CN115015690A

CN115015690A - Multi-end flexible direct-current power distribution network pilot comparison protection method and system

Info

Publication number: CN115015690A
Application number: CN202210562698.0A
Authority: CN
Inventors: 丛伟; 王泽乾; 撖奥洋; 邱吉福; 魏振; 杨天佑; 安树怀; 陈明; 时翔; 史蕾玚; 孙振海; 胡选正; 胡谅平
Original assignee: QINGDAO POWER SUPPLY Co OF STATE GRID SHANDONG ELECTRIC POWER Co; State Grid Corp of China SGCC; Shandong University
Current assignee: QINGDAO POWER SUPPLY Co OF STATE GRID SHANDONG ELECTRIC POWER Co; State Grid Corp of China SGCC; Shandong University
Priority date: 2022-05-23
Filing date: 2022-05-23
Publication date: 2022-09-06

Abstract

The invention belongs to the technical field of flexible direct current power distribution networks, and provides a multi-end flexible direct current power distribution network pilot comparison protection method and system suitable for each stage. The pilot comparison protection method of the multi-end flexible direct-current power distribution network comprises two parts, namely protection starting and fault judgment; protection starting: du/dt and di/dt are used as starting criteria; and (3) fault judgment: taking any end point at two ends of the protected line as a measuring point, and acquiring corresponding measuring voltage and measuring current; calculating a voltage integral value at a reference point as a reference voltage integral value according to a known line parameter model; wherein, the reference point is positioned outside the protected line; judging whether a fault point is positioned between the measuring point and the reference point according to the positive and negative of the reference voltage integral value; adopting pilot comparison logic to judge whether a fault point is positioned in the protected line, if so, executing protection and tripping off direct current circuit breakers at two ends of the line; otherwise, the protection is reset.

Description

Multi-end flexible direct-current power distribution network pilot comparison protection method and system

Technical Field

The invention belongs to the technical field of flexible direct current power distribution networks, and particularly relates to a multi-end flexible direct current power distribution network pilot comparison protection method and system.

Background

The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.

With the rapid development of power electronics technology, renewable energy is massively accessed into a power distribution system in a distributed manner. Compared with an alternating current distribution system, the flexible direct current distribution system can more efficiently accept distributed power sources, and has the advantages of high electric energy quality, large power supply capacity, high operation efficiency, no need of reactive compensation, strong compatibility, convenience for asynchronous system interconnection and the like.

However, the flexible dc power distribution network still faces many challenges and problems in engineering application, and the protection of the flexible dc power distribution network mainly has two difficulties, namely, speed and adaptability. The flexible direct-current power distribution network has small inertia constant, quick fault response and large fault current, so that power electronic elements in the converter can be greatly damaged, and the rapidity of a protection method is challenged; the intervention of the control system ensures that each fault stage is switched rapidly, and the fault characteristics of each stage are different, thereby providing a challenge to the applicability of the protection method. The flexible direct-current power distribution network protection needs to quickly and reliably identify the fault position according to transient fault information, and meanwhile, the applicability to each stage after the fault is guaranteed. Therefore, there is a need to provide a new protection principle to meet the requirements of speed and applicability, so as to further improve the safety of the flexible dc power distribution network.

The inventor finds in research that the protection principle of the flexible direct current power distribution network has the following problems:

the protection principle based on the single-end quantity has no communication and data synchronization problems, and can easily meet the requirement of the speed, but the method has no excellent selectivity, can not protect the whole length of a line, needs to be matched with other protection for working, and also has the problems of poor anti-interference capability, dead protection zone and the like; the protection principle based on the double-end quantity can fully utilize the electric quantity information at two ends of a line, has high reliability and good selectivity, but the method needs to solve the problems of data communication quantity and data synchronization, and the quick-action property of the method can not meet the requirement sometimes; in addition, most of the existing single-end quantity protection principle and double-end quantity protection principle are only applicable to the first stage after the fault, and the applicability of the protection principle to each stage after the fault is insufficient.

Disclosure of Invention

In order to solve the problems, the invention provides a multi-terminal flexible direct-current power distribution network pilot comparison protection method and a multi-terminal flexible direct-current power distribution network pilot comparison protection system.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention provides a pilot comparison protection method for a multi-terminal flexible direct-current power distribution network.

In one or more embodiments, a multi-terminal flexible dc distribution network pilot comparison protection method includes:

measuring voltage and current signals at two ends of the line in real time, and calculating corresponding starting criteria du/dt and di/dt;

taking any end point at two ends of the protected line as a measuring point, acquiring corresponding measuring voltage and measuring current, and calculating corresponding starting criteria du/dt and di/dt; judging whether the action condition is met, if so, calculating a voltage integral value at a reference point according to a known line parameter model to be used as a reference voltage integral value; wherein, the reference point is positioned outside the protected line;

judging whether a fault point is positioned in a protected line or not by combining pilot comparison logic according to the positive and negative of the reference voltage integral value, if so, executing protection and tripping off direct current circuit breakers at two ends of the line; otherwise, the protection is reset.

The invention provides a pilot comparison protection system for a multi-terminal flexible direct-current power distribution network.

In one or more embodiments, a multi-terminal flexible dc distribution network pilot comparison protection system includes:

a current-voltage acquisition module configured to: taking any end point at two ends of the protected line as a measuring point, and acquiring corresponding measuring voltage and measuring current;

a reference voltage integral value calculation module configured to: judging whether the action condition is met or not according to the measured voltage and the measured current, if so, calculating a voltage integral value at a reference point according to a known line parameter model to be used as a reference voltage integral value; wherein, the reference point is positioned outside the protected line;

a logic comparison module configured to: judging whether a fault point is positioned in a protected line or not by combining pilot comparison logic according to the positive and negative of the reference voltage integral value, if so, executing protection and tripping off direct current circuit breakers at two ends of the line; otherwise, the protection is reset.

A pilot comparison protection system of a multi-terminal flexible direct-current power distribution network comprises two relay protection devices which are communicated with each other, wherein the relay protection devices are respectively arranged at two ends of a protected circuit; the relay protection device is configured to:

taking any end point at two ends of the protected line as a measuring point, and acquiring corresponding measuring voltage and measuring current;

judging whether the action condition is met or not according to the measured voltage and the measured current, if so, calculating a voltage integral value at a reference point according to a known line parameter model to be used as a reference voltage integral value; wherein, the reference point is positioned outside the protected line;

A fourth aspect of the invention provides a computer-readable storage medium.

In one or more embodiments, a computer-readable storage medium stores thereon a computer program, which when executed by a processor implements the steps in the pilot comparison protection method for a multi-terminal flexible dc distribution network as described above.

A fifth aspect of the invention provides a computer apparatus.

In one or more embodiments, a computer device includes a memory, a processor, and a computer program stored on the memory and executable on the processor, and when the processor executes the program, the steps in the multi-terminal flexible dc power distribution network pilot comparison protection method as described above are implemented.

Compared with the prior art, the invention has the beneficial effects that:

the fault detection method based on the longitudinal comparison logic judges the internal fault and the external fault based on the positive and negative of the reference voltage integral values at two ends of the protected line, then obtains the fault detection result at the opposite side, and judges the internal fault and the external fault by utilizing the longitudinal comparison logic, thereby achieving the purpose of quickly and reliably judging the fault, having good applicability to different stages after the fault, having the characteristics of clear logic, good rapidity, high reliability, strong applicability and the like, and being particularly suitable for a multi-end flexible direct-current power distribution network to realize the line protection function.

The invention adopts the pilot comparison protection principle to logically compare the fault judgment results at two ends of the protected line to determine the fault position. Compared with current differential protection, the relay protection devices on two sides in pilot comparison protection independently judge faults, only fault judgment logic results on two sides need to be transmitted, the requirement on a communication system is not high, and the method can be used in a traditional alternating-current power distribution network and is more suitable for a multi-end flexible direct-current power distribution network.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are included to illustrate an exemplary embodiment of the invention and not to limit the invention.

Fig. 1 is a flowchart of a pilot comparison protection method for a multi-terminal flexible direct-current power distribution network according to an embodiment of the present invention;

fig. 2 is a schematic diagram of a model of a multi-terminal flexible dc distribution network according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of a network model of protected objects and port electrical quantities according to an embodiment of the present invention;

FIG. 4(a) is a schematic diagram of a forward out-of-band fault calculation equivalent circuit according to an embodiment of the present invention;

FIG. 4(b) is a schematic diagram of an equivalent circuit for reverse out-of-range fault calculation according to an embodiment of the present invention;

FIG. 4(c) is a schematic diagram of an equivalent circuit for calculating an intra-zone fault according to an embodiment of the present invention;

FIG. 5(a) is a schematic diagram of forward out-of-band fault reference point voltages in accordance with an embodiment of the present invention;

FIG. 5(b) is a schematic diagram of reverse out-of-range fault reference point voltages in accordance with an embodiment of the present invention;

FIG. 5(c) is a schematic diagram of reference point voltages for intra-zone faults in accordance with an embodiment of the present invention;

FIG. 6(a) is a view showing an example of before in-zone blocking F according to the present invention ₃ A reference point voltage simulation diagram of the fault;

FIG. 6(b) shows an embodiment of the present invention before block-in-zone F ₃ A reference point voltage integral simulation diagram of the fault;

FIG. 6(c) shows an embodiment of the present invention after in-zone blocking F ₃ A reference point voltage simulation diagram of the fault;

FIG. 6(d) shows an embodiment of the present invention after intra-block F ₃ A reference point voltage integral simulation diagram of the fault;

FIG. 7(a) is a view showing before F out-of-zone latch-up of an embodiment of the present invention ₁ A reference point voltage simulation diagram of the fault;

FIG. 7(b) is a view showing before F out-of-zone latch-up of an embodiment of the present invention ₁ A reference point voltage integral simulation diagram of the fault;

FIG. 7(c) shows an embodiment of the invention after extra-regional occlusion F ₁ A reference point voltage simulation diagram of the fault;

FIG. 7(d) shows an embodiment of the invention after extra-regional occlusion F ₁ A reference point voltage integral simulation diagram of the fault;

FIG. 7(e) is a view showing before F out-of-zone latch-up of an embodiment of the present invention ₅ A reference point voltage simulation diagram of the fault;

FIG. 7(F) is a view showing before F out-of-zone latch-up of an embodiment of the present invention ₅ A reference point voltage integral simulation diagram of the fault;

FIG. 7(g) shows an embodiment of the invention after extra-regional occlusion F ₅ A reference point voltage simulation diagram of the fault;

FIG. 7(h) shows an example of an out-of-zone latch-up F ₅ Reference point voltage integral simulation diagram of fault.

Detailed Description

The invention is further described with reference to the following figures and examples.

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

Example one

The embodiment provides a pilot comparison protection method for a multi-end flexible direct-current power distribution network.

A pilot comparison protection method for a multi-terminal flexible direct-current power distribution network comprises the following steps:

The electrical quantity of a port of an element of the power system is doubly constrained by a power supply and an equivalent model of the element. The electrical quantity is generated and maintained by the power source, but the magnitude and the distribution rule thereof satisfy the mathematical relationship determined by the element model. This mathematical relationship is independent of the characteristics of the power supply and only dependent on the model of the respective element. Therefore, regardless of the output characteristics of the power supply, if the model of the object to be studied is determined, the port electrical quantities of the elements normally satisfy the mathematical relationship determined by the model.

FIG. 3 is a schematic diagram of a network model of protected objects and port electrical quantities, in which lines are represented by lumped parameters R-L, u ₁ 、i ₁ 、u ₂ 、i ₂ And the instantaneous electric quantities of the two ports are respectively represented, and R and L are respectively the resistance and the inductance corresponding to the line model. According to the theory of the two-port network, a mathematical equation under the constraint of a model can be obtained as shown in the following formula:

when the line runs normally or an external fault occurs, the line model is kept intact, and the relation of the electrical quantities at two ends of the line still satisfies the formula (1); when the internal fault occurs in the line, the line model is not good any more, and at the moment, the electrical quantity relation does not satisfy the formula (1) any more. Therefore, when the line has a fault, the fault judgment inside and outside the area can be completed according to whether the line model is intact.

The above equation has no direct relation to the power type and its output characteristics, and is only related to the model of the protected component and the mathematical equation describing the physical model. Therefore, as long as the model of the protected element is selected, the relationship of the protected element port voltage current is determined regardless of the type of power source externally supplying the electrical quantity.

In this embodiment, the protection idea is applied to a multi-terminal flexible dc power distribution network, and a specific implementation process of the pilot comparison protection method for the multi-terminal flexible dc power distribution network in this embodiment is described in detail below by taking the multi-terminal flexible dc power distribution network shown in fig. 2 as an example, where the dc line faults in question are all bipolar short-circuit faults.

FIG. 2 is a schematic diagram of a multi-terminal flexible DC distribution network model, wherein A and B are buses on two sides of a DC distribution line and are installation positions of a relay protection device, and A terminal is a fixed DC voltage side，R ₁ The point is the corresponding reference point of the A end on the line to protect the line AR ₁ Fault analysis is carried out for example to illustrate that a solid theoretical basis is provided for a protection scheme. For the convenience of fault analysis, the following analysis is based on the line using lumped parameter R-L model.

The equivalent calculation circuit of the protected line AR1 in the case of the inside and outside fault is shown in FIGS. 4(a) -4 (c), in which i _dc1 And i _dc2 For the currents corresponding to the different phases after a fault, u _A For measuring voltage, R, of A-terminal protective relaying devices _AR 、L _AR Representing the line parameters.

Referring to fig. 1, when a forward out-of-range fault occurs, the reference point R can be found from the equivalent circuit, the measured voltage, the dc line current, and the line parameters of fig. 4(a) ₁ The voltage expression of (a) is as follows:

in case of forward out-of-range failure, AR ₁ The line model is perfect, the voltage amplitude at the fault point is 0, the voltage amplitudes on the line from the point a to the fault point are all positive, and the calculation process of equation (2) is correct, so the result obtained according to equation (2) is also necessarily positive.

Referring to fig. 1, when a reverse out-of-range fault occurs, reference point R can be found from the equivalent circuit, measured voltage, dc line current and line parameters of fig. 4(b) ₁ The voltage expression of (a) is as follows:

in reverse out-of-range faults, AR ₁ The line model is perfect, the voltage amplitude at the fault point is 0, the voltage amplitudes on the line from point a to the fault point are all positive, and the calculation process of equation (3) is correct. In addition, the voltage u is measured _A And reference point voltage u _R1 Are provided by the peer-to-peer system, the result obtained according to equation (3) is positive, and the reference point voltage isThe amplitude must be higher than the voltage amplitude at the measurement point.

Referring to FIG. 1, when an intra-area failure occurs, AR can be seen from FIG. 4(c) ₁ A fault path is added between the line models and the AR is protected ₁ The line model is destroyed, and therefore the reference point voltage u is calculated from the point A using equation (2) _R1 Is incorrect. When the fault point is located in the area, the line parameters from the point A to the fault point are compared with those from AR ₁ When the line parameter becomes smaller and still uses the formula (2) to calculate, the reference point voltage u is obtained _R1 Is negative in magnitude.

From the above analysis, it can be seen that no matter whether a forward direction out-of-area fault or a reverse direction out-of-area fault occurs, the protected line model is good, and the reference point voltage u is calculated from the point A by the formula (2) or the formula (3) _R1 Is correct, the obtained reference point voltage u _R1 Are all positive and the voltage u is measured _A And reference point voltage u _R1 The positive and negative laws of the amplitude are the same, as shown in fig. 5(a) and 5 (b); when the fault occurs in the area, the protected line model is destroyed, and the reference point voltage u is calculated from the point A by the formula (2) _R1 Is incorrect, the resulting reference point voltage u _R1 Is negative, the voltage u is measured _A And reference point voltage u _R1 The positive and negative regularity of the amplitude of (c) is opposite, as shown in fig. 5 (c). In addition, regardless of the phase of the converter after the fault, as long as the electrical quantities are detected at the measuring points and the model of the protected component is selected, the line model-oriented protection method can correctly and reliably identify the faults inside and outside the zone.

In order to ensure that each end protection device gives a correct judgment result, the embodiment reliably distinguishes the in-zone fault and the out-of-zone fault of the line. For this purpose, the following key technical problems must be solved: (1) selecting the position of a reference point R; (2) and selecting a line model and line parameters related to calculating the reference point voltage.

The selection principles of the reference point, the line model and the line parameters are as follows:

this embodiment selects the reference point R to be 1.2 times the full length of the AB line. The selection of the reference point R is considered as follows: (1) the reference point must be located outside the protected line to ensure reliable reaction to the internal fault of the line, and theoretically, the farther the position of the reference point R is, the higher the protection sensitivity is; (2) there is inevitably a difference between the line model and the actual line. The farther the position of the reference point R is, the larger the error of the voltage at the point R calculated based on the model will be. The position of the reference point R should not be too far away. Combining the above factors, the present embodiment selects the reference point R to be 1.2 times the full length of the AB line.

The selection of the line model and the parameters directly affects the accuracy of the voltage calculation result at the reference point R. Although the high-order and high-accuracy line model can improve the accuracy of the calculation result, the calculation process is complex, and the rapidity of fault detection is influenced. Therefore, the R-L type line model with high simplification degree in the centralized parameter model is selected for analysis, the calculation process can be greatly simplified, and the rapidity of fault judgment is guaranteed.

Therefore, the reference point voltage u of the present embodiment _R The calculation formula of (2) is as follows:

in the formula u _i And i _i The electrical quantity, R, of a measuring point at one end (e.g. end A or end B in FIG. 2) _i And L _i The line parameters from a point to a reference point are measured for a certain end.

Through the fault analysis, the positive and negative of the reference point voltage amplitude when the in-zone fault occurs and the positive and negative of the reference point voltage amplitude when the forward zone and the reverse zone are out of fault are obviously different, so that the in-zone fault and the out-zone fault can be reliably distinguished through the positive and negative of the reference point voltage amplitude. In addition, in order to avoid measurement errors and noise interference, and to continuously accumulate the difference of the faults inside and outside the region, the reference point voltage is integrated as shown in the following formula:

in the formula, T is an integration time, and T is 0.5ms in consideration of the reliability and the snap property of the protection.

And setting corresponding internal and external fault criteria according to the positive and negative values of the voltage integral value of the reference point. Considering that pilot comparison protection needs to solve the problem of strict synchronization of communication and data, a reference point voltage integral value positive and negative criterion is defined as a logical quantity, as shown in the following formula:

in the formula, j is 1 or 2, and represents both ends of the tandem comparison.

It should be noted that, in this embodiment, the reference point voltage is calculated based on the voltage and current instantaneous values of the positive line, and if the voltage and current instantaneous values of the negative line are used for calculation, the corresponding inside and outside fault judgments are just opposite, that is, the inside and outside fault judgments are opposite, that is, the reference point voltage is calculated based on the voltage and current instantaneous values of the negative line

Therefore, the failure determination method can be applied as well, only by changing the corresponding logic. In addition, the fault determining method of this embodiment does not distinguish whether the out-of-area fault is outside the forward area or outside the reverse area, and the corresponding protection does not act as long as it is determined as the non-in-area fault.

The pilot comparison protection logic in this embodiment is:

the pilot comparison protection logic is illustrated with the fault in fig. 2 as an example. When F is present ₃ When the point is in fault, the A side protection unit calculates to obtain a reference point R ₁ The voltage integral value is negative, the fault is positioned within the protection range, and the B-side protection unit also calculates to obtain a reference point R ₂ If the voltage integral value is negative, the fault is located within the protection range, and the fault judgment results of the side A and the side B are compared in a pilot mode, so that the fault can be determined to be located in the area and the action is protected; when F is present ₂ When the fault occurs, the B-side protection unit still calculates the reference point R ₂ Is negative, a protection is obtainedThe conclusion that the fault occurs in the range is reached, but the A-side protection unit calculates the reference point R ₁ The voltage integral value is positive, the conclusion that a fault occurs outside the protection range is obtained, and the fault judgment results of the side A and the side B are compared in a pilot mode, so that the fault can be determined to be located outside the area, and the protection does not act; when F is present ₁ When the fault occurs, the A-side protection unit and the B-side protection unit calculate that the voltage integral value of the reference point is positive, the conclusion that the fault occurs outside the protection range is obtained, the fault judgment results of the A side and the B side are compared in a pilot mode, the fact that the fault is located outside the area and the protection does not act can be determined. The analysis conditions of other fault points are similar and are not described in detail. In summary, when the voltage integral values of the reference points on the two sides are both negative, it can be determined as an intra-area fault; and when at least one of the voltage integral values of the reference points on the two sides is positive, judging that the result is an out-of-range fault.

For special case handling: the present embodiment takes into account two special cases that may cause insufficient protection sensitivity and provides a solution to this.

When a bipolar short-circuit fault occurs at a forward or reverse outlet of a line port, the measured voltage is very small, and the dead zone problem of the measured voltage exists. In this case, the measurement current is generally large. For the MMC converter, even under the serious condition that the submodule is locked immediately after the fault occurs, the fault current is very obvious in a short time due to the inductive follow current phenomenon. Reference point voltage u calculated at this time _R And will not be small. The positive and negative criteria of the value of the voltage integral employed in the present embodiment can still reliably determine the location of the fault.

When a bipolar short-circuit fault occurs through the transition resistor, the amplitude of the fault current is reduced, the locking threshold value of the sub-module may not be reached, and the sub-module is not locked. Therefore, only the influence of the initial stage after the fault on the protection method needs to be analyzed. The existence of the transition resistance can change the calculation result of the reference point voltage, and if the transition resistance is large, the situation that the voltage integral value of the reference point is positive when the fault occurs in the area can occur, so that the protection is rejected. Aiming at the situation, the solution is to adjust the position of the reference point to make the position of the reference point more than 1.2 times of the total length of the line, thereby achieving the purpose of improving the protection sensitivity. However, if the position of the reference point is too far away, the introduced calculation error will also increase, which is not favorable for the reliability of protection, and therefore, the position of the reference point needs to be adjusted reasonably on the premise of considering both the protection sensitivity and the reliability.

In fig. 2, the test object is protected with the line AB as a line model. The sampling frequency is 10 KHz; the MMC1 is controlled by constant direct current voltage, and the MMC2-MMC4 are controlled by constant active power; the time of occurrence of the fault is 1.5s, and the specific parameter conditions are shown in table 1.

TABLE 1

For the case of intra-zone failure:

in zone F ₃ When a bipolar short-circuit fault occurs, simulation results of reference point voltage and voltage integration at the time of the intra-zone fault can be obtained, as shown in fig. 6(a) -6 (d). U in the figure _R1 、u _R2 Respectively representing the corresponding reference point voltage value obtained from the line A terminal and the corresponding reference point voltage value obtained from the line B terminal, u _{R1_int} 、u _{R2_int} Respectively represent according to u _R1 、u _R2 And the integral value calculated by the equation (5). The meanings shown in fig. 7(a) to 7(h) are the same, and the description thereof will not be repeated.

When an intra-area fault occurs, in the stage before the sub-module is locked, as can be seen from fig. 6(a) -6 (b), the reference point voltage value and the reference point voltage integral value are constantly negative, and the occurrence of the intra-area fault can be reliably determined through the reference point voltage integral value positive-negative criterion formula (6) and the pilot comparison logic. At the later stage of locking the sub-modules, as can be seen from fig. 6(c) -6 (d), when the sub-modules have a sudden change in the reference voltage at the moment of locking, because the sub-modules have a sudden change in the measured voltage and the measured current increase and decrease change due to locking, and the sub-modules have different locking moments, the occurrence of the intra-area fault can be correctly determined by the reference point voltage integral value positive and negative criterion formula (6) and the pilot comparison logic. Although the reference point voltage changes suddenly when the fault stage changes, and misjudgment can occur according to the positive and negative of the reference point voltage, the influence of the sudden change point on the fault judgment result can be effectively avoided due to the integration of the reference point voltage.

From the above analysis, it can be seen that when an intra-area fault occurs, as long as the fault is not removed, no matter which stage the fault is in, the occurrence of the intra-area fault can be correctly and reliably determined, and the corresponding protection action occurs.

When a fault occurs in a transition resistance in a generation area, the reference point is taken as 2 times of the total length of a line, the protection adaptability under the condition that the transition resistance is 5 omega, 10 omega and 20 omega is tested, and the simulation results of two continuous voltage integrals after the fault are shown in the table 2.

TABLE 2

As can be seen from Table 2, when the reference point is located at 2 times of the full length of the line and the transition resistance reaches 20 omega, the fault in the area can still be accurately judged, and the transition resistance of the protection method is high.

Case for out-of-range fault:

outside the zone F ₁ 、F ₅ Bipolar short-circuit faults occur at the positions, and simulation results of reference point voltage and voltage integration during the out-of-area fault can be obtained, as shown in fig. 7(a) -7 (h).

When out of the occurrence zone F ₁ 、F ₅ In the event of a failure, in the sub-module before locking, as can be seen from fig. 7(a), 7(b), 7(e) and 7(f), the reference point voltage value and the reference point voltage integral value are always positive, and the occurrence of an out-of-area failure can be reliably determined by the reference point voltage integral value positive-negative criterion expression (6) and the pilot comparison logic. In the post-latch stage of the sub-modules, as can be seen from fig. 7(c), 7(d), 7(g) and 7(h), when the sub-modules are latched, they are far away from each otherOne end of fault point (F) ₁ End B and end F in fault ₅ End a) is near above zero point, and can be correctly judged to have an out-of-area fault through a reference point voltage integral value positive and negative criterion formula (6) and a pilot comparison logic. Even if the end far away from the fault point after locking is judged as an intra-zone fault, the end near the fault point can be reliably judged as an extra-zone fault, and the pilot comparison logic can know that the end still can be reliably judged as an extra-zone fault.

For the out-of-range transient resistance fault, the simulation results of two consecutive voltage integrations after the fault are shown in table 3.

TABLE 3

As can be seen from table 3, the existence of the transition resistor does not affect the criterion of reference point voltage integration, and the existence of the transition resistor raises the residual voltage at the fault point, which is beneficial to the positive and negative judgment of the reference point voltage integral value, and can reliably judge as an out-of-area fault, and correspondingly protect against actions.

For the case of voltage dead band:

when a double-pole short-circuit fault occurs at the forward and reverse outlets of the end a and the end B of the line, the simulation results of two continuous voltage integrals corresponding to different fault times can be obtained, as shown in table 4.

TABLE 4

As can be seen from table 4, when the dead zone fault occurs at the forward outlets of the end a and the end B, the reference point voltage integral value is negative no matter in the pre-locking stage or the post-locking stage, and the occurrence of the intra-zone fault at the moment can be judged correctly by the reference point voltage integral value positive-negative criterion formula (6) and the pilot comparison logic; when dead zone faults occur at the reverse outlets of the end A and the end B, no matter the stage before locking or the stage after locking, one end of the voltage integral value of the reference point is positive, and the other end of the voltage integral value of the reference point is negative, and the occurrence of out-of-range faults can be judged through the reference point voltage integral value positive and negative criterion formula (6) and the pilot comparison logic, so that the judgment is correct.

For the case of noise interference:

aiming at the stage before locking, Gaussian white noise with signal-to-noise ratios of 50dB, 40dB and 30dB is respectively added into voltage and current data acquired when faults at different positions occur; for the post-blocking stage, gaussian white noise with signal-to-noise ratios of 50dB and 45dB is added to the voltage and current data collected when faults at different positions, respectively, so as to test the anti-noise capability of the protection scheme, and the results are shown in table 5.

TABLE 5

It can be seen from table 5 that, in the pre-locking stage of the sub-module, when the signal-to-noise ratio reaches 30dB, the protection can still correctly and reliably realize the identification of the inside and outside faults; in the post-locking stage of the sub-modules, when the signal-to-noise ratio reaches 45dB, the protection can also correctly and reliably realize the identification of the faults inside and outside the zone. After locking, the amplitudes of the voltage and the current are smaller than those before locking, so that the noise resistance is reduced, and the noise interference with the signal-to-noise ratio of 45dB can be resisted. Because the used in-zone and out-of-zone fault criteria are constructed using the integral of the reference point voltage, this enhances the protection against noise to some extent.

Example two

This embodiment provides a flexible direct current distribution network pilot comparison protection system of multiterminal, includes:

a reference voltage integral value calculation module configured to: judging whether the action condition is met or not according to the measured voltage and the measured current, if so, calculating a voltage integral value at a reference point according to a known line parameter model to serve as a reference voltage integral value; wherein, the reference point is positioned outside the protected line;

The multi-terminal flexible direct-current distribution network pilot comparison protection system of the present embodiment corresponds to the multi-terminal flexible direct-current distribution network pilot comparison protection method of the first embodiment, and a description thereof will not be repeated here.

EXAMPLE III

The embodiment provides a multi-end flexible direct-current power distribution network pilot comparison protection system which comprises two relay protection devices which are communicated with each other, wherein the relay protection devices are respectively installed at two ends of a protected circuit; the relay protection device is configured to:

In a specific implementation, the relay protection device is configured to perform the steps in the pilot comparison protection method for the multi-terminal flexible dc distribution network according to the first embodiment.

The specific implementation process of the pilot comparison protection method for the multi-terminal flexible direct-current power distribution network is not described here again.

Example four

The present embodiment provides a computer-readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements the steps in the pilot comparison protection method for the multi-terminal flexible dc power distribution network according to the first embodiment.

EXAMPLE five

The embodiment provides a computer device, which includes a memory, a processor, and a computer program stored in the memory and executable on the processor, where the processor executes the computer program to implement the steps in the pilot comparison protection method for the multi-terminal flexible dc power distribution network according to the first embodiment.

As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of a hardware embodiment, a software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, optical storage, and the like) having computer-usable program code embodied therein.

The present invention has been described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by a computer program, which can be stored in a computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. The storage medium may be a magnetic disk, an optical disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), or the like.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A pilot comparison protection method for a multi-terminal flexible direct-current power distribution network is characterized by comprising the following steps:

2. The multi-terminal flexible direct current distribution network pilot comparison protection method as claimed in claim 1, wherein the fault location is determined according to the positive and negative of a reference voltage integral value.

3. The multi-terminal flexible direct-current distribution network pilot comparison protection method according to claim 2, wherein if the reference voltage integral value is positive, the fault point is located outside the range from the measurement point to the reference point, and belongs to an external fault; if the reference voltage integral value is negative, the fault point is located between the measuring point and the reference point and belongs to an internal fault.

4. The multi-terminal flexible direct-current distribution network pilot comparison protection method according to claim 1, wherein the determining whether the action condition is satisfied according to the measured voltage and the measured current specifically comprises: calculating the change rate of the voltage along with the time and the change rate of the current along with the time according to the measured voltage and the measured current; and judging whether the action condition is met or not according to the change rate of the voltage along with the time and the change rate of the current along with the time.

5. The pilot comparison protection method for the multi-terminal flexible direct-current distribution network according to claim 1, wherein the step of judging whether the fault point is located inside the protected line according to the positive and negative values of the reference voltage integral value and by combining pilot comparison logic specifically comprises the steps of: in the process of adopting the pilot comparison logic, whether a fault point is positioned in the protected line or not is judged by comparing reference voltage integral values at two ends of the protected line.

6. The multi-end flexible direct-current distribution network pilot comparison protection method according to claim 5, wherein if the reference voltage integral values at both ends of the protected line are negative, the fault point is located inside the protected line; otherwise, the fault point is located outside the protected line.

7. The utility model provides a flexible direct current distribution network pilot comparison protection system of multiterminal which characterized in that includes:

8. A multi-end flexible direct-current power distribution network pilot comparison protection system is characterized by comprising two relay protection devices which are communicated with each other, wherein the relay protection devices are respectively arranged at two ends of a protected circuit; the relay protection device is configured to:

9. A computer-readable storage medium, on which a computer program is stored, wherein the program, when being executed by a processor, implements the steps of the pilot comparison protection method for a multi-terminal flexible dc distribution network according to any one of claims 1 to 6.

10. Computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, characterized in that the processor implements the steps of the method for pilot comparison protection of a multi-terminal flexible dc power distribution network according to any of claims 1-6 when executing the program.