A method for arc fault detection and location based on system modeling analysis

Abstract

The present invention relates to an arc fault detection and location method based on system modeling analysis, including: simulating an arc fault experiment, recording the fault voltage and current of the branch where the arc is located, determining the series connection of the voltage source and the resistor, and constructing an arc electrical model; constructing a first state space equation and a second state space equation, and establishing an equivalent model based on the first state space equation and the second state space equation, and an equivalent simulation model; judging whether a system fails, if a fault occurs, determining the location of the fault, and judging the type of fault. The method of the present invention is based on real test data, and reduces the influence of power electronic devices on arc fault detection and location. The simulation verification algorithm has high accuracy, strong real-time performance and low cost, and is more suitable for DC microgrid systems.

Description

Technical Field

[0001] The present invention relates to the field of electrical engineering technology, and in particular to an arc fault detection and positioning method based on system modeling analysis. Background Art

[0002] During operation, DC microgrid systems are prone to DC arc faults due to loose cable joints, damaged insulation layers, and poor contact. If the arc is not extinguished in time, it is easy to cause electrical fires. Among them, DC series arc faults are more frequent, which will cause resistance to increase and current to decrease. Therefore, the arc current is lower than the set value of the traditional circuit breaker protection device, and the series arc fault detection and isolation cannot be triggered. The existing series arc fault detection method research focuses on the power supply resistor series circuit. By analyzing the current in the time and frequency domain, the arc fault is judged according to the signal difference between the normal state and the fault state. There is a lack of a deeper understanding of the arc fault. In the circuit containing power electronic devices, it is often misjudged due to noise interference; in addition, the current arc fault location research mostly requires external capacitors, Rogowski coils, etc. Among them, the external capacitor uses its low impedance characteristics in the high-order harmonics generated by the arc to judge the arc position according to the current change on the capacitor; the Rogowski coil is located by analyzing the radio frequency signal correlation function. This method has the limitation of external electromagnetic interference and may affect the original electrical system. In response to the above two problems, an arc fault detection and location method based on system modeling and analysis was proposed. Summary of the invention

[0003] The purpose of the present invention is to address the deficiencies of existing arc fault detection and location methods, and to propose an arc fault detection and location method based on arc and system modeling analysis, so as to ultimately achieve rapid detection and accurate location of arc faults.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] A method for detecting and locating arc faults based on system modeling analysis, comprising:

[0006] Simulate arc fault experiment and record the obstacle voltage and current of the branch where the arc is located;

[0007] According to the obstacle voltage and current of the branch where the arc is located, the series connection of the voltage source and the resistor is determined to construct an arc electrical model;

[0008] Constructing a first state space equation and a second state space equation, and establishing an equivalent model and an equivalent simulation model based on the first state space equation and the second state space equation respectively; wherein the first state space equation is a state space equation of the system under normal working conditions; the second state space equation is a state space equation when an arc fault occurs at different positions obtained by adding the arc electrical model to different positions in the system; the system is a DC microgrid system;

[0009] Based on the equivalent simulation model, it is determined whether a fault occurs in the system. If a fault occurs, the location of the fault is determined and the type of the fault is determined.

[0010] Furthermore, the arc fault simulation experiment is carried out on a constructed DC microgrid fault arc test experimental platform, wherein the experimental platform includes a DC microgrid system and an arc generating device; the DC microgrid system includes a DC power supply and a constant power load; the arc generating device includes a screw slide, a copper rod, a driver, and a controller; wherein the DC power supply is used for power supply, and the constant power load is used to simulate different load types of the DC microgrid.

[0011] Further, simulating the arc fault experiment includes:

[0012] Record the current waveform and voltage waveform at both ends of the arc generating device under normal conditions;

[0013] Adjusting the arc generating device controller to perform arc drawing operation, and recording the current waveform and voltage waveform at both ends of the arc generating device;

[0014] The arc length, arc branch voltage, and arc current are changed to perform arc drawing operations, and the current and voltage waveforms at different arc lengths and arc fault locations are recorded.

[0015] Furthermore, constructing the arc electrical model includes: obtaining the arc electrical model based on a curve fitting method according to the arc voltage and arc current obtained by simulating the arc fault experiment, as shown in the following formula (1):

[0016] U arc =aU+R arc I arc (a≈1) (1)

[0017] Among them, U arc is the voltage across the arc, I arc is the arc current, a is the equivalent voltage source coefficient, the total voltage of the branch where U is located, R arc is the arc equivalent resistance.

[0018] Furthermore, the first state space equation is constructed as:

[0019]

[0020] Among them, i L1 ,…i Ln are the inductor currents on the n Buck branches, u C1 ,…u Cn are the capacitor voltages on the n Buck branches, d1,…d n Respectively represent the duty cycle of n branches, A 1(n×n) represents an n-dimensional zero matrix, R1,…R n They represent the loads on the n branches, C1,…C n They represent the capacitances on the n branches respectively.

[0021] Furthermore, the second state space equation is constructed as:

[0022]

[0023] in, B'2=B'3=…B' m-1 =B' m+1 =…=B' n is an n-dimensional zero vector, U1,…U m ,…U n Represents the arc fault equivalent voltage source of n branches.

[0024] Furthermore, determining whether the system has a fault includes: measuring actual values ​​of the inductor current and capacitor voltage of the system in actual operation, and subtracting them from theoretical estimated values ​​of the inductor current and capacitor voltage under normal working conditions obtained by modeling to obtain a residual r1; if the residual r1 is greater than a threshold value J1, determining that the system has a fault; wherein the threshold value J1 is a preset difference between the inductor current and capacitor voltage of the physical system and the modeling system under normal working conditions, and is a constant close to 0 that is set by comprehensively considering system noise and modeling errors.

[0025] Furthermore, determining the location where the system fails includes: after determining that the system has a fault, measuring the actual values ​​of the inductor current and capacitor voltage of the system actually working after the fault, and subtracting them from the theoretical values ​​of the inductor current and capacitor voltage of arc faults occurring at different locations obtained by modeling to obtain a residual r2; if the residual r2 is less than a state threshold J2 of an arc fault at a certain location, then it is determined that the system has failed at that location; wherein the threshold J2 is a preset difference between the inductor current and capacitor voltage of the physical system and the modeling system when an arc fault occurs at different locations, and is a constant close to 0 that is set by comprehensively considering system noise, system modeling error, and arc modeling error.

[0026] Further, judging the fault type includes: after determining the system fault location, numerically integrating the portion exceeding the threshold value J2; if the numerical integral is greater than a set threshold value x, determining that the fault occurring at the location is an arc fault; otherwise, changing the load.

[0027] The beneficial effects of the present invention are:

[0028] (1) Compared with the existing arc fault detection method, the present invention only uses time domain information, has low computational complexity, and improves the fault detection speed.

[0029] (2) The present invention does not require any additional electrical components or sensors during the detection and positioning process, which has no impact on the original circuit and saves costs.

[0030] (3) After determining the unconventional action, the present invention further performs an over-threshold integral calculation to distinguish between arc faults and load changes, two unconventional and easily confused actions, thereby improving the accuracy of the overall algorithm. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0032] Figure 1 A circuit diagram of a DC microgrid fault arc system for testing an embodiment of the present invention;

[0033] Figure 2 Implementation flow chart of the present invention;

[0034] Figure 3 This is a simulation verification diagram of the present invention;

[0035] Figure 4It is a simulation waveform diagram of the residual error of the state quantity of the system action judgment after an arc fault occurs in the present invention;

[0036] Figure 5 It is a simulation diagram of the residual error of the state quantity of the judgment position after the arc fault occurs in the present invention;

[0037] Figure 6 It is a simulation diagram of the residual error of the state quantity of the judgment position ② after the arc fault occurs in the present invention;

[0038] Figure 7 It is a simulation diagram of the residual error of the state quantity of the judgment position ① and ② after an arc fault occurs in the present invention;

[0039] Figure 8 It is a simulation diagram of the residual error of the corresponding position state quantity when the load change action occurs in the present invention;

[0040] Among them, 1 is the system simulation model, 2 is the normal system state equation model, 3 is the state equation model of the arc fault at position ①, 4 is the state equation model of the arc fault at position ②, 5 is the state space model of arc faults occurring simultaneously at positions ① and ②, 6 is the input signal, and 7 is the residual output observation part. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0043] The DC microgrid fault arc test experimental platform constructed in the embodiment of the present invention includes a DC microgrid system and an arc generating device. Figure 1 As shown in the figure, the whole system is powered by a 110V DC source; the load is a constant power load, which is composed of a 110V to 48V unidirectional DC / DC converter and a resistor to simulate different types of loads in a DC microgrid. The arc generating device includes a screw slide, a copper rod, a driver, and a controller.

[0044] The algorithm model of the embodiment of the present invention is constructed as follows Figure 2 As shown in the figure, it includes the preparation work before model building and the subsequent modeling from the normal working state of the system and the arc faults occurring at different positions of the system. The simulation model is built as shown in the figure. Figure 3 shown.

[0045] (1) Simulated arc fault experiment: (a) Set different arc occurrence locations, current magnitudes, and arc lengths. Figure 1 ①-②, referring to the UL1699B experimental standard and the common voltage levels of DC microgrids, the voltage was selected as 110V, the current sizes were 3A, 4A, 5A, 6A, 7A, 8A, 9A and 10A, and the arc lengths were 0.5mm, 0.7mm, 0.9mm, 1.1mm, 1.3mm, respectively, and other experimental conditions remained unchanged; (b) the arc generating device was adjusted to control the copper rods to separate at a uniform speed to generate an arc; (c) the experimental data and current waveform were recorded by an oscilloscope, the experimental parameters were changed and the experiment was repeated, and each experimental condition was repeated 10 groups.

[0046] (2) Study the relationship between the arc equivalent model and the current in the normal working state: According to the arc voltage and arc current measured by the simulated arc fault experiment, the arc electrical model is obtained based on the curve fitting method, as shown in the following formula (1):

[0047] U arc =aU+R arc I arc (a≈1) (1)

[0048] Among them, U arc is the voltage across the arc, I arc is the arc current, a is the equivalent voltage source coefficient, the total voltage of the branch where U is located, R arc is the arc equivalent resistance.

[0049] (3) Establish the spatial state equation of the system under normal working conditions:

[0050]

[0051] Among them, i L1 ,…i Ln are the inductor currents on the n Buck branches, u C1 ,…u Cn are the capacitor voltages on the n Buck branches, d1,…d n Respectively represent the duty cycle of n branches, A 1(n×n) represents an n-dimensional zero matrix, R1,…R n They represent the loads on the n branches, C1,…C n They represent the capacitances on the n branches respectively.

[0052] (4) The arc electrical equivalent model is added to different positions in the system to establish the state space equation when an arc fault occurs at different positions. Now assume that an arc fault occurs in the mth branch:

[0053]

[0054] in, B'2=B'3=…B' m-1 =B' m+1 =…=B' n is an n-dimensional zero vector, U1,…U m ,…U n Represents the arc fault equivalent voltage source of n branches.

[0055] Determining whether a system fault occurs includes: measuring the actual values ​​of the inductor current and the capacitor voltage of the system in actual operation by means of a tunnel magnetoresistance sensor and a Hall voltage sensor respectively, subtracting the actual values ​​from the theoretical estimated values ​​of the inductor current and the capacitor voltage under normal working conditions obtained by modeling, and obtaining a residual r1 by comprehensively considering the system noise and the modeling error. If the residual r1 is greater than a threshold value J1, it is determined that the system has a fault.

[0056] Determining the location where the system fails includes: after determining that the system has a fault, measuring the actual values ​​of the inductor current and the capacitor voltage of the system actually working after the fault through a tunnel magnetoresistance sensor and a Hall voltage sensor respectively, and subtracting them from the theoretical values ​​of the inductor current and the capacitor voltage of arc faults occurring at different locations obtained by modeling, and obtaining a residual r2 by comprehensively considering system noise, modeling error and arc model error. If the residual r2 is less than a state threshold J2 of an arc fault at a certain location, it is determined that the system has failed at that location.

[0057] The residual result output of the embodiment of the present invention simulating arc fault and changing load action is as follows: Figure 3-Figure 8 shown.

[0058] The theoretical basis for determining the two thresholds for judging system faults and fault locations is:

[0059] The residual evaluation function in the system is established based on the residual signal r between the range (k, k+N):

[0060]

[0061] Set the threshold to the supremum of the residual r:

[0062] J th =sup||r(k)|| RMS (5)

[0063] Specifically: (a) Since the experimental platform used in this experiment is an integrated DC / DC device, it is impossible to directly measure the inductor current and capacitor voltage. The DC / DC input current is as follows: Figure 1 ③-④ and the voltage on the front side of the load are as follows Figure 1 ⑤-⑥ replace the inductor current and capacitor voltage, and the following relationship exists: i in =di L ,i in represents the input current, d represents the duty cycle, i L represents the inductor current, and the voltage on the front side of the load is equal to the capacitor voltage; (b) the experimental data and current waveform are recorded by an oscilloscope, and the experimental parameters are changed to repeat the experiment, and each experimental condition is repeated 10 groups; (c) the experimental data under normal operation are subtracted from the theoretical data to obtain the residual r1, and the threshold J1 is determined according to formula (5); (d) according to the formula, the theoretical waveform after the arc fault occurs can be obtained, and the experimental state quantity waveform is subtracted from the theoretical waveform to obtain the residual r2. Considering that the current drop amplitude of the arc fault is related to the current value itself, the threshold J2 here is J2 = 0.05I, where I represents the inductor current under normal operation.

[0064] The specific steps of determining the fault type are as follows: (a) after determining that the system has a fault, numerically integrate the residual exceeding the threshold J2 within a specified time to obtain x1; (b) Figure 1 The load is increased on the experimental platform shown, and the actual values ​​of the inductor current and capacitor voltage actually working after the system fault are subtracted from the theoretical values ​​of the inductor current and capacitor voltage at different locations where arc faults occur obtained by modeling. The residual r2 is obtained by comprehensively considering the system noise, modeling error and arc model error, and the part exceeding the threshold value J2 is numerically integrated within a specified time to obtain x2; (c) it can be concluded that x1>>x2; (d) the threshold value x=0.1 is set. When the integral value is greater than 0.1, it is determined that an arc fault occurs at this location; when the integral value is less than 0.1, it is determined that the load changes at this location.

[0065] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for arc fault detection and location based on system modeling analysis, characterized in that: include: Simulate arc fault experiment and record the obstacle voltage and current of the branch where the arc is located; According to the obstacle voltage and current of the branch where the arc is located, the series connection of the voltage source and the resistor is determined to construct an arc electrical model; Constructing a first state space equation and a second state space equation, and establishing an equivalent model and an equivalent simulation model based on the first state space equation and the second state space equation respectively; wherein the first state space equation is a state space equation of the system under normal working conditions; the second state space equation is a state space equation when an arc fault occurs at different positions obtained by adding the arc electrical model to different positions in the system; the system is a DC microgrid system; Determine whether a fault occurs in the system based on the equivalent simulation model, and if a fault occurs, determine the location of the fault and determine the type of fault; The first state space equation is constructed as follows: (2) in, are the inductor currents on the n Buck branches, are the capacitor voltages on the n Buck branches, Respectively represent the duty cycle of the n branches, represents an n-dimensional zero matrix, , , , They represent the loads on the n branches respectively, Respectively represent the capacitances on the n branches; The second state space equation is constructed as: (3) in, , , is an n-dimensional zero vector, , represents the arc fault equivalent voltage source of n branches; Determining whether the system fails includes: measuring the actual values ​​of the inductor current and capacitor voltage of the system in actual operation, and subtracting them from the theoretical estimated values ​​of the inductor current and capacitor voltage under normal working conditions obtained by modeling to obtain a residual error. , if the residual Greater than threshold , it is determined that the system has a fault; wherein the threshold The difference between the inductor current and the capacitor voltage under a preset normal working state and an arc fault state; Determining the location where the system fails includes: after determining that the system has a fault, measuring the actual values ​​of the inductor current and capacitor voltage of the system actually working after the fault, and subtracting them from the theoretical values ​​of the inductor current and capacitor voltage of arc faults at different locations obtained by modeling to obtain a residual error. , if the residual Less than the state threshold of an arc fault at a certain location , it is determined that the system has failed at this location; wherein the threshold The difference between the inductor current and the capacitor voltage under a preset normal working state and an arc fault state at different positions; Determining the fault type includes: after determining the fault location of the system, exceeding the threshold A numerical integration is performed on the part. If the numerical integration is greater than a set threshold value x, it is determined that the fault occurring at this position is an arc fault, otherwise the load is changed.

2. The arc fault detection and location method based on system modeling analysis according to claim 1 is characterized in that: The arc fault simulation experiment is carried out on a constructed DC microgrid fault arc test experimental platform, wherein the experimental platform includes a DC microgrid system and an arc generating device; the DC microgrid system includes a DC power supply and a constant power load; the arc generating device includes a screw slide, a copper rod, a driver, and a controller; wherein the DC power supply is used for power supply, and the constant power load is used to simulate different load types of the DC microgrid.

3. The arc fault detection and location method based on system modeling analysis according to claim 2 is characterized in that: The arc fault simulation experiment includes: Record the current waveform and voltage waveform at both ends of the arc generating device under normal conditions; Adjusting the arc generating device controller to perform arc drawing operation, and recording the current waveform and voltage waveform at both ends of the arc generating device; The arc length, arc branch voltage, and arc current are changed to perform arc drawing operations, and the current and voltage waveforms at different arc lengths and arc fault locations are recorded.

4. The arc fault detection and location method based on system modeling analysis according to claim 1, characterized in that: Constructing the arc electrical model includes: obtaining the arc electrical model based on a curve fitting method according to the arc voltage and arc current obtained by simulating the arc fault experiment, as shown in the following formula (1): (1) in, is the voltage across the arc, is the arc current, is the equivalent voltage source coefficient, The total voltage of the branch, is the arc equivalent resistance.

Images