in understanding the concept and technical solution of this application, and does not necessarily provide technical instruction. Summary of the Invention

[0007] The purpose of this invention is to provide a polarity identification method for measuring DC current with dual-core symmetrical nonlinear magnetic modulation, so as to realize real-time identification and signal self-correction of DC current polarity reversal in high-voltage DC transmission systems.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a polarity identification method for measuring dual-core symmetrical nonlinear magnetically modulated DC current, applied to a dual-core symmetrical nonlinear magnetically modulated DC current measuring device. The measuring device includes two iron cores connected in parallel with symmetrical magnetic circuits, an excitation power supply providing AC excitation to the two iron cores, rectifier diodes connected to the secondary windings of the two iron cores respectively, and sampling resistors R connected to the secondary windings of the two iron cores respectively. C R f ; The polarity identification method includes the following steps: Acquisition sampling resistor R C Voltage signal V at both endsRc and the sampling resistor R f Voltage signal V at both ends Rf ; Calculate voltage signal V Rc Effective value V C and calculate voltage signal V Rf Effective value V f ; Compare the effective value V C With V f The magnitude, and based on the magnitude comparison result, from the voltage signal V Rc V Rf Choose one of the signals as the output signal U; Combined with V C With V f The magnitude comparison results, along with the positive and negative polarities of the output signal U, are used to perform combinational logic operations to determine the direction of the primary DC current in the iron core.

[0009] Furthermore, based on any or a combination of the aforementioned technical solutions, the secondary winding of the first iron core among the two iron cores is defined to have a first terminal and a second terminal, and the secondary winding of the second iron core among the two iron cores is defined to have a third terminal and a fourth terminal. The number of rectifier diodes is four, wherein the first rectifier diode and the second rectifier diode are connected in series between the first terminal and the fourth terminal; The third rectifier diode and the fourth rectifier diode are connected in series between the second terminal and the third terminal; The positive terminal of the excitation power supply is connected to the connection point of the first rectifier diode and the second rectifier diode, and the negative terminal of the excitation power supply is connected to the connection point of the third rectifier diode and the fourth rectifier diode. The sampling resistor R C The sampling resistor R is disposed at both ends of the series branch of the third and fourth rectifier diodes. f It is set at both ends of the series branch of the first rectifier diode and the second rectifier diode.

[0010] Furthermore, following any one or a combination of the aforementioned technical solutions, the two iron cores are of the same specification and are coaxially arranged, and the primary DC current passes through the central hole of the two iron cores via a single DC bus.

[0011] Furthermore, following any one or a combination of the aforementioned technical solutions, the effective value V is compared using a first voltage comparator. C With V f Size; When V C ≥V fWhen V is in the first voltage comparator, the first voltage comparator outputs the first logic level; when V is in the first voltage comparator, the first voltage comparator outputs the first logic level. C <V f At that time, the first voltage comparator outputs the second logic level.

[0012] Furthermore, following any one or a combination of the aforementioned technical solutions, the logic level output by the first voltage comparator is used as a control signal to drive the switching circuit to turn on or off, thereby affecting the voltage signal V. Rc V Rf Select one of them as the output signal U, including: If the control signal is the first logic level, then select V. Rf As the signal to be output, U; If the control signal is the second logic level, then V is selected. Rc As the output signal U.

[0013] Furthermore, following any one or a combination of the aforementioned technical solutions, the output signal U and a zero potential are input to a second voltage comparator to determine the polarity of the output signal U: When U > 0, the four rectifier diodes are determined to be connected in the positive direction; when U ≤ 0, the four rectifier diodes are determined to be connected in the reverse direction.

[0014] Furthermore, following any one or a combination of the aforementioned technical solutions, the combinational logic operation is implemented using a simulated multiplier: The output signals of the first voltage comparator and the second voltage comparator are input into the multiplier, and the direction of the DC current is determined based on the sign of the multiplication result signal output by the multiplier.

[0015] Furthermore, following any one or a combination of the aforementioned technical solutions, the combination logic operation is as follows: When V C ≥V f If the judgment result of the signal and the judgment result of the output signal U>0 are both true or both false, the DC current is determined to be in the positive direction; otherwise, the DC current is determined to be in the reverse direction.

[0016] Furthermore, following any one or a combination of the aforementioned technical solutions, a true RMS converter chip is used to calculate the effective value of the voltage signal, wherein the model of the true RMS converter chip is AD637AQ.

[0017] According to another aspect of the present invention, a polarity identification system for measuring dual-core symmetrical nonlinear magnetic modulation DC current is provided, applied to a dual-core symmetrical nonlinear magnetic modulation DC current measuring device. The measuring device includes two iron cores arranged in parallel and with symmetrical magnetic circuits, an excitation power supply providing AC excitation to the two iron cores, rectifier diodes respectively connected to the secondary windings of the two iron cores, and sampling resistors R respectively connected to the secondary windings of the two iron cores. C R f ; The polarity identification system includes the following circuitry: The sampling circuit is configured to acquire the sampling resistor R. C Voltage signal V at both ends Rc and the sampling resistor R f Voltage signal V at both ends Rf ; The effective value calculation circuit is configured to calculate the voltage signal V. Rc Effective value V C and calculate voltage signal V Rf Effective value V f ; The effective value discrimination circuit is configured to detect the effective value V. C With V f The magnitude, and based on the magnitude comparison result, from the voltage signal V Rc V Rf Choose one of the signals as the output signal U; A primary current direction determination circuit is configured to combine V C With V f The magnitude comparison results, along with the positive and negative polarities of the output signal U, are used to perform combinational logic operations to determine the direction of the primary DC current in the iron core.

[0018] The beneficial effects of the technical solution provided by this invention are as follows: This patent addresses the core flaw of magnetically modulated DC high-current measuring devices, which, due to their symmetrical structure and open-loop principle, cannot identify the direction of DC current. This inherent flaw leads to potential distortion or interruption of the measurement signal when polarity reverses in a high-voltage DC transmission system, severely affecting the accuracy of current measurement and potentially causing system control malfunctions or protective device misoperations, threatening the safe and stable operation of the system. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A schematic diagram of the secondary current circuit of the device during the positive half-cycle of AC excitation, provided as an exemplary embodiment of the present invention; Figure 2 A schematic diagram of the equivalent circuit of the secondary circuit during the positive half-cycle of AC excitation, provided as an exemplary embodiment of the present invention; Figure 3 A schematic diagram of the secondary current circuit of the device during the negative half-cycle of AC excitation, provided as an exemplary embodiment of the present invention. Figure 4 A schematic diagram of the equivalent circuit of the secondary circuit during the negative half-cycle of AC excitation, provided for an exemplary embodiment of the present invention; Figure 5 A circuit diagram showing the primary current reversed and the diode positively connected condition, provided as an exemplary embodiment of the present invention; Figure 6 A circuit diagram showing the primary current in the forward direction and the diode in reverse connection condition, provided as an exemplary embodiment of the present invention; Figure 7 A circuit diagram showing the reverse primary current and reverse diode connection conditions provided for an exemplary embodiment of the present invention; Figure 8 A schematic diagram of the working logic for polarity identification in dual-core symmetrical nonlinear magnetic modulation DC current measurement, provided as an exemplary embodiment of the present invention; Figure 9 Based on Figure 8 A schematic diagram of the polarity recognition circuit built using the judgment logic in the diagram; Figure 10 A schematic diagram of the diode access determination process provided for an exemplary embodiment of the present invention; Figure 11 A schematic diagram of the signal flow of the polarity reversal identification circuit provided for an exemplary embodiment of the present invention; Figure 12 A simulation output interface diagram of the polarity reversal identification circuit when the operating condition 1 in Table 1 suddenly changes to operating condition 2, provided as an exemplary embodiment of the present invention; Figure 13 A complete hardware circuit diagram of an identification system provided for an exemplary embodiment of the present invention; Figure 14 for Figure 13 The circuit diagram of the first effective value calculation circuit in [the circuit]. Figure 15 for Figure 13 The circuit diagram of the second effective value calculation circuit in the example; Figure 16 for Figure 13 The circuit diagram of the effective value discrimination circuit in the image; Figure 17 for Figure 13 The circuit diagram of the diode state discrimination circuit in the image; Figure 18 for Figure 13 The circuit diagram of the primary current direction determination circuit; Figure 19 for Figure 13 The circuit diagram of the absolute value output circuit in the example. Detailed Implementation

[0021] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0022] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, apparatus, product, or device that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or devices.

[0023] The dual-core symmetrical nonlinear magnetic modulation DC high-current measuring device adopts the magnetic modulation measurement principle to achieve accurate measurement of DC high current. Based on the nonlinear magnetization characteristics of the iron core, it utilizes the measured DC current to establish a magnetic field bias point in the iron core's magnetic circuit. This bias point, combined with the AC magnetic field applied by the secondary winding, causes the iron core's magnetization state to exhibit controllable asymmetry. This allows for the linear conversion of DC current information into a detection signal, and the DC high-current amplitude can be obtained by extracting the characteristics of the detection signal.

[0024] This innovative measuring device boasts significant technological advantages: its simple structure eliminates the need for complex optical components and numerous precision electronic parts, resulting in high hardware reliability; it exhibits outstanding long-term stability and adaptability to extreme environments; simultaneously, it possesses excellent wideband measurement performance and rapid transient response capabilities, with electromagnetic interference resistance reaching industry-leading levels. This device has independent intellectual property rights, enabling domestic substitution of similar equipment. It holds immense value for widespread application in power systems and represents a highly promising measurement solution for high-voltage direct current transmission systems.

[0025] Because this device cleverly utilizes a fully symmetrical dual-core structure to achieve magnetic modulation measurement, it cannot effectively identify current polarity changes directly through the measurement signal output from the existing symmetrical structure when a polarity reversal occurs on the primary side. This inherent defect is particularly pronounced in polarity reversal conditions caused by power flow reversal, fault restart, or operation mode switching in high-voltage direct current transmission systems. Current engineering practices typically employ external auxiliary discrimination methods for polarity identification, including logical discrimination based on background software algorithms, hardware discrimination using additional independent directional relays, and indirect comparison methods relying on external voltage and current synchronization signals. These conventional methods not only introduce additional signal delays and potential fault points, but their millisecond-level response speed also fails to meet the high-speed response requirements of real-time system control and relay protection.

[0026] To address the problem of inability to autonomously identify polarity reversal in DC high-current measurements using a dual-core symmetrical nonlinear magnetic modulation principle, this invention proposes a dedicated polarity identification method. This method utilizes the inherent amplitude variation characteristics of the dual-channel output signals of the magnetic modulation measuring device under current polarity reversal. Through an original design of true RMS comparison and signal polarity discrimination hardware decision logic, it achieves rapid, real-time identification of the current direction directly from within the measurement mechanism, without relying on any external auxiliary equipment, background software algorithms, or synchronization signals. This invention forms an original technical solution fully adapted to the structure and principle of magnetic modulation measuring devices, significantly improving the response speed and adaptability of the measuring device under polarity reversal conditions.

[0027] In one embodiment of the present invention, a polarity identification method for measuring dual-core symmetrical nonlinear magnetic modulation DC current is provided, applied to a dual-core symmetrical nonlinear magnetic modulation DC current measuring device. The current measuring device includes two iron cores arranged in parallel and with symmetrical magnetic circuits, an excitation power supply providing AC excitation to the two iron cores, rectifier diodes respectively connected to the secondary windings of the two iron cores, and sampling resistors R respectively connected to the secondary windings of the two iron cores. C R fThe dual-core symmetrical nonlinear magnetic modulation DC current measuring device is a magnetic modulation type DC high current measuring device. Its core is designed with a parallel dual-core symmetrical arrangement. By simultaneously applying an AC excitation current and the primary-side DC current to be measured to the dual cores, DC measurement is achieved using the nonlinear magnetization characteristics of the cores. Its open-loop measurement principle gives it advantages such as relatively simple structure, no reliance on special precision components, strong long-term stability, excellent resistance to environmental interference, wide frequency range, and good transient response performance.

[0028] However, due to the symmetry of the current measuring device's structure and the perfect symmetry of the magnetic circuit and electrical circuit, the current measuring device cannot directly distinguish the direction of change of the magnetic field in the magnetic circuit when the polarity of the primary current reverses or the rectifier diode is mistakenly reversed, thus failing to identify the absolute polarity of the primary current. This leads to errors in determining the effective signal path, resulting in distortion or interruption of the measurement signal. This not only affects the accuracy of current measurement but may also cause control logic disorder in the DC transmission system, and even lead to malfunctions or failures of protection devices, directly threatening the safe and stable operation of the high-voltage DC transmission system.

[0029] Due to the symmetry of the current measuring device's structure and its open-loop measurement principle, it is impossible to directly identify a single current polarity reversal. However, during a single current polarity reversal, the sampling resistor R... C R f The AC modulation signals on the two sampling resistors exhibit significant differences. This patent utilizes the differences in the effective values ​​and polarity characteristics of the signals under different polarity conditions. By calculating and comparing the effective values ​​of the two voltages in real time, and combining this with polarity detection logic, it achieves automatic identification of the primary current direction and judgment of the diode connection status. This hardware-based effective value discrimination and absolute value output mechanism, while fully retaining the core advantages of magnetic modulation high current measurement devices such as simple structure, high reliability, and strong anti-interference ability, fundamentally overcomes the inherent defect of its inability to autonomously identify current polarity. It greatly improves the measurement reliability, response speed, and system adaptability of the current measurement device under complex dynamic conditions such as polarity reversal, providing key technical support for the safe and reliable application of current measurement devices in high-voltage direct current transmission projects.

[0030] In this embodiment of the dual-core symmetrical nonlinear magnetic modulation DC current measuring device, the two cores are of the same specification and coaxially arranged. The primary DC current passes through the central hole of the two cores via a single DC bus. The first core of the two cores is defined as... Figure 1 The secondary winding of the iron core A in the middle has a first terminal ( Figure 1 The right terminal of the iron core A) and the second terminal ( Figure 1 The left terminal of the middle iron core A), defines the second iron core of the two iron cores (i.e. Figure 1The secondary winding of the iron core B has a third terminal ( Figure 1 The right-side terminal of the core B) and the fourth terminal ( Figure 1 (Left terminal of core B) The number of rectifier diodes is four, of which the first rectifier diode ( Figure 1 (Die 3) and second rectifier diode ( Figure 1 Diode D2 is connected in series between the first terminal and the fourth terminal, and diodes D2 and D3 are in the same direction; Third rectifier diode ( Figure 1 (D4) and the fourth rectifier diode ( Figure 1 Diode D1 is connected in series between the second and third terminals, and diodes D4 and D1 are oriented in the same direction; The positive terminal of the excitation power supply is connected to the connection point of the first rectifier diode D3 and the second rectifier diode D2, and the negative terminal of the excitation power supply is connected to the connection point of the third rectifier diode D4 and the fourth rectifier diode D1; in this embodiment, the excitation power supply is a 220V / 50Hz AC excitation power supply.

[0031] The sampling resistor R C The sampling resistor R is disposed across the series branch of the third rectifier diode D4 and the fourth rectifier diode D1. f It is set at both ends of the series branch of the first rectifier diode D3 and the second rectifier diode D2.

[0032] The polarity identification method includes the following steps: Step 1: Acquire sampling resistance R C Voltage signal V at both ends Rc and the sampling resistor R f Voltage signal V at both ends Rf ; Step 2: Calculate the voltage signal V Rc Effective value V C and calculate voltage signal V Rf Effective value V f This embodiment uses a true RMS converter chip to calculate the effective value of the voltage signal. The model of the true RMS converter chip is AD637AQ. The RMS calculation circuit structure is described in [reference needed]. Figure 14 and Figure 15 The details will be explained below.

[0033] Step 3: Compare the effective values ​​V C With V f The magnitude, and based on the magnitude comparison result, from the voltage signal V Rc V Rf Choose one of the signals as the output signal U; Specifically, the effective value V is compared using the first voltage comparator. C With V f Size; when V C ≥V f When V is in the first voltage comparator, the first voltage comparator outputs the first logic level; when V is in the first voltage comparator, the first voltage comparator outputs the first logic level. C <V f At this time, the first voltage comparator outputs a second logic level. Using the logic level output by the first voltage comparator as a control signal, the switching circuit is driven to turn on or off, thereby affecting the voltage signal V. Rc V Rf Selecting one of them as the output signal U includes: if the control signal is the first logic level, then selecting V. Rf As the output signal U; if the control signal is the second logic level, then V is selected. Rc As the output signal U.

[0034] Step 4: Combine with V C With V f The magnitude comparison results, along with the positive and negative polarities of the output signal U, are used to perform combinational logic operations to determine the direction of the primary DC current in the iron core.

[0035] The polarity of the output signal U is determined as follows: the output signal U and zero potential are input to the second voltage comparator to determine the polarity of the output signal U; when U>0, the four rectifier diodes are determined to be positively connected; when U≤0, the four rectifier diodes are determined to be reversely connected.

[0036] like Figure 8 As shown, when V C ≥V f If the judgment result of the first voltage comparator and the judgment result of the output signal U>0 are both true or both false, the DC current is determined to be in the positive direction; otherwise, the DC current is determined to be in the reverse direction. The combinational logic operation here is implemented through an analog multiplier: the output signals of the first voltage comparator and the second voltage comparator are input into the multiplier, and the direction of the DC current is determined according to the sign of the multiplication result signal output by the multiplier.

[0037] Taking the positive direction of primary current as defined as flowing from right to left as an example, Figure 1 , Figure 3 , Figure 6 The positive primary current is shown. Figure 5 , Figure 7 The reverse primary current is shown.

[0038] In another embodiment of the present invention, a polarity identification system for measuring dual-core symmetrical nonlinear magnetic modulation DC current is provided, applied to a dual-core symmetrical nonlinear magnetic modulation DC current measuring device. The measuring device includes two iron cores arranged in parallel and with symmetrical magnetic circuits, an excitation power supply providing AC excitation to the two iron cores, rectifier diodes respectively connected to the secondary windings of the two iron cores, and sampling resistors R respectively connected to the secondary windings of the two iron cores. C R f ; The polarity identification system includes the following circuitry: The sampling circuit is configured to acquire the sampling resistor R. C Voltage signal V at both ends Rc and the sampling resistor R f Voltage signal V at both ends Rf ; The effective value calculation circuit is configured to calculate the voltage signal V. Rc Effective value V C and calculate voltage signal V Rf Effective value V f ; The effective value discrimination circuit is configured to detect the effective value V. C With V f The magnitude, and based on the magnitude comparison result, from the voltage signal V Rc V Rf Choose one of the signals as the output signal U; A primary current direction determination circuit is configured to combine V C With V f The magnitude comparison results, along with the positive and negative polarities of the output signal U, are used to perform combinational logic operations to determine the direction of the primary DC current in the iron core.

[0039] In one embodiment, the polarity identification system is implemented entirely with hardware circuitry, such as... Figure 13 As shown, the voltage signal V is used to calculate the voltage signal V. Rf Effective value V f First effective value calculation circuit 100 Figure 14 As shown, this is used to calculate the voltage signal V. Rc Effective value V C The second effective value calculation circuit 200, as shown Figure 15 As shown, the effective value discrimination circuit 300 is as follows: Figure 16 As shown, the effective value V output by the AD637AQ chip in the first effective value calculation circuit 100 is... f The inverting input of the comparator in the input RMS value discrimination circuit 300, and the RMS value V output by the AD637AQ chip in the second RMS value calculation circuit 100. CThe non-inverting input terminal of the comparator in the input effective value discrimination circuit 300.

[0040] The polarity identification system also includes a diode state discrimination circuit 400, such as Figure 17 As shown, the inverting input of the comparator is at zero potential, and the non-inverting input is connected to the sampling resistor R. C Voltage signal V at both ends Rc Sampling resistor R f Voltage signal V at both ends Rf The larger of V: ​​when V Rc >V Rf V Rc The first power switch between the non-inverting input terminal of the comparator in the diode state discrimination circuit 400 and V is turned on; Rc <V Rf V Rf The second power switch between the non-inverting input terminal of the comparator in the diode state discrimination circuit 400 is turned on.

[0041] The power switches on these two paths cannot be turned on simultaneously. The principle is as follows: The RMS value discrimination circuit 300 has another comparator. The first comparator compares the RMS value V. C V f The output of the first comparator is connected to the control terminal of the first power switch and the inverting input terminal of the other comparator. The non-inverting input terminal of the other comparator is a zero-potential input, and its output terminal is connected to the control terminal of the second power switch. In this way, the output signals of the first comparator and the other comparator are different, that is, only one comparator outputs a high-level signal at the same time to control its corresponding power switch to turn on.

[0042] 500 primary current direction determination circuit Figure 18 As shown, U10 is the core arithmetic unit—an analog multiplier. One of its inputs is the output of the comparator in the RMS value discrimination circuit 300, and the other input is the output of the comparator in the diode state discrimination circuit 400. The inverting input of the comparator in the diode state discrimination circuit 400 is a zero-potential input. When its non-inverting input (V... Rc V Rf If the larger of the two values ​​is greater than 0, the diode state discrimination circuit 400 inputs a high-level signal to the analog multiplier of the primary current direction discrimination circuit 500; otherwise, it inputs a low-level signal.

[0043] The sign of the multiplication result signal output by the analog multiplier can determine the direction of the primary DC current: if the output signal U(V) is positive or negative... Rc V Rf The larger of the two values ​​is greater than 0 (which indicates the diode is positively connected), and V C ≥Vf Then the product result of the analog multiplier is positive, and the direction of the primary DC current is positive; If the output signal is U(V) Rc V Rf The larger of the two values ​​is less than 0 (which indicates the diode is reverse-connected), and V C <V f Then the product result of the analog multiplier is positive, and the direction of the primary DC current is positive; If the output signal is U(V) Rc V Rf The larger of the two values ​​is less than 0 (which indicates the diode is reverse-connected), and V C ≥V f If the product of the analog multiplier is negative, the direction of the primary DC current is reversed. If the output signal is U(V) Rc V Rf The larger of the two values ​​is greater than 0 (which indicates the diode is positively connected), and V C <V f If the result of multiplication by the analog multiplier is reversed, the direction of the primary DC current will also be reversed.

[0044] The polarity identification system also includes an absolute value output circuit 600, such as Figure 19 As shown, when the input is a positive voltage, the signal is directly output through the non-inverting path with a gain of +1; when the input is a negative voltage, the circuit is equivalent to an inverting amplifier with a gain of -1, so that the output is also a positive voltage.

[0045] Taking the primary current in the forward direction (flowing from right to left) as an example, the secondary side of the magnetic modulation device consists of a double iron core, a rectifier diode, and R. C R f It consists of a sampling resistor and a 220V / 50Hz AC excitation power supply. See [link / reference] Figures 1 to 4 By conducting simulation experiments on this magnetically modulated DC high current measuring device, R can be obtained. C R f The signal pattern across the sampling resistor is shown in Table 1 under operating condition 1: Table 1: Systematic Analysis of Four Operating Conditions Finally, combining all operating conditions of primary current polarity and diode connection, and analyzing signal characteristics through simulation experiments, we summarized the R values ​​under four operating conditions. C R f The signal patterns on the two sampling resistors are shown in Table 1, which provides a quantitative criterion for polarity identification.

[0046] Specifically, operating condition 2 is as follows: Figure 5 As shown, operating condition 3 is as follows Figure 6 As shown, operating condition 4 is as follows Figure 7 As shown: Sampling resistor R under different operating conditions C With R f The AC modulated signal exhibits differences in effective value and stability. Based on this physical characteristic, the designed identification system is implemented entirely in hardware, consisting of five core modules: an effective value calculation circuit, an effective value discrimination circuit, a diode state discrimination circuit, an absolute value output circuit, and a primary current direction judgment circuit. These modules together form a complete signal processing chain. The specific working logic is detailed in [link to documentation]. Figure 8 The system first extracts the two sampled signals and calculates their effective values, converting them into discrimination signals that accurately reflect the effective measurement branches before performing subsequent logical discrimination. Figure 9 This is a polarity identification circuit diagram built based on the effective value discrimination logic.

[0047] (1) Effective value calculation circuit Based on the signal characteristics of the two measuring resistors, the amplitudes of the two AC modulation voltages can be monitored in real time with high precision, thereby achieving rapid and reliable determination of current polarity. For this purpose, this patent selects a chip with wideband, high-precision true RMS conversion capability to build the RMS extraction circuit.

[0048] This circuit is built around the AD637AQ dedicated RMS converter chip and employs an implicit calculation method. By sequentially performing square, average, and square root operations on the input signal, it directly outputs a DC voltage proportional to the true RMS value of the input signal, which is then used by the subsequent comparison circuit to determine the RMS value. It features high accuracy, wide bandwidth, and large dynamic range, and is suitable for extracting the RMS value of non-sinusoidal AC signals and AC signals containing DC components, meeting the measurement requirements under complex operating conditions in high-voltage direct current transmission systems.

[0049] The application environment for magnetically modulated DC current measurement in high-voltage direct current transmission scenarios is characterized by strong electromagnetic interference and superposition of high and low frequency noise. The peripheral circuit is configured with two high-frequency decoupling capacitors C1 (100pF) and C5 (100pF) and two low-frequency decoupling capacitors C2 (10μF) and C6 (10μF), which are connected in parallel near the power supply pin.

[0050] C1 and C5 have relatively small capacitance values, presenting low impedance to high-frequency signals, and can form an LC filter with the wiring inductance. This value is usually determined based on the noise frequency and PCB layout inductance, and is generally taken as 100pF to 100nF. Here, 100pF is selected to suppress noise above tens of MHz.

[0051] To filter out potential noise from the power supply and provide transient current, the capacitance values ​​must meet the power supply ripple suppression requirements. C2 (10μF) and C6 (10μF) are low-frequency decoupling capacitors for the positive and negative power supplies (VDD and VEE), respectively. The calculation formula is as follows: Where Imax is the chip's maximum operating current (approximately 2.5mA), Δt is the noise period (assumed to be 10μs), and ΔV is the allowable power supply ripple (set to 50mV). Calculations show C ≥ 0.5μF, but 10μF is actually chosen to allow sufficient margin. The polarity identification circuit should also consider the signal response speed and the accuracy of the effective value calculation. Therefore, this solution also includes the design of the average capacitance of the chip's peripheral circuit and the input signal ripple capacitance.

[0052] C3 (2.2μF) and C7 (2.2μF) are external average capacitors, which determine the average time constant τ for RMS value calculation. This directly affects the smoothness and response speed of the output signal, and their selection requires a trade-off between response speed and ripple suppression. Based on the AD637AQ's internal equivalent resistance of approximately 8kΩ, a filter time constant of 10 to 50ms can balance signal smoothness and dynamic response speed. Considering the polarity reversal time of the DC transmission system and the response time of the electronic circuit itself, and to ensure fast and reliable polarity identification, this patent designs the filter time constant τ of the polarity identification circuit to be approximately 20ms, resulting in the following formula: In engineering, 2.2μF capacitors are commonly used, which are close to the theoretical calculation value. Their corresponding cutoff frequency is: C4 is a filter capacitor. In general practical engineering applications, it has a specific correlation with the two average capacitors, which satisfies the following relationship: In practical applications, a larger C4 results in smaller ripple but slower conversion speed and smaller error. Conversely, a smaller C4 results in larger ripple but faster conversion speed and larger error. To achieve a balance between response speed and calculation accuracy, in this circuit design, C3 = C7 = 2.2uF, and C4 is set to 1uF.

[0053] (2) RMS value discrimination circuit The equipment operates in an environment with strong magnetic fields and vibration interference, and requires long-term continuous and stable operation. This places stringent requirements on the measurement circuit's anti-interference capability, environmental adaptability, and operational reliability. The LM741, with its excellent industrial-grade wide-temperature operating characteristics, high power supply rejection ratio, and strong electromagnetic interference resistance, is perfectly suited to the aforementioned complex engineering environment and can meet the circuit's requirement for fast and reliable comparison of two DC voltage signals.

[0054] The effective value discrimination circuit receives the DC voltage signal V from the previous stage. C and V fBy comparing the amplitudes of the two signals, the corresponding logic level is output. This level signal controls an analog switching circuit composed of a 2N3904 transistor, thereby automatically selecting and turning on the correct signal path (R). C or R f This enables automatic determination of current polarity and switching of signal paths.

[0055] (3) Diode state discrimination circuit When the diode is connected in the forward direction, the voltage signals across both sampling resistors are positive; conversely, when the diode is connected in the reverse direction, the voltage signals across both sampling resistors are negative. The specific diode connection determination process is as follows: Figure 10 As shown.

[0056] Reference Figure 10 The flowchart illustrates the design of a diode state discrimination circuit, which integrates signal logic recognition functionality. This design fully utilizes the advantages of the LM741 voltage comparator—simple structure, fast response, and stable and reliable operation—to implement the polarity comparison logic for voltage signals. The circuit monitors the selected signal in real time and accurately identifies the signal's polarity characteristics by setting a reasonable decision threshold. In this design, the decision threshold is set to 0, and the negative terminal of the LM741 is grounded. When a negative output signal is detected, a low-level output is generated, indicating a reverse diode connection; when a positive output signal is generated, a high-level output is generated, indicating a forward diode connection.

[0057] (4) Absolute value output circuit The polarity identification circuit also needs to consider signal normalization, system interface compatibility, and response speed. Therefore, a high-speed, low-offset voltage operational amplifier (such as the 3288RT) is selected, paired with a diode and resistor network to construct a precision full-wave rectifier topology. Its working principle cleverly utilizes the high gain of the operational amplifier and the unidirectional conduction characteristic of the diode: when the input is a positive voltage, the signal is directly output through a non-inverting path with a gain of +1; when the input is a negative voltage, the circuit is equivalent to an inverting amplifier with a gain of -1, making the output also a positive voltage. Ultimately, the amplitude of the output voltage precisely corresponds to the absolute value of the input signal.

[0058] Regarding the working mechanism of the polarity reversal recognition system, taking the primary current as positive and the diode as positively connected as an example, the sampling resistor R... f The effective value of the voltage signal stabilizes at approximately 0.75V, while R C The effective value of the signal is approximately 1.75V and fluctuates significantly, satisfying V f <V C The RMS comparator U1 outputs a low level accordingly. This low level keeps the switch Q1 off, blocking R. CThe signal path; on the other hand, it is fed into the inverting input of comparator U2 and compared with the zero-potential reference connected to the non-inverting input. Since the output of U1 is low (below 0V), the output of U2 is high, driving Q3 to conduct, thereby turning on R. f A stable positive voltage signal is selected and sent to the subsequent processing circuit. The output signal is positive, and the diode state determination circuit determines that the diode is positively connected, ultimately outputting the correct voltage proportional to the magnitude of the primary forward current. The final signal selection path is shown in the attached figure. Figure 11 .

[0059] (5) Primary current direction discrimination circuit Based on Table 1, further analysis yielded Table 2: Table 2: Summary Table of Circuit Discrimination Parameters Where V C V f These are the effective values ​​calculated from the signals across the two sampling resistors, respectively. u This indicates that the sampled resistor signal selected as the output signal after comparison with the effective value is 1. The 1 in the parentheses indicates that the logical judgment result is correct, and the 0 in the parentheses indicates that the logical judgment result is incorrect.

[0060] When the effective value V C >V f Logic and output signal u When all logic outputs >0 are either correct or all are incorrect, the primary current direction is positive. Corresponding to the circuit, that is... Figure 10 When the comparison outputs of operational amplifiers U1 and U4 in the circuit are both positive or both negative, the primary current is positive.

[0061] Based on this, this invention uses the AD633 multiplier chip to determine the direction of the primary current. The main function of the AD633 is to calculate and output the product of two input signals in real time. In this design, the outputs of operational amplifiers U1 and U4 are connected to the input of the multiplier circuit, and the direction information of the primary current is obtained by the sign of the final output signal. Specifically, when the outputs of U1 and U4 are both greater than 0 or both are less than 0, the primary current direction determination circuit outputs a positive voltage signal, indicating that the primary current is in the forward direction; when the outputs of U1 and U4 are both greater than 0 or both are less than 0, the primary current direction determination circuit outputs a negative voltage signal, indicating that the primary current is in the reverse direction. The specific circuit implementation is shown in [link to circuit diagram]. Figure 10 .

[0062] To address the aforementioned issues, this method deeply analyzes and utilizes the two sampling resistors (R0, R0) on the secondary side of the magnetically modulated high-current measurement device. C and R fThe inherent characteristics of the output signal on the diode. Through simulation and experiment, it was found that under different primary current polarities and diode connection states, R C With R f The AC modulation signal has stable and distinguishable effective value differences and polarity characteristics (as shown in Table 1). Based on this physical law, this method proposes a fully hardware-implemented polarity identification scheme. By calculating and comparing the true effective values ​​of the two signals in real time, combined with polarity detection logic, the scheme automatically determines the direction of the primary current and the diode connection status, and outputs a corrected unified polarity signal.

[0063] When the diode is connected in the positive direction, and the primary current suddenly reverses (i.e., changes abruptly from condition 1 to condition 2 in Table 1), the simulation output of the polarity reversal identification circuit is as follows: Figure 12 It is not difficult to see that the circuit completes the identification of a current reversal within 10ms.

[0064] The protection point of this method lies in its innovative use of two secondary-side sampling resistors (R). C and R f The inherent differences in the modulation signal are revealed through simulation and experimentation. Regardless of the direction of the primary current or whether the front-end rectifier diodes are connected in either direction, the effective signal representing the true current magnitude always appears stably across one of the resistors, and its true effective voltage value is consistently less than the saturation and harmonic signal across the other resistor. This physical characteristic forms the logical basis for subsequent hardware decision-making. This solution requires no external judgment signal and does not rely on external auxiliary criteria; it accurately identifies the current polarity and diode connection status solely through the effective value calculation and real-time comparison of the device's own measured signals.

[0065] In terms of specific technical implementation, the protection scope covers the calculation circuit centered on a dedicated RMS conversion chip (such as AD637), the RMS value discrimination and diode state discrimination circuit based on a voltage comparator, and the final absolute value output and signal gating circuit, as well as the primary current direction discrimination circuit. The entire signal link is constructed using analog hardware, and key parameters (such as the relationship between the values ​​of average capacitors C3 and C7 and ripple filter capacitor C4) have been designed to achieve the best balance between response speed and measurement accuracy.

[0066] The final output of this scheme is a calibrated voltage signal with uniform polarity, the amplitude of which precisely corresponds to the absolute value of the primary current. Simulation results show that when the polarity of the primary current suddenly reverses, the circuit can automatically switch to the correct signal path within tens of microseconds and maintain continuous and stable output, far exceeding the requirements of the power grid for polarity identification. This not only fundamentally compensates for the lack of directional sensing capability in magnetically modulated high-current measurement devices, but also inherits the advantages of strong anti-interference capability and good environmental adaptability of magnetic modulation technology itself due to its all-hardware, closed-loop comparison working mechanism, ultimately forming an integrated solution with high dynamic performance, high reliability, and strong engineering practicality.

[0067] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0068] The above description is only a specific embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A polarity identification method for measuring dual-core symmetrical nonlinear magnetic modulation DC current, characterized in that, This invention relates to a dual-core symmetrical nonlinear magnetic modulation DC current measuring device. The measuring device includes two iron cores connected in parallel with symmetrical magnetic circuits, an excitation power supply providing AC excitation to the two iron cores, rectifier diodes connected to the secondary windings of the two iron cores respectively, and sampling resistors R connected to the secondary windings of the two iron cores respectively. C R f ; The polarity identification method includes the following steps: Acquisition sampling resistor R C Voltage signal V at both ends Rc and the sampling resistor R f Voltage signal V at both ends Rf ; Calculate voltage signal V Rc Effective value V C And calculate the voltage signal V Rf Effective value V f ; Compare the effective value V C With V f The magnitude, and based on the magnitude comparison result, from the voltage signal V Rc V Rf Choose one of the signals as the output signal U; Combined with V C With V f The magnitude comparison results, along with the positive and negative polarities of the output signal U, are used to perform combinational logic operations to determine the direction of the primary DC current in the iron core.

2. The polarity identification method for measuring dual-core symmetrical nonlinear magnetic modulation DC current according to claim 1, characterized in that, The secondary winding of the first iron core of the two iron cores is defined to have a first terminal and a second terminal, and the secondary winding of the second iron core of the two iron cores is defined to have a third terminal and a fourth terminal. The number of rectifier diodes is four, wherein the first rectifier diode and the second rectifier diode are connected in series between the first terminal and the fourth terminal; The third rectifier diode and the fourth rectifier diode are connected in series between the second terminal and the third terminal; The positive terminal of the excitation power supply is connected to the connection point of the first rectifier diode and the second rectifier diode, and the negative terminal of the excitation power supply is connected to the connection point of the third rectifier diode and the fourth rectifier diode. The sampling resistor R C The sampling resistor R is disposed at both ends of the series branch of the third and fourth rectifier diodes. f It is set at both ends of the series branch of the first rectifier diode and the second rectifier diode.

3. The polarity identification method for measuring dual-core symmetrical nonlinear magnetic modulation DC current according to claim 1, characterized in that, The two iron cores are identical in specifications and coaxially arranged, and the primary DC current passes through the central hole of the two iron cores via a single DC bus.

4. The polarity identification method for measuring dual-core symmetrical nonlinear magnetic modulation DC current according to claim 1, characterized in that, The effective value V is compared using the first voltage comparator. C With V f Size; When V C ≥V f When V is in the first voltage comparator, the first voltage comparator outputs the first logic level; when V is in the first voltage comparator, the first voltage comparator outputs the first logic level. C <V f At that time, the first voltage comparator outputs the second logic level.

5. The polarity identification method for measuring dual-core symmetrical nonlinear magnetic modulation DC current according to claim 4, characterized in that, The logic level output by the first voltage comparator is used as a control signal to drive the switching circuit to turn on or off, thereby affecting the voltage signal V. Rc V Rf Select one of them as the output signal U, including: If the control signal is the first logic level, then select V. Rf As the signal to be output, U; If the control signal is the second logic level, then V is selected. Rc As the output signal U.

6. The polarity identification method for measuring dual-core symmetrical nonlinear magnetic modulation DC current according to claim 5, characterized in that, The output signal U is input to a second voltage comparator along with a zero potential to determine the polarity of the output signal U. When U > 0, the four rectifier diodes are determined to be positively connected; When U≤0, the four rectifier diodes are determined to be reverse-connected.

7. The polarity identification method for measuring dual-core symmetrical nonlinear magnetic modulation DC current according to claim 6, characterized in that, The combinational logic operation is implemented by simulating a multiplier: The output signals of the first voltage comparator and the second voltage comparator are input into the multiplier, and the direction of the DC current is determined based on the sign of the multiplication result signal output by the multiplier.

8. The polarity identification method for measuring dual-core symmetrical nonlinear magnetic modulation DC current according to claim 4, characterized in that, The combinational logic operation is as follows: When V C ≥V f If the judgment result of the signal and the judgment result of the output signal U>0 are both true or both false, the DC current is determined to be in the positive direction; otherwise, the DC current is determined to be in the reverse direction.

9. The polarity identification method for measuring dual-core symmetrical nonlinear magnetic modulation DC current according to claim 1, characterized in that, The effective value of the voltage signal is calculated using a true RMS converter chip, the model of which is AD637AQ.

10. A polarity identification system for measuring dual-core symmetrical nonlinear magnetic modulation DC current, characterized in that, This invention relates to a dual-core symmetrical nonlinear magnetic modulation DC current measuring device. The measuring device includes two iron cores connected in parallel with symmetrical magnetic circuits, an excitation power supply providing AC excitation to the two iron cores, rectifier diodes connected to the secondary windings of the two iron cores respectively, and sampling resistors R connected to the secondary windings of the two iron cores respectively. C R f ; The polarity identification system includes the following circuitry: The sampling circuit is configured to acquire the sampling resistor R. C Voltage signal V at both ends Rc and the sampling resistor R f Voltage signal V at both ends Rf ; The effective value calculation circuit is configured to calculate the voltage signal V. Rc Effective value V C And calculate the voltage signal V Rf Effective value V f ; The effective value discrimination circuit is configured to detect the effective value V. C With V f The magnitude, and based on the magnitude comparison result, from the voltage signal V Rc V Rf Choose one of the signals as the output signal U; A primary current direction determination circuit is configured to combine V C With V f The magnitude comparison results, along with the positive and negative polarities of the output signal U, are used to perform combinational logic operations to determine the direction of the primary DC current in the iron core.

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