CN108199372B

CN108199372B - Method and device for establishing homopolar cross-over fault model between direct current systems

Info

Publication number: CN108199372B
Application number: CN201810013123.7A
Authority: CN
Inventors: 王长香; 张帆; 赵利刚; 黄冠标; 杨诚
Original assignee: CSG Electric Power Research Institute; Power Grid Technology Research Center of China Southern Power Grid Co Ltd
Current assignee: Research Institute of Southern Power Grid Co Ltd
Priority date: 2018-01-03
Filing date: 2018-01-03
Publication date: 2020-03-27
Anticipated expiration: 2038-01-03
Also published as: CN108199372A

Abstract

The embodiment of the invention provides a method and a device for establishing a homopolar cross-over fault model between direct current systems, relates to the field of power systems, and can establish an equivalent model of homopolar cross-over ungrounded faults between direct current systems. The method comprises the following steps: acquiring a homopolar cross-over ungrounded fault model by utilizing thevenin equivalence; simulating the ungrounded fault model to obtain a first network topological graph and a second network topological graph; establishing a first boundary equation set and a second boundary equation set according to a preset rule according to the first network topological graph and the second network topological graph; acquiring trigger angle values of the converter stations in the first network topological graph and the second network topological graph according to the simulation result of the ungrounded fault model; establishing a homopolar cross-over ungrounded fault equivalent model; and calculating the value of the fault equivalent impedance of the equivalent model of the homopolar cross-over ungrounded fault according to the trigger angle value of the converter station in the first network topological graph and the second network topological graph, the first boundary equation set, the second boundary equation set, the preset rectifying side equation set and the inversion side equation set.

Description

Method and device for establishing homopolar cross-over fault model between direct current systems

Technical Field

The invention relates to the field of power system analysis, in particular to a method and a device for establishing a homopolar cross-over fault model between direct current systems.

Background

The advantages of direct current engineering in power transmission are obvious, and in recent years, direct current power transmission is mostly adopted in large-capacity long-distance power transmission in China. According to the planning, a large amount of long-distance high-voltage direct-current transmission projects are still operated and built in the future. Because the main energy bases and the load centers in China are reversely distributed, the planned power transmission lines are mostly in the south-north or east-west directions. With the increase of the number of lines, the situation of cross-over of the direct current and the direct current transmission line is inevitable, and the probability of short-circuit fault of the cross-over of the direct current and the direct current is increased. The direct current-direct current cross-over is a complex fault type, and particularly when direct current lines of different voltage levels have cross-over faults, a rectification valve and an inversion valve of a fault pole of a certain return direct current line are completely turned off, and the fault pole is locked and stops running. Therefore, the research on the fault characteristics of the DC-DC cross fault and the fault analysis method have very important guiding significance on the configuration of the DC line protection. The electromagnetic transient simulation can simulate the detailed dynamic process of direct current and a control system thereof in detail, but the calculation scale and the calculation time required by the integral electromagnetic transient simulation are large; the electromechanical transient simulation is an important content of safety and stability analysis and calculation of a power system, and the application of the electromechanical transient simulation relates to the whole power production process such as power grid planning, scheduling, mode making, post inversion analysis and the like, so that a direct current-direct current cross-over fault analysis and calculation method suitable for electromechanical transient simulation is needed to be researched.

However, in the prior art, there is only an overall research and analysis on the dc-dc cross-over ungrounded fault, and an analysis method for a dc system, whether a traveling wave theory or a switching function method is difficult to apply to the dc-dc cross-over ungrounded electromechanical transient analysis, and cannot meet the analysis requirement on the dc-dc cross-over ungrounded fault in the engineering.

Disclosure of Invention

The embodiment of the invention provides a method and a device for establishing a homopolar cross-over fault model between direct current systems, which are used for realizing electromechanical transient analysis of homopolar cross-over ungrounded faults between direct current transmission systems with different voltage levels.

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

the method comprises the steps that a first direct current system and a second direct current system are included, the first direct current system is a bipolar two-end direct current power transmission system with a first voltage level, the second direct current system is a bipolar two-end direct current power transmission system with a second voltage level, a first power transmission line of the first direct current system and a second power transmission line of the second direct current system are bridged at a preset crossover point, the first power transmission line and the second power transmission line are of the same polarity, and the crossover point is suspended; the method comprises the following steps:

performing single-port Thevenin equivalence on a rectification side and an inversion side of the first direct current system and the second direct current system to obtain a homopolar cross-over ungrounded fault model formed by an equivalent circuit of the first direct current system and an equivalent circuit of the second direct current system;

carrying out simulation operation on the homopolar crossing ungrounded fault model and acquiring a first network topological graph and a second network topological graph according to the result of the simulation operation of the homopolar crossing ungrounded fault model; the first network topological graph is a simplified model which comprises a converter station through which current passes in a first power transmission line and a second power transmission line and line resistance when a homopolar cross-over ungrounded fault model has a fault at a first stage; the second network topological graph is a simplified model which comprises a converter station through which current passes in the first transmission line and the second transmission line and line resistance when the homopolar cross-over ungrounded fault model has a fault at the second stage;

establishing a first boundary equation set according to a first network topological graph and a preset rule; establishing a second boundary equation set according to a second network topological graph and a preset rule;

acquiring trigger angle values of converter stations in a first network topological graph and a second network topological graph according to a simulation operation result of a homopolar cross-over ungrounded fault model, wherein the converter stations comprise a rectifier station and an inverter station;

according to an electromechanical transient simulation rule, buses of a rectification side and an inversion side of a first power transmission line and a second power transmission line in the homopolar cross-over ungrounded fault model are grounded through fault equivalent impedance, so that a homopolar cross-over ungrounded fault equivalent model is established;

calculating a value of fault equivalent impedance of the equivalent model of the same polarity cross-over ungrounded fault in the first stage fault according to a trigger angle value of a converter station in a first network topological graph, a first boundary equation set, a preset rectifying side equation set and a preset inverting side equation set;

and calculating the value of the fault equivalent impedance of the equivalent model of the same polarity crossing ungrounded fault in the second stage fault according to the trigger angle value of the converter station in the second network topological graph, the second boundary equation set, the preset rectifying side equation set and the preset inverting side equation set.

Optionally, the performing single-port thevenin equivalence on the rectification side and the inversion side of the first direct current system and the second direct current system to obtain the homopolar cross-over ungrounded fault model formed by the equivalent circuit of the first direct current system and the equivalent circuit of the second direct current system includes:

performing single-port Thevenin equivalence on the rectification side and the inversion side of the first direct current system and the second direct current system to obtain Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the first direct current system and Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the second direct current system;

establishing an equivalent circuit of the first direct current system according to the Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the first direct current system; establishing an equivalent circuit of the second direct current system according to the Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the second direct current system;

and constructing a homopolar cross-over ungrounded fault model according to the equivalent circuit of the first direct current system and the equivalent circuit of the second direct current system.

Optionally, the obtaining the first network topology diagram and the second network topology diagram according to the result of the simulation operation of the homopolar crossing ungrounded fault model includes:

obtaining current simulation curves of all converter stations in the same-polarity cross-over ungrounded fault model after simulation operation of the same-polarity cross-over ungrounded fault model;

and acquiring a first network topological graph and a second network topological graph according to current simulation curves of all converter stations in the same-polarity crossing ungrounded fault model.

Further optionally, the obtaining the firing angle values of the converter stations in the first network topology diagram and the second network topology diagram according to the result of the simulation operation of the homopolar crossing ungrounded fault model includes:

acquiring trigger angle simulation curves of all converter stations in the same-polarity cross-over ungrounded fault model after simulation operation of the same-polarity cross-over ungrounded fault model;

selecting current simulation curves of the converter stations in the first network topological graph and the second network topological graph from current simulation curves of all converter stations in the homopolar cross-over ungrounded fault model; simultaneously selecting trigger angle simulation curves of the converter stations in the first network topological graph and the second network topological graph from the trigger angle simulation curves of all the converter stations in the homopolar cross-over ungrounded fault model;

acquiring a first moment when the current is maximum in a first-stage fault time period in a current simulation curve of each converter station in a first network topological graph;

acquiring a second moment when the current is maximum in the time period of the second-stage fault in the current simulation curve of each converter station in the second network topological graph;

selecting trigger angle values of all first moments in a trigger angle simulation curve of a first converter station in a first network topological graph as the trigger angle values of the first converter station, wherein the first converter station is any one converter station in the first network topological graph;

and selecting all the trigger angle values at the second moment in the trigger angle simulation curve of the second converter station in the second network topological graph as the trigger angle values of the second converter station, wherein the second converter station is any converter station in the second network topological graph.

Optionally, calculating a value of the fault equivalent impedance of the equivalent model of the cross-over non-grounded fault in the same polarity at the first stage according to the trigger angle value of the converter station in the first network topology, the first boundary equation set, the preset rectifying side equation set and the preset inverting side equation set includes:

calculating a voltage value and a current value of a bus corresponding to fault equivalent impedance of the equivalent model of the cross-over ungrounded fault in the first stage of the fault according to a trigger angle value, a first boundary equation set, a preset rectifying side equation set and a preset inversion side equation set of the converter station in the first network topological graph;

and calculating the value of the fault equivalent impedance of the equivalent model of the same-polarity crossing ungrounded fault in the first-stage fault according to the voltage value and the current value of the bus corresponding to the fault equivalent impedance of the equivalent model of the same-polarity crossing ungrounded fault in the first-stage fault.

Optionally, calculating a value of the fault equivalent impedance of the equivalent model of the cross-over non-grounded fault in the same polarity at the second stage according to the trigger angle value of the converter station in the second network topology, the second boundary equation set, the preset rectifying side equation set and the preset inverting side equation set includes:

calculating a voltage value and a current value of a bus corresponding to the fault equivalent impedance of the equivalent model of the cross-over ungrounded fault in the same polarity during the second stage fault according to a trigger angle value of the converter station in the second network topological graph, a second boundary equation set, a preset rectifying side equation set and a preset inverting side equation set;

and calculating the value of the fault equivalent impedance of the equivalent model of the same-polarity crossing ungrounded fault in the second stage fault according to the voltage value and the current value of the bus corresponding to the fault equivalent impedance of the equivalent model of the same-polarity crossing ungrounded fault in the second stage fault.

In a second aspect, a homopolar crossing fault model building device between direct current systems is provided, wherein the direct current systems comprise a first direct current system and a second direct current system, the first direct current system is a bipolar two-end direct current power transmission system with a first voltage level, the second direct current system is a bipolar two-end direct current power transmission system with a second voltage level, a first power transmission line of the first direct current system and a second power transmission line of the second direct current system are bridged at a preset crossover point, the first power transmission line and the second power transmission line have the same polarity, and the crossover point is suspended; the method comprises the following steps: the system comprises a model building module, a simulation module and a processing module;

the model establishing module is used for performing single-port Thevenin equivalence on a rectification side and an inversion side of the first direct current system and the second direct current system so as to obtain a homopolar cross-over ungrounded fault model formed by an equivalent circuit of the first direct current system and an equivalent circuit of the second direct current system;

the simulation module is used for carrying out simulation operation on the homopolar cross-over ungrounded fault model established by the model establishing module;

the model establishing module is also used for acquiring a first network topological graph and a second network topological graph according to a simulation result of the simulation module after the simulation operation of the homopolar cross-over ungrounded fault model; the first network topological graph is a simplified model which comprises a converter station through which current passes and line resistance of a first power transmission line and a second power transmission line when a homopolar cross-over ungrounded fault model fails in a first stage; the second network topological graph is a simplified model which comprises a converter station through which current passes in the first transmission line and the second transmission line and line resistance when the homopolar cross-over ungrounded fault model has a fault at the second stage;

the processing module is used for establishing a first boundary equation set according to a preset rule according to the first network topological graph acquired by the model establishing module, and establishing a second boundary equation set according to a preset rule according to the second network topological graph acquired by the model establishing module;

the processing module is further used for acquiring trigger angle values of the converter station in the first network topological graph and the second network topological graph acquired by the model establishing module according to the simulation operation result of the simulation module on the homopolar crossing ungrounded fault model, and the converter station comprises a rectifier station and an inverter station;

the model establishing module is also used for grounding buses of the rectifying side and the inverting side of the first power transmission line and the second power transmission line in the homopolar cross-over ungrounded fault model through fault equivalent impedance according to an electromechanical transient simulation rule so as to establish a homopolar cross-over ungrounded fault equivalent model;

the processing module is further used for calculating the value of the fault equivalent impedance of the model establishing module for establishing the same polarity cross-over ungrounded fault equivalent model in the first stage of fault according to the trigger angle value of the converter station in the first network topological graph, the first boundary equation set, the preset rectifying side equation set and the preset inverting side equation set;

the processing module is further used for calculating the value of the fault equivalent impedance of the model establishing module for establishing the same polarity cross-over ungrounded fault equivalent model in the second stage of the fault according to the trigger angle value of the converter station in the second network topological graph, the second boundary equation set, the preset rectifying side equation set and the preset inverting side equation set.

Optionally, the model building module is specifically configured to: performing single-port Thevenin equivalence on the rectification side and the inversion side of the first direct current system and the second direct current system to obtain Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the first direct current system and Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the second direct current system;

establishing an equivalent circuit of the first direct current system according to the Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the first direct current system;

establishing an equivalent circuit of the second direct current system according to the Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the second direct current system;

Optionally, the simulation module is specifically configured to obtain current simulation curves of the same polarity crossing over all converter stations in the ungrounded fault model after performing simulation operation on the same polarity crossing over ungrounded fault model established by the model establishing module;

the model establishing module is used for acquiring a first network topological graph and a second network topological graph according to the current simulation curves of all converter stations in the same-polarity cross-over ungrounded fault model acquired by the simulation module.

Optionally, the simulation module is configured to perform simulation operation on the same-polarity cross-over ungrounded fault model established by the model establishing module, and then obtain a firing angle simulation curve of the same-polarity cross-over all converter stations in the ungrounded fault model;

the processing module is used for: selecting current simulation curves of the converter stations in the first network topological graph and the second network topological graph from current simulation curves of all converter stations in the homopolar crossing ungrounded fault model acquired by the simulation module, and selecting trigger angle simulation curves of the converter stations in the first network topological graph and the second network topological graph from trigger angle simulation curves of all converter stations in the homopolar crossing ungrounded fault model;

acquiring a first moment when the current is maximum in a first-stage fault time period in a current simulation curve of each converter station in a first network topological graph; acquiring a second moment when the current is maximum in the time period of the second-stage fault in the current simulation curve of each converter station in the second network topological graph;

selecting trigger angle values of all first moments in a trigger angle simulation curve of a first converter station in a first network topological graph as the trigger angle values of the first converter station, wherein the first converter station is any one converter station in the first network topological graph; and selecting all the trigger angle values at the second moment in the trigger angle simulation curve of the second converter station in the second network topological graph as the trigger angle values of the second converter station, wherein the second converter station is any converter station in the second network topological graph.

Optionally, the processing module is specifically configured to: according to a trigger angle value of a converter station in a first network topological graph, a first boundary equation set, a preset rectifying side equation set and a preset inversion side equation set, calculating a voltage value and a current value of a bus corresponding to a fault equivalent impedance of an equivalent model of the same polarity crossing ungrounded fault established by a model establishing module when the equivalent model of the same polarity crossing ungrounded fault is in a first-stage fault;

Optionally, the processing module is specifically configured to: according to a trigger angle value of the converter station in the second network topological graph, a second boundary equation set, a preset rectifying side equation set and a preset inversion side equation set, calculating a voltage value and a current value of a bus corresponding to the fault equivalent impedance of the equivalent model of the cross-over ungrounded fault established by the model establishing module in the second stage of fault;

The method and the device for establishing the homopolar cross-over fault model between the direct current systems provided by the embodiment of the invention comprise that the direct current system comprises a first direct current system and a second direct current system, the first direct current system is a bipolar two-end direct current power transmission system with a first voltage level, the second direct current system is a bipolar two-end direct current power transmission system with a second voltage level, a first power transmission line of the first direct current system and a second power transmission line of the second direct current system are bridged at a preset crossover point, the first power transmission line and the second power transmission line have the same polarity, and the crossover point is suspended; the method comprises the following steps: performing single-port Thevenin equivalence on a rectification side and an inversion side of the first direct current system and the second direct current system to obtain a homopolar cross-over ungrounded fault model formed by an equivalent circuit of the first direct current system and an equivalent circuit of the second direct current system; carrying out simulation operation on the homopolar crossing ungrounded fault model and acquiring a first network topological graph and a second network topological graph according to the result of the simulation operation of the homopolar crossing ungrounded fault model; the first network topological graph is a simplified model which comprises a converter station through which current passes in a first power transmission line and a second power transmission line and line resistance when a homopolar cross-over ungrounded fault model has a fault at a first stage; the second network topological graph is a simplified model which comprises a converter station through which current passes in the first transmission line and the second transmission line and line resistance when the homopolar cross-over ungrounded fault model has a fault at the second stage; establishing a first boundary equation set according to a first network topological graph and a preset rule; establishing a second boundary equation set according to a second network topological graph and a preset rule; acquiring trigger angle values of converter stations in a first network topological graph and a second network topological graph according to a simulation operation result of a homopolar cross-over ungrounded fault model, wherein the converter stations comprise a rectifier station and an inverter station; according to an electromechanical transient simulation rule, buses of a rectification side and an inversion side of a first power transmission line and a second power transmission line in the homopolar cross-over ungrounded fault model are grounded through fault equivalent impedance, so that a homopolar cross-over ungrounded fault equivalent model is established; calculating a value of fault equivalent impedance of the equivalent model of the same polarity cross-over ungrounded fault in the first stage fault according to a trigger angle value of a converter station in a first network topological graph, a first boundary equation set, a preset rectifying side equation set and a preset inverting side equation set; and calculating the value of the fault equivalent impedance of the equivalent model of the same polarity crossing ungrounded fault in the second stage fault according to the trigger angle value of the converter station in the second network topological graph, the second boundary equation set, the preset rectifying side equation set and the preset inverting side equation set. According to the technical scheme provided by the embodiment of the invention, firstly, a homopolar cross-over ungrounded fault model of a direct current transmission system with different voltage levels is obtained by utilizing thevenin equivalence, then a network topological graph only having line resistance and a current converter in each fault stage and a current curve and a trigger angle curve of each converter station in the homopolar cross-over ungrounded fault model are obtained according to a simulation result of the homopolar cross-over ungrounded fault model, then a boundary equation set related to the current and voltage of the converter station can be obtained according to a preset rule according to the network topological graph, and the trigger angle of the converter station in the network topological graph in each fault stage is obtained according to the current curve and the trigger angle curve; finally, according to the trigger angle of the converter station in the network topological graph of each fault stage, the boundary equation set of each network topological graph, the preset rectifying side equation set and the preset inversion side equation set, calculating to enable the bus of the rectifying side and the inversion side of the bipolar line with the short-circuit fault in the ungrounded fault model crossed in the same polarity to be grounded through fault equivalent impedance according to an electromechanical transient simulation rule so as to obtain the value of the fault equivalent impedance in each fault stage in the equivalent model of the same polarity cross-crossing ungrounded fault which can be used for electromechanical transient simulation; and finally, combining known element parameters obtained from the homopolar cross-over ungrounded fault model and the calculated value of the fault equivalent impedance to obtain a homopolar cross-over ungrounded fault equivalent model for analyzing homopolar cross-over ungrounded faults among different direct current systems.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

Fig. 1 is a schematic flow chart of a method for establishing a homopolar cross-over fault model between dc systems according to an embodiment of the present invention;

fig. 2 is a schematic structural diagram of a homopolar cross-over ungrounded fault model according to an embodiment of the present invention;

FIG. 3 is a schematic structural diagram of an equivalent model of a homopolar cross-over ungrounded fault according to an embodiment of the present invention;

FIG. 4 is a diagram illustrating a quasi-steady-state model structure for electromechanical transient simulation analysis according to an embodiment of the present invention;

fig. 5 is a schematic flow chart of a method for establishing a homopolar crossing fault model between dc systems according to another embodiment of the present invention;

fig. 6 is a first network topology diagram provided by an embodiment of the present invention;

fig. 7 is a second network topology diagram provided by an embodiment of the invention;

fig. 8 is a schematic structural diagram of an apparatus for establishing a homopolar crossing fault model between dc systems according to an embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of 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 invention.

It should be noted that, in the embodiments of the present invention, words such as "exemplary" or "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design described as "exemplary" or "e.g.," an embodiment of the present invention is not necessarily to be construed as preferred or advantageous over other embodiments or designs. Rather, use of the word "exemplary" or "such as" is intended to present concepts related in a concrete fashion.

It should be noted that, in the embodiments of the present invention, "of", "corresponding" and "corresponding" may be sometimes used in combination, and it should be noted that, when the difference is not emphasized, the intended meaning is consistent.

For the convenience of clearly describing the technical solutions of the embodiments of the present invention, in the embodiments of the present invention, the words "first", "second", and the like are used for distinguishing the same items or similar items with basically the same functions and actions, and those skilled in the art can understand that the words "first", "second", and the like are not limited in number or execution order.

In the prior art, there is little overall research and analysis on the dc-dc cross-over fault, and an analysis method for a dc system, whether a traveling wave theory or a switching function method, is difficult to apply to the dc-dc cross-over electromechanical transient analysis, and cannot meet the analysis requirement on the engineering on the dc-dc cross-over fault.

In view of the above problem, referring to fig. 1, an embodiment of the present invention provides a method for establishing a homopolar crossing fault model between dc systems, including:

101. and performing single-port Thevenin equivalence on the rectification side and the inversion side of the first direct current system and the second direct current system to obtain a homopolar cross-over ungrounded fault model formed by an equivalent circuit of the first direct current system and an equivalent circuit of the second direct current system.

Specifically, the direct current system comprises a first direct current system and a second direct current system, the first direct current system is a bipolar two-end direct current power transmission system with a first voltage level, the second direct current system is a bipolar two-end direct current power transmission system with a second voltage level, the first voltage level is different from the second voltage level, a first power transmission line of the first direct current system is bridged over a second power transmission line of the second direct current system at a preset crossover point, the first power transmission line and the second power transmission line have the same polarity, and the crossover point is suspended and is not grounded; the crossover point refers to a point at which the first direct current transmission line and the second direct current transmission line are short-circuited, and actually, one crossover point is arranged in each of the first direct current transmission line and the second direct current transmission line;

for example, a homopolar cross-over ungrounded fault model is shown with reference to fig. 2, where the dc voltage level of the first dc system is ± UdH, the dc voltage level of the second dc system is ± UdL, and UdH is greater than UdL; s1 and S2 are thevenin equivalent power supplies of two ports after thevenin equivalent is worn by the first dc system, S3 and S4 are thevenin equivalent power supplies of two ports after thevenin equivalent is worn by the second dc system, Zeq4 and Zeq4 are thevenin equivalent impedances of two ports after thevenin equivalent is worn by the first dc system, Zeq4 and Zeq4 are thevenin equivalent impedances of two ports after thevenin equivalent is worn by the second dc system, T4 are converter transformers of the first dc system, T4 are converter transformers of the first dc system, Rec 4 and Rec 4 are rectifier stations of the second dc system, Inv4 and Inv4 are inverter stations of the first dc system, Inv4, inverter resistors of the second dc system 4, R36r 4, R4, the first power transmission line is a positive-polarity line in the first direct current system, the second power transmission line is a positive-polarity line in the second direct current system, the crossover point on the first power transmission line is f1, the crossover point on the second power transmission line is f2, and f1 and f2 are bridged, suspended and ungrounded; in practice, the homopolar cross-over ungrounded fault only appears in the positive polarity line of the two direct current systems, and can also be the negative polarity line of the two direct current systems.

102. And carrying out simulation operation on the homopolar crossing ungrounded fault model and acquiring a first network topological graph and a second network topological graph according to the result of the simulation operation of the homopolar crossing ungrounded fault model.

Specifically, because the same-polarity cross-over ungrounded fault between the direct current systems with different voltage levels exists in two stages, firstly, when the fault just begins to occur, the control part in the direct current system needs to be continuously changed and adjusted so that the direct current system can avoid the influence of the fault as much as possible, the first fault stage is the time, then the control part becomes stable after the control part fluctuates for a period, and the second fault stage is the time; then, in order to better study the change of a control part (a rectifying station and an inverter station) in the fault, a simplified model, namely a network topology model, aiming at different fault stages needs to be established, wherein a first network topology graph is a simplified model which comprises a converter station through which current passes and line resistance in a first transmission line and a second transmission line when a homopolar cross-over ungrounded fault model is in the first stage of fault; the second network topological graph is a simplified model which comprises a converter station through which current passes in the first transmission line and the second transmission line and line resistance when the homopolar cross-over ungrounded fault model has a fault at the second stage.

103. And establishing a first boundary equation set according to a preset rule according to the first network topological graph, and establishing a second boundary equation set according to a preset rule according to the second network topological graph.

Specifically, the preset rule herein refers to an equation establishment rule set in the program according to Kirchhoff's Current Law (KCL) and Kirchhoff's Voltage Law (KVL).

104. And acquiring trigger angle values of the converter stations in the first network topological graph and the second network topological graph according to the simulation operation result of the homopolar crossing ungrounded fault model.

The converter station comprises a rectifier station and an inverter station, and the specific trigger angle value is obtained by extracting according to a simulation curve obtained by simulation.

105. And according to an electromechanical transient simulation rule, buses of a rectification side and an inversion side of the first transmission line and the second transmission line which cross the same polarity are grounded through fault equivalent impedance so as to establish the equivalent model of the fault of crossing the same polarity and the ungrounded fault.

Specifically, when a cross-over fault occurs between the dc systems, the dc systems may be simulated by using dc blocking and connecting an equivalent impedance in parallel at the converter bus in an electromechanical transient simulation, for example, the equivalent model of the same-polarity cross-over non-ground fault transformed according to the above rule across the non-ground fault in fig. 2 is shown in fig. 3, where Z11 replaces the converter transformer T11, the rectifier station Rec11 and the line resistor R11 in the first transmission line in fig. 2, Z12 replaces the converter transformer T21, the inverter station Inv21 and the line resistor R21 in the first transmission line in fig. 2, Z31 replaces the converter transformer T31, the inverter station Rec31 and the line resistor R31 in the second transmission line in fig. 2, and Z12 replaces the converter transformer T41, the inverter station Inv41 and the line resistor R41 in the second transmission line in fig. 2.

1061. And calculating the value of the fault equivalent impedance of the equivalent model of the same polarity crossing ungrounded fault in the first stage fault according to the trigger angle value of the converter station in the first network topological graph, the first boundary equation set, the preset rectifying side equation set and the preset inverting side equation set.

1062. And calculating the value of the fault equivalent impedance of the equivalent model of the same polarity crossing ungrounded fault in the second stage fault according to the trigger angle value of the converter station in the second network topological graph, the second boundary equation set, the preset rectifying side equation set and the preset inverting side equation set.

Specifically, in the electromechanical transient simulation analysis of the alternating current-direct current system, a quasi-steady-state model is adopted for the converter station of the direct current system, as shown in fig. 4, each parameter in the circuit of the rectifier station with the structure shown in fig. 4 conforms to the following preset rectifier side equation set formula, and the circuits of the inverter station after being turned left and right in fig. 4 conform to the following preset inverter side equation set formula:

presetting a rectification side equation set:

wherein E is_sr、

For the amplitude and angle of the effective value of the rectification side Thevenin equivalent voltage source potential,

Z_eqr、

for the amplitude and angle of the rectification side thevenin equivalent impedance,

E_busr、

for rectifying the amplitude and angle of the primary side bus voltage of the side converter,

I_busr、

the effective value and the angle of the current injected into the direct current system for the primary side bus of the rectifier side converter transformer,

U_dr、I_drfor rectifying side DC voltage and current α_r、μ_rThe angle is a rectification side direct current trigger angle and a commutation overlap angle; x_cr、k_rThe phase change reactance and the phase change transformation ratio are obtained; the subscript r for each of the above parameters represents the rectification side.

Presetting an inversion side equation set:

wherein E is_si、

The effective value and the angle of the potential of the inversion side thevenin equivalent voltage source,

Z_eqi、

the amplitude and angle of the equivalent impedance of thevenin on the inversion side,

E_busi、

for the inversion side current conversion to change the primary side bus voltage amplitude and angle,

I_busi、

the effective value and the angle of the current injected into the direct current system for the primary side bus of the inversion side converter transformer,

U_di、I_difor inverting side DC voltage and current α_i、μ_i、δ_iThe DC trigger angle, the commutation overlap angle and the extinction angle of the inversion side are respectively; x_ci、k_iThe phase change reactance and the phase change transformation ratio are obtained; the subscript i of each of the above parameters represents the inversion side.

It should be noted that the preset rectification side equation set is used when obtaining the parameter value of the rectification station circuit (rectification side), and the preset inversion side equation set is used when obtaining the parameter value of the inversion station circuit (inversion side).

According to the technical scheme provided by the embodiment, firstly, a homopolar cross-over ungrounded fault model of a direct current transmission system with different voltage levels is obtained by utilizing thevenin equivalence, then a network topological graph only having line resistance and a current converter in each fault stage and a current curve and a trigger angle curve of each converter station in the homopolar cross-over ungrounded fault model are obtained according to a simulation result of the homopolar cross-over ungrounded fault model, then a boundary equation set related to the current and voltage of the converter station can be obtained according to a preset rule according to the network topological graph, and the trigger angle of the converter station in the network topological graph in each fault stage is obtained according to the current curve and the trigger angle curve; finally, calculating values of fault equivalent impedance in each fault stage in the homopolar cross-over ungrounded fault equivalent model which can be used for electromechanical transient simulation by grounding through fault equivalent impedance by crossing homopolar cross-over buses on the rectifying side and the inverting side of a bipolar line with a short-circuit fault in the ungrounded fault model in a homopolar cross-over manner according to a trigger angle of a converter station, a boundary equation set, a preset rectifying side equation set and a preset inverting side equation set in a network topological graph of each fault stage; and finally, combining known element parameters obtained from the homopolar cross-over ungrounded fault model and the calculated value of the fault equivalent impedance to obtain a homopolar cross-over ungrounded fault equivalent model for analyzing homopolar cross-over ungrounded faults among different direct current systems.

Referring to fig. 5, an embodiment of the present invention further provides a method for establishing a homopolar crossing fault model between dc systems as a supplement to the technical solution provided in the above embodiment, where the dc system includes a first dc system and a second dc system, the first dc system is a bipolar two-terminal dc power transmission system with a first voltage class, the second dc system is a bipolar two-terminal dc power transmission system with a second voltage class, the first voltage class is different from the second voltage class, a first power transmission line of the first dc system and a second power transmission line of the second dc system are bridged at a predetermined crossover point, the first power transmission line and the second power transmission line have the same polarity, and the crossover point is suspended; the method comprises the following steps:

501. and performing single-port Thevenin equivalence on the rectification side and the inversion side of the first direct current system and the second direct current system to obtain Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the first direct current system and Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the second direct current system.

502. Establishing an equivalent circuit of the first direct current system according to the Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the first direct current system; and establishing an equivalent circuit of the second direct current system according to the Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the second direct current system.

503. And constructing a homopolar cross-over ungrounded fault model according to the equivalent circuit of the first direct current system and the equivalent circuit of the second direct current system.

504. And carrying out simulation operation on the homopolar cross-over ungrounded fault model to obtain current simulation curves and trigger angle simulation curves of all converter stations in the homopolar cross-over ungrounded fault model.

Specifically, the simulation operation generally includes performing simulation after constructing a homopolar cross-over ungrounded fault model by electromagnetic transient simulation software emtdc (electro magnetic transfer in DC system)/pscad (power Systems Computer Aided design).

505. And acquiring a first network topological graph and a second network topological graph according to current simulation curves of all converter stations in the same-polarity crossing ungrounded fault model.

Specifically, the first network topological graph is a simplified model which comprises a converter station through which current passes in a first power transmission line and a second power transmission line and line resistance when a homopolar cross-over ungrounded fault model fails in a first stage; the second network topological graph is a simplified model which comprises a converter station through which current passes in the first transmission line and the second transmission line and line resistance when the homopolar cross-over ungrounded fault model has a fault at the second stage;

in practice, it can be obtained according to the simulation operation result that in different fault stages, fault current operation paths in the same-polarity cross-over ungrounded fault model are different, which causes that different fault stages have different network topology diagrams including a converter station and a line resistor, and for the same-polarity cross-over ungrounded fault model, two fault stages exist, which can obtain a first network topology diagram and a second network topology diagram according to the simulation operation result.

506. Establishing a first boundary equation set according to a first network topological graph and a preset rule; and establishing a second boundary equation set according to a preset rule according to the second network topological graph.

507. Selecting current simulation curves of the converter stations in the first network topological graph and the second network topological graph from current simulation curves of all converter stations in the homopolar cross-over ungrounded fault model; and selecting the trigger angle simulation curves of the converter stations in the first network topological graph and the second network topological graph from the trigger angle simulation curves of all the converter stations in the homopolar cross-over ungrounded fault model.

Specifically, the converter station comprises a rectifying station and an inverter station.

508. And acquiring a first moment when the current is maximum in the time period of the first-stage fault in the current simulation curve of each converter station in the first network topology map, and acquiring a second moment when the current is maximum in the time period of the second-stage fault in the current simulation curve of each converter station in the second network topology map.

509. And selecting all the trigger angle values at the first moment in the trigger angle simulation curve of the first converter station in the first network topological graph as the trigger angle values of the first converter station, and selecting all the trigger angle values at the second moment in the trigger angle simulation curve of the second converter station in the second network topological graph as the trigger angle values of the second converter station.

Specifically, the first converter station is any one converter station in a first network topology diagram, and the second converter station is any one converter station in a second network topology diagram; each converter station aims at a current simulation curve and a trigger angle simulation curve, so that under the condition that current exists in each converter station all the time, each converter station also aims at a first moment with a first preset number and a second moment with a second preset number, the first preset number is the number of the converter stations in the first network topology diagram, the second preset number is the number of the converter stations in the second network topology diagram, and finally each converter station can obtain trigger angle values aiming at two fault stages.

510. And according to an electromechanical transient simulation rule, buses of a rectification side and an inversion side of the first transmission line and the second transmission line which cross the same polarity are grounded through fault equivalent impedance so as to establish the equivalent model of the fault of crossing the same polarity and the ungrounded fault.

5111. And calculating the value of the fault equivalent impedance of the equivalent model of the same polarity crossing ungrounded fault in the first stage fault according to the trigger angle value of the converter station in the first network topological graph, the first boundary equation set, the preset rectifying side equation set and the preset inverting side equation set.

5112. And calculating the value of the fault equivalent impedance of the equivalent model of the same polarity crossing ungrounded fault in the second stage fault according to the trigger angle value of the converter station in the second network topological graph, the second boundary equation set, the preset rectifying side equation set and the preset inverting side equation set.

The embodiment of the invention provides a method for establishing a homopolar cross-over fault model between direct current systems, which comprises the following steps: performing single-port Thevenin equivalence on a rectification side and an inversion side of the first direct current system and the second direct current system to obtain a homopolar cross-over ungrounded fault model formed by an equivalent circuit of the first direct current system and an equivalent circuit of the second direct current system; carrying out simulation operation on the homopolar crossing ungrounded fault model and acquiring a first network topological graph and a second network topological graph according to the result of the simulation operation of the homopolar crossing ungrounded fault model; the first network topological graph is a simplified model which comprises a converter station through which current passes in a first power transmission line and a second power transmission line and line resistance when a homopolar cross-over ungrounded fault model has a fault at a first stage; the second network topological graph is a simplified model which comprises a converter station through which current passes in the first transmission line and the second transmission line and line resistance when the homopolar cross-over ungrounded fault model has a fault at the second stage; establishing a first boundary equation set according to a first network topological graph and a preset rule; establishing a second boundary equation set according to a second network topological graph and a preset rule; acquiring trigger angle values of converter stations in a first network topological graph and a second network topological graph according to a simulation operation result of a homopolar cross-over ungrounded fault model, wherein the converter stations comprise a rectifier station and an inverter station; according to an electromechanical transient simulation rule, buses of a rectification side and an inversion side of a first power transmission line and a second power transmission line in the homopolar cross-over ungrounded fault model are grounded through fault equivalent impedance, so that a homopolar cross-over ungrounded fault equivalent model is established; calculating a value of fault equivalent impedance of the equivalent model of the same polarity cross-over ungrounded fault in the first stage fault according to a trigger angle value of a converter station in a first network topological graph, a first boundary equation set, a preset rectifying side equation set and a preset inverting side equation set; and calculating the value of the fault equivalent impedance of the equivalent model of the same polarity crossing ungrounded fault in the second stage fault according to the trigger angle value of the converter station in the second network topological graph, the second boundary equation set, the preset rectifying side equation set and the preset inverting side equation set. According to the technical scheme provided by the embodiment of the invention, firstly, a homopolar cross-over ungrounded fault model of a direct current transmission system with different voltage levels is obtained by utilizing thevenin equivalence, then a network topological graph only having line resistance and a current converter in each fault stage and a current curve and a trigger angle curve of each converter station in the homopolar cross-over ungrounded fault model are obtained according to a simulation result of the homopolar cross-over ungrounded fault model, then a boundary equation set related to the current and voltage of the converter station can be obtained according to a preset rule according to the network topological graph, and the trigger angle of the converter station in the network topological graph in each fault stage is obtained according to the current curve and the trigger angle curve; finally, according to the trigger angle of the converter station in the network topological graph of each fault stage, the boundary equation set of each network topological graph, the preset rectifying side equation set and the preset inversion side equation set, calculating to enable the bus of the rectifying side and the inversion side of the bipolar line with the short-circuit fault in the ungrounded fault model crossed in the same polarity to be grounded through fault equivalent impedance according to an electromechanical transient simulation rule so as to obtain the value of the fault equivalent impedance in each fault stage in the equivalent model of the same polarity cross-crossing ungrounded fault which can be used for electromechanical transient simulation; and finally, combining known element parameters obtained from the homopolar cross-over ungrounded fault model and the calculated value of the fault equivalent impedance to obtain a homopolar cross-over ungrounded fault equivalent model for analyzing homopolar cross-over ungrounded faults among different direct current systems.

In order to more clearly show the method for establishing the homopolar crossing-over fault model between the dc systems according to the embodiment of the present invention, two dc systems corresponding to the homopolar crossing-over ungrounded fault model shown in fig. 2 are taken as an example for explanation:

step one, single-port Thevenin equivalence is carried out on the rectifying side and the inverting side of the first direct current system and the second direct current system, so that Thevenin equivalent voltage sources (S1 and S2) and Thevenin equivalent impedances (Zeq1 and Zeq2) of all ports of the first direct current system are obtained; and thevenin equivalent voltage sources (S3 and S4) and thevenin equivalent impedances (Zeq3 and Zeq4) of the respective ports of the second direct current system; establishing an equivalent circuit 1 of the first direct current system according to the Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the first direct current system; establishing an equivalent circuit 2 of the second direct current system according to the Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the second direct current system; and constructing a same-polarity cross-over ungrounded fault model diagram 2 according to the equivalent circuit of the first direct current system and the equivalent circuit of the second direct current system, wherein the first transmission line (positive-polarity line) of the first direct current system is bridged to a crossover point f2 on the second transmission line (positive-polarity line) of the second direct current system through a crossover point f 1.

Step two, performing simulation operation on the model shown in the figure 2 by utilizing EMTDC/PSCAD to obtain current simulation curves and trigger angle simulation curves of all converter stations in the figure 2; acquiring a first network topology map and a second network topology map according to current (Id11, Id21, Id31 and Id41) simulation curves of converter stations of the first transmission line and the second transmission line in the graph of FIG. 2; in practice, the fault of the model shown in fig. 2 is divided into two stages, the fault of the first stage lasts from the beginning of the fault to 600ms after the fault, and the fault of the second stage lasts from 600ms after the fault to the end of the simulation, so that the first network topology describes the flow paths of the direct current in the first transmission line and the second transmission line between the beginning of the fault and 600ms after the fault, and the second network topology describes the flow paths of the direct current in the first transmission line and the second transmission line between 600ms after the fault and the end of the simulation;

specifically, as shown in fig. 6, in the first network topology diagram, the rectified side direct current Id11 of the first transmission line (positive direct current line) of the first direct current system with a high voltage class flows to the jumper point f1 through the direct current line resistor R11, the f1 is short-circuited to the jumper point f2, the rectified side direct current Id31 of the second transmission line (positive direct current line) with a low voltage class flows to the fault jumper point f2 through the direct current resistor R31, and the direct current Id41 flows to the inversion side of the second transmission line of the second direct current system from the fault jumper point f2 through the direct current resistor R41;

referring to fig. 7, in the first network topology diagram, a rectification-side direct current Id31 of a second transmission line (positive dc line) of the second dc system of the low voltage class flows to a jumper point f2 through a dc line resistor R31, f2 is short-circuited to the jumper point f1, a direct current Id21 flows from a fault point f1 to an inversion side of a first transmission line (positive dc line) of the first dc system of the high voltage class through a dc resistor R21, and a direct current Id41 flows from the fault jumper point f2 to the inversion side of the second transmission line of the second dc system through a dc resistor R41.

Step three, establishing a first boundary equation for the first network topological graph and a second boundary equation set for the second network topological graph according to the rules of kirchhoff current law and kirchhoff voltage law according to the first network topological graph and the second network topological graph shown in the figures 6 and 7,

the first set of boundary equations is:

the first set of boundary equations is:

fourthly, determining the trigger angle of the converter station in the first network topological graph applicable to the first-stage fault and the trigger angle of the converter station in the second network topological graph applicable to the second-stage fault according to the current simulation curve and the trigger angle simulation curve corresponding to each converter station obtained in the second step;

for the converter stations in the first network topology, selecting simulation curves of Id11, Id31 and Id41 to find the maximum fault current time respectively, recording the maximum fault current time as T1n (n is 1, 3, 4), and finding the trigger angle α corresponding to the T1n time in the trigger angle simulation curves of the rectifier station Rec11 of the first power transmission line, the rectifier station Rec31 of the second power transmission line and the inverter station Inv41 of the second power transmission line_11,T1n、α_31,T1n、α_41,T1nWherein α_11,T1nFiring Angle for Rec11 failure in the first stage, α_31,T1nFiring Angle for Rec31 failure in the first stage, α_41,T1nThe firing angle for Inv41 failure in the first stage;

for the converter station in the second network topology, selecting simulation curves of Id21, Id31 and Id41 to find the maximum time of the fault current, which is recorded as T2n (n is 2, 3, 4), and finding the trigger angle α corresponding to the T2n time from the simulation curves of the trigger angles of the inverter station Inv21 of the first power transmission line, the rectifier station Rec31 of the second power transmission line and the inverter station Inv41 of the second power transmission line_21,T2n、α_31,T2n、α_41,T2nWherein α_21,T2nThe firing angle for Inv21 failure in the second stage, α_31,T2nFiring angle for Rec31 failure in the second phase，α_41,T2nIs the firing angle at which Inv41 failed in the second stage.

And step five, according to an electromechanical transient simulation rule, grounding buses on the rectification side and the inversion side of the first power transmission line and the second power transmission line in the homopolar cross-over ungrounded fault model shown in the figure 2 through fault equivalent impedances (Z11, Z21, Z31 and Z41) so as to establish the homopolar cross-over ungrounded fault equivalent model as shown in the figure 3.

Step six, because only the parameters of four equivalent impedances in the equivalent model of the homopolar cross-over ungrounded fault obtained in the step five do not exist in practice, the values of the four equivalent impedances at different stages of faults need to be calculated;

specifically, because the model shown in fig. 3 is obtained from the equivalent values of the model shown in fig. 2, the bus voltage and the bus current value corresponding to four equivalent impedances of Z11, Z21, Z31 and Z41 in fig. 3 are the same as the bus voltage and the bus current corresponding to four converter stations of Rec11, Inv21, Rec31 and Inv41 in fig. 2; the rectification side or inversion side circuit where Rec11, Inv21, Rec31 and Inv41 are located meets a preset rectification side formula (1) or a preset inversion side formula (2), and the current and voltage of Rec11, Inv21, Rec31 and Inv41 in two-stage fault respectively meet a first boundary equation set (3) and a second boundary equation set (4);

when a first-stage fault occurs, no current exists on the inversion side of the first power transmission line, so that the value of Z21 in the first-stage fault is infinite, an equation set about the rectification side where Rec11 and Rec31 are located is obtained according to a preset rectification side formula (1) and parameters of a rectification side circuit where Rec11 is located and parameters of a rectification side circuit where Rec31 is located, an equation set about the rectification side where Inv41 is located is obtained according to parameters of an inversion side circuit where Inv41 is located and preset inversion side formula (2) and equations corresponding to Rec11 and Rec31 both have I_dr、E_busr、μ_r、U_dr、

And I_busrSeven unknowns, Inv41, have δ in the corresponding equation set_i、μ_i、U_di、E_busi、I_di、

And I_busiEight unknowns, so that the three equation sets corresponding to Rec11, Rec31 and Inv41 have 22 unknowns in total, and therefore the three equation sets are required to be combined with the first boundary equation set (3) to solve the converter bus voltages (at the moment of the first-stage fault T1n, the converter bus voltages of the converter stations Rec11, Rec31 and Inv 41), (the converter bus voltages being equal to the voltage of the first-stage fault T1n and the voltage of the converter bus voltages of the converter stations Rec31 and the voltage

And

) The converter bus currents of the converter stations Rec11, Rec31 and Inv41 at the time of the first stage fault T1n (c 1

And

)；

then, the average voltage of the bus corresponding to Rec11 in the first-stage fault can be obtained

Average voltage of bus corresponding to Rec31 in first-stage fault

Average voltage of bus corresponding to Inv41 during first-stage fault

Average current of bus corresponding to Rec11 in first-stage fault

Average current of bus corresponding to Rec31 in first-stage fault

Average current of bus corresponding to Inv41 during first-stage fault

Finally, the equivalent impedance in the first stage of fault can be obtained

Similarly, when the second-stage fault occurs, no current exists on the rectifying side of the first power transmission line, so the value of the fault of Z11 in the second stage is infinite, an equation set about the inverting side where Inv21 and Inv41 are obtained according to the preset inverting side formula (2), the parameter of the inverting side circuit where Inv21 is located and the parameter of the inverting side circuit where Inv41 is located, an equation set about the rectifying side where Rec31 is located is obtained according to the preset rectifying side formula (1) and the parameter of the rectifying side circuit where Rec31 is located, and δ exists in the equation sets corresponding to Inv21 and Inv41_i、μ_i、U_di、E_busi、I_di、

And I_busiEight unknowns, Rec31, are associated with a set of equations with I_dr、E_busr、μ_r、U_dr、

And I_busrSeven unknowns are provided, so that the three corresponding equation sets of Inv21, Inv41 and Rec31 have 23 unknowns in total, and the three equation sets are combined with the second boundary equation set (4) to solve the converter bus voltages (at the moment of the second-stage fault T2i, Inv21, Inv41 and Rec 31) of the converter stations Inv21, Inv41 and Rec31

And

) The converter bus lines of the converter stations Inv21, Inv41 and Rec31 at the moment of the first phase fault T1iFlow (A)

And

)；

then, the average voltage of the bus corresponding to Inv21 during the second stage fault is calculated

Average voltage of bus corresponding to Inv41 during second-stage fault

Average voltage of bus corresponding to Rec31 in second-stage fault

Average current of bus corresponding to Inv21 in second-stage fault

Average current of bus corresponding to Inv41 in second-stage fault

Average current of bus corresponding to Rec31 in second-stage fault

Finally, the equivalent impedance of the second stage fault can be obtained

In summary, according to the method for establishing the homopolar cross-over fault model between the dc systems provided by the embodiments of the present invention, an equivalent model for analyzing the homopolar cross-over ungrounded fault between different dc systems can be established.

Referring to fig. 8, an embodiment of the present invention further provides a device 01 for establishing a homopolar crossing fault model between dc systems, where the dc systems include a first dc system and a second dc system, the first dc system is a bipolar two-terminal dc power transmission system of a first voltage class, the second dc system is a bipolar two-terminal dc power transmission system of a second voltage class, a first power transmission line of the first dc system and a second power transmission line of the second dc system are bridged at a predetermined crossover point, the first power transmission line and the second power transmission line have the same polarity, and the crossover point is suspended; the device includes: a model building module 81, a simulation module 82 and a processing module 83;

the model establishing module 81 is used for performing single-port Thevenin equivalence on a rectification side and an inversion side of the first direct current system and the second direct current system so as to obtain a homopolar cross-over ungrounded fault model formed by an equivalent circuit of the first direct current system and an equivalent circuit of the second direct current system;

the simulation module 82 is used for performing simulation operation on the homopolar cross-over ungrounded fault model established by the model establishing module 81;

the model establishing module 81 is further configured to obtain a first network topology map and a second network topology map according to a simulation result of the simulation module 82 after the homopolar cross-over ungrounded fault model is subjected to simulation operation; the first network topological graph is a simplified model which comprises a converter station through which current passes and line resistance of a first power transmission line and a second power transmission line when a homopolar cross-over ungrounded fault model fails in a first stage; the second network topological graph is a simplified model which comprises a converter station through which current passes in the first transmission line and the second transmission line and line resistance when the homopolar cross-over ungrounded fault model has a fault at the second stage;

the processing module 83 is configured to establish a first boundary equation set according to a preset rule according to the first network topology map obtained by the model establishing module 81, and establish a second boundary equation set according to a preset rule according to the second network topology map obtained by the model establishing module 81;

the processing module 83 is further configured to obtain a trigger angle value of the converter station in the first network topology diagram and the second network topology diagram obtained by the model establishing module 81 according to a result of simulation operation of the simulation module 82 on the homopolar crossing ungrounded fault model, where the converter station includes a rectifier station and an inverter station;

the model establishing module 81 is further configured to connect the buses of the rectifying side and the inverting side of the first power transmission line and the second power transmission line in the homopolar cross-over ungrounded fault model to ground through the equivalent fault impedance according to the electromechanical transient simulation rule, so as to establish an equivalent model of the homopolar cross-over ungrounded fault;

the processing module 83 is further configured to calculate a value of the fault equivalent impedance of the model of equivalent cross-over ungrounded fault at the first stage according to the trigger angle value of the converter station in the first network topology map, the first boundary equation set, the preset rectifying side equation set and the preset inverting side equation set, where the model is established by the model establishing module 81;

the processing module 83 is further configured to calculate a value of the fault equivalent impedance of the model of equivalent cross-over ungrounded fault in the second stage according to the trigger angle value of the converter station in the second network topology, the second boundary equation set, the preset rectifying side equation set, and the preset inverting side equation set, which are established by the model establishing module 81.

Optionally, the model building module 81 is specifically configured to: performing single-port Thevenin equivalence on the rectification side and the inversion side of the first direct current system and the second direct current system to obtain Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the first direct current system and Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the second direct current system;

Optionally, the simulation module 82 is specifically configured to obtain current simulation curves of all converter stations in the same-polarity cross-over ungrounded fault model after performing simulation operation on the same-polarity cross-over ungrounded fault model established by the model establishing module 81;

the model establishing module 81 is configured to obtain a first network topology map and a second network topology map according to the current simulation curves of all converter stations in the non-grounded fault model crossed by the same polarity, which are obtained by the simulation module 82.

Optionally, the simulation module 82 is configured to obtain a firing angle simulation curve of all converter stations in the same-polarity cross-over ungrounded fault model after performing simulation operation on the same-polarity cross-over ungrounded fault model established by the model establishing module 81;

the processing module 83 is configured to: selecting current simulation curves of the converter stations in the first network topological graph and the second network topological graph from current simulation curves of all converter stations in the homopolar cross-over ungrounded fault model obtained by the simulation module 82, and selecting trigger angle simulation curves of the converter stations in the first network topological graph and the second network topological graph from trigger angle simulation curves of all converter stations in the homopolar cross-over ungrounded fault model;

Optionally, the processing module 83 is specifically configured to: according to a trigger angle value of a converter station, a first boundary equation set, a preset rectifying side equation set and a preset inversion side equation set in a first network topological graph, calculating a voltage value and a current value of a bus corresponding to fault equivalent impedance of a homopolar cross-over ungrounded fault equivalent model established by a model establishing module 81 in the first stage of fault;

Optionally, the processing module 83 is specifically configured to: according to a trigger angle value of the converter station in the second network topological graph, a second boundary equation set, a preset rectifying side equation set and a preset inversion side equation set, calculating a voltage value and a current value of a bus corresponding to the fault equivalent impedance of the equivalent model of the homopolar cross-over ungrounded fault established by the model establishing module 81 in the second stage of fault;

The homopolar crossing fault model building device between the direct current systems provided by the embodiment of the invention comprises: the system comprises a model building module, a simulation module and a processing module; the model establishing module is used for performing single-port Thevenin equivalence on a rectification side and an inversion side of the first direct current system and the second direct current system so as to obtain a homopolar cross-over ungrounded fault model formed by an equivalent circuit of the first direct current system and an equivalent circuit of the second direct current system; the simulation module is used for carrying out simulation operation on the homopolar cross-over ungrounded fault model established by the model establishing module; the model establishing module is also used for acquiring a first network topological graph and a second network topological graph according to a simulation result of the simulation module after the simulation operation of the homopolar cross-over ungrounded fault model; the first network topological graph is a simplified model which comprises a converter station through which current passes and line resistance of a first power transmission line and a second power transmission line when a homopolar cross-over ungrounded fault model fails in a first stage; the second network topological graph is a simplified model which comprises a converter station through which current passes in the first transmission line and the second transmission line and line resistance when the homopolar cross-over ungrounded fault model has a fault at the second stage; the processing module is used for establishing a first boundary equation set according to a preset rule according to the first network topological graph acquired by the model establishing module, and establishing a second boundary equation set according to a preset rule according to the second network topological graph acquired by the model establishing module; the processing module is further used for acquiring trigger angle values of the converter station in the first network topological graph and the second network topological graph acquired by the model establishing module according to the simulation operation result of the simulation module on the homopolar crossing ungrounded fault model, and the converter station comprises a rectifier station and an inverter station; the model establishing module is also used for grounding buses of the rectifying side and the inverting side of the first power transmission line and the second power transmission line in the homopolar cross-over ungrounded fault model through fault equivalent impedance according to an electromechanical transient simulation rule so as to establish a homopolar cross-over ungrounded fault equivalent model; the processing module is further used for calculating the value of the fault equivalent impedance of the model establishing module for establishing the same polarity cross-over ungrounded fault equivalent model in the first stage of fault according to the trigger angle value of the converter station in the first network topological graph, the first boundary equation set, the preset rectifying side equation set and the preset inverting side equation set; the processing module is further used for calculating the value of the fault equivalent impedance of the model establishing module for establishing the same polarity cross-over ungrounded fault equivalent model in the second stage of the fault according to the trigger angle value of the converter station in the second network topological graph, the second boundary equation set, the preset rectifying side equation set and the preset inverting side equation set. Therefore, when the technical scheme provided by the embodiment of the invention is used for establishing an equivalent model for analyzing the homopolar crossing and ungrounded fault between different direct current systems, the homopolar crossing and ungrounded fault model of the direct current transmission system with different voltage levels can be obtained by utilizing thevenin equivalent firstly, then a network topological graph only having line resistance and a converter in each fault stage and a current curve and a trigger angle curve of each converter station in the homopolar crossing and ungrounded fault model are obtained according to a simulation result of the homopolar crossing and ungrounded fault model, and then a boundary equation set related to the current and voltage of the converter station can be obtained according to a preset rule according to the network topological graph, and the trigger angle of the converter station in the network topological graph in each fault stage is obtained according to the current curve and the trigger angle curve; finally, according to the trigger angle of the converter station in the network topological graph of each fault stage, the boundary equation set of each network topological graph, the preset rectifying side equation set and the preset inversion side equation set, calculating to enable the bus of the rectifying side and the inversion side of the bipolar line with the short-circuit fault in the ungrounded fault model crossed in the same polarity to be grounded through fault equivalent impedance according to an electromechanical transient simulation rule so as to obtain the value of the fault equivalent impedance in each fault stage in the equivalent model of the same polarity cross-crossing ungrounded fault which can be used for electromechanical transient simulation; and finally, combining known element parameters obtained from the homopolar cross-over ungrounded fault model and the calculated value of the fault equivalent impedance to obtain a homopolar cross-over ungrounded fault equivalent model for analyzing homopolar cross-over ungrounded faults among different direct current systems.

The steps of a method or algorithm described in connection with the disclosure herein may be embodied in hardware or in software instructions executed by a processor. An embodiment of the present invention further provides a storage medium, where the storage medium may include a memory, and the memory is configured to store computer software instructions for a method for building a homopolar cross-over fault model between dc systems, and the computer software instructions include program codes designed to execute the method for building a homopolar cross-over fault model between dc systems. Specifically, the software instructions may be composed of corresponding software modules, and the software modules may be stored in a Random Access Memory (RAM), a flash Memory, a Read Only Memory (ROM), an Erasable Programmable Read Only Memory (EPROM), an Electrically Erasable Programmable Read Only Memory (EEPROM), a register, a hard disk, a removable hard disk, a compact disc Read Only Memory (CD-ROM), or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. Of course, the storage medium may also be integral to the processor. The processor and the storage medium may reside in an ASIC. Additionally, the ASIC may reside in a core network interface device. Of course, the processor and the storage medium may reside as discrete components in a core network interface device.

The embodiment of the invention also provides a computer program which can be directly loaded into the memory and contains software codes, and the computer program can realize the method for establishing the homopolar cross-over fault model between the direct current systems after being loaded and executed by the computer.

Those skilled in the art will recognize that, in one or more of the examples described above, the functions described in this invention may be implemented in hardware, software, firmware, or any combination thereof. When implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a general purpose or special purpose computer.

The above description is only for the specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method for establishing homopolar cross-over fault model between DC systems is characterized in that,

the direct current system comprises a first direct current system and a second direct current system, the first direct current system is a bipolar two-end direct current power transmission system with a first voltage level, the second direct current system is a bipolar two-end direct current power transmission system with a second voltage level, a first power transmission line of the first direct current system and a second power transmission line of the second direct current system are bridged at a preset crossover point, the first power transmission line and the second power transmission line have the same polarity, and the preset crossover point is suspended; the method comprises the following steps:

carrying out simulation operation on the homopolar crossing ungrounded fault model and acquiring a first network topological graph and a second network topological graph according to the result of the simulation operation of the homopolar crossing ungrounded fault model; the first network topological graph is a simplified model which comprises a converter station through which current passes and line resistance in the first transmission line and the second transmission line when the homopolar cross-over ungrounded fault model has a fault in a first stage; the second network topological graph is a simplified model which comprises a converter station through which current passes in the first transmission line and the second transmission line and line resistance when the homopolar cross-over ungrounded fault model has a fault in a second stage;

establishing a first boundary equation set according to the first network topological graph and a preset rule; establishing a second boundary equation set according to the second network topological graph and a preset rule;

acquiring trigger angle values of converter stations in the first network topological graph and the second network topological graph according to a simulation operation result of the homopolar crossing ungrounded fault model, wherein the converter stations comprise a rectifier station and an inverter station;

grounding buses on rectification sides and inversion sides of the first power transmission line and the second power transmission line in the homopolar cross-over ungrounded fault model through fault equivalent impedance according to an electromechanical transient simulation rule to establish a homopolar cross-over ungrounded fault equivalent model;

calculating the value of the fault equivalent impedance of the homopolar cross-over ungrounded fault equivalent model in the first stage of fault according to a trigger angle value of a converter station in the first network topological graph, the first boundary equation set, a preset rectifying side equation set and a preset inverting side equation set;

and calculating the value of the fault equivalent impedance of the homopolar cross-over ungrounded fault equivalent model in the second stage of fault according to the trigger angle value of the converter station in the second network topological graph, the second boundary equation set, the preset rectifying side equation set and the preset inverting side equation set.

2. The method according to claim 1, wherein the performing single-port Thevenin equivalence on the rectification side and the inversion side of the first DC system and the second DC system to obtain a homopolar cross-over ungrounded fault model formed by an equivalent circuit of the first DC system and an equivalent circuit of the second DC system comprises:

and constructing the homopolar cross-over ungrounded fault model according to the equivalent circuit of the first direct current system and the equivalent circuit of the second direct current system.

3. The method of claim 1, wherein obtaining a first network topology map and a second network topology map from results of a simulation run of the same polarity crossing across ungrounded fault models comprises:

obtaining current simulation curves of all converter stations in the same-polarity cross-over ungrounded fault model after the same-polarity cross-over ungrounded fault model is subjected to simulation operation;

and acquiring the first network topological graph and the second network topological graph according to the current simulation curves of all converter stations in the homopolar crossing ungrounded fault model.

4. The method according to claim 1, wherein said obtaining the firing angle values of the converter stations in the first network topology map and the second network topology map according to the result of the simulation run of the same polarity crossing across the ungrounded fault model comprises:

acquiring trigger angle simulation curves of all converter stations in the same-polarity cross-over ungrounded fault model after the same-polarity cross-over ungrounded fault model is subjected to simulation operation;

selecting current simulation curves of the converter stations in the first network topology diagram and the second network topology diagram from current simulation curves of all converter stations in the same-polarity cross-over ungrounded fault model, and selecting trigger angle simulation curves of the converter stations in the first network topology diagram and the second network topology diagram from trigger angle simulation curves of all converter stations in the same-polarity cross-over ungrounded fault model;

acquiring a first moment when the current is maximum in the time period of the first-stage fault in the current simulation curve of each converter station in the first network topological graph;

selecting all trigger angle values at a first moment in a trigger angle simulation curve of a first converter station in the first network topological graph as the trigger angle values of the first converter station, wherein the first converter station is any one converter station in the first network topological graph;

and selecting all the trigger angle values at the second moment in the trigger angle simulation curve of the second converter station in the second network topology map as the trigger angle values of the second converter station, wherein the second converter station is any converter station in the second network topology map.

5. The method according to claim 1, wherein the calculating the value of the fault equivalent impedance of the homopolar cross-over ungrounded fault equivalent model at the first stage of fault according to the firing angle values of the converter stations in the first network topology map, the first set of boundary equations, the set of preset rectifying side equations and the set of preset inverting side equations comprises:

according to a trigger angle value of a converter station in the first network topological graph, the first boundary equation set, a preset rectifying side equation set and a preset inverting side equation set, calculating a voltage value and a current value of a bus corresponding to the fault equivalent impedance of the homopolar cross-over ungrounded fault equivalent model in the first-stage fault;

and calculating the value of the fault equivalent impedance of the same-polarity cross-over ungrounded fault equivalent model in the first-stage fault according to the voltage value and the current value of the bus corresponding to the fault equivalent impedance of the same-polarity cross-over ungrounded fault equivalent model in the first-stage fault.

6. The method according to claim 1, wherein the calculating the value of the fault equivalent impedance of the homopolar cross-over ungrounded fault equivalent model at the second stage fault according to the firing angle value of the converter station in the second network topology map, the second boundary equation set, the preset rectifying side equation set and the preset inverting side equation set comprises:

according to the trigger angle value of the converter station in the second network topological graph, the second boundary equation set, a preset rectifying side equation set and a preset inverting side equation set, calculating the voltage value and the current value of a bus corresponding to the fault equivalent impedance of the homopolar cross-over ungrounded fault equivalent model in the second-stage fault;

and calculating the value of the equivalent impedance of the fault when the equivalent model of the same polarity cross-over ungrounded fault is in the second stage fault according to the voltage value and the current value of the bus corresponding to the equivalent impedance of the fault when the equivalent model of the same polarity cross-over ungrounded fault is in the second stage fault.

7. A device for establishing homopolar cross-over fault model between DC systems is characterized in that,

the direct current system comprises a first direct current system and a second direct current system, the first direct current system is a bipolar two-end direct current power transmission system with a first voltage level, the second direct current system is a bipolar two-end direct current power transmission system with a second voltage level, a first power transmission line of the first direct current system and a second power transmission line of the second direct current system are bridged at a preset crossover point, the first power transmission line and the second power transmission line have the same polarity, and the preset crossover point is suspended; the device comprises: the system comprises a model building module, a simulation module and a processing module;

the model establishing module is used for performing single-port Thevenin equivalence on the rectification side and the inversion side of the first direct current system and the second direct current system so as to obtain a homopolar cross-over ungrounded fault model formed by an equivalent circuit of the first direct current system and an equivalent circuit of the second direct current system;

the model establishing module is also used for acquiring a first network topological graph and a second network topological graph according to a simulation result of the simulation module after the homopolar cross-over ungrounded fault model is subjected to simulation operation; the first network topological graph is a simplified model which comprises a converter station through which current passes and line resistance in the first transmission line and the second transmission line when the homopolar cross-over ungrounded fault model has a fault in a first stage; the second network topological graph is a simplified model which comprises a converter station through which current passes in the first transmission line and the second transmission line and line resistance when the homopolar cross-over ungrounded fault model has a fault in a second stage;

the processing module is further configured to obtain a trigger angle value of a converter station in the first network topology diagram and the second network topology diagram obtained by the model building module according to a result of simulation operation of the model for the homopolar crossing ungrounded fault by the simulation module, where the converter station includes a rectifier station and an inverter station;

the model establishing module is further used for enabling buses of the rectifying side and the inverting side of the same-polarity cross-over ungrounded fault model to be grounded through equivalent fault impedance according to an electromechanical transient simulation rule so as to establish an equivalent model of the same-polarity cross-over ungrounded fault;

the processing module is further configured to calculate a value of the fault equivalent impedance of the equivalent model of the same polarity cross-over ungrounded fault established by the model establishing module in the first-stage fault according to a trigger angle value of a converter station in the first network topology map, the first boundary equation set, a preset rectifying side equation set and a preset inverting side equation set;

the processing module is further configured to calculate a value of the fault equivalent impedance of the equivalent model of the same polarity cross-over ungrounded fault established by the model establishing module in the second stage of the fault according to the trigger angle value of the converter station in the second network topology, the second boundary equation set, the preset rectifying side equation set and the preset inverting side equation set.

8. The apparatus of claim 7, wherein the model building module is specifically configured to:

9. The apparatus of claim 7,

the simulation module is specifically configured to perform simulation operation on the homopolar crossing ungrounded fault model established by the model establishing module and then obtain current simulation curves of all converter stations in the homopolar crossing ungrounded fault model;

the model establishing module is used for acquiring the first network topological graph and the second network topological graph according to the current simulation curves of all converter stations in the same polarity cross ungrounded fault model acquired by the simulation module.

10. The apparatus of claim 7,

the simulation module is used for carrying out simulation operation on the homopolar crossing ungrounded fault model established by the model establishing module and then acquiring trigger angle simulation curves of all converter stations in the homopolar crossing ungrounded fault model;

the processing module is used for: selecting current simulation curves of the converter stations in the first network topology diagram and the second network topology diagram from current simulation curves of all converter stations in the same polarity cross-over ungrounded fault model acquired by the simulation module, and selecting trigger angle simulation curves of the converter stations in the first network topology diagram and the second network topology diagram from trigger angle simulation curves of all converter stations in the same polarity cross-over ungrounded fault model;

acquiring a first moment when the current is maximum in the time period of the first-stage fault in the current simulation curve of each converter station in the first network topological graph; acquiring a second moment when the current is maximum in the time period of the second-stage fault in the current simulation curve of each converter station in the second network topological graph;

selecting all trigger angle values at a first moment in a trigger angle simulation curve of a first converter station in the first network topological graph as the trigger angle values of the first converter station, wherein the first converter station is any one converter station in the first network topological graph; and selecting all the trigger angle values at the second moment in the trigger angle simulation curve of the second converter station in the second network topology map as the trigger angle values of the second converter station, wherein the second converter station is any converter station in the second network topology map.

11. The apparatus of claim 7, wherein the processing module is specifically configured to:

according to a trigger angle value of a converter station in the first network topological graph, the first boundary equation set, a preset rectifying side equation set and a preset inverting side equation set, calculating a voltage value and a current value of a bus corresponding to the fault equivalent impedance of the homopolar cross-over ungrounded fault equivalent model established by the model establishing module when the first-stage fault occurs;

12. The apparatus of claim 7, wherein the processing module is specifically configured to:

according to the trigger angle value of the converter station in the second network topological graph, the second boundary equation set, a preset rectifying side equation set and a preset inverting side equation set, calculating the voltage value and the current value of a bus corresponding to the fault equivalent impedance when the homopolar cross-over ungrounded fault equivalent model established by the model establishing module fails at the second stage;