摘要:There were many accidents of large-scale wind turbines disconnecting from power grid in2011.As single- phase-to-ground fault cannot be correctly detected，single-phase-to-ground fault evolved to phase-to-phase fault. Phase-to-phase fault was isolated slowly，thus leading to low voltage.And wind turbines without enough low voltage ride-through capacity had to be disconnected from the grid.After some wind turbines being disconnected from the grid，overvoltage caused by reactive power surplus made more wind turbines disconnect from the grid. Based on the accident analysis，this paper presents solutions to above problems，including travelling waves based single-phase-to-ground protection，adaptive low voltage protection，integrated protection and control，and high impedance fault detection.The solutions lay foundations in theory and technology to prevent large-scale wind turbines disconnecting from the operating power grid.
摘要:To study the effects of wind generators on distribution system protection，the short-circuit current（SCC） characteristics of wind generators is important.Although there are many researches on the issue，a clear agreementhas not been reached so far.The SCC characteristics for different wind generators are studied.PSCAD simulation isperformed in the same system integrated with different kinds of wind generators，and their results are comparedwith those reported in IEEE papers.The detection possibility by overcurrent relay（OCR）is discussed based on thesimulation results.
摘要:A simulation system for power grid with concentrated large-scale wind farm integration is establishedbased on the electro-magnetic transient model of wind turbine equipped with doubly-fed induction generator （DFIG），which is built by real-time digital simulator（RTDS）.Using the hardware communication interface ofRTDS，a closed-loop testing experiment is accomplished to study the impacts of large-scale wind farms on theexisting relay protection devices for wind farm outgoing transmission line.This paper points out problems existingin current relay protection devices as follows:fault phase selector can select unwanted phase due to the changes offault features caused by special network connection of wind farms;blocking condition for distance protections needsto bere-examined due to the weak power-feed characteristics of wind farms;and power frequency parameter basedrelay protection devices cannot accurately operate due to the special transient voltage and current characteristics ofwind farms during fault period.Results lay the foundation for improving the performances of the existing relayprotection device and developing new principle relay protection.
摘要:Because of the large-scale integration of wind power，the dynamic characteristics of power system havemany uncertain effects.Based on deterministic analysis methods，traditional on-line security assessment systemcannot quantitatively estimate the actual operating conditions of the power system for only considering the mostserious and credible accidents.Therefore，the risk theory is introduced into an on-line security assessment systemand then an on-line risk assessment system for wind power is designed and implemented by combining with thedynamic security assessment system.Based on multiple data integration，the wind power disturbance probability isavailable and the security assessment of the power grid can obtain security indices in different aspects.The operatingrisk index is an expectation of severity，computed by summing up all the products of the result probability and itsseverity.Analysis results are reported to the dispatchers in on-line environment，while the comprehensive weaklinks are automatically provided to the power dispatching center.The risk assessment system in operation can verifythe reasonableness of the system.
摘要:The impacts of large-scale grid-connected wind farm on direct-driven permanent magnet synchronousgenerator（PMSG）type are discussed on the small signal stability performances of power systems.Firstly，asimplified practical model of wind farm of PMSG type is derived for analyzing small signal stability.The rotor-flux- oriented control strategy is applied to the modelling of PMSG.Secondly，the framework of small signal stabilityanalysis incorporating wind farm of PMSG type is built.Finally，the different simulation scenarios based on theIEEE3-generator-9-bus test system as benchmark are designed to conduct the eigenvalue analysis and to assess theimpacts of wind farm of PMSG type on power system small signal stability.Some conclusions are drawn withsimulation results.
摘要:The characteristics of induction generator based fixed-speed wind turbines（FSWT）are investigated.Theimpacts of different execution time in protective operations are studied under different fault duration and variouswind velocity situations，e.g.，FSWT stabilities of load shedding in distribution systems.Based on this research，adynamic protective control strategy for a distributed generation system（DGS）with FSWT is proposed.Finally， simulation results demonstrate the effectiveness of the strategy.
摘要:With the increasing penetration of distributed generations（DGs）into power grids，the fault ride-throughability of DG is attracting more and more attention.Recent grid codes require a DG to maintain its connection withthe grid during grid faults and to play an active role in the recovery of grid voltage.This paper chooses the doubly- fed induction generator（DFIG）as the typical wind turbine for study.Firstly，a dynamic reactive power controlstrategy is proposed to improve the fault ride-through characteristic of a DFIG.The contributions of a DFIG to thefault current under the dynamic reactive power control and the Crowbar control are analyzed and compared based onthe mathematical expressions and control behaviors.The impacts of a DFIG under two control strategies ondistribution protections are discussed.Studies show that although a DFIG under the dynamic reactive power controlprovides more fault current component than one under the Crowbar control，its impacts on distribution protectionsare acceptable.Finally，a10kV distribution network with a DFIG is simulated in PowerFactory DIgSILENT.Thesimulation results prove the correctness of above theoretical analysis.
摘要:Future power system faces several challenges，one of them is the high penetration level of intermittentwind power generation，providing small or even no inertial response and being not contributing to the frequencystability.The effect of shaft stiffness on inertial response of fixed speed wind turbines is presented.Four differentdrive-train models based on the multi-body system are developed.The small-signal analysis demonstrates nosignificant differences between models in terms of electro-mechanical eigen-values for increasing shaft stiffness.Thenatural resonance frequency of drive-train torsion modes shows slightly different values between damped andundamped models，but no significant differences are found in the number-mass models.Time-domain simulationsshow the changes in the active power contribution of a wind farm based on a fixed speed wind turbine during thesystem frequency disturbance.The changes in the kinetic energy during the dynamic process are calculated and theircontribution to the inertia constant is small and effective.The largest contribution of the kinetic energy is providedat the beginning of the system frequency disturbance to reduce the rate of the frequency change，it is positive for thefrequency stability.
摘要:The distributed generator over the last30years has posed several challenges when they are connected to adistributed network.The most immediate problem is to change the voltage at the connection point depending on thepower supplied to the network and may cause it to exceed statutory limits.This paper describes a new controlscheme for a distributed generator for supporting the voltage control in the network，thus ensuring the distributedgenerator to contribute to network voltage management.The scheme performance is demonstrated by a model for adistributed generator connected to a distribution network.The result shows that using the new control scheme，thedistribution network voltage constraints are maintained while maximizing the active power delivered by distributedgenerators.
摘要:As the penetration of wind power into power grids increases，higher demands are made on the stability andprotection of power systems.Unlike traditional synchronous generators，wind turbines are different on the short-circuit and impedance characteristics，thus some problems exist in pilot protections of transmission linesconnecting wind farms.When a single-phase fault occurs on a transmission line，the phase selector based on current-difference sudden-change may mistake the single-phase fault for a phase-to-phase fault.This paper studiesthe impedance characteristics of an asynchronous wind generator，and analyzes the behavior of a fault phase selectorunder different conditions.Then，the paper explains that inequality between positive and negative branch coefficientsis the cause for the mal-operation of the fault phase selector.Finally，some simulations are done in MATLAB tovalidate analysis results.
摘要:Besides common characteristics of wind power，there are some special characteristics in China powersystem，including large-scale，long distance transmission and lack of flexible regulating power sources.Thesespecial characteristics make power dispatch more challenging in China.Many studies have been carried out and someimprovements are presented including wind power monitoring and control as well as evaluation of wind powerintegration capabilities.As a demonstration project，the technologies are integrated into the energy managementsystem and are implemented in the Northwest China power system.They provide effective measures for wind powerdispatch in the grid.
摘要:The optimization of black-start decision-making plays an important role in the rapid restoration of a powersystem after a major failure/outage.With the introduction of the concept of smart grids and the development of real-time communication networks，the black-start decision-makers are no longer limited to only one or a few powersystem experts such as dispatchers，but rather a large group of professional people in practice.The overall behaviorsof a large decision-making group of decision-makers/experts are more complicated and unpredictable.However，theexisting methods for black-start decision-making cannot handle the situations with a large group of decision-makers. Given this background，a clustering algorithm is presented to optimize the black-start decision-making problem witha large group of decision-makers.Group decision-making preferences are obtained by clustering analysis，and thefinal black-start decision-making results are achieved by combining the weights of black-start indexes and thepreferences of the decision-making group.The effectiveness of the proposed method is validated by a practical case. This work extends the