CN109713649B - Self-synchronizing resistor differential protection method for direct current boosting convergence access system - Google Patents
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Abstract
The application provides a self-synchronizing resistor differential protection method of a direct current boosting convergence access system, which comprises the following steps: continuously obtaining NDVoltage sampling value of each sampling point, if NDEach sampling point satisfies | u [ n]‑u[n‑N]If the I is more than epsilon, the direct current boosting convergence access system fluctuates; determining the NthDTime scale t of sampling pointsDAs a time setting starting point; defining a differential resistor, and judging the specific fault type according to the specific numerical value of the differential resistor; and sending a starting differential protection command for the faults in the zone with the transition resistance and the metallic zone. Determination of Nth in the present applicationDTime scale t of sampling pointsDFor the time synchronization starting point, the characteristic that the length of a cable of a direct current boosting convergence access system is short is utilized, the time synchronization starting point is determined by utilizing a voltage or current break variable, the instant synchronization of data at different ends is realized, a differential resistor is defined, a mechanism of resistor differential protection is established, the identification of faults in a region is realized, and the method has good protection sensitivity and selectivity.
Description
Technical Field
The application relates to the technical field of power grid protection, in particular to a self-synchronizing resistor differential protection method for a direct current boosting convergence access system.
Background
Along with the continuous development of national power distribution networks and the continuous improvement of the automation degree of the power distribution networks, the requirement on the reliability of power supply is higher and higher, various intelligent monitoring and protecting devices for the automation of the power distribution networks are important guarantees for improving the reliability of power supply, particularly the functions of fault isolation and power supply self-recovery in the power distribution networks, and the rapid detection and isolation of the faults of the power distribution networks by differential protection have the advantages which are incomparable with other intelligent devices. Differential protection generally refers to pilot protection of a power transmission line, in which protection devices at two ends of the power transmission line are longitudinally connected by a communication channel, electrical quantities at each end are transmitted to an opposite end, and the electrical quantities at the two ends are compared to judge whether a fault is within or outside the range of the line, so as to determine whether to cut off the protected line.
The differential protection digitizes the waveform of the electric gas quantity at each end, transmits the waveform by means of communication, and then judges the action by the protection of a microcomputer. The differential protection algorithm requires that the electric quantity input and compared must be a synchronous sampling value or corresponding electric quantity obtained through synchronization processing; therefore, the data synchronization technology is the key to realize differential protection. The traditional high-voltage power grid generally adopts hard real-time communication of a hard switching technology to realize pilot protection, and because the communication delay of hard switching is fixed, differential protection can utilize a synchronization technology based on a data channel to complete current sampling data synchronization of each end, wherein the Ping-Pong algorithm is most widely applied. The GPS time synchronization and the NTP time synchronization are common synchronization methods for high-voltage transmission lines, but due to the fact that auxiliary equipment is added, the technical economy is reduced, and meanwhile the risk of incorrect protection actions caused by faults of the auxiliary equipment is brought. In addition, a method for realizing synchronization by using a reference vector is proposed, but the accuracy of the synchronization method is influenced by a line model and a direct current attenuation factor, so that the practical application is difficult.
For the photovoltaic power station, the direct current boosting collection access system has more branches and complex system topology, the data synchronization method utilizing the traditional high-voltage power grid has no good economic and technical performance, and the data synchronization and differential protection difficulty of the direct current boosting collection access system is relatively high on the premise of not increasing any auxiliary equipment.
Disclosure of Invention
The application provides a self-synchronizing resistor differential protection method for a direct current boosting convergence access system, which aims to realize data synchronization and differential protection of the direct current boosting convergence access system on the premise of not adding any auxiliary equipment and improve the technical economy.
In order to solve the technical problem, the embodiment of the application discloses the following technical scheme:
the application provides a self-synchronizing resistor differential protection method of a direct current boosting convergence access system, which comprises the following steps:
continuously obtaining NDVoltage sample values of a sampling point, said voltage sample values including a present voltage sample value u [ n ]]A cycle front voltage sample valueu[n-N]；
If said N isDEach sampling point satisfies | u [ n]-u[n-N]If the voltage is greater than epsilon, the direct current boosting convergence access system fluctuates, and the epsilon is a threshold value;
determining the NthDTime scale t of sampling pointsDAs a time setting starting point;
obtain measuring resistance R at feeder both endsRAAnd RRBAnd a feeder line resistance Rl；
According to the measured resistance R at two ends of the feeder lineRAAnd RRBAnd a feeder line resistance RlCalculating differential resistance RdiffThe differential resistance satisfies Rdiff＝RRA+RRB-Rl；
Obtaining the differential resistance RdiffThe specific numerical values of (a);
if the differential resistance RdiffSatisfy Rdiff≥rset..mWhen the direct current boosting convergence access system is in failure, the direct current boosting convergence access system generates an in-zone fault with a transition resistor; if the differential resistance RdiffSatisfy | Rdiff+Rl|≥Kres|RRA-RRBIf yes, the direct current boosting convergence access system generates a metal region internal fault; if the differential resistance RdiffSatisfy | Rdiff+Rl|＜Kres|RRA-RRBIf yes, the direct current boosting convergence access system generates an out-of-area fault; wherein, KresIs the braking coefficient;
and when the direct current boosting collection access system has the internal fault with the transition resistor and the metallic internal fault, sending a differential protection starting command.
Preferably, the method further comprises:
the voltage sampling values further comprise two cycle front voltage sampling values u [ N-2N ];
if said N isDEach sampling point satisfies | | u [ n |)]-u[n-N]|-|u[n-N]-u[n-2N]If | | is greater than epsilon, the direct current boosting convergence access system fluctuates, and epsilon is a threshold value.
Preferably, the method further comprises:
continuously obtaining NDCurrent sample values of a sampling point, including a present current sample value i [ n ]]A cycle front current sample value i [ N-N ]]And two periodic wavefront current sampling values i [ N-2N ]]；
If said N isDEach sampling point satisfies | i [ n ]]-i[n-N]If is greater than epsilon or if i n]-i[n-N]|-|i[n-N]-i[n-2N]If | | is greater than epsilon, the direct current boosting convergence access system fluctuates, and epsilon is a threshold value;
determining the NthDTime scale t of sampling pointsDIs the starting point of time setting.
Preferably, the measuring resistors R at two ends of the feeder line are obtainedRAAnd RRBThe method comprises the following steps:
when the fault occurs between the phases of the feeder lines,
when the single-phase earth fault of the feeder line occurs,
wherein, IfAAnd IfBRepresenting fault currents flowing through the protections RA and RB, respectively;
RAand RlRespectively a resistor for protecting the distance between RA and a fault point and a line resistor;
Rfand RgRespectively representing phase-to-phase fault and single-phase earth fault transition resistances.
Preferably, said differential resistance RdiffSatisfy Rdiff≥rset..mIf the direct current boost collecting and connecting system has an internal fault with a transition resistor, the fault comprises t and tset.m，tset.mRepresenting the action time.
Compared with the prior art, the beneficial effect of this application is:
(1) according to the method and the device, on the premise of not adding any auxiliary equipment, data synchronization and differential protection of the direct current boosting convergence access system are achieved, and good economic applicability is achieved.
(2) Determination of Nth in the present applicationDTime scale t of sampling pointsDIn order to set time, the characteristic that the cable length of the direct current boosting convergence access system is short is fully utilized, the time setting point is determined by utilizing the voltage or current break variable, the time setting in the prior art is not needed to be set by a mode of sending and receiving the signals, the instant synchronization of data at different ends can be realized, the application condition of differential protection in the direct current convergence access system is simplified, and the differential protection efficiency and performance are improved.
(3) The method defines the concept of differential resistance, and uses the differential resistance to roughly estimate the extra energy loss brought by the fault transition resistance; meanwhile, the internal fault and the external fault are analyzed according to the size of the differential resistor, a resistor differential protection mechanism is established, the identification of the internal fault is realized, and the protection sensitivity and the protection selectivity are good.
(4) Differential protection in the prior art is mostly completed by using current, a direct current boosting collection access system in the application comprises a plurality of current converters, the current amount is continuously changed after a fault due to the corresponding fault characteristics of the current converters, a measuring resistor is related to a fault position and a transition resistor, and the change range is correspondingly small, so that the mode of forming the differential protection by using the resistor is slightly influenced by the current converters, and the precision and the sensitivity are higher than those of the differential protection in the prior art.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the application.
Drawings
In order to more clearly explain the technical solution of the present application, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious to those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic view of a topology structure of a photovoltaic power station dc boost collective access system in the present application;
FIG. 2 is a schematic diagram illustrating a method for synchronizing resistor differential protection data according to the present disclosure;
fig. 3 is a schematic flowchart of a differential protection method for self-synchronous resistors of a dc boost collective access system according to the present application;
FIG. 4 is a schematic diagram of the detection waveforms of the current faults at the power electronic type power supply side and the large power grid side according to the embodiment of the invention;
fig. 5 is a schematic diagram of a fault analysis of a dc boost collection access system of a photovoltaic power station according to an embodiment of the present invention;
FIG. 6 is a graph showing the relationship between the change in the differential resistance and the change in the transition resistance.
Detailed Description
In order to make those skilled in the art better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
Different from a high-voltage power transmission network, the direct-current boosting convergence access system is practical to realize differential protection by adopting a soft real-time communication technology in consideration of cost, scheme implementation difficulty, topology flexibility and the like; when the data channel-based synchronization technology adopts hard real-time communication, the delay sizes of the receiving channel and the transmitting channel can be considered to be consistent; for the soft real-time communication technology, the basic assumption is not established, so that the data synchronization is a great challenge for the differential protection of the dc boost collective access system without adding any auxiliary equipment.
Fig. 1 is a schematic view of a topology structure of a photovoltaic power station dc boost collective access system in the present application; fig. 1 shows that the dc boost collection access system of the photovoltaic power station mainly comprises two parts: the photovoltaic array and the DC/DC converter form a power generation unit; a collection and transmission unit consisting of low-voltage and high-voltage collection lines, a boost converter and an inverter converter. Large photovoltaic power stations often employ maximum power control; the DC/DC converter can improve the quality of the direct-current voltage output by the photovoltaic array and stabilize the direct-current voltage; the direct-current voltage output by the power generation unit is boosted through the direct-current boosting converter, the voltage level is boosted to 30kV or 35kV for collecting and transmission, and the direct-current voltage is inverted into alternating current at the large power grid side through the converter and is merged into the large power grid.
Fig. 2 is a schematic diagram illustrating a principle of a resistor differential protection data synchronization method provided by the present application, and from the perspective of the superposition principle, when a fault occurs in the photovoltaic dc boost collection access system, it is equivalent to superimpose a dc voltage source having the same size and the opposite direction as before the fault at the fault point; the presence of this additional voltage source causes variations in the voltage and current at the protective installation. At the moment of failure, the influence generated by the additional voltage source is propagated to each end of the cable in a traveling wave mode; when a fault F occurs, the fault travelling wave will quickly follow the line to the two-sided protection installation, as shown in figure 1. Unlike a traditional high-voltage direct-current transmission network, the connecting line cable of the direct-current boosting convergence access system is short, and the traveling wave propagates at the speed close to the speed of light, so that the current and the voltage of the protection installation positions on two sides can be changed at the same time no matter where the fault occurs in the direct-current convergence and access cable. Based on the method, the time scales of all the ends can be synchronized in the photovoltaic direct current boosting and collecting access system by a method for detecting the fault time.
Fig. 3 is a schematic flow chart of a differential protection method for self-synchronous resistors of a dc boost convergence access system provided by the present application; as can be seen from fig. 3, the method includes:
s01: continuously obtaining NDVoltage sample values of a sampling point, said voltage sample values including a present voltage sample value u [ n ]]A cycle front voltage sample value u [ N-N ]]。
A Fault detector and a protected start element (Starting element) can be used to quickly detect disturbances in a dc link system, which have a much higher sensitivity of operation than the protection criterion. In the digital microcomputer protection, all the calculation and processing are completed by taking a sampling point as a unit; to improve the reliability of the detection, the failure detection component or the start-up component usually needs to verify a plurality of sampling points to determine whether there is actually a disturbance in the system. When the disturbance is confirmed by the fault detection element or the startup element, it can be considered that the last verified sampling point at each end of the cable is acquired at the same time, i.e. with the same time scale. Certain errors exist in the process, but as long as the detection algorithm is reasonable, the errors do not exceed one sampling time interval.
S02: if said N isDEach sampling point satisfies | u [ n]-u[n-N]If | > epsilon, the direct current boosting convergence access system fluctuates, and epsilon is a threshold value.
S03: determining the NthDTime scale t of sampling pointsDIs the starting point of time setting.
The resistor differential protection data synchronization algorithm can be implemented by using the variation of the voltage sampling value or the current sampling value. The length of a cable of the direct current boosting convergence access system is very short, when a fault occurs, although the short-circuit capacity difference of a power supply connected with each end of the cable is large, the measured voltage of each end of the cable is basically the same as the voltage of a fault point, namely, the voltage of each end is still greatly reduced; therefore, the variation of the voltage sampling value can be preferentially used to form the fault detection, as shown in the following formula:
|u[n]-u[n-N]|＞ε
in the formula, u [ n ] is the current voltage sampling value; u [ N-N ] is a periodic wave front voltage sampling value; n is the sampling point number of each cycle; ε is the threshold value.
Because the voltage variation of each end of the cable is basically the same during fault, the epsilon of each end can take the same value, and the error brought to the fault moment detection by the threshold value setting difference is avoided. When a fault with transition resistance occurs, the measured voltage at each end of the cable is still basically the same as the voltage of a fault point, and the performance of the formula | u [ N ] -u [ N-N ] | > epsilon is not influenced.
S04: obtain measuring resistance R at feeder both endsRAAnd RRBAnd a feeder line resistance Rl。
S05: according to the measured resistance R at two ends of the feeder lineRAAnd RRBAnd a feeder line resistance RlCalculating differential resistance RdiffThe differential resistance satisfies Rdiff＝RRA+RRB-Rl。
The fault transition resistance brings extra energy loss, and the differential protection principle formed by the resistors can be used for roughly estimating the energy loss. Analogous to current differential protection, the differential resistance can be defined by adding the measured resistances at the two ends of the feed line and subtracting the resistance of the feed line.
S06: obtaining the differential resistance RdiffThe specific numerical value of (1).
S07: if the differential resistance RdiffSatisfy Rdiff≥rset..mWhen the direct current boosting convergence access system is in failure, the direct current boosting convergence access system generates an in-zone fault with a transition resistor; if the differential resistance RdiffSatisfy | Rdiff+Rl|≥Kres|RRA-RRBIf yes, the direct current boosting convergence access system generates a metal region internal fault; if the differential resistance RdiffSatisfy | Rdiff+Rl|＜Kres|RRA-RRBIf yes, the direct current boosting convergence access system generates an out-of-area fault; wherein, KresIs the braking coefficient.
The direct current boost collecting access system faults comprise an intra-zone fault and an extra-zone fault, wherein the intra-zone fault comprises an intra-zone fault with a transition resistor and an intra-metallic zone fault, and the differential resistance value of the intra-metallic zone fault and the extra-zone fault is zero, so that the intra-metallic zone fault and the extra-zone fault need to be distinguished specially if the differential resistance R is specifically set to be zerodiffSatisfy | Rdiff+Rl|≥Kres|RRA-RRBIf yes, the direct current boosting convergence access system generates a metal region internal fault; if the differential resistance RdiffSatisfy | Rdiff+Rl|＜Kres|RRA-RRBIf yes, the direct current boosting convergence access system generates an out-of-area fault; wherein, KresIs the braking coefficient.
S08: and when the direct current boosting collection access system has the internal fault with the transition resistor and the metallic internal fault, sending a differential protection starting command.
Preferably, the method further comprises:
the voltage sampling values further comprise two cycle front voltage sampling values u [ N-2N ];
if said N isDEach sampling point satisfies | | u [ n |)]-u[n-N]|-|u[n-N]-u[n-2N]If | | is greater than epsilon, the direct current boosting convergence access system fluctuates, and epsilon is a threshold value.
Similar to the protection starting criterion, in order to improve the detection reliability, the fluctuation can be detected by utilizing the absolute u [ N ] -u [ N-N ] - | u [ N-N ] -u [ N-2N ] | > epsilon, wherein u [ N-2N ] is a voltage sampling value before two cycles.
Preferably, the method further comprises:
continuously obtaining NDCurrent sample values of a sampling point, including a present current sample value i [ n ]]A cycle front current sample value i [ N-N ]]And two periodic wavefront current sampling values i [ N-2N ]]；
If said N isDEach sampling point satisfies | i [ n ]]-i[n-N]If is greater than epsilon or if i n]-i[n-N]|-|i[n-N]-i[n-2N]If | | is greater than epsilon, the direct current boosting convergence access system fluctuates, and epsilon is a threshold value;
determining the NthDTime scale t of sampling pointsDIs the starting point of time setting.
Voltage magnitude and electric current volume all can be used to detect the trouble moment, and the mutual-inductor is comparatively complete in photovoltaic electricity generation direct current steps up and collects access system in mutual-inductor configuration usually, and usable electric current volume detects the direct current system disturbance, therefore this application utilizes voltage magnitude except, still can utilize the current sampling value to detect undulant, as shown in the following formula:
i [ N ] -i [ N-N ] > epsilon or i [ N-N ] - | i [ N-N ] -i [ N-2N ] | > epsilon
In the formula, i [ N ], i [ N-N ] and i [ N-2N ] are respectively a current sampling value, a cycle front current sampling value and a cycle front current sampling value.
Because the power supply short-circuit capacities at different ends of the cable are different, the current changes after the fault are different, and therefore the influence of the factor needs to be considered during setting of epsilon. Direct current boost collection access systemIn the power electronic type power supply, the short-circuit current is limited by the control system, but the system response speed is high, and the fault current is increased rapidly. Fig. 4 is a schematic diagram of the current fault detection waveforms of the power electronic type power source side and the large power grid side according to the embodiment of the present invention, wherein the waveforms on both sides are respectively normalized by the respective power source short-circuit capacities. As can be seen from the figure, the current rise trends in the fault detection elements on both sides are consistent; in order to enable the fault detection elements or the starting elements on the two sides to find faults at the same time, epsilon can be set uniformly according to a weak feed value. In the actual sampling process, because the time synchronization adjustment is not carried out on the two sides, a certain error exists when the fault detection element is used for detecting the fault moment. The case of the maximum error is shown in fig. 2, i.e. sampling is completed on one side immediately before the occurrence of the fault, sampling is completed on the other side immediately after the occurrence of the fault, and the time difference Δ t between the two sides when the fault is found issampI.e. one sampling interval time.
Preferably, the measuring resistors R at two ends of the feeder line are obtainedRAAnd RRBThe method comprises the following steps:
when the fault occurs between the phases of the feeder lines,
when the single-phase earth fault of the feeder line occurs,
wherein, IfAAnd IfBRepresenting fault currents flowing through the protections RA and RB, respectively;
RAand RlRespectively a resistor for protecting the distance between RA and a fault point and a line resistor;
Rfand RgRespectively representing phase-to-phase fault and single-phase earth fault transition resistances.
Specifically referring to fig. 5, fig. 5 is a schematic diagram illustrating a fault analysis of a dc boost collection access system of a photovoltaic power station according to an embodiment of the present invention; in this case, for the protection RA and RB, when f is an intra-zone fault, the differential resistance expression can be obtained as shown in the following equation:
when an out-of-range fault occurs or normal operation occurs, a differential resistance expression such as RdiffIs shown as 0.
From the above equation, it can be seen that the in-zone fault R is in addition to the metallic faultdiffWill not equal 0. FIG. 6 is a graph showing the relationship between the change in differential resistance and the change in transition resistance; rf.cThe critical transition resistance value is shown, which divides the curve into two parts, the left half showing that the differential resistance increases with increasing transition resistance, and the right half showing that the differential resistance decreases with increasing transition resistance. Rdiff.maxRepresents the transition resistance Rf.cCorresponding maximum differential resistance value, Rf.cAnd Rdiff.maxBoth side power supply short circuit capacity. Therefore, it is possible to construct the dc cable protection principle using differential resistors.
Preferably, said differential resistance RdiffSatisfy Rdiff≥rset..mIf the direct current boost collecting and connecting system has an internal fault with a transition resistor, the fault comprises t and tset.m，tset.mRepresenting the action time. When the value of the fault differential resistance is relatively large, detection and operation are easy. Therefore, the differential resistance value is compared with the setting value to be used as the criterion of the medium resistance fault protection, which is shown as the following formula.
In the formula, rset.mIndicating the setting value, tset.mThe operation time is set to 0.
Since the above embodiments are all described by referring to and combining with other embodiments, the same portions are provided between different embodiments, and the same and similar portions between the various embodiments in this specification may be referred to each other. And will not be described in detail herein.
Other embodiments of the present application will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the application and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the application being indicated by the following claims.
The above-described embodiments of the present application do not limit the scope of the present application.
Claims (5)
1. A self-synchronizing resistor differential protection method of a direct current boosting convergence access system is characterized by comprising the following steps:
continuously obtaining NDVoltage sample values of a sampling point, said voltage sample values including a present voltage sample value u [ n ]]A cycle front voltage sample value u [ N-N ]]；
If said N isDEach sampling point satisfies | u [ n]-u[n-N]If the voltage is greater than epsilon, the direct current boosting convergence access system fluctuates, and the epsilon is a threshold value;
determining the NthDTime scale t of sampling pointsDAs a time setting starting point;
obtain measuring resistance R at feeder both endsRAAnd RRBAnd a feeder line resistance Rl；
According to the measured resistance R at two ends of the feeder lineRAAnd RRBAnd a feeder line resistance RlCalculating differential resistance RdiffThe differential resistance satisfies Rdiff＝RRA+RRB-Rl；
Obtaining the differential resistance RdiffThe specific numerical values of (a);
if the differential resistance RdiffSatisfy Rdiff≥rset.mWhen the direct current boosting convergence access system is in failure, the direct current boosting convergence access system generates an in-zone fault with a transition resistor; if the differential resistance RdiffSatisfy | Rdiff+Rl|≥Kres|RRA-RRBIf yes, the direct current boosting is collected to be connected to a system generation goldenA failure in the attribute zone; if the differential resistance RdiffSatisfy | Rdiff+Rl|＜Kres|RRA-RRBIf yes, the direct current boosting convergence access system generates an out-of-area fault; wherein r isset.mIndicating differential resistance setting value, KresIs the braking coefficient;
and when the direct current boosting collection access system has the internal fault with the transition resistor and the metallic internal fault, sending a differential protection starting command.
2. The method of claim 1, further comprising:
the voltage sampling values further comprise two cycle front voltage sampling values u [ N-2N ];
if said N isDEach sampling point satisfies | | u [ n |)]-u[n-N]|-|u[n-N]-u[n-2N]If | | is greater than epsilon, the direct current boosting convergence access system fluctuates, and epsilon is a threshold value.
3. The method of claim 1, further comprising:
continuously obtaining NDCurrent sample values of a sampling point, including a present current sample value i [ n ]]A cycle front current sample value i [ N-N ]]And two periodic wavefront current sampling values i [ N-2N ]]；
If said N isDEach sampling point satisfies | i [ n ]]-i[n-N]If is greater than epsilon or if i n]-i[n-N]|-|i[n-N]-i[n-2N]If | | is greater than epsilon, the direct current boosting convergence access system fluctuates, and epsilon is a threshold value;
determining the NthDTime scale t of sampling pointsDIs the starting point of time setting.
4. The method of claim 1, wherein the obtaining a measured resistance R across the feed lineRAAnd RRBThe method comprises the following steps:
when the fault occurs between the phases of the feeder lines,
when the single-phase earth fault of the feeder line occurs,
wherein, IfAAnd IfBRepresenting fault currents flowing through the protections RA and RB, respectively;
RAand RlRespectively a resistor for protecting the distance between RA and a fault point and a line resistor;
Rfand RgRespectively representing phase-to-phase fault and single-phase earth fault transition resistances.
5. The method of claim 1, wherein said differential resistance R is greater than said threshold resistancediffSatisfy Rdiff≥rset.mIf the direct current boost collecting and connecting system has an internal fault with a transition resistor, the fault comprises t and tset.mT denotes the current time, tset.mRepresenting the action time.
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