A segmented modeling method of a fuse for a direct current networking system based on arc resistance characteristics

Abstract

The application provides a segmented modeling method of a fuse for a direct current networking system based on arc resistance characteristics, relates to the technical field of common direct current bus system design, and comprises the following steps: calculating real-time arc resistance data of the fuse according to short-circuit voltages and short-circuit currents of two sides of the fuse in a continuously collected short-circuit test process to form an arc resistance curve; intercepting the arc resistance curve between a peak value moment of the short-circuit current and a slope drop moment of the arc resistance curve to obtain an arc resistance curve in an arc striking stage, and intercepting the arc resistance curve between the slope drop moment and a moment when the short-circuit current is zero to obtain an arc resistance curve in an arc burning stage; respectively performing data fitting according to the arc resistance curve in the arc striking stage and the arc resistance curve in the arc burning stage to obtain a segmented arc resistance curve equation; and building a fuse simulation model based on a controlled resistance by taking the arc resistance curve equation as a control signal. The beneficial effect is that the arc resistance curve is divided into two segments and corresponding arc resistance curve equations are designed, the simulation precision is higher, and the method can be better applied to different working conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of common DC bus system design, and particularly relates to a segmented modeling method of a fuse for a DC networking system based on arc resistance characteristics. BACKGROUND

[0002] In today's industrial field, the rapid development of power electronics technology is driving the widespread application of various complex electrical systems. As an advanced power configuration architecture, the common DC bus system has been widely adopted and promoted in industrial applications due to its excellent flexibility and reliability.

[0003] The common DC bus system usually connects multiple rectifiers and DC converters in parallel to the DC bus. The rectifier is responsible for converting AC power to DC power, providing stable power input for the DC bus. The DC converter can adjust and transform the voltage of the DC bus according to the needs of different loads. In the common DC bus system, short-circuit fault is a common and serious fault type. Once a short-circuit occurs, a large short-circuit current will quickly flow into the system, causing serious damage to the bus and other non-fault branch devices. In order to protect the safety of the system, fuses are widely used for short-circuit fault protection.

[0004] As a non-linear overcurrent protection device, the working principle of the fuse is based on the thermal effect of current. When current flows through the fuse, the fuse will generate heat. If the current exceeds the rated value, the fuse temperature will rise rapidly and melt, thereby cutting off the circuit. The arc resistance characteristic of the fuse is one of the important indicators of its protection performance. Arc resistance refers to the resistance characteristic presented by the electric arc during the fuse blowing process. The internal quenching filler material has a significant impact on the arc resistance characteristics of the fuse. Different quenching filler materials have different physical and chemical properties, such as melting point, thermal conductivity, electrical conductivity, etc. These properties will affect the generation, development and extinction process of the electric arc, thereby changing the size and variation of the arc resistance. For example, some filler materials can quickly absorb the energy of the electric arc, making the electric arc extinguish quickly, thereby reducing the arc resistance; while other filler materials may cause the electric arc to last longer, increasing the arc resistance. This complex change in arc resistance characteristics makes it very difficult to accurately model the fuse.

[0005] Generally, the industry uses a variable resistor or a controlled source structure equivalent to a variable resistor to establish a simulation model by repeatedly manually iterating approximation method to simulate the arc resistance characteristics of the fuse under different currents. In order to facilitate the iterative optimization of parameters, this kind of scheme usually uses a unique and relatively simple low-order function as the control quantity, which cannot accurately fit the arc resistance characteristics of the fuse to the outside. In actual application, there are problems such as large difference between the peak current, external voltage and the measured value, complex and tedious modeling process, which causes inconvenience to the safety and reliability design of the whole system.

[0006] Therefore, it is urgent to improve the existing modeling method. SUMMARY

[0007] In view of the problems in the prior art, the present application provides a segmented modeling method for a fuse for a direct current networking system based on arc resistance characteristics, comprising the following steps: S1, short-circuit testing of the fuse is performed, and the short-circuit voltage and the short-circuit current on both sides of the fuse during the short-circuit testing process are continuously collected; S2, real-time arc resistance data of the fuse is calculated according to the short-circuit voltage and the short-circuit current, and an arc resistance curve is constructed according to the real-time arc resistance data; S3, the arc resistance curve between the peak time of the short-circuit current and the time when the slope of the arc resistance curve decreases is intercepted to obtain an arc initiation stage arc resistance curve, and the arc resistance curve between the time when the slope decreases and the time when the short-circuit current is zero is intercepted to obtain an arc burning stage arc resistance curve; S4, data fitting is respectively performed according to the arc initiation stage arc resistance curve and the arc burning stage arc resistance curve to obtain a segmented arc resistance curve equation; and S5, a fuse simulation model based on a controlled resistance is built by taking the arc resistance curve equation as a control signal.

[0008] Preferably, in the step S1, the short-circuit testing of the fuse is performed by a short-circuit testing platform of the fuse which is pre-built, and the short-circuit testing platform comprises: a direct current stabilizing source, two ends of the direct current stabilizing source are connected with one end of a contactor and one end of a support capacitor respectively, the other end of the contactor is connected with the other end of the support capacitor; a fuse branch, which is connected in parallel to both ends of the support capacitor, the fuse branch comprises a first circuit breaker and the fuse connected in series; and an impedance device, one end of the impedance device is connected with the other end of the support capacitor, and the other end of the impedance device is connected with one end of the fuse branch.

[0009] Preferably, the process of short-circuit testing the fuse includes: step S11, opening the first circuit breaker, and then closing the contactor, so that the DC voltage source charges the support capacitor; step S12, closing the first circuit breaker after the support capacitor is fully charged, to perform short-circuit test on the fuse, and recording the short-circuit voltage and the short-circuit current across the fuse by using an oscilloscope.

[0010] Preferably, the short-circuit test platform further includes a discharge branch parallel to the fuse branch, the discharge branch further includes a second circuit breaker and a discharge resistor connected in series; after performing short-circuit test on the fuse, the process further includes closing the second circuit breaker, to discharge the residual voltage in the support capacitor through the discharge resistor.

[0011] Preferably, the expression of the arc resistance curve is as follows:

[0012]

[0013] wherein, represents the arc resistance value of the fuse at time t; represents the arc resistance curve in the arcing stage; represents the arc resistance curve in the burning stage; and are constants, obtained by data fitting of the arc resistance curve in the arcing stage; and are constants, obtained by data fitting of the arc resistance curve in the burning stage.

[0014] Preferably, in step S4, the LM least square method is used to perform data fitting on the arc resistance curve in the arcing stage and the arc resistance curve in the burning stage, respectively, to obtain the corresponding constants.

[0015] Preferably, after performing step S5, the process further includes: obtaining the simulation current of the fuse and the Joule integral curve of the simulation current simulated by the fuse simulation model, and determining whether the difference between the simulation current and the Joule integral curve and the corresponding measured data is greater than a difference threshold: if not, taking the fuse simulation model as the segmented modeling result of the fuse; if yes, adjusting the initial guess value of the LM least square method, and then returning to step S4.

[0016] Preferably, the initial guess value is preliminarily estimated by a linear regression method.

[0017] Preferably, the fuse simulation model comprises: an input module, input ends of a first current judgment module and a second current judgment module are connected to the input module respectively, an output end of the first current judgment module is connected to an input end of a first multiplier, an output end of the second current judgment module is connected to a second multiplier, an integrator and an arc starting time judgment module in sequence, an output end of the arc starting time judgment module is connected to an input end of the first multiplier through a NOT gate; a first switching switch, input ends of the input module and the arc starting time judgment module are connected to an input end of the first switching switch respectively, an output end of the first switching switch is connected to a negative output port of a fuse through a fuse rated resistance; a second switching switch, input ends of the input module and the first multiplier are connected to an input end of the second switching switch respectively, an output end of the second switching switch is connected to the negative output port through a variable resistor, a resistance control end of the variable resistor is connected to an arc resistance curve equation as a control signal; the output end of the NOT gate is a fuse working state output port, an output end of the input module is a simulation current output port, and an output end of the integrator is a joule integral curve output port of the simulation current.

[0018] Preferably, the calculation formula of the real-time arc resistance data is as follows:

[0019]

[0020] Wherein, z(t) represents the real-time arc resistance data at t time, represents the short-circuit voltage at t time, represents the short-circuit current at t time.

[0021] The above technical scheme has the following advantages or beneficial effects:

[0022] 1) According to the actual working condition of the fuse, the peak value time of the short-circuit current is taken as the starting time of the arc resistance curve in the arc starting stage, the time when the slope of the arc resistance curve decreases is taken as the termination time of the arc resistance curve in the arc starting stage and the starting time of the arc resistance curve in the arc burning stage, and the time when the short-circuit current is zero is taken as the termination time of the arc resistance curve in the arc burning stage, so as to realize the division of the arc resistance curve into two sections and the design of the corresponding arc resistance curve equation, the simulation precision is higher, and the arc resistance curve can be better applied to different working conditions;

[0023] 2) Compared with the traditional arc resistance theoretical analysis scheme, the present application does not need to analyze the specific filling material and internal structure, only needs to analyze the real-time arc resistance data, and has higher practicability;

[0024] 3) Compared with the traditional scheme based on the variable resistance or controlled source equivalent circuit, the present application has fewer iteration times, and the obtained arc resistance curve equation can already reproduce the arc resistance characteristics of the fuse, and usually does not need to adjust the simulation model. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 For the preferred embodiments of the present application, a flowchart of the segmented modeling method of the fuse for the arc resistance characteristic-based DC networking system is shown in

[0026] Figure 2 For the preferred embodiments of the present application, a structural diagram of the short-circuit test platform is shown in

[0027] Figure 3 For the preferred embodiments of the present application, a flowchart of the process of performing the short-circuit test on the fuse is shown in

[0028] Figure 4 For the preferred embodiments of the present application, a structural diagram of the fuse simulation model is shown in

[0029] Figure 5 For the preferred embodiments of the present application, a waveform comparison diagram between the simulation current output by the fuse simulation model and the measured short-circuit current is shown in

[0030] Figure 6 For the preferred embodiments of the present application, a waveform comparison diagram between the Joule integral curve output by the fuse simulation model and the integral value of the measured short-circuit current is shown in DETAILED DESCRIPTION

[0031] The present application will be described in detail below with reference to the drawings and specific embodiments. The present application is not limited to this embodiment, and other embodiments can also fall within the scope of the present application as long as they comply with the main idea of the present application.

[0032] For the preferred embodiments of the present application, based on the above-mentioned problems existing in the prior art, a segmented modeling method of a fuse for an arc resistance characteristic-based DC networking system is provided, as shown in Figure 1 The method comprises the following steps: S1, performing a short-circuit test on the fuse and continuously collecting the short-circuit voltage and short-circuit current on both sides of the fuse during the short-circuit test; S2, calculating the real-time arc resistance data of the fuse according to the short-circuit voltage and short-circuit current, and constructing an arc resistance curve according to the real-time arc resistance data; S3, intercepting the arc resistance curve between the peak time of the short-circuit current and the time when the slope of the arc resistance curve decreases to obtain the arc resistance curve in the arcing stage, and intercepting the arc resistance curve between the time when the slope decreases and the time when the short-circuit current is zero to obtain the arc resistance curve in the burning stage; S4, respectively performing data fitting according to the arc resistance curve in the arcing stage and the arc resistance curve in the burning stage to obtain a segmented arc resistance curve equation; and S5, building a fuse simulation model based on a controlled resistance by taking the arc resistance curve equation as a control signal.

[0033] Specifically, in the embodiment, the short-circuit voltage and short-circuit current in the short-circuit test process of the fuse are obtained by actually measuring the fuse, then the real-time arc resistance data of the fuse are calculated, and then the arc resistance curve formed by the real-time arc resistance data is analyzed, so that the arc resistance curve equation representing the change of the arc resistance of the fuse with time is obtained, thereby the fuse simulation model is built by taking the arc resistance curve equation as the control signal, and the whole process does not need to analyze the specific filling material and internal structure of the fuse, and has high practicability.

[0034] Further, in order to realize the actual measurement of the fuse, it is necessary to previously build a short-circuit test platform of the fuse to perform the short-circuit test on the fuse, as shown in Figure 2 The short-circuit test platform includes: a direct current stabilizing source 100, two ends of the direct current stabilizing source 100 are respectively connected to one end of a contactor 200 and one end of a support capacitor 300, the other end of the contactor 200 is connected to the other end of the support capacitor 300; a fuse branch, which is connected to the two ends of the support capacitor 300 in parallel, and the fuse branch includes a first circuit breaker 400 and a fuse 500 connected in series; and an impedance device 600, one end of the impedance device 600 is connected to the other end of the support capacitor 300, and the other end of the impedance device 600 is connected to one end of the fuse branch.

[0035] Specifically, in the embodiment, the direct current stabilizing source 100 is preferably a programmable direct current stabilizing source, on the one hand, the output voltage and current value can be accurately set, so that in the short-circuit test of the fuse, the voltage and current conditions under various actual working conditions can be accurately simulated according to different test requirements. For example, when testing the short-circuit characteristics of fuses of different specifications, the current size can be accurately adjusted from a small overload current to a large short-circuit current, so as to comprehensively evaluate the response time and fusing characteristics of the fuse under different current levels. On the other hand, the programmable characteristic makes it convenient for the tester to change the output parameters without the need for complex mechanical adjustment of the traditional power supply. The voltage and current value can be modified in real time during the test process, or the parameters can be gradually changed according to the preset program, so as to realize the test of the fuse under different dynamic conditions, such as simulating the sudden change of the current.

[0036] In the preferred embodiment of the present application, as shown in Figure 3 The process of performing the short-circuit test on the fuse includes: step S11, opening the first circuit breaker, and then closing the contactor to charge the support capacitor by the direct current stabilizing source; step S12, closing the first circuit breaker after the charging of the support capacitor is completed to perform the short-circuit test on the fuse, and using an oscilloscope to record the short-circuit voltage and short-circuit current at the two ends of the fuse.

[0037] In the preferred embodiment of the present application, the short-circuit test platform further comprises a discharging branch connected in parallel with the fuse branch, and the discharging branch further comprises a second circuit breaker 700 and a discharging resistor 800 connected in series; after the short-circuit test of the fuse is completed, the second circuit breaker is further closed to release the residual voltage in the support capacitor through the discharging resistor.

[0038] Specifically, in the embodiment, the entire process of the short-circuit test of the fuse based on the short-circuit test platform comprises the following four stages:

[0039] 1. Initial state setting stage

[0040] Before the short-circuit test of the fuse is performed, the first task is to ensure that the entire test circuit is in a safe initial state. Specifically, the first circuit breaker 400 and the second circuit breaker 700 are carefully checked and confirmed to be in an open state. This operation is crucial because when the two circuit breakers are in an open state, it means that the fuse branch and the discharging branch are both not conductive, which can effectively avoid accidental current flow in the preparation stage and prevent damage to the test equipment, the fuse sample and the operator. For example, if the subsequent operation is performed without confirming the state of the circuit breaker, an arc may be generated due to accidental conduction of the circuit, causing a safety accident, and also interfering with the accuracy of the experimental data.

[0041] 2. Support capacitor charging stage

[0042] After the initial state setting is completed, the support capacitor charging stage is entered. At this time, the contactor 200 needs to be closed. The contactor 200 plays a key role in controlling the on-off of the current in the circuit, and when it is closed, the DC voltage source 100 and the support capacitor 300 form a conductive loop, and the DC voltage source 100 starts to charge the support capacitor 300.

[0043] Preferably, during the charging process, the charging state needs to be closely monitored to ensure that the charging process proceeds smoothly. Generally, whether the charging is completed can be judged by monitoring the voltage change on both sides of the support capacitor 300. When the voltage reaches the preset value and stabilizes for a period of time, it is considered that the charging is completed.

[0044] 3. Short-circuit test stage

[0045] After the charging is completed, the contactor 200 is closed in time to cut off the connection between the DC voltage source 100 and the support capacitor 300, so as to avoid the interference of the DC voltage source 100 on the test results. Then, the first circuit breaker 400 of the fuse branch is closed, and at this time the fuse 500 is connected to the circuit, and the short-circuit test is formally started. During the short-circuit test, the oscilloscope is used to capture the voltage and current changes in the circuit in real time, and display them in the form of waveforms. The data to be recorded specifically include the short-circuit voltage v f(t) with the short-circuit current i f (t) and the voltage i across the support capacitor 300 c (t) and the voltage i across the support capacitor 300

[0046] 4. End of experiment

[0047] After the short-circuit test is completed, the experiment cannot be immediately ended, and important end-of-experiment work needs to be done. At this time, the second circuit breaker 700 of the discharge branch needs to be closed. After the second circuit breaker 700 is closed, the support capacitor 300 and the discharge resistor 800 form a conduction loop, and the remaining voltage stored in the support capacitor 300 will be gradually discharged through the discharge resistor 800. This step is very necessary because if the residual voltage in the capacitor, it may cause an electric shock hazard to the operator during the next experiment or equipment maintenance, and it may also affect the accuracy of the next experiment. During the discharging process, the voltage across the support capacitor 300 can be monitored, and when the voltage drops below a safe value, the discharging is considered complete, and the entire experiment is ended.

[0048] After obtaining the measured short-circuit voltage and short-circuit current of the fuse based on the above short-circuit test process, the real-time arc resistance data of the fuse can be calculated. In the preferred embodiment of the present application, the calculation formula of the real-time arc resistance data is as follows:

[0049]

[0050] where z(t) represents the real-time arc resistance data at time t, represents the short-circuit voltage at time t, represents the short-circuit current at time t.

[0051] It can be understood that the above real-time arc resistance data is a series of discrete data of the arc resistance of the fuse changing with time, and the arc resistance curve can be constructed by taking time as the horizontal axis and the corresponding arc resistance value as the vertical axis. The arc resistance curve here contains the arc resistance data of the entire short-circuit test process.

[0052] Further, the three key moments are then located in the arc resistance curve, which serves as the basis for subsequent stage division and equation construction. The above three key moments include:

[0053] 1) Peak time of short-circuit current

[0054] At the moment of short-circuit occurrence, the current will rise rapidly and reach a peak value. This moment marks the maximum of short-circuit current, at which the arc is just formed and the physical state in the arc channel changes dramatically. By monitoring the change curve of short-circuit current and using numerical analysis methods (such as derivation method, when the derivative of current with respect to time is zero, the corresponding time point is the peak moment), the peak moment of short-circuit current can be accurately determined. This moment is an important feature point in the initial stage of arc, reflecting the dynamic characteristics of current at the moment of short-circuit fault occurrence.

[0055] 2) The moment when the slope of arc resistance curve decreases

[0056] The slope of arc resistance curve reflects the rate of change of arc resistance with time. During the development of arc, due to the changes in temperature, pressure, particle concentration and other factors in the arc channel, the rate of change of arc resistance will also change. When the slope of arc resistance curve decreases significantly, it means that the development of arc enters a new stage. By taking the derivative of arc resistance curve, the rate of change of arc resistance with time curve can be obtained, and then the trend of the curve can be analyzed to determine the moment when the slope decreases. This moment usually marks the end of the arc initiation stage and the beginning of the arc burning stage.

[0057] 3) The moment when short-circuit current is zero

[0058] With the burning of arc and the consumption of energy, the short-circuit current will gradually decrease to zero. The moment when the short-circuit current is zero indicates that the arc has been extinguished and the short-circuit fault has ended. Similarly, by monitoring the short-circuit current curve, when the current value approaches zero and remains near zero for a period of time, the moment when the short-circuit current is zero can be determined. This moment is the end point of the arc development process, and it is of great significance for analyzing the extinction characteristics of arc and the recovery process of power system.

[0059] After locating the above key moments, the arc resistance curve can be divided into different stages according to these moments, and the arc resistance curves of the arc initiation stage and the arc burning stage can be extracted respectively.

[0060] Among them, the peak moment of short-circuit current is taken as the starting moment, and the moment when the slope of arc resistance curve decreases is taken as the ending moment. The curve in this time period is cut from the complete arc resistance curve, which is the arc initiation stage arc resistance curve. The arc initiation stage is the process from the formation to the initial stabilization of arc, in which the physical process in the arc channel is very complex, including evaporation of electrode material, ionization and recombination of gas, etc. The characteristics of arc initiation stage arc resistance curve reflect the energy accumulation and channel establishment process in the initial stage of arc, which is of great value for studying the initiation mechanism and arc initiation characteristics of arc.

[0061] The arc resistance curve in the arcing stage is obtained by intercepting the arc resistance curve in a time period, where the starting time is the time when the slope of the arc resistance curve decreases, and the ending time is the time when the short-circuit current is zero. The arcing stage is a process in which the arc is steadily combusted and gradually extinguished. In this stage, the energy of the arc is mainly dissipated to the surrounding environment through heat conduction, convection, radiation and other ways. The change of the arc resistance curve in the arcing stage reflects the energy balance and the change of the physical state of the arc in the combustion process, and is of great significance for analyzing the combustion characteristics and extinguishing conditions of the arc.

[0062] After the arc resistance curves in the arcing stage and the arcing stage are separated, the arc resistance curve equation can be constructed according to the characteristics of each stage. In the preferred embodiment of the present application, the expression of the arc resistance curve equation is as follows:

[0063]

[0064] wherein, represents the arc resistance value of the fuse at time t; represents the arc resistance curve in the arcing stage; represents the arc resistance curve in the arcing stage; and are constants, which are obtained by data fitting of the arc resistance curve in the arcing stage; and are constants, which are obtained by data fitting of the arc resistance curve in the arcing stage.

[0065] Specifically, in this embodiment, the arcing stage is a process in which the arc is gradually formed from nothing. In this stage, the change of the arc resistance is mainly affected by the increase of the arc length and the change of the electrode surface state. The effects of these factors make the change of the arc resistance relatively regular, which usually presents an approximately linear growth trend. Using a linear equation to describe the change of the arc resistance in the arcing stage can simplify the model structure, reduce the number of parameters to be determined, and thus reduce the calculation complexity and improve the calculation efficiency.

[0066] The arcing stage is a process in which the arc is steadily combusted and gradually extinguished. The change of the arc resistance is affected by various complex factors such as energy dissipation, arc contraction, gas ionization and recombination, and presents a highly nonlinear change characteristic. The curve shape of the low-order equation is relatively simple and cannot flexibly adapt to the complex changes such as bending and turning that may occur in the arc resistance curve in the arcing stage. The high-order equation increases the degrees of freedom of the equation by introducing high-order terms, which can better fit the various shape characteristics of the curve and make the fitted curve closer to the measured curve. The high-order equation can be regarded as a mathematical abstraction and approximation of these complex physical processes. By introducing high-order quantities to reflect the nonlinear coupling relationship between different physical factors, the change rule of the arc resistance in the arcing stage can be more accurately described.

[0067] In the preferred embodiment of the present application, in step S4, the LM least square method is used to perform data fitting on the arc resistance curve in the arcing stage and the arc resistance curve in the burning arc stage respectively to obtain the corresponding constants.

[0068] Specifically, in the present embodiment, the arc resistance curve in the arcing stage is formed by the arc resistance values corresponding to different time points in the arcing stage obtained by measurement. The initial guess value can be obtained according to the preliminary analysis of the measured arc resistance values, and then the LM least square method is used for iterative fitting on the basis of the initial guess value, and finally the above-mentioned and The fitting process of the arc resistance curve in the burning arc stage is the same, which will not be described here again. The segmented arc resistance characteristic curve equation established according to the coefficients obtained by fitting can more accurately describe the change rule of the arc resistance with time, and provide a more reliable theoretical basis for the design and protection of the electric arc related research and power equipment.

[0069] In the preferred embodiment of the present application, after step S5 is performed, the simulation current of the fuse obtained by the fuse simulation model and the joule integral curve of the simulation current are obtained, and it is judged whether the difference between the simulation current and the joule integral curve and the corresponding measured data is greater than the difference threshold value: if not, the fuse simulation model is taken as the segmented modeling result of the fuse; if yes, the initial guess value of the LM least square method is adjusted, and then step S4 is returned.

[0070] In the preferred embodiment of the present application, the initial guess value is obtained by preliminary estimation through the linear regression method.

[0071] In the preferred embodiment of the present application, as shown in Figure 4 The fuse simulation model comprises: an input module 1, an input end of a first current judgment module 2 and an input end of a second current judgment module 3 are connected respectively, an output end of the first current judgment module 2 is connected to an input end of a first multiplier 4, an output end of the second current judgment module 3 is connected to a second multiplier 5, an integrator 6 and an arcing time point judgment module 7 in sequence, an output end of the arcing time point judgment module 7 is connected to the input end of the first multiplier 4 through a NOT gate 8; a first switching switch 9, an input end of the first switching switch 9 is connected to the output end of the input module 1 and the output end of the arcing time point judgment module 7 respectively, an output end of the first switching switch 9 is connected to a negative output port of the fuse through a fuse rated resistance 10; a second switching switch 11, an input end of the second switching switch 11 is connected to the output end of the input module 1 and the output end of the first multiplier 4 respectively, an output end of the second switching switch 11 is connected to the negative output port through a variable resistor 12, and a resistance control end of the variable resistor 12 is connected to the arc resistance curve equation as a control signal; the output end of the NOT gate 8 is a fuse working state output port, the output end of the input module 1 is a simulation current output port, and the output end of the integrator 6 is a joule integral curve output port of the simulation current.

[0072] Specifically, in the embodiment, as shown in the figure, Figure 4 the input module 1 includes a positive input port Fuse1+ of the fuse for accessing the current signal of the external circuit as the current input source of the fuse simulation model, which is preferably connected to the current sensing module, and the output of the current sensing module is connected to the input of the absolute value module and the input of the first current judgment module 2 and the second current judgment module 3.

[0073] The first current judgment module 2 is a conditional operator, which is used to determine whether the current exceeds the rated current of the fuse. The output of the absolute value module is connected to the condition judgment port of the conditional operator, which is used to output 1 when the input current is greater than the set rated current value, and otherwise output 0.

[0074] The second current judgment module 3 is also a conditional operator, which is used to determine whether the current exceeds the rated current of the fuse. The output of the absolute value module is connected to the condition judgment port and the first output port of the conditional operator, which is used to output the absolute value of the input current, i.e. a high-level signal, when the input current is greater than the set rated current value, and otherwise output 0.

[0075] In the normal working stage of the fuse: the input current is not greater than the rated current, the outputs of the first current judgment module 2 and the second current judgment module 3 are both 0, so that the output of the first multiplier 4 is 0, i.e. the second switching switch 11 (i.e. the arcing branch switch) is in the open state, and the first switching switch 9 (i.e. the rated resistance branch) is in the closed state. At this time, the current mainly passes through the rated resistance branch, i.e. the current input from Fuse1+ passes through the branch where the first switching switch 9 is located, and then is output from Fuse1-.

[0076] The fuse rated resistance 10 here represents the resistance value of the fuse in the normal working state. In the simulation model, the resistance is connected in series in the circuit, and when the first switching switch 9 is closed, it will hinder the current, and the resistance value is set according to the specifications of the actual fuse, which is used to accurately simulate the resistance effect of the fuse on the circuit.

[0077] At this time, since the arcing and fusing conditions have not been reached, the arc resistance is in a normal state (which can be understood as an initial fixed resistance value, represented by the fuse rated resistance), and the fuse will not be fused and will continuously and stably conduct current.

[0078] In the overcurrent and heat accumulation stage of the fuse: when the input current exceeds the rated current, the outputs of the first current judgment module 2 and the second current judgment module 3 are both high-level signals. The integrator 6 (1 / s) starts to perform integral operation on the current to calculate the current square time (i 2 t) value. As the current continues to overcurrent, the integral value continuously increases. However, the first switching switch 9 (i.e., the rated resistance branch) is still in a closed state, and the second switching switch 11 (i.e., the arc starting branch switch) is still in an open state, and the current continues to pass through the rated resistance branch.

[0079] At this time, the arc resistance has no obvious change, but as the i 2 t value increases, the heat accumulation inside the fuse gradually increases, preparing for the subsequent possible fusing. At this time, the fuse is still in a conducting state, but it is already in the pre-warning stage of overcurrent.

[0080] Arc starting stage: when the output value (i 2 t value) of the integrator 6 exceeds the threshold value set by the arc starting time judgment module 7, it means that the heat accumulation of the current has reached a degree that may cause arc starting, the arc starting time judgment module 7 outputs a low-level signal, and after being inverted by the NOT gate, a high-level signal is output. The second switching switch 11 (i.e., the arc starting branch switch) is closed, the arc starting branch is turned on, and the current starts to partially or completely pass through the arc starting branch. The arc starting branch here simulates the current path when the arc is generated in the fuse simulation model. After the switch is closed, the current can pass through the branch, thereby changing the current distribution and electrical characteristics of the entire circuit to simulate the situation when the actual fuse arcs.

[0081] At this time, with the conduction of the arc starting branch, the arc resistance begins to play a role. The size of the arc resistance will change with the conditions such as current and voltage after the arc starting. Generally, the arc resistance will have a dynamic change process after the arc starting, which may be small at first and then change as the arc develops. At this time, the fuse has not been completely fused, but the electrical characteristics of the circuit have already changed because of the arc starting.

[0082] Fusing stage: as the current continues to overcurrent and heat accumulation, when the i 2 t value reaches the rated fusing i 2 t value of the fuse, the first switching switch 9 (i.e., the rated resistance branch) is opened, cutting off the rated resistance branch, and the current can no longer pass through the normal path.

[0083] At this time, the fuse completes the fusing action, and the circuit is cut off. The arc resistance may have a large change at the moment of fusing, for example, the arc resistance becomes infinite (in an ideal case) after the arc is extinguished, thereby realizing the protection function of the fuse on the circuit, preventing the current from continuing to flow, and protecting other devices in the circuit from damage caused by overcurrent.

[0084] The fuse simulation model has three model output ports, specifically including: a fuse working state output port, which is led out by the output end of the NOT gate 8, and corresponds to outputting the fuse working state, that is, outputting the current working state information of the fuse. For example, identification signals of different states such as normal working, arcing, and fusing can be output. This enables the external system to timely understand the running condition of the fuse, and take corresponding measures according to different states, such as cutting off the circuit or sending an alarm signal when the fuse is fused.

[0085] A simulation current output port is led out by the output end of the input module 1, and corresponds to outputting the current passed by the fuse, that is, the current value input into the fuse simulation model from Fuse1+. This output can enable the user to monitor the actual current size in the fuse in real time, understand the flow condition of the current in the fuse, and has important significance for analyzing the overcurrent protection of the circuit.

[0086] A Joule integral curve output port is led out by the output end of the integrator 6, and corresponds to outputting the i 2 t (current square time) value of the fuse. The value is calculated by integrating the current through the integrator, and reflects the heat accumulation condition of the fuse in the power-on process. It is one of the key parameters for judging whether the fuse will be fused, and the user can predict the working state and service life of the fuse by monitoring this value, for example, when the i 2 t value reaches the rated fusing i 2 t value of the fuse, the fuse will be fused

[0087] As a preferred embodiment, taking a certain fuse as an example, the data fitting result is as follows:

[0088]

[0089] Taking it as the control signal of the fuse simulation model, the simulation current i(t) of the fuse and its Joule integral curve i 2 t(t) are obtained, wherein the waveform of the simulation current i(t) is as shown in the smooth curve in Figure 5 , and the waveform of the corresponding measured short-circuit current is as shown in the sawtooth curve in Figure 5 . The waveform of the Joule integral curve i 2 t(t) and the waveform of the corresponding measured data are as shown in the two curves in Figure 6 . It can be seen that the simulation data and the measured data have small differences, that is, the fuse simulation model built by using the segmented modeling method of the application has high precision.

[0090] The specific data comparison is as shown in the following table:

[0091] Table 1 Comparison of simulation and measured results

[0092]

[0093] From the above table 1, the fuse simulation model built by the scheme has high precision, can simulate the actual working condition of the fuse well, and provides corresponding reference for the selective protection of the common DC bus system.

[0094] In conclusion, the fuse model established by the present application can simulate the transient process of the fuse together with the external circuit configuration of the fuse, and the fuse model has good adjustability. After actual test on the fuse blowing process, the model is adjusted by using the measured short-circuit current, voltage waveform and other data, so as to obtain an accurate fuse model, better simulate the details of the fuse blowing process, and achieve high simulation precision. The present application has guiding significance for the protection design and protection selectivity verification of the common DC bus system. Compared with the previous fuse modeling and simulation method, the present application is closely combined with the protection characteristics of the common DC bus distribution system, does not need to use a complex arc resistance model, and has better engineering implementation.

[0095] The above description is only the preferred embodiment of the present application, and does not limit the implementation and protection scope of the present application. For those skilled in the art, it should be realized that any equivalent replacement and obvious changes made according to the content of the present application should be included in the protection scope of the present application.

Claims

1. A method for piecewise modeling of a fuse for a DC meshed system based on arc resistance characteristics, characterized by, The application relates to a method for building a controlled-resistance fuse simulation model. The method comprises the following steps: S1, short-circuit testing of a fuse and continuous acquisition of short-circuit voltage and short-circuit current on both sides of the fuse during the short-circuit testing; S2, real-time arc resistance data of the fuse are calculated according to the short-circuit voltage and the short-circuit current, and an arc resistance curve is constructed according to the real-time arc resistance data; S3, an arc resistance curve in an arc initiation stage is obtained by intercepting the arc resistance curve between a peak time of the short-circuit current and a slope drop time of the arc resistance curve, and an arc resistance curve in an arc burning stage is obtained by intercepting the arc resistance curve between the slope drop time and a time when the short-circuit current is zero; S4, data fitting is respectively performed according to the arc resistance curve in the arc initiation stage and the arc resistance curve in the arc burning stage, and a segmented arc resistance curve equation is obtained; and S5, a controlled-resistance fuse simulation model is built by taking the arc resistance curve equation as a control signal. In the step S1, the short-circuit testing of the fuse is performed through a short-circuit testing platform of the fuse which is built in advance, and the short-circuit testing platform comprises a direct-current voltage stabilizer, one end of a contactor and one end of a support capacitor connected to two ends of the direct-current voltage stabilizer, the other end of the contactor connected to the other end of the support capacitor, a fuse branch connected to two ends of the support capacitor, the fuse branch comprising a first circuit breaker and the fuse connected in series, and an impedance device, one end of the impedance device connected to the other end of the support capacitor and the other end of the impedance device connected to one end of the fuse branch.

2. The method of claim 1, wherein, The process of the short-circuit testing of the fuse comprises the following steps: S11, the first circuit breaker is opened, and then the contactor is closed, so that the direct-current voltage stabilizer charges the support capacitor; S12, after the charging of the support capacitor is completed, the contactor is closed, and then the first circuit breaker is closed, so that the short-circuit testing of the fuse is performed, and an oscilloscope is used to record the short-circuit voltage and the short-circuit current on both sides of the fuse.

3. The method of claim 2, wherein, The short-circuit testing platform further comprises a discharge branch connected in parallel with the fuse branch, the discharge branch further comprising a second circuit breaker and a discharge resistor connected in series; and after the short-circuit testing of the fuse, the second circuit breaker is closed, so that the remaining voltage in the support capacitor is discharged through the discharge resistor.

4. The method of claim 2, wherein, The expression of the arc resistance curve equation is as follows:

5. The method of claim 1, wherein, In the step S4, the LM least square method is used to perform data fitting on the arc resistance curve in the arc initiation stage and the arc resistance curve in the arc burning stage, so that corresponding constants are obtained. ； wherein, represents the arc resistance value of the fuse at time t; represents the arc resistance curve of the arcing phase; represents the arc resistance curve of the burning phase; and are constants obtained by data fitting of the arc resistance curve of the arcing phase; and are constants obtained by data fitting of the arc resistance curve of the burning phase.

6. The method of claim 5, wherein, After the step S5 is performed, the following steps are further included: simulation current of the fuse obtained by simulation of the fuse simulation model and joule integral curve of the simulation current are obtained, and whether a difference value between the simulation current and the joule integral curve and corresponding measured data is greater than a difference threshold value is judged; if not, the fuse simulation model is taken as a segmented modeling result of the fuse; and if yes, an initial guess value of the LM least square method is adjusted, and then the step S4 is returned.

7. The method of claim 6, wherein, The initial guess value is obtained by preliminary estimation through a linear regression method.

8. The method of claim 7, wherein, ​ 9. The method of claim 1, wherein, The fuse simulation model comprises: an input module, input ends of first current judgment modules and second current judgment modules are connected respectively, an output end of the first current judgment module is connected with an input end of a first multiplier, an output end of the second current judgment module is connected with a second multiplier, an integrator and an arc starting time judgment module in sequence, an output end of the arc starting time judgment module is connected with an input end of the first multiplier through a NOT gate; a first switching switch, input ends of the input module and the arc starting time judgment module are connected with an output end of the first switching switch, an output end of the first switching switch is connected with a negative output port of a fuse through a fuse rated resistance; a second switching switch, input ends of the input module and the first multiplier are connected with an output end of the second switching switch, an output end of the second switching switch is connected with the negative output port through a variable resistor, a resistance control end of the variable resistor is connected with an arc resistance curve equation as a control signal; an output end of the NOT gate is a fuse working state output port, an output end of the input module is a simulation current output port, an output end of the integrator is a joule integral curve output port of the simulation current.

10. The method of claim 1, wherein, The calculation formula of the real-time arc resistance data is as follows: ； wherein z(t) represents the real-time arc resistance data at time t, Vsc(t) represents the short-circuit voltage at time t, Isc(t) represents the short-circuit current at time t.

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