CN109217337A - A kind of isolated island detection of four ends DC distribution net and stable control method - Google Patents

A kind of isolated island detection of four ends DC distribution net and stable control method Download PDF

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CN109217337A
CN109217337A CN201811201999.0A CN201811201999A CN109217337A CN 109217337 A CN109217337 A CN 109217337A CN 201811201999 A CN201811201999 A CN 201811201999A CN 109217337 A CN109217337 A CN 109217337A
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circuit breaker
bus
transformer
voltage
island
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CN109217337B (en
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宋伟伟
张勇军
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South China University of Technology SCUT
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South China University of Technology SCUT
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/001—Methods to deal with contingencies, e.g. abnormalities, faults or failures
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/28—Arrangements for balancing of the load in a network by storage of energy
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/36—Arrangements for transfer of electric power between AC networks via a high-tension DC link
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/48—Controlling the sharing of the in-phase component
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/388—Islanding, i.e. disconnection of local power supply from the network
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Supply And Distribution Of Alternating Current (AREA)

Abstract

本发明公开了一种四端直流配电网的孤岛检测和稳定控制方法，包括步骤：1)基于开关状态组合的孤岛检测主判据；2)基于无流‑压差复合的孤岛检测辅助判据；3)基于直流变压器和储能协同控制的孤岛稳定控制。本发明将基于开关状态组合的主判据和基于无流‑压差复合的辅助判据相结合，对四端直流配电网的孤岛进行检测，并设计成孤岛检测器；当孤岛检测器检测到孤岛后，对T3的直流变压器和储能进行控制方式的切换，实现孤岛的稳定控制，从而维持整个孤岛电网的稳定运行。

The invention discloses an islanding detection and stability control method for a four-terminal direct current distribution network, comprising the steps of: 1) a main criterion for islanding detection based on switch state combination; 2) an auxiliary islanding detection criterion based on no-current-voltage difference combination 3) Island stability control based on the coordinated control of DC transformer and energy storage. The invention combines the main criterion based on switch state combination and the auxiliary criterion based on no-current-voltage difference combination to detect the islanding of the four-terminal DC distribution network, and is designed as an islanding detector; when the islanding detector detects After reaching the island, the control mode of the DC transformer and energy storage of T3 is switched to realize the stable control of the island, thereby maintaining the stable operation of the entire island grid.

Description

A kind of isolated island detection of four ends DC distribution net and stable control method
Technical field
The present invention relates to the technical field of DC distribution net, refer in particular to a kind of four end DC distribution nets isolated island detection and Stable control method.
Background technique
Compared with AC distribution net, direct-flow distribution system have can smoothly access various distributed generation resources, realization on the spot The Electromagnetic coupling of more power supplys neatly carries out two-way flow and control, improvement user side power quality, the isolation system of active power The series of advantages such as failure of uniting.Therefore, the research of direct-flow distribution system has important social effect and broad application prospect.
Currently, for DC distribution net research still in its infancy, be concentrated mainly on DC distribution net topology knot On structure and control method, rarely has research to the isolated island detection and stability contorting aspect of DC distribution net.So-called island phenomenon refers to: When micro-capacitance sensor disconnects due to failure accident or power failure maintenance from alternating-current system, distributed generation resource fails to detect to stop immediately Electricity, and continue the state of power supply.When isolated island once generating the safety that will jeopardize power grid transmission line road maintenance personal；Influence is matched The operation program of protective switch in electric system impacts electric network protection device；Transmission power quality is influenced, electric power isolated island region Supply voltage will be unstable.In addition, making DC distribution netting gear for isolated island mould due to having accessed distributed generation resource, especially energy storage Formula service ability.And in the operation of four end DC distribution nets, for the power supply reliability for enhancing important load, both-end or single-ended can be used Power supply.But in failure or maintenance, for the uninterrupted power supply for guaranteeing important load, island mode operation can switch to, by being distributed Formula power supply or energy storage for power supply.Therefore, study four end DC distribution nets isolated island detection and stability contorting to improve its safety and Power supply reliability is significant.
The isolated island that the present invention provides a kind of four end DC distribution nets detects and stable control method.It is based on firstly, proposing The main criterion of Switch State Combination in Power Systems and the isolated island method for comprehensive detection combined based on the compound assistant criteria of no stream-pressure difference, Under dc circuit breaker communication delay or failure and the special operation condition of four end direct current distribution active power balances, the standard to isolated island is realized Really detection.Meanwhile a kind of isolated island Stable Control Strategy based on commutator transformer and energy storage Collaborative Control is devised, remain entire The stable operation of island-grid.In addition, using commutator transformer and energy storage scale parameter difference and determine DC voltage and refer to It is worth the method for slope variation, solves the problems, such as commutator transformer DC low-voltage side voltage big ups and downs in handoff procedure.
Summary of the invention
The purpose of the present invention is to overcome the shortcomings of the existing technology and deficiency, proposes a kind of orphan of four end DC distribution nets Island detection and stable control method.For without frequency term, and traditional island detection method needs to detect frequency term in direct current signal, Breaking through traditional isolated island detection mode can not apply the four end DC distribution nets the shortcomings that, propose a kind of based on Switch State Combination in Power Systems Main criterion and the isolated island method for comprehensive detection that is combined based on the compound assistant criteria of no stream-pressure difference.The island detection method Under the special operation condition of dc circuit breaker communication delay or failure and four end direct current distribution active power balances, realize to isolated island Accurate detection.A kind of isolated island Stable Control Strategy based on commutator transformer and energy storage Collaborative Control has also been devised in the present invention, when When detecting that isolated island occurs, commutator transformer and the energy storage energy mode of switching control in time, to maintain the steady of entire island-grid Fixed operation.In addition, utilizing commutator transformer and energy storage ratio parameter differences and the side for determining direct voltage reference value slope variation Method solves the problems, such as commutator transformer DC low-voltage side voltage big ups and downs in handoff procedure.
To achieve the above object, a kind of technical solution provided by the present invention are as follows: isolated island detection of four end DC distribution nets And stable control method, the four ends DC distribution net include the first AC network ACgrid1, the second AC network ACgrid2, First AC circuit breaker ACCB1, the second AC circuit breaker ACCB2, the first dc circuit breaker DCCB1, the second dc circuit breaker DCCB2, third dc circuit breaker DCCB3, the 4th dc circuit breaker DCCB4, the 5th dc circuit breaker DCCB5, the 6th direct current are disconnected Road device DCCB6, the 7th dc circuit breaker DCCB7, the 8th dc circuit breaker DCCB8, the first DC line L1, the second DC line L2, third DC line L3, the first DC bus #1, the second DC bus #2, third DC bus #3, the 4th DC bus # 4, how electric the 5th DC bus #5, the first ac bus #6, the second ac bus #7, third ac bus #8, the first modularization be Level voltage source code converter MMC-VSC1, the second modular multilevel voltage source type converter MMC-VSC2, commutator transformer DCSST, third modular multilevel voltage source type converter MMC-VSC3, DC/DC converter, two-way DC/DC converter, light Volt, energy storage, AC load, synchronous generator, the first transformer TM1, the second transformer TM2, third transformer TM3；Wherein, institute The exchange side of the first modular multilevel voltage source type converter MMC-VSC1 is stated successively through the first AC circuit breaker ACCB1, One ac bus #6, the first transformer TM1 are connect with the first AC network ACgrid1, and DC side is successively disconnected through the first direct current Road device DCCB1, the first DC bus #1, the second dc circuit breaker DCCB2, the first DC line L1, the 5th dc circuit breaker DCCB5, third DC bus #3 are connect with the high-pressure side of commutator transformer DCSST；The second modular multilevel voltage source The exchange side of code converter MMC-VSC2 is successively through the second AC circuit breaker ACCB2, the second ac bus #7, the second transformer TM2 is connect with the second AC network ACgrid2, and DC side is successively through third dc circuit breaker DCCB3, the second DC bus # 2, the 4th dc circuit breaker DCCB4, the second DC line L2, the 8th dc circuit breaker DCCB8, the 4th DC bus #4 and third The DC side of modular multilevel voltage source type converter MMC-VSC3 connects；The photovoltaic is successively through DC/DC converter, the 5th DC bus #5 is connect with the low-pressure side of commutator transformer DCSST；The energy storage is female through two-way DC/DC converter and the 5th direct current Line #5 connection；The AC load is successively through third ac bus #8, third transformer TM3 and third modular multilevel voltage The exchange side of source code converter MMC-VSC3 connects；The synchronous generator is connect with third ac bus #8；The third is straight It is successively straight through the 6th dc circuit breaker DCCB6, third DC line L3, the 7th dc circuit breaker DCCB7 and the 4th to flow bus #3 Flow bus #4 connection；The first AC network ACgrid1, the first transformer TM1, the first ac bus #6, the first exchange are disconnected Road device ACCB1 and the first modular multilevel voltage source type converter MMC-VSC1 constitutes first port circuit T1；Described second AC network ACgrid2, the second transformer TM2, the second ac bus #7, the second AC circuit breaker ACCB2 and the second modularization Multi-level voltage source code converter MMC-VSC2 constitutes second port circuit T2；The commutator transformer DCSST, the 5th direct current are female Line #5, DC/DC converter, two-way DC/DC converter, photovoltaic and energy storage constitute third port circuit T3；The third modularization Multi-level voltage source code converter MMC-VSC3, third transformer TM3, third ac bus #8, AC load and synchronous generator Mechanism is at the 4th port circuit T4；
The isolated island detection and stable control method, comprising the following steps:
1) isolated island based on Switch State Combination in Power Systems detects main criterion: the switch by judging dc circuit breaker on DC line Combinations of states, whether there is or not the generations of isolated island for four end DC distribution nets of detection；
2) assistant criteria is detected based on the compound isolated island of no stream-pressure difference: by judging there is no current on dc circuit breaker, and It whether there is voltage difference on corresponding DC bus, deposited in dc circuit breaker communication failure or delay and four end DC distribution nets In active power balance, whether there is or not the generations of isolated island for four end DC distribution nets of detection；
3) the isolated island stability contorting based on commutator transformer and energy storage Collaborative Control: when detecting that isolated island occurs, direct current Transformer and the energy storage energy mode of switching control in time, to maintain the stable operation of entire isolated island.
In step 1), by judging dc circuit breaker DCCB2, DCCB5 and DCCB4, the Switch State Combination in Power Systems of DCCB8, And then identify whether T3 and T4 is in island mode, comprising the following steps:
1.1) defining converter station and receiving the switching signal of 8 dc circuit breakers of system is respectively s1、s2、s3、s4、s5、s6、s7 And s8, and the switch function for defining dc circuit breaker is as follows:
In formula, x indicates the number 1,2,3,4,5,6,7 and 8 of dc circuit breaker, works as sxWhen being 0, indicate that dc circuit breaker closes It closes, works as sxWhen being 1, indicate that dc circuit breaker disconnects；
1.2) DCCB is definedstateIt is the isolated island criterion of the dc circuit breaker by Switch State Combination in Power Systems as a result, based on by following formula It obtains:
DCCBstate=(s2∪s5)∩(s4∪s8)
Work as DCCBstateWhen=0, indicate that there is no isolated islands；Work as DCCBstateWhen=1, indicate that isolated island occurs；When DCCBstateWhen=null, indicate that the switch state of dc circuit breaker can not obtain.
In step 2), the assistant criteria compound based on no stream-pressure difference is proposed, with settlement steps to deal 1) in dc circuit breaker The problem of switch state can not obtain, comprising the following steps:
2.1) without stream criterion: when T3 and T4 is detached from T1 and T2 simultaneously, and forms isolated island, due to opening for dc circuit breaker Off status can not be detected accurately, can be by judging have on dc circuit breaker DCCB2 or DCCB5 and DCCB4 or DCCB8 No current, and then judge whether T3 and T4 is in island mode；
Define Il1For the electric current for flowing through DC line L1；Il2For the electric current for flowing through DC line L2；
In one detection cycle, no stream criterion value calculation formula is shown below:
In formula, t0The time started is detected for isolated island；T is the detection sampling period；ΔIl1For I in detection cycle Tl1Absolute value The sum of；ΔIl2For I in detection cycle Tl2The sum of absolute value；
When the active power definite value of the second modular multilevel voltage source type converter MMC-VSC2 in T2 is arranged to When zero or T2 is disconnected, the active power of T3 and T4 are cancelled out each other, and the system running state defined at this time is active power balance State；
It is shown below without stream criterion:
In formula, Δ Il1、ΔIl2Respectively DC line L1 and DC line L2 without stream criterion value；Imax1、Imax2To have When function power-balance state, the maximum current of dc circuit breaker DCCB2, DCCB4 are flowed through；
2.2) pressure difference criterion: when active power balance state, although above-mentioned criterion is set up, T3, T4 still are able to be in Networked mode increases the assistant criteria of " pressure difference " to avoid judging by accident；
Define Udc1For the voltage value of DC bus #1, Udc2For the voltage value of DC bus #2, Udc3For DC bus #3's Voltage value, Udc4For the voltage value of DC bus #4；
By detecting Udc1And Udc3Difference in voltage and Udc2And Udc4Difference in voltage as without stream criterion assistant criteria, Judge whether system is in island mode, pressure difference criterion value Δ Udc1、ΔUdc2Calculation formula be shown below:
In formula, t0The time started is detected for isolated island；T is the detection sampling period；ΔUdc1For Udc1And Udc3Between pressure difference sentence According to value；ΔUdc2For Udc2And Udc4Between pressure difference criterion value；
Pressure difference criterion is shown below:
In formula, Δ Umax1For the U under active power balance statedc1And Udc3Maximum value of the difference in detection cycle T；Δ Umax2For the U under active power balance statedc2And Udc4Maximum value of the difference in detection cycle T；
The isolated island method for comprehensive detection combined according to main criterion and assistant criteria, obtains the process of the island detection method Figure, and it is designed to isolated island detector.
In step 3), the isolated island detector designed first by step 1) and 2) detects isolated island signal, to direct current transformation Device and energy storage carry out the stability contorting of isolated island, and the realization of stability contorting has following steps:
3.1) commutator transformer of T3 is under networked mode, using determining DC low-voltage side voltage UdclvControl mode, as DC low-voltage side active power balance node, i.e. PV node, the fluctuation for allowing photovoltaic to generate；When isolated island detector detects isolated island When generation, since the T1 and T2 of four end DC distribution nets at this time are all exited, commutator transformer is using determining high direct voltage side voltage UdchvControl mode, as the active power balance node of isolated island, i.e. PV node；
3.2) the two-way DC/DC converter of the energy storage of T3 is under networked mode, using determining active-power PESControl mode, both It can work in constant charging and discharging state, also be capable of the output of the active power of tracing compensation photovoltaic, so that photovoltaic and energy storage The output summation of active power be in stable state, easily meet the requirement of scheduling；When isolated island detector detects isolated island When generation, the two-way DC/DC converter of energy storage, which uses, determines DC low-voltage side voltage UdclvControl mode has as DC low-voltage side Function power-balance node, i.e. PV node control commutator transformer DC low-voltage side voltage, to maintain the stable operation of isolated island；
3.3) when networked mode is transferred to island mode, direct current transformer and energy storage switching control mode, since direct current becomes Influence of the variation of depressor high direct voltage side voltage to DC low-voltage side voltage and active power is very big, in design commutator transformer When controlling with the island mode of energy storage, it is designed the voltage-controlled scale parameter in DC low-voltage side of determining of energy storage to compare direct current transformation It is big that device determines the voltage-controlled scale parameter in high direct voltage side；In addition, commutator transformer determines the voltage-controlled electricity in high direct voltage side Pressure reference value is designed to slope variation to 1Pu, to solve voltage violent wave in commutator transformer DC low-voltage side in handoff procedure Dynamic problem.
Compared with prior art, the present invention have the following advantages that with the utility model has the advantages that
1, present invention firstly provides and realize the isolated island detections of four end DC distribution nets, detect in the detection method Without frequency term in signal, and traditional island detection method needs to detect frequency term, thus breach traditional isolated island detection mode without Method is applied the four end DC distribution nets the shortcomings that.
2, the present invention is realized the main criterion based on Switch State Combination in Power Systems for the first time and is sentenced based on the compound auxiliary of no stream-pressure difference According to the isolated island method for comprehensive detection combined, the isolated island of four end DC distribution nets is broken through in dc circuit breaker communication delay or failure When be difficult to the shortcomings that detecting.
3, the present invention is realized the main criterion based on Switch State Combination in Power Systems for the first time and is sentenced based on the compound auxiliary of no stream-pressure difference According to the isolated island method for comprehensive detection combined, this method can accurately identify the special of four end DC distribution net active power balances Isolated island under operating condition realizes the accurate detection to isolated island.
4, the present invention devises a kind of isolated island Stable Control Strategy based on commutator transformer and energy storage Collaborative Control, works as inspection When measuring isolated island generation, commutator transformer and the energy storage energy mode of switching control in time, to maintain the stabilization of entire island-grid Operation.
5, the present invention using commutator transformer and energy storage ratio parameter differences and determines direct voltage reference value in design The method of slope variation solves the problems, such as commutator transformer DC low-voltage side voltage big ups and downs in handoff procedure.
6, the method for the present invention has extensive use space, operation letter in the detection of DC distribution net isolated island and stability contorting It is single, adaptable, there are bright prospects in the stability and reliability for improving DC distribution net.
Detailed description of the invention
Fig. 1 is the structure chart of four end DC distribution nets of the invention.
Fig. 2 is the structure chart of island mode of the invention.
Fig. 3 is the main criterion and the assistant criteria phase compound based on no stream-pressure difference of the invention based on Switch State Combination in Power Systems In conjunction with isolated island method for comprehensive detection flow chart.
Fig. 4 is the pattern switching figure of commutator transformer of the invention under the control of isolated island detector.
Fig. 5 is the pattern switching figure of energy storage of the invention under the control of isolated island detector.
Fig. 6 is the system construction drawing that the present invention is built on RTDS emulation platform.
Fig. 7 is one of RTDS analogous diagram of the invention.
Fig. 8 is the two of RTDS analogous diagram of the invention.
Specific embodiment
The present invention is further explained in the light of specific embodiments.
The isolated island of four end DC distribution nets provided by the present embodiment detects and stable control method, in RTDS emulation platform On be achieved, as shown in Figure 1, the four ends DC distribution net include the first AC network ACgrid1, the second AC network ACgrid2, the first AC circuit breaker ACCB1, the second AC circuit breaker ACCB2, the first dc circuit breaker DCCB1, the second direct current Breaker DCCB2, third dc circuit breaker DCCB3, the 4th dc circuit breaker DCCB4, the 5th dc circuit breaker DCCB5, the 6th Dc circuit breaker DCCB6, the 7th dc circuit breaker DCCB7, the 8th dc circuit breaker DCCB8, the first DC line L1, second are directly Flow Line L2, third DC line L3, the first DC bus #1, the second DC bus #2, third DC bus #3, the 4th direct current Bus #4, the 5th DC bus #5, the first ac bus #6, the second ac bus #7, third ac bus #8, the first modularization Multi-level voltage source code converter MMC-VSC1, the second modular multilevel voltage source type converter MMC-VSC2, direct current transformation Device DCSST, third modular multilevel voltage source type converter MMC-VSC3, DC/DC converter, two-way DC/DC converter, light Volt, energy storage, AC load, synchronous generator, the first transformer TM1, the second transformer TM2, third transformer TM3；Wherein, institute The exchange side of the first modular multilevel voltage source type converter MMC-VSC1 is stated successively through the first AC circuit breaker ACCB1, One ac bus #6, the first transformer TM1 are connect with the first AC network ACgrid1, and DC side is successively disconnected through the first direct current Road device DCCB1, the first DC bus #1, the second dc circuit breaker DCCB2, the first DC line L1, the 5th dc circuit breaker DCCB5, third DC bus #3 are connect with the high-pressure side of commutator transformer DCSST；The second modular multilevel voltage source The exchange side of code converter MMC-VSC2 is successively through the second AC circuit breaker ACCB2, the second ac bus #7, the second transformer TM2 is connect with the second AC network ACgrid2, and DC side is successively through third dc circuit breaker DCCB3, the second DC bus # 2, the 4th dc circuit breaker DCCB4, the second DC line L2, the 8th dc circuit breaker DCCB8, the 4th DC bus #4 and third The DC side of modular multilevel voltage source type converter MMC-VSC3 connects；The photovoltaic is successively through DC/DC converter, the 5th DC bus #5 is connect with the low-pressure side of commutator transformer DCSST；The energy storage is female through two-way DC/DC converter and the 5th direct current Line #5 connection；The AC load is successively through third ac bus #8, third transformer TM3 and third modular multilevel voltage The exchange side of source code converter MMC-VSC3 connects；The synchronous generator is connect with third ac bus #8；The third is straight It is successively straight through the 6th dc circuit breaker DCCB6, third DC line L3, the 7th dc circuit breaker DCCB7 and the 4th to flow bus #3 Flow bus #4 connection；The first AC network ACgrid1, the first transformer TM1, the first ac bus #6, the first exchange are disconnected Road device ACCB1 and the first modular multilevel voltage source type converter MMC-VSC1 constitutes first port circuit T1；Described second AC network ACgrid2, the second transformer TM2, the second ac bus #7, the second AC circuit breaker ACCB2 and the second modularization Multi-level voltage source code converter MMC-VSC2 constitutes second port circuit T2；The commutator transformer DCSST, the 5th direct current are female Line #5, DC/DC converter, two-way DC/DC converter, photovoltaic and energy storage constitute third port circuit T3；The third modularization Multi-level voltage source code converter MMC-VSC3, third transformer TM3, third ac bus #8, AC load and synchronous generator Mechanism is at the 4th port circuit T4.
The isolated island of four end DC distribution nets described in the present embodiment detects and stable control method, concrete condition are as follows:
1) structure that four end DC distribution nets have been built in RTDS emulation platform is as shown in Figure 6.It is each to hold in simulation process Parameter and control mode it is as shown in table 1:
1 four end DC distribution net major parameter of table and operational mode
For four end DC distribution nets in networked mode, the MMC-VSC1 of T1, which is used, determines DC voltage and reactive power (Udc- Q) control mode；The MMC-VSC2 of T2, which is used, determines active power and reactive power (P-Q) control mode；The commutator transformer of T3 is adopted With DC low-voltage side voltage control mode is determined, energy storage uses maximal power tracing using active power controller mode, photovoltaic is determined (MPPT) control mode；The MMC-VSC3 at the end T4 is using frequency and alternating voltage (V-F) control mode is determined, with engine alternator It is operated with AC load.Under island mode, T1 and T2 are exited；The commutator transformer of T3 is controlled using high direct voltage side voltage is determined Mode, energy storage control the DC low-voltage side voltage of commutator transformer, photovoltaic is still using DC low-voltage side voltage control mode is determined Using maximal power tracing (MPPT) control mode；The control mode of T4 is identical as networked mode.The structure of island mode such as Fig. 2 It is shown；The switching of the networked mode and island mode of commutator transformer is as shown in Figure 4；The networked mode of energy storage and island mode Switching is as shown in Figure 5.
2) flow chart of island detection method as shown in Figure 3 is designed.Under networked mode, isolated island detector detects direct current The switch state of breaker, according to the main criterion DCCB based on Switch State Combination in Power SystemsstateOperation result, judge that four end direct currents are matched Whether net occurs isolated island；(the DCCB in the failure of main criterionstateWhen=null), enable the auxiliary compound without stream based on pressure difference- Criterion judges whether four end DC distribution nets network first with without stream criterion, determines that four ends are straight if being unsatisfactory for without stream criterion Stream distribution system is centainly networked, and main criterion judgement is returned to；If without stream criterion meet, switch DP criterion, pressure difference criterion if satisfied, Then determine that four end DC distribution nets are in island mode, four end DC distribution nets switch to island mode control；If pressure difference criterion It is unsatisfactory for, repetition is detected without the compound assistant criteria of stream-pressure difference, detects number TmAdd 1, as detection number TmGreater than setting Number TsetAfterwards, the compound assistant criteria of no stream-pressure difference is still unsatisfactory for, then changes the active power reference value of energy storage, then enable nothing Criterion is flowed, if meeting without stream criterion, is rapidly switched to island mode control, determines four end direct currents if being still unsatisfactory for without stream criterion Power distribution network is in networked mode.
It 3) is the verifying island detection method in dc circuit breaker communication delay or failure and four end direct current distribution wattful powers Under the special operation condition of rate balance, it is able to achieve the accurate detection to isolated island.Following hypothesis is done to simulation process:
3.1) assume that T2 is in inspecting state, i.e. DCCB4 and DCCB8 are in an off state, and T2 is out of service, and T1 is using fixed DC voltage and reactive power (Udc-Q) control mode are run with T3 and T4；
3.2) switch state of DCCB5 is invalid state, i.e. s5=null, is calculated DCCBstate=null, at this time without Method by Switch State Combination in Power Systems decision-making system operational mode, this mode operation for a period of time after, due to maloperation or transient fault Etc. reasons, the dc circuit breaker tripping, at this time T3, T4 formed island mode；
3.3) during emulation, illumination simulation intensity constantly changes, and the active power of photovoltaic output also changes therewith；
3.4) the detection window step-length for designing isolated island detector is 700ms, and the fixed reference value of no stream criterion is 0.02Pu, pressure The reference value of poor criterion is also 0.02Pu.
3.5) for convenience of explanation, by taking T3 and T4 forms isolated island after T1 disconnection as an example.
4) effectively to examine isolated island detection and stable control method, entire simulation process is up to 8s, entire simulation process point It include: networking normal phase (State1) for 4 stages, network active power balance stage (State2), isolated island detection-phase (StateAnd isolated island power step response phase (St 3)ate4).Entire isolated island simulation waveform is as shown in Figure 7 and Figure 8.In Fig. 7, Udc1、Udc3The respectively voltage value of DC bus #1 and #3；Il1p、Il1nAnode and the negative DC electricity of respectively DC line L1 Stream；VDVC is pressure difference criterion value；VNCC is without stream criterion value；DCCB5 is the switch state of dc circuit breaker DCCB5；NCC is nothing Flow criterion；DVC is pressure difference criterion；IslandC is isolated island detected value.In fig. 8, Udc4For the voltage value of DC bus #4；Udc5 For the voltage value of DC bus #5, i.e. the DC low-voltage side voltage of commutator transformer；UESFor the DC voltage value of energy storage；Il3p、 Il3nThe anode and negative DC electric current of respectively DC line L3；PT1For the active power of T1；PPV、PESThe respectively photovoltaic of T3 With the active power of energy storage；PSG、PloadThe respectively active power of the synchronous generator of T4 and AC load；
4.1) network normal phase (State1): networking normal operation, from Fig. 7's and Fig. 8staTe1 simulation result comes It sees, T1 is active power sending end as active power balance node (PV node)；T3 due to energy storage and photovoltaic presence, it is active Power is in submitting state and active power sending end；The AC load capacity of T4 is greater than synchronous generator capacity, is wattful power Rate receiving end.Since the impedance of DC line L1 is smaller, even if Il1pAnd Il1nElectric current is larger, Udc1And Udc3Difference in voltage is very small, Pressure difference criterion and without stream criterion be not satisfied, isolated island criterion is unsatisfactory for, and T1, T3 and T4 are all made of networked mode control.
4.2) it networks active power balance stage (State2): as the active power that energy storage and photovoltaic export constantly increases Greatly, direct current system enters active power balance state, from the point of view of simulation result, although at this point, T1 active power balance node (PV node), but the active power of T3 and T4 is in equilibrium state, i.e. and the active power of the energy storage of T3 and photovoltaic output is almost complete It is dissolved by the AC load of T4, at this time Il1pAnd Il1nElectric current it is almost nil, VNCC is less than 0.02pu, and no stream criterion meets, orphan NCC is set 1 by island detector.But Udc1And Udc3Between there is no voltage difference, pressure difference criterion is unsatisfactory for, isolated island detector determine isolated island item Part is unsatisfactory for, and T1, T3 and T4 still use networked mode to control.
4.3) isolated island detection-phase (State3): under active power balance state, dc circuit breaker DCCB5 tripping, T3 and T4 and T1 are detached from, and system enters isolated island detection process, and since T1 is detached from, T3 and T4 lose clamping down on for the DC voltage of T1, Udc3 Constantly lifting, with Udc1Difference it is increasing, pressure difference criterion value is increasingly greater than 0.02Pu, and DVC is set 1 by isolated island detector.This When, isolated island detector is combined without stream criterion and pressure difference criterion, judges that T3 and T4 forms isolated island, IslandC is set 1.T3 is received To after the isolated island criterion of isolated island detector, commutator transformer control mode is switched to and determines high direct voltage side voltage control mode, Commutator transformer becomes the active power balance node (PV node) of the isolated island；Energy storage is switched to and determines the voltage control of DC low-voltage side Mode processed, energy storage become the active power balance node (PV node) of DC low-voltage side.As T3 changes to island mode, direct current becomes Depressor controls Udc3By set slope adjustment DC voltage to 1Pu；Energy storage controls Udc5, which there is wave in pattern switching moment It is dynamic, it then keeps stablizing；The active-power P of energy storageESStablize after there is fluctuation；The active-power P of photovoltaic outputPVWith illumination Strength Changes and change.The synchronous generator of T4 and the active power of AC load remain unchanged.T3 and T4 enter island mode Operation.
4.4) isolated island power step response phase (State4): when T3 and T4 enter island mode operation, simulate T4's AC load puts into 1MW AC load again, from simulation result as can be seen that the active power of the AC load of T4 is from 4MW step To 5MW, synchronous generator exports constant.The high direct voltage side voltage U of the direct current transformer of T3dc3It is kept after there are slight fluctuations Stablize, DC low-voltage side voltage Udc5It is fluctuated in AC load investment moment, then keeps stablizing.The active power of energy storage PESAnd fluctuated in AC load investment moment, it then keeps stablizing；And the active-power P of photovoltaic outputPVIt can be with illumination Strength Changes and change.
In conclusion the present invention is that the detection of four end DC distribution net isolated islands and stability contorting mention after using above scheme New method is supplied, the island detection method of proposition is in dc circuit breaker communication delay or failure and four end direct current distribution wattful powers Under the special operation condition of rate balance, the accurate detection to isolated island is realized；The isolated island Stable Control Strategy of design, can timely switching control Mode maintains the stable operation of entire island-grid, solves the problems, such as that four end DC distribution net isolated islands are difficult to detect and control, The development for effectively pushing DC distribution net, has actual promotional value, is worthy to be popularized.
Embodiment described above is only the preferred embodiments of the invention, and but not intended to limit the scope of the present invention, therefore All shapes according to the present invention change made by principle, should all be included within the scope of protection of the present invention.

Claims (4)

1.一种四端直流配电网的孤岛检测和稳定控制方法，所述四端直流配电网包括第一交流电网ACgrid1、第二交流电网ACgrid2、第一交流断路器ACCB1、第二交流断路器ACCB2、第一直流断路器DCCB1、第二直流断路器DCCB2、第三直流断路器DCCB3、第四直流断路器DCCB4、第五直流断路器DCCB5、第六直流断路器DCCB6、第七直流断路器DCCB7、第八直流断路器DCCB8、第一直流线路L1、第二直流线路L2、第三直流线路L3、第一直流母线#1、第二直流母线#2、第三直流母线#3、第四直流母线#4、第五直流母线#5、第一交流母线#6、第二交流母线#7、第三交流母线#8、第一模块化多电平电压源型变换器MMC-VSC1、第二模块化多电平电压源型变换器MMC-VSC2、直流变压器DCSST、第三模块化多电平电压源型变换器MMC-VSC3、DC/DC变换器、双向DC/DC变换器、光伏、储能、交流负载、同步发电机、第一变压器TM1、第二变压器TM2、第三变压器TM3；其中，所述第一模块化多电平电压源型变换器MMC-VSC1的交流侧依次经第一交流断路器ACCB1、第一交流母线#6、第一变压器TM1与第一交流电网ACgrid1连接，其直流侧依次经第一直流断路器DCCB1、第一直流母线#1、第二直流断路器DCCB2、第一直流线路L1、第五直流断路器DCCB5、第三直流母线#3与直流变压器DCSST的高压侧连接；所述第二模块化多电平电压源型变换器MMC-VSC2的交流侧依次经第二交流断路器ACCB2、第二交流母线#7、第二变压器TM2与第二交流电网ACgrid2连接，其直流侧依次经第三直流断路器DCCB3、第二直流母线#2、第四直流断路器DCCB4、第二直流线路L2、第八直流断路器DCCB8、第四直流母线#4与第三模块化多电平电压源型变换器MMC-VSC3的直流侧连接；所述光伏依次经DC/DC变换器、第五直流母线#5与直流变压器DCSST的低压侧连接；所述储能经双向DC/DC变换器与第五直流母线#5连接；所述交流负载依次经第三交流母线#8、第三变压器TM3与第三模块化多电平电压源型变换器MMC-VSC3的交流侧连接；所述同步发电机与第三交流母线#8连接；所述第三直流母线#3依次经第六直流断路器DCCB6、第三直流线路L3、第七直流断路器DCCB7与第四直流母线#4连接；所述第一交流电网ACgrid1、第一变压器TM1、第一交流母线#6、第一交流断路器ACCB1和第一模块化多电平电压源型变换器MMC-VSC1构成第一端口电路T1；所述第二交流电网ACgrid2、第二变压器TM2、第二交流母线#7、第二交流断路器ACCB2和第二模块化多电平电压源型变换器MMC-VSC2构成第二端口电路T2；所述直流变压器DCSST、第五直流母线#5、DC/DC变换器、双向DC/DC变换器、光伏和储能构成第三端口电路T3；所述第三模块化多电平电压源型变换器MMC-VSC3、第三变压器TM3、第三交流母线#8、交流负载和同步发电机构成第四端口电路T4；1. A method for islanding detection and stabilization control of a four-terminal DC power distribution network, the four-terminal DC power distribution network comprising a first alternating current grid ACgrid1, a second alternating current grid ACgrid2, a first alternating current circuit breaker ACCB1, and a second alternating current circuit breaker ACCB2, first DC circuit breaker DCCB1, second DC circuit breaker DCCB2, third DC circuit breaker DCCB3, fourth DC circuit breaker DCCB4, fifth DC circuit breaker DCCB5, sixth DC circuit breaker DCCB6, seventh DC circuit breaker DCCB7, eighth DC circuit breaker DCCB8, first DC line L1, second DC line L2, third DC line L3, first DC bus #1, second DC bus #2, third DC bus #3 , the fourth DC bus #4, the fifth DC bus #5, the first AC bus #6, the second AC bus #7, the third AC bus #8, the first modular multi-level voltage source converter MMC- VSC1, Second Modular Multilevel Voltage Source Converter MMC-VSC2, DC Transformer DCSST, Third Modular Multilevel Voltage Source Converter MMC-VSC3, DC/DC Converter, Bidirectional DC/DC Converter , photovoltaic, energy storage, AC load, synchronous generator, first transformer TM1, second transformer TM2, third transformer TM3; wherein, the AC side of the first modular multi-level voltage source converter MMC-VSC1 It is connected to the first AC grid ACgrid1 through the first AC circuit breaker ACCB1, the first AC bus #6, and the first transformer TM1 in sequence, and its DC side is connected through the first DC circuit breaker DCCB1, the first DC bus #1, and the first AC grid. The two DC circuit breakers DCCB2, the first DC line L1, the fifth DC circuit breaker DCCB5, and the third DC bus #3 are connected to the high-voltage side of the DC transformer DCSST; the second modular multi-level voltage source converter MMC -The AC side of the VSC2 is connected to the second AC grid ACgrid2 through the second AC circuit breaker ACCB2, the second AC bus #7 and the second transformer TM2 in sequence, and the DC side of the VSC2 is connected to the second AC grid ACgrid2 through the third DC circuit breaker DCCB3 and the second DC bus # 2. The fourth DC circuit breaker DCCB4, the second DC line L2, the eighth DC circuit breaker DCCB8, and the fourth DC bus #4 are connected to the DC side of the third modular multi-level voltage source converter MMC-VSC3; The photovoltaic is connected to the low-voltage side of the DC transformer DCST via the DC/DC converter and the fifth DC bus #5 in sequence; the energy storage is connected to the fifth DC bus #5 via the bidirectional DC/DC converter; the AC load is sequentially The third AC bus #8 and the third transformer TM3 are connected to the AC side of the third modular multi-level voltage source converter MMC-VSC3; the synchronous generator is connected to the third AC bus #8; the third The third DC bus #3 is sequentially connected to the fourth DC bus #4 through the sixth DC circuit breaker DCCB6, the third DC line L3, and the seventh DC circuit breaker DCCB7; An AC grid ACgrid1, a first transformer TM1, a first AC bus #6, a first AC circuit breaker ACCB1 and a first modular multilevel voltage source converter MMC-VSC1 constitute a first port circuit T1; the second The AC grid ACgrid2, the second transformer TM2, the second AC bus #7, the second AC circuit breaker ACCB2 and the second modular multi-level voltage source converter MMC-VSC2 constitute the second port circuit T2; the DC transformer DCST , the fifth DC bus #5, DC/DC converter, bidirectional DC/DC converter, photovoltaic and energy storage constitute a third port circuit T3; the third modular multi-level voltage source converter MMC-VSC3, The third transformer TM3, the third AC bus #8, the AC load and the synchronous generator form a fourth port circuit T4; 其特征在于，所述的孤岛检测和稳定控制方法，包括以下步骤：It is characterized in that, the described island detection and stability control method comprises the following steps: 1)基于开关状态组合的孤岛检测主判据：通过判断直流线路上直流断路器的开关状态组合，检测四端直流配电网有无孤岛的产生；1) The main criterion of island detection based on switch state combination: by judging the switch state combination of the DC circuit breaker on the DC line, it can detect whether there is islanding in the four-terminal DC distribution network; 2)基于无流-压差复合的孤岛检测辅助判据：通过判断直流断路器上有无电流，和相应的直流母线上是否存在电压差，在直流断路器通信失败或延时且四端直流配电网中存在有功功率平衡时，检测四端直流配电网有无孤岛的产生；2) Auxiliary criterion for island detection based on the combination of no current and voltage difference: by judging whether there is current on the DC circuit breaker and whether there is a voltage difference on the corresponding DC bus, the communication of the DC circuit breaker fails or is delayed and the four-terminal DC When there is active power balance in the distribution network, detect whether there is islanding in the four-terminal DC distribution network; 3)基于直流变压器和储能协同控制的孤岛稳定控制：当检测到孤岛发生时，直流变压器和储能能及时切换控制方式，从而维持整个孤岛的稳定运行。3) Island stability control based on the coordinated control of DC transformer and energy storage: When islanding is detected, the DC transformer and energy storage can switch the control mode in time to maintain the stable operation of the entire island. 2.根据权利要求1所述的一种四端直流配电网的孤岛检测和稳定控制方法，其特征在于：在步骤1)中，通过判断直流断路器DCCB2，DCCB5与DCCB4，DCCB8的开关状态组合，进而识别T3和T4是否处于孤岛模式，包括以下步骤：2. the islanding detection and stabilization control method of a kind of four-terminal direct current distribution network according to claim 1, is characterized in that: in step 1), by judging the switch state of direct current circuit breaker DCCB2, DCCB5 and DCCB4, DCCB8 combination to identify whether T3 and T4 are in island mode, including the following steps: 1.1)定义换流站接收系统8个直流断路器的开关信号分别为s1、s2、s3、s4、s5、s6、s7和s8，并定义直流断路器的开关函数如下：1.1) Define the switching signals of the 8 DC circuit breakers of the converter station receiving system as s 1 , s 2 , s 3 , s 4 , s 5 , s 6 , s 7 and s 8 , and define the switching functions of the DC circuit breakers as follows: 式中，x表示直流断路器的编号1、2、3、4、5、6、7和8，当sx为0时，表示直流断路器闭合，当sx为1时，表示直流断路器断开；In the formula, x represents the number 1, 2, 3, 4, 5, 6, 7 and 8 of the DC circuit breaker. When s x is 0, it means that the DC circuit breaker is closed, and when s x is 1, it means that the DC circuit breaker is closed. disconnect; 1.2)定义DCCBstate是基于开关状态组合的直流断路器的孤岛判据结果，由下式计算得到：1.2) Definition DCCB state is the result of islanding criterion of DC circuit breaker based on switch state combination, which is calculated by the following formula: DCCBstate＝(s2∪s5)∩(s4∪s8)DCCB state =(s 2 ∪s 5 )∩(s 4 ∪s 8 ) 当DCCBstate＝0时，表示没有发生孤岛；当DCCBstate＝1时，表示发生孤岛；当DCCBstate＝null时，表示直流断路器的开关状态无法获取。When DCCB state = 0, it means that no islanding occurs; when DCCB state = 1, it means that islanding occurs; when DCCB state = null, it means that the switching state of the DC circuit breaker cannot be obtained. 3.根据权利要求1所述的一种四端直流配电网的孤岛检测和稳定控制方法，其特征在于：在步骤2)中，提出基于无流-压差复合的辅助判据，以解决步骤1)中直流断路器的开关状态无法获取的问题，包括以下步骤：3. the islanding detection and stabilization control method of a kind of four-terminal direct current distribution network according to claim 1, is characterized in that: in step 2), propose the auxiliary criterion based on no-current-pressure difference compound, to solve The problem that the switching state of the DC circuit breaker cannot be obtained in step 1) includes the following steps: 2.1)无流判据：当T3和T4同时与T1和T2脱离，而形成孤岛时，由于直流断路器的开关状态无法被准确检测到，能够通过判断直流断路器DCCB2或DCCB5以及DCCB4或DCCB8上有无电流，进而判断T3和T4是否处于孤岛模式；2.1) No-current criterion: When T3 and T4 are separated from T1 and T2 at the same time and form an island, since the switching state of the DC circuit breaker cannot be accurately detected, it can be determined by judging the DC circuit breaker DCCB2 or DCCB5 and DCCB4 or DCCB8. Whether there is current, and then judge whether T3 and T4 are in island mode; 定义Il1为流过直流线路L1的电流；Il2为流过直流线路L2的电流；Definition I l1 is the current flowing through the DC line L1; I l2 is the current flowing through the DC line L2; 一个检测周期内，无流判据值计算公式如下式所示：In a detection period, the calculation formula of the no-flow criterion value is as follows: 式中，t0为孤岛检测开始时间；T为检测采样周期；ΔIl1为检测周期T内Il1的绝对值之和；ΔIl2为检测周期T内Il2的绝对值之和；In the formula, t 0 is the start time of island detection; T is the detection sampling period; ΔI l1 is the sum of the absolute values of I l1 in the detection period T; ΔI l2 is the sum of the absolute values of I l2 in the detection period T; 当T2中的第二模块化多电平电压源型变换器MMC-VSC2的有功功率定值被设置为零或T2被断开时，T3和T4的有功功率相互抵消，定义此时的系统运行状态为有功功率平衡态；When the active power setting of the second modular multilevel voltage source converter MMC-VSC2 in T2 is set to zero or T2 is disconnected, the active powers of T3 and T4 cancel each other out, which defines the system operation at this time The state is active power balance state; 无流判据如下式所示：The no-flow criterion is as follows: 式中，ΔIl1、ΔIl2分别为直流线路L1和直流线路L2的无流判据值；Imax1、Imax2为有功功率平衡态时，流过直流断路器DCCB2、DCCB4的最大电流；In the formula, ΔI l1 and ΔI l2 are the no-current criterion values of the DC line L1 and the DC line L2 respectively; I max1 and I max2 are the maximum currents flowing through the DC circuit breakers DCCB2 and DCCB4 when the active power is in equilibrium state; 2.2)压差判据：当有功功率平衡态时，虽然上述判据成立，但T3、T4仍然能够处于联网模式，为避免误判，增加“压差”的辅助判据；2.2) Differential pressure criterion: When the active power is in equilibrium, although the above criterion is established, T3 and T4 can still be in the networking mode. In order to avoid misjudgment, an auxiliary criterion of "pressure difference" is added; 定义Udc1为直流母线#1的电压值，Udc2为直流母线#2的电压值，Udc3为直流母线#3的电压值，Udc4为直流母线#4的电压值；Define U dc1 as the voltage value of DC bus #1, U dc2 as the voltage value of DC bus #2, U dc3 as the voltage value of DC bus #3, and U dc4 as the voltage value of DC bus #4; 通过检测Udc1和Udc3电压之差，以及Udc2和Udc4电压之差作为无流判据的辅助判据，判断系统是否处于孤岛模式，压差判据值ΔUdc1、ΔUdc2的计算公式如下式所示：By detecting the difference between the voltages of U dc1 and U dc3 , and the difference between the voltages of U dc2 and U dc4 as the auxiliary criterion for the no-current criterion, it is judged whether the system is in the island mode, and the calculation formula of the pressure difference criterion values ΔU dc1 and ΔU dc2 As shown in the following formula: 式中，t0为孤岛检测开始时间；T为检测采样周期；ΔUdc1为Udc1和Udc3之间的压差判据值；ΔUdc2为Udc2和Udc4之间的压差判据值；In the formula, t 0 is the start time of island detection; T is the detection sampling period; ΔU dc1 is the pressure difference criterion value between U dc1 and U dc3 ; ΔU dc2 is the pressure difference criterion value between U dc2 and U dc4 ; 压差判据如下式所示：The differential pressure criterion is as follows: 式中，ΔUmax1为有功功率平衡态下的Udc1和Udc3之差在检测周期T内的最大值；ΔUmax2为有功功率平衡态下的Udc2和Udc4之差在检测周期T内的最大值；In the formula, ΔU max1 is the maximum value of the difference between U dc1 and U dc3 in the active power equilibrium state in the detection period T; ΔU max2 is the difference between U dc2 and U dc4 in the active power equilibrium state in the detection period T. maximum value; 根据主判据和辅助判据相结合的孤岛综合检测方法，得到该孤岛检测方法的流程图，并设计成孤岛检测器。According to the comprehensive island detection method combining the main criterion and the auxiliary criterion, the flow chart of the island detection method is obtained, and an island detector is designed. 4.根据权利要求1所述的一种四端直流配电网的孤岛检测和稳定控制方法，其特征在于：在步骤3)，首先通过步骤1)和2)设计的孤岛检测器，检测到孤岛信号，对直流变压器和储能进行孤岛的稳定控制，稳定控制的实现有以下步骤：4. the islanding detection and stability control method of a kind of four-terminal DC distribution network according to claim 1, it is characterized in that: in step 3), at first by the islanding detector designed in steps 1) and 2), detect Islanding signal, the stable control of the DC transformer and the energy storage is carried out. The realization of the stable control has the following steps: 3.1)T3的直流变压器在联网模式下，采用定直流低压侧电压Udclv控制方式，作为直流低压侧有功功率平衡节点，即PV节点，允许光伏产生的波动；当孤岛检测器检测到孤岛发生时，由于此时四端直流配电网的T1和T2全部退出，直流变压器采用定直流高压侧电压Udchv控制方式，作为孤岛的有功功率平衡节点，即PV节点；3.1) In the networking mode, the DC transformer of T3 adopts the constant DC low-voltage side voltage U dclv control mode, as the active power balance node of the DC low-voltage side, that is, the PV node, to allow fluctuations generated by photovoltaics; when the islanding detector detects the occurrence of islanding , since T1 and T2 of the four-terminal DC distribution network are all withdrawn at this time, the DC transformer adopts the constant DC high-voltage side voltage U dchv control mode as the active power balance node of the island, that is, the PV node; 3.2)T3的储能的双向DC/DC变换器在联网模式下，采用定有功功率PES控制方式，既能够工作在恒定的充放电状态，也能够跟踪补偿光伏的有功功率的输出，使得光伏和储能的有功功率的输出总和处于稳定状态，方便地满足调度的要求；当孤岛检测器检测到孤岛发生时，储能的双向DC/DC变换器采用定直流低压侧电压Udclv控制方式，作为直流低压侧有功功率平衡节点，即PV节点，控制直流变压器直流低压侧电压，从而维持孤岛的稳定运行；3.2) In the networking mode, the bidirectional DC/DC converter of T3 energy storage adopts the constant active power PES control mode, which can not only work in a constant charging and discharging state, but also track and compensate the output of the active power of the photovoltaic, so that the photovoltaic The output sum of the active power of the energy storage and the energy storage is in a stable state, which can easily meet the requirements of dispatching; when the islanding detector detects the occurrence of islanding, the bidirectional DC/DC converter of the energy storage adopts the constant DC low-voltage side voltage U dclv control mode, As the active power balance node on the DC low voltage side, that is, the PV node, it controls the DC low voltage side voltage of the DC transformer to maintain the stable operation of the island; 3.3)当联网模式转入孤岛模式时，直流电压器和储能切换控制方式，由于直流变压器直流高压侧电压的变化对直流低压侧电压和有功功率的影响很大，在设计直流变压器和储能的孤岛模式控制时，将储能的定直流低压侧电压控制的比例参数设计得比直流变压器定直流高压侧电压控制的比例参数大；另外，直流变压器的定直流高压侧电压控制的电压参考值设计成斜率变化到1Pu，从而解决切换过程中直流变压器直流低压侧电压剧烈波动的问题。3.3) When the networking mode is switched to the island mode, the DC voltage converter and the energy storage switch control mode, because the change of the DC high voltage side voltage of the DC transformer has a great influence on the DC low voltage side voltage and active power, in the design of the DC transformer and energy storage. In the island mode control, the proportional parameter of the constant DC low voltage side voltage control of the energy storage is designed to be larger than the proportional parameter of the constant DC high voltage side voltage control of the DC transformer; in addition, the voltage reference value of the constant DC high voltage side voltage control of the DC transformer is designed. It is designed to change the slope to 1Pu, so as to solve the problem of severe fluctuations in the DC low-voltage side voltage of the DC transformer during the switching process.
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