CN111799766B - Offshore wind power flexible direct grid-connected overcurrent protection method, system and equipment - Google Patents
Offshore wind power flexible direct grid-connected overcurrent protection method, system and equipment Download PDFInfo
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Abstract
The invention discloses an offshore wind power soft-direct grid-connected over-current protection method, system and equipment. According to the method, the offshore wind power flexible and direct grid-connected system equivalent model is constructed by obtaining system parameters of the offshore wind power flexible and direct grid-connected system, when bipolar short circuit occurs, fault discharge circuits of different types of regions of the offshore wind power flexible and direct grid-connected system equivalent model are analyzed, so that a protection strategy of a blocking current converter is formulated, a current limiting scheme and an overvoltage protection scheme are formulated according to the protection strategy, and finally, a final current limiting scheme and an overvoltage protection scheme are determined by checking. According to the invention, the protection strategy is formulated by constructing the offshore wind power flexible and direct grid-connected system equivalent model, and the coordination among the protection strategy, the current limiting scheme and the overvoltage protection scheme is comprehensively considered, so that the short-circuit current when short-circuit fault occurs can be reduced, and the operation safety and reliability of the offshore wind power flexible and direct grid-connected system are improved.
Description
Technical Field
The invention relates to the field of overcurrent protection, in particular to an offshore wind power flexible-direct grid-connected overcurrent protection method, system and equipment.
Background
Offshore wind power has the advantages of rich wind energy resources, no land resource occupation, higher wind speed, larger single-machine capacity of a wind turbine generator and the like, and becomes an important direction for the development of renewable energy sources of all countries in the world in recent years. Typical wind power plant grid connection modes include a high-voltage alternating current grid connection mode, a high-voltage direct current grid connection mode and a flexible direct current grid connection mode. With the increase of wind power penetration power in a power system, a power grid puts more and more requirements on the design, grid connection and operation of a wind power plant. Direct current transmission technology, especially flexible direct current transmission technology, has been increasingly favored by wind power plants for large-scale long-distance transmission due to its flexible control performance and alternating current-direct current isolation advantages, and has gradually been applied and popularized in offshore wind power projects.
At present, the purpose of protection is mainly realized by configuring a current-limiting reactor for the over-current in the flexible direct current access mode of offshore wind power. However, practical researches find that the overcurrent peak is related to a protection strategy, the size of a current-limiting reactor and an overvoltage protection scheme, and the conventional overcurrent protection scheme does not comprehensively consider the coordination among the overvoltage protection, the overcurrent protection and the protection strategy, so that the overcurrent protection effect is poor.
In summary, in the overcurrent protection scheme in the prior art, coordination among the overvoltage protection, the overcurrent protection, and the protection strategy is not considered comprehensively, and a technical problem that the overcurrent protection effect is poor exists.
Disclosure of Invention
The invention provides an offshore wind power soft-direct grid-connected over-current protection method, system and equipment, which are used for solving the technical problem that an over-current protection effect is poor due to the fact that coordination optimization among over-voltage protection, over-current protection and a protection strategy is not comprehensively considered in an over-current protection scheme in the prior art.
The invention provides an offshore wind power flexible-direct grid-connected over-current protection method, which comprises the following steps of:
s1: acquiring system parameters and an operation mode of the offshore wind power flexible-direct grid-connected system, and constructing an equivalent model of the offshore wind power flexible-direct grid-connected system according to the system parameters and the operation mode;
s2: carrying out region division on the offshore wind power flexible-direct grid-connected system equivalent model to obtain different types of regions;
s3: analyzing fault discharge loops of different types of areas when the offshore wind power flexible-direct grid-connected system has a bipolar short circuit, and formulating a protection strategy for locking the converter according to the fault discharge loops;
s4: obtaining a blocking converter fault discharging loop according to a protection strategy, establishing an equivalent circuit model of the blocking converter fault discharging loop, and formulating a current limiting scheme according to the equivalent circuit model;
s5: making an overvoltage protection scheme according to a protection strategy;
s6: analyzing voltage parameters and current parameters of the offshore wind power flexible and direct grid-connected system equivalent model under different faults after a current limiting scheme and an overvoltage protection scheme are formulated, and judging whether the current limiting scheme and the overvoltage protection scheme meet requirements or not according to the voltage parameters and the current parameters; if the requirements are met, outputting a current limiting scheme and an overvoltage protection scheme; if not, re-executing the steps S3-S6.
Preferably, the system parameters of the offshore wind power flexible-direct grid system comprise external alternating current power grid parameters, direct current side parameters, converter station parameters, transformer parameters, line parameters and lightning arrester parameters.
Preferably, the offshore wind power flexible direct grid system equivalent model adopts a VSC-HVDC system topological structure.
Preferably, the different types of zones comprise ac zones, converter zones, dc line zones, ac line zone faults and wind farm zones.
Preferably, an equivalent circuit model of the blocking converter fault discharging loop is established based on a capacitance-inductance second-order circuit.
Preferably, the current limiting scheme is that a current limiting reactor is configured in a system of the offshore wind power flexible-direct grid-connected system, and parameters of the current limiting reactor are determined.
Preferably, the overvoltage protection scheme is to configure lightning arrester parameters of the offshore wind power flexible direct grid-connected system.
An offshore wind power flexible direct grid-connected overcurrent protection system, comprising: the device comprises an equivalent model building module, a region dividing module, a protection strategy making module, an overvoltage protection scheme making module, a current limiting scheme making module and a checking module;
the equivalent model building module is used for obtaining system parameters and an operation mode of the offshore wind power flexible-direct grid-connected system and building an offshore wind power flexible-direct grid-connected system equivalent model according to the system parameters and the operation mode;
the regional division module is used for carrying out regional division on the offshore wind power flexible-direct grid-connected system equivalent model to obtain different types of regions;
the protection strategy formulation module is used for analyzing fault discharge loops of different types of areas when the offshore wind power flexible-direct grid-connected system has a bipolar short circuit, and formulating a protection strategy for locking the current converter according to the fault discharge loops
The overvoltage protection scheme making module is used for making an overvoltage protection scheme according to the protection strategy;
the current limiting scheme making module is used for obtaining a blocking converter fault discharging circuit according to a protection strategy, establishing an equivalent circuit model of the blocking converter fault discharging circuit, and making a current limiting scheme according to the equivalent circuit model;
the verification module is used for analyzing voltage parameters and current parameters of the offshore wind power flexible-direct grid-connected system equivalent model under different faults after the current limiting scheme and the overvoltage protection scheme are determined, and judging whether the current limiting scheme and the overvoltage protection scheme meet requirements or not according to the voltage parameters and the current parameters; if the requirements are met, outputting a current limiting scheme and an overvoltage protection scheme; and if the requirements are not met, the protection strategy making module, the overvoltage protection scheme making module, the current limiting scheme making module and the verification module are executed again.
Preferably, the system parameters acquired by the equivalent model building module include external ac power grid parameters, dc side parameters, converter station parameters, transformer parameters, line parameters, and arrester parameters.
An offshore wind power flexible direct grid-connected over-current protection device comprises a processor and a memory;
the memory is used for storing program codes and transmitting the program codes to the processor;
the processor is used for executing the offshore wind power flexible direct grid-connected overcurrent protection method according to instructions in the program codes.
According to the technical scheme, the embodiment of the invention has the following advantages:
according to the embodiment of the invention, the offshore wind power flexible and direct grid-connected system equivalent model is constructed by obtaining the system parameters of the offshore wind power flexible and direct grid-connected system, the protection strategy of the blocking current converter is formulated by analyzing the fault discharge loops of different types of regions of the offshore wind power flexible and direct grid-connected system equivalent model when the bipolar short circuit occurs, the current limiting scheme and the overvoltage protection scheme are formulated according to the protection strategy, and finally the final current limiting scheme and the overvoltage protection scheme are determined by checking. According to the invention, the protection strategy is formulated by constructing the offshore wind power flexible and direct grid-connected system equivalent model, and the coordination among the protection strategy, the current limiting scheme and the overvoltage protection scheme is comprehensively considered, so that the short-circuit current when short-circuit fault occurs can be reduced, and the operation safety and reliability of the offshore wind power flexible and direct grid-connected system are improved.
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, and 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 these drawings without inventive exercise.
Fig. 1 is a flowchart of a method for offshore wind power flexible-direct-grid overcurrent protection, system and equipment according to an embodiment of the present invention.
Fig. 2 is a meaning diagram and a region division schematic diagram of an offshore wind power soft-direct grid-connected system equivalent model of the offshore wind power soft-direct grid-connected overcurrent protection, system and equipment provided by the embodiment of the invention.
Fig. 3 is a schematic diagram of three-phase short-circuit faults of an ac system of the offshore wind power flexible-direct-grid overcurrent protection, system and equipment provided by the embodiment of the invention.
Fig. 4 is a schematic diagram of a fault discharge circuit of an ac system during a blocking converter of the offshore wind power flexible-direct-grid overcurrent protection, system and equipment provided by the embodiment of the present invention.
Fig. 5 is an equivalent circuit model of a blocking converter fault discharging circuit of offshore wind power grid overcurrent protection, system and equipment according to an embodiment of the present invention.
Fig. 6 is a schematic view of a system discharge circuit when an arrester of the offshore wind power grid overcurrent protection system and equipment is operated according to an embodiment of the present invention.
Fig. 7 is a schematic view of a lightning arrester configuration scheme of an offshore wind power flexible-direct grid-connected system of the offshore wind power flexible-direct grid-connected overcurrent protection, system and equipment provided by the embodiment of the invention.
Fig. 8 is a system framework diagram of an offshore wind power grid overcurrent protection system and equipment according to an embodiment of the present invention.
Fig. 9 is an equipment framework diagram of an offshore wind power grid overcurrent protection system and equipment according to an embodiment of the present invention.
Detailed Description
The embodiment of the invention provides an offshore wind power soft-direct grid-connected overcurrent protection method, system and equipment, which are used for solving the technical problem that the overcurrent protection effect is poor due to the fact that coordination optimization among overvoltage protection, overcurrent protection and protection strategies is not comprehensively considered in an overcurrent protection scheme in the prior art.
In order to make the objects, features and advantages of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the embodiments described below 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.
Referring to fig. 1, fig. 1 is a flowchart of a method for offshore wind power grid overcurrent protection, system and equipment according to an embodiment of the present invention.
Example 1
As shown in fig. 1, the offshore wind power flexible-direct grid-connected overcurrent protection method provided by the invention comprises the following steps:
s1: the method comprises the steps of obtaining system parameters of the offshore wind power flexible-direct grid-connected system from the offshore wind power flexible-direct grid-connected system, wherein the system parameters comprise external alternating current power grid parameters, direct current side parameters, converter station parameters, transformer parameters, line parameters and lightning arrester parameters, and constructing an equivalent model of the offshore wind power flexible-direct grid-connected system according to the obtained system parameters, so that the offshore wind power flexible-direct grid-connected system can be conveniently analyzed subsequently;
s2: the offshore wind power direct current grid-connected system is complex in structure, and the types and positions of faults which can occur are various, so that the offshore wind power flexible direct grid-connected system equivalent model is subjected to region division according to the structure of the offshore wind power direct current grid-connected system to obtain regions of different types;
s3: when the offshore wind power flexible-direct grid-connected system has a bipolar short circuit, the offshore wind power flexible-direct grid-connected system generates overcurrent due to the fact that line impedance is reduced, different types of regions begin to discharge to a short-circuit point to form a fault discharge loop, and a protection strategy of a blocking converter is formulated by analyzing the fault discharge loop to limit short-circuit overcurrent;
s4: after a protection strategy of the blocking converter is formulated, a blocking converter fault discharging loop is obtained according to the current flow direction after the converter acts blocking, an equivalent circuit model of the blocking converter fault discharging loop is established based on a capacitance-inductance second-order circuit, and a current limiting scheme is formulated according to the equivalent circuit model;
s5: making an overvoltage protection scheme according to a protection strategy; taking the overcurrent of the bridge arm reactor as an example, when the converter is locked, if the lightning arrester is not configured in the system, only the alternating current system discharges to the short-circuit point. After the system is provided with the lightning arrester, overvoltage is generated due to sudden change of current on the bridge arm reactor, the overvoltage causes the lightning arrester to act, and at the moment, the action current of the lightning arrester flows through the bridge arm reactor;
s6: after a current limiting scheme and an overvoltage protection scheme are formulated, voltage parameters and current parameters of an equivalent model of the offshore wind power flexible and direct grid-connected system under different faults are obtained through analysis, and whether the current limiting scheme and the overvoltage protection scheme can meet overcurrent protection requirements or not is judged according to the voltage parameters and the current parameters; if the requirements are met, outputting a current limiting scheme and an overvoltage protection scheme; if the requirement is not met, the steps S3-S6 are executed again until the requirement is met.
Example 2
As shown in fig. 1, the offshore wind power flexible-direct grid-connected overcurrent protection method provided by the invention comprises the following steps:
s1: the method comprises the steps of obtaining system parameters of the offshore wind power flexible-direct grid-connected system from the offshore wind power flexible-direct grid-connected system, wherein the system parameters comprise external alternating current power grid parameters, direct current side parameters, converter station parameters, transformer parameters, line parameters and lightning arrester parameters, and constructing an equivalent model of the offshore wind power flexible-direct grid-connected system according to the obtained system parameters, so that the offshore wind power flexible-direct grid-connected system can be conveniently analyzed subsequently;
wherein, it needs to be further explained that the external ac power grid parameters include: the node is the positive sequence impedance, the negative sequence impedance and the zero sequence impedance of the earth equivalent branch. The direct current side parameters include: dc voltage level, rated current, etc. The converter station parameters include: the current limiting device comprises an MMC rated capacity, a direct current side rated voltage, a direct current side rated current, the number of sub-modules of a bridge arm of the current converter, sub-module capacitors, a bridge arm reactor and a current limiting reactor. The transformer parameters include: transformer type, transformer capacity, voltage rating, short circuit impedance, and grounding scheme. The line parameters include: conductor resistivity and conductor radius. The arrester parameters include: nominal voltage and current-voltage characteristic.
In this embodiment, a topology structure of an equivalent model of an offshore wind power flexible-direct grid-connected system adopts a "two-end hand-in-hand" VSC-HVDC system topology structure, as shown in fig. 2, fans are arranged in a matrix form, power transmitted by the fans is transmitted to an offshore booster station 2 through a section of 35kV medium-voltage cable with a length of 2km, the voltage level is raised to 220kV, the power is transmitted to a flexible direct current converter station 4 of 220kV AC/± 160kV DC through a first coupling transformer 3 to be converted into direct current for transmission, the power is transmitted to a flexible direct current converter station 6 of ± 160kV DC/220kV AC through a high-voltage direct current transmission cable 5 with a length of 28km, and the flexible direct current converter station 7 transmits the power to an external power grid through a second coupling transformer 6.
S2: since the offshore wind power direct current grid-connected system is complex in structure and various in possible fault types and fault positions, the offshore wind power flexible and direct grid-connected system equivalent model is subjected to region division according to the structure of the offshore wind power direct current grid-connected system to obtain different types of regions, and in fig. 2, the offshore wind power flexible and direct grid-connected system equivalent model is divided into an alternating current region, a current converter region, a direct current line region, an alternating current line region fault and a wind power plant region;
s3: when the offshore wind power flexible-direct grid-connected system has a bipolar short circuit, the offshore wind power flexible-direct grid-connected system generates overcurrent due to the fact that line impedance is reduced, different types of regions begin to discharge to a short-circuit point to form a fault discharge loop, and a protection strategy of a blocking converter is formulated by analyzing the fault discharge loop to limit short-circuit overcurrent;
it should be further noted that, for the ac region, as shown in fig. 3, when a three-phase short-circuit fault occurs in the offshore wind power grid-connected system, an overcurrent is generated due to the reduction of the line impedance, u in fig. 3a、ub、ucRespectively representing three-phase voltages; rfAnd LfRespectively representing the resistance and the inductance of a line on the left side of a short-circuit point; r 'and L' represent the line resistance and inductance, respectively, to the right of the short circuit point. For the direct current region, because the converter submodule is provided with the parallel capacitor, when a bipolar short circuit fault occurs at a certain position in the offshore wind power flexible and direct grid-connected system, the parallel capacitor of the converter submodule is rapidly discharged through a short circuit point, and meanwhile, an alternating current system 8 of the offshore wind power flexible and direct grid-connected system also sequentially passes through the equivalent impedance Z of the first connecting transformer 31The bridge arm reactor 9, the anti-parallel diode 10 and the current limiting reactor 11 provide the short-circuit point withShort-circuit current, which causes a large overcurrent in the system, and a fault discharge circuit of the ac system is shown in fig. 4. When the offshore wind power soft and straight grid-connected system has a double-pole short-circuit fault, the parallel capacitors of the converter submodule and the alternating current system 8 can discharge to the short-circuit point, if the converter is locked at the moment, the parallel capacitors of the converter submodule cannot discharge to the short-circuit point, and only the alternating current system 8 discharges to the short-circuit point, so that overcurrent is limited.
S4: after a protection strategy of the blocking converter is formulated, a blocking converter fault discharging loop is obtained according to the current flow direction after the converter acts blocking, an equivalent circuit model of the blocking converter fault discharging loop is established based on a capacitance-inductance second-order circuit, and a current limiting scheme is formulated according to the equivalent circuit model;
fig. 5 is an equivalent circuit model of a blocking converter fault discharging circuit, and the initial conditions of the equivalent circuit model are as follows: u. ofC(0+)＝uC(0-)＝Udc、i(0+)＝i(0-)＝IL(ii) a According to fig. 5, an expression of the converter submodule outlet bipolar short-circuit fault overcurrent can be obtained, as shown in formula (1).
In the formula:
in the formula: u shapedcA direct current voltage representing an equivalent circuit model; l is equivalent inductance of equivalent circuit model, and L is 2L0/3+LMMC，ILThe current of an equivalent inductor of the equivalent circuit model; l is0Being bridge arm reactors, LMMCInductance of the current limiting reactor; c is equivalent capacitance of converter submodule, C is 6C0N, wherein C0The number of the sub-modules is n; reqIs an equivalent resistance of an equivalent circuit model, Req＝RC+RD+RL+RDCB+RfWherein R isCIs the capacitance equivalent resistance, R, of the sub-module of the converterDIs the equivalent resistance, R, of the power electronic device when it is onLIs an equivalent resistance of a current-limiting reactor, RDCBIs an equivalent resistance R when the DC breaker is conductedfIs the equivalent resistance of the short circuit point. β represents a phase angle; ω represents angular frequency; δ represents a constant.
According to the formula (1), increasing the equivalent reactance of the equivalent circuit model has a good current limiting effect. And formulating a current limiting scheme, configuring a current limiting reactor and determining parameters of the current limiting reactor through theoretical calculation and simulation calculation results.
S5: making an overvoltage protection scheme according to a protection strategy; taking the overcurrent of the arm reactor 9 as an example, when the converter is locked, if the arrester 12 is not arranged in the system, only the ac system 8 discharges to the short-circuit point. When the system is equipped with a lightning arrester 12, as shown in fig. 6, u in fig. 6LP、uLNThe voltages at two ends of the bridge arm reactors are respectively shown, the MMC is a modular multilevel converter, overvoltage is generated due to sudden change of current on the bridge arm reactors 9, the overvoltage can cause the lightning arrester 12 to act, at the moment, the action current of the lightning arrester 12 flows through the bridge arm reactors 9, and the action current of the lightning arrester 12 flowing through the bridge arm reactors 9 can not suddenly change and needs to pass through a certain discharging time, so that the current of the bridge arm reactors 9 can be superposed with the discharging current of the alternating current system 8 on the basis of the action current of the lightning arrester 12, and further serious overvoltage is causedCurrent, and therefore, an overvoltage protection scheme needs to be formulated according to a protection strategy;
the overvoltage protection scheme mainly refers to the configuration of the lightning arrester 12, and fig. 7 shows the lightning arrester configuration scheme of the offshore wind power flexible grid-connected system. In fig. 7, a is an a-type arrester which is an ac system side arrester and adopts a 220kV ac system common arrester; a2 is an A2 type arrester used for protecting a bridge arm reactor and the secondary valve side of a connecting transformer and protecting a grounding branch of a winding on the valve side of the connecting transformer; DB is a DB type lightning arrester used for protecting a direct current bus and related equipment and is matched with an A2 type lightning arrester to realize the protection of the converter valve; the DL is a DL-type lightning arrester which is arranged on the side of the direct current line and is used for protecting the direct current bus and related equipment; SR is SR type arrester used for protecting current-limiting reactor, SM is valves submodule piece. The volt-ampere characteristic parameters of different arresters are shown in tables 1 and 2, and the specific configuration can be adjusted according to actual engineering.
TABLE 1
TABLE 2
S6: according to the analysis, the offshore wind power flexible-direct grid-connected system can effectively reduce the overcurrent level after the converter is locked and the current-limiting reactor is configured, and can increase the overcurrent after the lightning arrester is configured. However, in order to limit the overvoltage of the system, the offshore wind power flexible grid-connected system needs to be provided with a lightning arrester to reduce the overvoltage level of a key position. After a current limiting scheme and an overvoltage protection scheme are formulated, voltage parameters and current parameters of an equivalent model of the offshore wind power flexible and direct grid-connected system under different faults are obtained through analysis, and whether the current limiting scheme and the overvoltage protection scheme can meet overcurrent protection requirements or not is judged according to the voltage parameters and the current parameters; if the requirements are met, outputting a current limiting scheme and an overvoltage protection scheme; if the requirement is not met, the steps S3-S6 are executed again until the requirement is met.
Example 3
As shown in fig. 8, an offshore wind power grid overcurrent protection system includes: the protection system comprises an equivalent model building module 201, a region dividing module 202, a protection strategy making module 203, an overvoltage protection scheme making module 204, a current limiting scheme making module 205 and a checking module 206;
the equivalent model building module 201 is used for obtaining system parameters of the offshore wind power flexible-direct grid-connected system and building an offshore wind power flexible-direct grid-connected system equivalent model according to the system parameters;
the region division module 202 is used for performing region division on the offshore wind power flexible-direct grid-connected system equivalent model to obtain different types of regions;
the protection strategy formulation module 203 is used for analyzing fault discharge loops of different types of regions when the offshore wind power flexible-direct grid-connected system has a double-pole short circuit, and formulating a protection strategy for locking the current converter according to the fault discharge loops
The overvoltage protection scheme making module 204 is used for making an overvoltage protection scheme according to the protection strategy;
the current limiting scheme making module 205 is configured to obtain a blocking converter fault discharging circuit according to a protection strategy, establish an equivalent circuit model of the blocking converter fault discharging circuit, and make a current limiting scheme according to the equivalent circuit model;
the checking module 206 is configured to analyze voltage parameters and current parameters of the offshore wind power flexible-direct grid-connected system equivalent model under different faults after the current limiting scheme and the overvoltage protection scheme are determined, and determine whether the current limiting scheme and the overvoltage protection scheme meet requirements according to the voltage parameters and the current parameters; if the requirements are met, outputting a current limiting scheme and an overvoltage protection scheme; and if the requirements are not met, the protection strategy making module, the overvoltage protection scheme making module, the current limiting scheme making module and the verification module are executed again.
As a preferred embodiment, the system parameters obtained by the equivalent model building module 201 include external ac power grid parameters, dc side parameters, converter station parameters, transformer parameters, line parameters, and lightning arrester parameters.
As shown in fig. 9, an offshore wind power grid overcurrent protection apparatus 30 includes a processor 300 and a memory 301;
the memory 301 is used for storing a program code 302 and transmitting the program code 302 to the processor;
the processor 300 is configured to execute the steps of a offshore wind power grid overcurrent protection method as described above according to the instructions in the program code 302.
Illustratively, the computer program 302 may be partitioned into one or more modules/units that are stored in the memory 301 and executed by the processor 300 to accomplish the present application. The one or more modules/units may be a series of computer program instruction segments capable of performing specific functions, which are used to describe the execution process of the computer program 302 in the terminal device 30.
The terminal device 30 may be a desktop computer, a notebook, a palm computer, a cloud server, or other computing devices. The terminal device may include, but is not limited to, a processor 300, a memory 301. Those skilled in the art will appreciate that fig. 9 is merely an example of a terminal device 30 and does not constitute a limitation of terminal device 30 and may include more or fewer components than shown, or some components may be combined, or different components, e.g., the terminal device may also include input-output devices, network access devices, buses, etc.
The Processor 300 may be a Central Processing Unit (CPU), other general purpose Processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), an off-the-shelf ProgrammaBle Gate Array (FPGA) or other ProgrammaBle logic device, discrete Gate or transistor logic, discrete hardware components, etc. A general purpose processor may be a microprocessor or the processor may be any conventional processor or the like.
The storage 301 may be an internal storage unit of the terminal device 30, such as a hard disk or a memory of the terminal device 30. The memory 301 may also be an external storage device of the terminal device 30, such as a plug-in hard disk, a Smart Media Card (SMC), a Secure Digital (SD) Card, a Flash memory Card (Flash Card), and the like, which are provided on the terminal device 30. Further, the memory 301 may also include both an internal storage unit and an external storage device of the terminal device 30. The memory 301 is used for storing the computer program and other programs and data required by the terminal device. The memory 301 may also be used to temporarily store data that has been output or is to be output.
It is clear to those skilled in the art that, for convenience and brevity of description, the specific working processes of the above-described systems, apparatuses and units may refer to the corresponding processes in the foregoing method embodiments, and are not described herein again.
In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus and method may be implemented in other manners. For example, the above-described apparatus embodiments are merely illustrative, and for example, the division of the units is only one logical division, and other divisions may be realized in practice, for example, a plurality of units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or units, and may be in an electrical, mechanical or other form.
The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.
In addition, functional units in the embodiments of the present invention may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit. The integrated unit can be realized in a form of hardware, and can also be realized in a form of a software functional unit.
The integrated unit, if implemented in the form of a software functional unit and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present invention may be embodied in the form of a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present invention. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk, and other various media capable of storing program codes.
The above-mentioned embodiments are only used for illustrating the technical solutions of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (9)
1. The over-current protection method for the offshore wind power flexible direct grid-connected system is characterized by comprising the following steps of:
s1: acquiring system parameters and an operation mode of the offshore wind power flexible-direct grid-connected system, and constructing an equivalent model of the offshore wind power flexible-direct grid-connected system according to the system parameters and the operation mode;
s2: carrying out region division on the offshore wind power flexible-direct grid-connected system equivalent model to obtain different types of regions;
s3: analyzing fault discharge loops of different types of areas when the offshore wind power flexible-direct grid-connected system has a bipolar short circuit, and formulating a protection strategy for locking the converter according to the fault discharge loops;
s4: obtaining a blocking converter fault discharging loop according to a protection strategy, establishing an equivalent circuit model of the blocking converter fault discharging loop, and formulating a current limiting scheme according to the equivalent circuit model, wherein the equivalent circuit model of the blocking converter fault discharging loop specifically comprises the following steps:
the initial conditions of the equivalent circuit model are: u. ofC(0+)＝uC(0-)＝Udc、i(0+)＝i(0-)＝IL；
The expression of the over-current of the bipolar short-circuit fault at the outlet of the submodule of the converter is as follows:
in the formula:
in the formula: u shapedcA direct current voltage representing an equivalent circuit model; l is equivalent inductance of equivalent circuit model, and L is 2L0/3+LMMC，ILThe current of an equivalent inductor of the equivalent circuit model; l is0Being bridge arm reactors, LMMCInductance of the current limiting reactor; c is equivalent capacitance of converter submodule, C is 6C0N, wherein C0The number of the sub-modules is n; reqIs an equivalent resistance of an equivalent circuit model, Req＝RC+RD+RL+RDCB+RfWherein R isCIs the capacitance equivalent resistance, R, of the sub-module of the converterDIs the equivalent resistance, R, of the power electronic device when it is onLIs an equivalent resistance of a current-limiting reactor, RDCBIs an equivalent resistance R when the DC breaker is conductedfIs the equivalent resistance of the short circuit point; β represents a phase angle; ω represents angular frequency; δ represents a constant;
s5: an overvoltage protection scheme is formulated according to a protection strategy, wherein the overvoltage protection scheme is to configure lightning arrester parameters of an offshore wind power flexible and straight grid-connected system;
s6: analyzing voltage parameters and current parameters of the offshore wind power flexible and direct grid-connected system equivalent model under different faults after a current limiting scheme and an overvoltage protection scheme are formulated, and judging whether the current limiting scheme and the overvoltage protection scheme meet requirements or not according to the voltage parameters and the current parameters; if the requirements are met, outputting a current limiting scheme and an overvoltage protection scheme; if not, re-executing the steps S3-S6.
2. The offshore wind power flexible-direct-grid overcurrent protection method according to claim 1, wherein the system parameters of the offshore wind power flexible-direct-grid system comprise external alternating current grid parameters, direct current side parameters, converter station parameters, transformer parameters, line parameters and arrester parameters.
3. The offshore wind power flexible direct networking overcurrent protection method according to claim 1, wherein the offshore wind power flexible direct networking system equivalent model adopts a VSC-HVDC system topology structure.
4. The offshore wind power grid overcurrent protection method according to claim 1, wherein the different types of regions include an ac region, a converter region, a dc link region, an ac link region fault, and a wind farm region.
5. The offshore wind power flexible-direct-grid overcurrent protection method according to claim 1, wherein an equivalent circuit model of a blocking converter fault discharge circuit is established based on a capacitance-inductance second-order circuit.
6. The offshore wind power flexible direct grid-connected over-current protection method according to claim 1, wherein the current limiting scheme is that a current limiting reactor is configured in a system of the offshore wind power flexible direct grid-connected system, and parameters of the current limiting reactor are determined.
7. The utility model provides a gentle straight grid-connected overcurrent protection system of offshore wind power which characterized in that includes: the device comprises an equivalent model building module, a region dividing module, a protection strategy making module, an overvoltage protection scheme making module, a current limiting scheme making module and a checking module;
the equivalent model building module is used for obtaining system parameters and an operation mode of the offshore wind power flexible-direct grid-connected system and building an offshore wind power flexible-direct grid-connected system equivalent model according to the system parameters and the operation mode;
the regional division module is used for carrying out regional division on the offshore wind power flexible-direct grid-connected system equivalent model to obtain different types of regions;
the protection strategy making module is used for analyzing fault discharge circuits of different types of regions when the offshore wind power flexible-direct grid-connected system has a bipolar short circuit, and making a protection strategy for locking the current converter according to the fault discharge circuits;
the overvoltage protection scheme making module is used for making an overvoltage protection scheme according to the protection strategy;
the current limiting scheme making module is used for obtaining a blocking converter fault discharging loop according to a protection strategy, establishing an equivalent circuit model of the blocking converter fault discharging loop, and making a current limiting scheme according to the equivalent circuit model, wherein the equivalent circuit model of the blocking converter fault discharging loop specifically comprises the following steps:
the initial conditions of the equivalent circuit model are: u. ofC(0+)＝uC(0-)＝Udc、i(0+)＝i(0-)＝IL；
The expression of the over-current of the bipolar short-circuit fault at the outlet of the submodule of the converter is as follows:
in the formula:
in the formula: u shapedcA direct current voltage representing an equivalent circuit model; l is equivalent inductance of equivalent circuit model, and L is 2L0/3+LMMC，ILIs equivalent electricityThe current of the equivalent inductance of the path model; l is0Being bridge arm reactors, LMMCInductance of the current limiting reactor; c is equivalent capacitance of converter submodule, C is 6C0N, wherein C0The number of the sub-modules is n; reqIs an equivalent resistance of an equivalent circuit model, Req＝RC+RD+RL+RDCB+RfWherein R isCIs the capacitance equivalent resistance, R, of the sub-module of the converterDIs the equivalent resistance, R, of the power electronic device when it is onLIs an equivalent resistance of a current-limiting reactor, RDCBIs an equivalent resistance R when the DC breaker is conductedfIs the equivalent resistance of the short circuit point; β represents a phase angle; ω represents angular frequency; δ represents a constant;
the verification module is used for analyzing voltage parameters and current parameters of the offshore wind power flexible-direct grid-connected system equivalent model under different faults after the current limiting scheme and the overvoltage protection scheme are determined, and judging whether the current limiting scheme and the overvoltage protection scheme meet requirements or not according to the voltage parameters and the current parameters; if the requirements are met, outputting a current limiting scheme and an overvoltage protection scheme; and if the requirements are not met, the protection strategy making module, the overvoltage protection scheme making module, the current limiting scheme making module and the verification module are executed again.
8. The offshore wind power flexible-direct-grid overcurrent protection system according to claim 7, wherein the system parameters obtained by the equivalent model building module include external alternating current grid parameters, direct current side parameters, converter station parameters, transformer parameters, line parameters, and arrester parameters.
9. The over-current protection equipment for the offshore wind power flexible direct grid-connected system is characterized by comprising a processor and a memory;
the memory is used for storing program codes and transmitting the program codes to the processor;
the processor is used for executing the offshore wind power flexible direct grid-connected overcurrent protection method according to any one of claims 1 to 6 according to instructions in the program code.
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