A method used for determining the number of equivalent π sections oftransmission line model according to the frequency range of interest and the model accura-cy defined herein is proposed.Factors influencing the disc...A method used for determining the number of equivalent π sections oftransmission line model according to the frequency range of interest and the model accura-cy defined herein is proposed.Factors influencing the discrepancies between continuous ordistributed parameter and multiple π or lumped parameter models are discussed.Generalconclusions concerning the π section lengths of line models used in transient stability,faulttransient and switching over-voltage studies are drawn.Time-domain simulation resultsconfirm the effectiveness of this method.展开更多
How to comprehensively consider the power flow constraints and various stability constraints in a series of power system optimization problems without affecting the calculation speed is always a problem.The computatio...How to comprehensively consider the power flow constraints and various stability constraints in a series of power system optimization problems without affecting the calculation speed is always a problem.The computational burden of probabilistic security assessment is even more unimaginable.In order to solve such problems,a security region(SR)methodology is proposed,which is a brand-new methodology developed on the basis of the classical point-wise method.Tianjin University has been studying the SR methodology since the 1980s,and has achieved a series of original breakthroughs that are described in this paper.The integrated SR introduced in this paper is mainly defined in the power injection space,and includes SRs to ensure steady-state security,transient stability,static voltage stability,and smalldisturbance stability.These SRs are uniquely determined for a given network topology(as well as location and clearing process for transient faults)and given system component parameters,and are irrelevant to operation states.This paper presents 11 facts and related remarks to introduce the basic concepts,composition,dynamics nature,and topological and geometric characteristics of SRs.It also provides a practical mathematical description of SR boundaries and fast calculation methods to determine them in a concise and systematic way.Thus,this article provides support for the systematic understanding,future research,and applications of SRs.The most critical finding on the topological and geometric characteristics of SRs is that,within the scope of engineering concern,the practical boundaries of SRs in the power injection space can be approximated by one or a few hyperplanes.Based on this finding,the calculation time for power system probabilistic security assessment(i.e.,risk analysis)and power system optimization with security constraints can be decreased by orders of magnitude.展开更多
The transient stability issues caused by doubly fed induction generator(DFIG)-based wind turbines(WTs)are receiving increasing attention.The q-axis reactive power control(QCtrl),as an essential part of DFIG-based WTs,...The transient stability issues caused by doubly fed induction generator(DFIG)-based wind turbines(WTs)are receiving increasing attention.The q-axis reactive power control(QCtrl),as an essential part of DFIG-based WTs,has a significant impact on its transient response.In this paper,the impact of QCtrl on the phase/amplitude transient stability of a DFIGbased WT-dominated system is analyzed from the perspective of internal voltage amplitude-phase coupling characteristics.First,an amplitude/phase dynamic model of a DFIG-based WT in rotor speed control timescale(in seconds,corresponding to traditional electromechanical timescale)is developed.Then,in comparison with familiar synchronous generators(SGs),an inherently amplitude-phase characteristic of internal voltage for a DFIG-based WT is identified.Next,taking the DFIG-based WTdominated system as an example,the impact of QCtrl on system transient stability via the internal coupling paths is analyzed.A novel phase-amplitude coupling instability mechanism is found,which is different from that in a traditional SG-dominated system.Finally,the effects of different QCtrl strategies on transient stability are discussed.展开更多
Traditional transient angle stability analysis methods do not fully consider the spatial characteristics of the network topology and the temporal characteristics of the time-series disturbance.Hence,a data-driven meth...Traditional transient angle stability analysis methods do not fully consider the spatial characteristics of the network topology and the temporal characteristics of the time-series disturbance.Hence,a data-driven method is proposed in this study,combining graph convolution network and long short-term memory network(GCN-LSTM)to analyze the transient power angle sta-bility by exploring the spatiotemporal disturbance char-acteristics of future power systems with high penetration of renewable energy sources(wind and solar energy)and power electronics.The key time-series electrical state quantities are considered as the initial input feature quantities and normalized using the Z-score,whereas the network adjacency matrix is constructed according to the system network topology.The normalized feature quan-tities and network adjacency matrix were used as the inputs of the GCN to obtain the spatial features,reflecting changes in the network topology.Subsequently,the spa-tial features are inputted into the LSTM network to ob-tain the temporal features,reflecting dynamic changes in the transient power angle of the generators.Finally,the spatiotemporal features are fused through a fully con-nected network to analyze the transient power angle stability of future power systems,and the softmax activa-tion cross-entropy loss functions are used to predict the stability of the samples.The proposed transient power angle stability assessment method is tested on a 500 kV AC-DC practical power system,and the simulation results show that the proposed method could effectively mine the spatiotemporal disturbance characteristics of power sys-tems. Moreover, the proposed model has higher accuracy, higher recall rate, and shorter training and testing times than traditional transient power angle stability algo-rithms.展开更多
A modified flux-coupling type superconducting fault current limiter(SFCL)is proposed here for suppressing fault currents.The modified SFCL consists of a coupling transformer,an yttrium barium copper oxide(YBCO)pancake...A modified flux-coupling type superconducting fault current limiter(SFCL)is proposed here for suppressing fault currents.The modified SFCL consists of a coupling transformer,an yttrium barium copper oxide(YBCO)pancake coil,and a controlled switch.By flexibly adjusting the controlled switch’s contact states based on the system operational conditions,the coupling transformer’s primary inductance as well as the YBCO coil’s normal-state resistance are incorporated into the main system for current limitation.Because the modified SFCL has the advantages of resistive and inductive SFCLs,it may improve the power system’s transient behavior.Hence,the SFCL’s effect on the transient stability of a multi-machine power system was also theoretically investigated.Further,simulations were conducted for accessing the SFCL’s performance characteristics under different fault conditions.The results show that using the proposed SFCL can effectively restrain the increased fault current and improve the bus voltage sag;meanwhile,the imitated multi-machine system’s power-angle oscillation can be obviously reduced.展开更多
More and more large capacity wind power will be integrated into power system in the future,and certain technical challenges will emerge due to the fluctuation characteristics of wind power and the complex control of p...More and more large capacity wind power will be integrated into power system in the future,and certain technical challenges will emerge due to the fluctuation characteristics of wind power and the complex control of power electronic devices inside the wind turbines(e.g.,low voltage ride through(LVRT)).By comparing a wind power integration grid with a hydropower integration grid,the special transient phenomena caused by the wind power integration is studied and simulation results are presented.Furthermore,the potential impacts on the traditional protection are discussed.Results show that the special transient phenomena can decrease the sensitivity,reliability and operation speed of conventional protections.展开更多
文摘A method used for determining the number of equivalent π sections oftransmission line model according to the frequency range of interest and the model accura-cy defined herein is proposed.Factors influencing the discrepancies between continuous ordistributed parameter and multiple π or lumped parameter models are discussed.Generalconclusions concerning the π section lengths of line models used in transient stability,faulttransient and switching over-voltage studies are drawn.Time-domain simulation resultsconfirm the effectiveness of this method.
文摘How to comprehensively consider the power flow constraints and various stability constraints in a series of power system optimization problems without affecting the calculation speed is always a problem.The computational burden of probabilistic security assessment is even more unimaginable.In order to solve such problems,a security region(SR)methodology is proposed,which is a brand-new methodology developed on the basis of the classical point-wise method.Tianjin University has been studying the SR methodology since the 1980s,and has achieved a series of original breakthroughs that are described in this paper.The integrated SR introduced in this paper is mainly defined in the power injection space,and includes SRs to ensure steady-state security,transient stability,static voltage stability,and smalldisturbance stability.These SRs are uniquely determined for a given network topology(as well as location and clearing process for transient faults)and given system component parameters,and are irrelevant to operation states.This paper presents 11 facts and related remarks to introduce the basic concepts,composition,dynamics nature,and topological and geometric characteristics of SRs.It also provides a practical mathematical description of SR boundaries and fast calculation methods to determine them in a concise and systematic way.Thus,this article provides support for the systematic understanding,future research,and applications of SRs.The most critical finding on the topological and geometric characteristics of SRs is that,within the scope of engineering concern,the practical boundaries of SRs in the power injection space can be approximated by one or a few hyperplanes.Based on this finding,the calculation time for power system probabilistic security assessment(i.e.,risk analysis)and power system optimization with security constraints can be decreased by orders of magnitude.
基金This work was supported in part by the China South Grid Consulting Project,in part by the Natural Science Foundation of China under Grant 51777083.
文摘The transient stability issues caused by doubly fed induction generator(DFIG)-based wind turbines(WTs)are receiving increasing attention.The q-axis reactive power control(QCtrl),as an essential part of DFIG-based WTs,has a significant impact on its transient response.In this paper,the impact of QCtrl on the phase/amplitude transient stability of a DFIGbased WT-dominated system is analyzed from the perspective of internal voltage amplitude-phase coupling characteristics.First,an amplitude/phase dynamic model of a DFIG-based WT in rotor speed control timescale(in seconds,corresponding to traditional electromechanical timescale)is developed.Then,in comparison with familiar synchronous generators(SGs),an inherently amplitude-phase characteristic of internal voltage for a DFIG-based WT is identified.Next,taking the DFIG-based WTdominated system as an example,the impact of QCtrl on system transient stability via the internal coupling paths is analyzed.A novel phase-amplitude coupling instability mechanism is found,which is different from that in a traditional SG-dominated system.Finally,the effects of different QCtrl strategies on transient stability are discussed.
基金supported by the National Key R&D Program of China“Response-driven Intelligent Enhanced Analysis and Control for Bulk Power System Stability”(No.2021YFB2400800 and No.SGSDDKOOWJJS 2200092).
文摘Traditional transient angle stability analysis methods do not fully consider the spatial characteristics of the network topology and the temporal characteristics of the time-series disturbance.Hence,a data-driven method is proposed in this study,combining graph convolution network and long short-term memory network(GCN-LSTM)to analyze the transient power angle sta-bility by exploring the spatiotemporal disturbance char-acteristics of future power systems with high penetration of renewable energy sources(wind and solar energy)and power electronics.The key time-series electrical state quantities are considered as the initial input feature quantities and normalized using the Z-score,whereas the network adjacency matrix is constructed according to the system network topology.The normalized feature quan-tities and network adjacency matrix were used as the inputs of the GCN to obtain the spatial features,reflecting changes in the network topology.Subsequently,the spa-tial features are inputted into the LSTM network to ob-tain the temporal features,reflecting dynamic changes in the transient power angle of the generators.Finally,the spatiotemporal features are fused through a fully con-nected network to analyze the transient power angle stability of future power systems,and the softmax activa-tion cross-entropy loss functions are used to predict the stability of the samples.The proposed transient power angle stability assessment method is tested on a 500 kV AC-DC practical power system,and the simulation results show that the proposed method could effectively mine the spatiotemporal disturbance characteristics of power sys-tems. Moreover, the proposed model has higher accuracy, higher recall rate, and shorter training and testing times than traditional transient power angle stability algo-rithms.
基金Supported by the Fujian Young and Middle-Aged Teachers’Science and Technology Research Project(JAT201101).
文摘A modified flux-coupling type superconducting fault current limiter(SFCL)is proposed here for suppressing fault currents.The modified SFCL consists of a coupling transformer,an yttrium barium copper oxide(YBCO)pancake coil,and a controlled switch.By flexibly adjusting the controlled switch’s contact states based on the system operational conditions,the coupling transformer’s primary inductance as well as the YBCO coil’s normal-state resistance are incorporated into the main system for current limitation.Because the modified SFCL has the advantages of resistive and inductive SFCLs,it may improve the power system’s transient behavior.Hence,the SFCL’s effect on the transient stability of a multi-machine power system was also theoretically investigated.Further,simulations were conducted for accessing the SFCL’s performance characteristics under different fault conditions.The results show that using the proposed SFCL can effectively restrain the increased fault current and improve the bus voltage sag;meanwhile,the imitated multi-machine system’s power-angle oscillation can be obviously reduced.
文摘More and more large capacity wind power will be integrated into power system in the future,and certain technical challenges will emerge due to the fluctuation characteristics of wind power and the complex control of power electronic devices inside the wind turbines(e.g.,low voltage ride through(LVRT)).By comparing a wind power integration grid with a hydropower integration grid,the special transient phenomena caused by the wind power integration is studied and simulation results are presented.Furthermore,the potential impacts on the traditional protection are discussed.Results show that the special transient phenomena can decrease the sensitivity,reliability and operation speed of conventional protections.
