Based on the transmission line code TLCODE, a 1D circuit model for a transmission- line impedance transformer was developed and the simulation results were compared with those in the literature. The model was used to ...Based on the transmission line code TLCODE, a 1D circuit model for a transmission- line impedance transformer was developed and the simulation results were compared with those in the literature. The model was used to quantify the efficiencies of voltage-transport, energy- transport and power-transport for a transmission-line impedance transformer as functions of ψ （the ratio of the output impedance to the input impedance of the transformer） and Г （the ratio of the pulse width to the one-way transit time of the transformer） under a large scale of m （the coefficient of the generalized exponential impedance profile）. Simulation results suggest that with the increase in Г, from 0 to ∞, the power transport efficiency first increases and then decreases. The maximum power transport efficiency can reach 90% or even higher for an exponential impedance profile （m = 1）. With a consideration of dissipative loss in the dielectric and electrodes of the transformer, two representative designs of the water-insulated transformer are investigated for the next generation of petawatt-class z-pinch drivers. It is found that the dissipative losses in the electrodes are negligibly small, below 0.1%, but the dissipative loss in the water dielectric is about 1% to 4%.展开更多
With a live wire, line impedance could be measured by means of only passive elements such as inductors or resistors, whose techniques are well known. However, as the voltage and current used for the measurement are in...With a live wire, line impedance could be measured by means of only passive elements such as inductors or resistors, whose techniques are well known. However, as the voltage and current used for the measurement are increased, the size of the inductor or resistor being used also needs to be increased, so it would be virtually impossible to make an accurate measurement. Because of this, the authors have developed a novel measurement method for line impedance using LC resonance, which the authors describe first place. In the second place, the authors propose another line impedance. The novel method is that the rectangular wave with minimum voltage is injected into the distribution line system. By means of this method, the line capacitance and the line inductance can be measured. These proposals are confirmed by the simulation or experiment. Finally, the frequency response analysis method is to be examined, whose mechanism and results are to be presented and discussed.展开更多
After the digital revolution, the power system security becomes an important issue and it urges the power producers to maintain a well secured system in order to supply a quality power to the end users. This paper pre...After the digital revolution, the power system security becomes an important issue and it urges the power producers to maintain a well secured system in order to supply a quality power to the end users. This paper presents an integrated Corrective Security Constrained Optimal Power Flow (CSCOPF) with Flexible Transmission Line Impedance (FTLI) to enhance the power system security. The corrective approach of SCOPF is chosen, because it allows the corrective equipment to bring back the system to a stable operating point and hence, it offers high flexibility and better economics. The concept of FTLI arises from the ability of FACTS devices such as Thyristor Controlled Series Capacitor (TCSC), which can vary the line reactance to a certain extent. An enhanced security can be achieved by incorporating FTLI into the CSCOPF problem, since the power flow in a system is highly dependent on the line reactance. FTLI based CSCOPF can reduce the amount of rescheduling of generators, but it will result in an increased number of variables and thus, the complexity to the optimization process is increased. This highly complex problem is solved by using nonlinear programming. The AC based OPF model is preferred, since the corrective security actions require highly accurate solutions. IEEE 30 bus system is used to test the proposed scheme and the results are compared with the traditional CSCOPF. It can be seen that the proposed idea provides a notable improvement in the reduction of cost incurred for restoring the system security.展开更多
An adaptive droop control strategy is proposed for a parallel distributed multi-energy storage system of an isolated DC microgrid with unmatched line impedance and abnormal communication.System line impedance mismatch...An adaptive droop control strategy is proposed for a parallel distributed multi-energy storage system of an isolated DC microgrid with unmatched line impedance and abnormal communication.System line impedance mismatch can cause unbalanced load power distribution and reduce service life of distributed energy storage unit(DESU).Therefore,an improved droop control based on mixed coefficient compensation of state of charge(SOC)and voltage is designed,which can adaptively adjust a power characteristic curve according to the sampling period,so as to ensure precise distribution of load power while minimizing voltage deviation.Considering the stability of the system under communication anomaly,a non-communication backup control based on Metropolis acceptance criterion is proposed,which only uses internal data to adaptively adjust the droop coefficient.In addition,a gradual smooth handover strategy is designed through gradient coefficient to optimize control stability under communication anomaly.Finally,effectiveness and correctness of the proposed control strategy are verified by mathematical analysis and RTDS/DSP hardware-in-the-loop experiments.展开更多
At present,electrode line impedance supervision(ELIS)based protection is widely used to detect faults on grounding electrode lines,which are indispensable elements of high-voltage direct current(HVDC)systems.The exist...At present,electrode line impedance supervision(ELIS)based protection is widely used to detect faults on grounding electrode lines,which are indispensable elements of high-voltage direct current(HVDC)systems.The existing theoretical analysis of measured impedance is based on lumped line model and the threshold value is generally set according to engineering experience,which have caused the dead zone problem and even accidents.Therefore,a study on measured impedance of ELIS-based protection and its threshold value selection method is carried out to solve this problem.In this study,the expressions of measured impedance under normal operation and fault conditions are deduced based on rigorous and accurate line model.Based on the expressions,the characteristics of the measured impedance are calculated and analyzed.With the characteristics of the measured impedance,the applicability of the protection with the traditional threshold value is further discussed and the distribution of the dead zone can be located.Then,the method to calculate the threshold value of ELIS-based protection is proposed.With a proper threshold value selected by the proposed method,the dead zone of ELIS-based protection is effectively eliminated,and the protection can identify all types of faults even with large transition resistances.Case studies on PSCAD/EMTDC have been conducted to verify the conclusion.展开更多
Transmission expansion planning(TEP)addresses the intricate task of optimizing new transmission infrastructure within an existing grid to meet system objectives.As a critical strategy in power system development,TEP s...Transmission expansion planning(TEP)addresses the intricate task of optimizing new transmission infrastructure within an existing grid to meet system objectives.As a critical strategy in power system development,TEP significantly influences the long-term efficiency,reliability,and scalability of the network,with enduring effects on overall system performance.This paper explores the application of unconventional high surge impedance loading(HSIL)lines as a cost-effective alternative to conventional extra high-voltage(EHV)transmission lines.By optimizing the geometry of subconductors,HSIL designs could achieve higher power delivery capacities while operating at reduced voltage levels,addressing the increased demand for sustainable energy infrastructure.Two 500 kV HSIL line configurations are analyzed for their feasibility in replacing the conventional 765 kV transmission lines for the TEP to integrate the large-scale wind energy sources located in far remote areas.The analysis is carried out within the 23-bus EHV test system.This study reveals that both HSIL line configurations successfully meet the technical constraints of the TEP problem,ensuring reliable system operation even under contingency conditions.Therefore,the HSIL lines offer significant cost savings due to infrastructure and accessories at reduced voltage levels with much smaller right of way(ROW)than conventional counterparts.This underscores the potential of unconventional HSIL lines to contribute to more sustainable and cost-effective grid planning strategies for integrating large-scale renewable energy sources.展开更多
This paper gives an insight on the effect of transmission line temperature variations, resulting from loading and weather conditions changes, on a power system＇s steady state and dynamic performance. The impact of dy...This paper gives an insight on the effect of transmission line temperature variations, resulting from loading and weather conditions changes, on a power system＇s steady state and dynamic performance. The impact of dynamic load models on system stability is also studied. The steady-state and dynamic stability simulation results of a 39 bus system for constant line impedance （the traditional simulation practice） are compared to the results with estimated, but realistic, temperature varied line impedances using PSLF （positive sequence load flow） software. The modulated line impedances will affect the thermal loading levels and voltage profiles of buses under steady state response, while the dynamic results will show improved damping in electro-mechanical oscillations at generator buses.展开更多
In this paper,an improved load sharing strategy is proposed for distributed generation units(DGs)connected in a microgrid.Conventional frequency and voltage droop control result in unacceptable active and reactive pow...In this paper,an improved load sharing strategy is proposed for distributed generation units(DGs)connected in a microgrid.Conventional frequency and voltage droop control result in unacceptable active and reactive power sharing.The proposed method formulates a suitable algorithm for load sharing in the islanded microgrid.The feeder power loss and the line impedance voltage drops are minimized so as to regulate the voltage at the point of common coupling(PCC)at its nominal value.The desired DG output voltages are calculated and a linear relationship is obtained between the shared active and reactive powers and the DG output voltages.A master DG controller sets the frequency which is followed by other DG units.The reference powers for the DG units are adjusted so as to maintain the rated PCC voltage.The proposed strategy is verified taking into account the DG ratings,unequal line impedance drops,feeder losses,change in system impedance and effect of DG local loads and formulates an improved power sharing strategy that also facilitates PCC voltage regulation under variable loading conditions.Simulation and experimental results are presented to verify the effectiveness of the proposed method.展开更多
基金supported by National Natural Science Foundation of China(No.50637010)
文摘Based on the transmission line code TLCODE, a 1D circuit model for a transmission- line impedance transformer was developed and the simulation results were compared with those in the literature. The model was used to quantify the efficiencies of voltage-transport, energy- transport and power-transport for a transmission-line impedance transformer as functions of ψ （the ratio of the output impedance to the input impedance of the transformer） and Г （the ratio of the pulse width to the one-way transit time of the transformer） under a large scale of m （the coefficient of the generalized exponential impedance profile）. Simulation results suggest that with the increase in Г, from 0 to ∞, the power transport efficiency first increases and then decreases. The maximum power transport efficiency can reach 90% or even higher for an exponential impedance profile （m = 1）. With a consideration of dissipative loss in the dielectric and electrodes of the transformer, two representative designs of the water-insulated transformer are investigated for the next generation of petawatt-class z-pinch drivers. It is found that the dissipative losses in the electrodes are negligibly small, below 0.1%, but the dissipative loss in the water dielectric is about 1% to 4%.
文摘With a live wire, line impedance could be measured by means of only passive elements such as inductors or resistors, whose techniques are well known. However, as the voltage and current used for the measurement are increased, the size of the inductor or resistor being used also needs to be increased, so it would be virtually impossible to make an accurate measurement. Because of this, the authors have developed a novel measurement method for line impedance using LC resonance, which the authors describe first place. In the second place, the authors propose another line impedance. The novel method is that the rectangular wave with minimum voltage is injected into the distribution line system. By means of this method, the line capacitance and the line inductance can be measured. These proposals are confirmed by the simulation or experiment. Finally, the frequency response analysis method is to be examined, whose mechanism and results are to be presented and discussed.
文摘After the digital revolution, the power system security becomes an important issue and it urges the power producers to maintain a well secured system in order to supply a quality power to the end users. This paper presents an integrated Corrective Security Constrained Optimal Power Flow (CSCOPF) with Flexible Transmission Line Impedance (FTLI) to enhance the power system security. The corrective approach of SCOPF is chosen, because it allows the corrective equipment to bring back the system to a stable operating point and hence, it offers high flexibility and better economics. The concept of FTLI arises from the ability of FACTS devices such as Thyristor Controlled Series Capacitor (TCSC), which can vary the line reactance to a certain extent. An enhanced security can be achieved by incorporating FTLI into the CSCOPF problem, since the power flow in a system is highly dependent on the line reactance. FTLI based CSCOPF can reduce the amount of rescheduling of generators, but it will result in an increased number of variables and thus, the complexity to the optimization process is increased. This highly complex problem is solved by using nonlinear programming. The AC based OPF model is preferred, since the corrective security actions require highly accurate solutions. IEEE 30 bus system is used to test the proposed scheme and the results are compared with the traditional CSCOPF. It can be seen that the proposed idea provides a notable improvement in the reduction of cost incurred for restoring the system security.
基金supported by National Key Research and Development Plan of China(2018YFB1503001).
文摘An adaptive droop control strategy is proposed for a parallel distributed multi-energy storage system of an isolated DC microgrid with unmatched line impedance and abnormal communication.System line impedance mismatch can cause unbalanced load power distribution and reduce service life of distributed energy storage unit(DESU).Therefore,an improved droop control based on mixed coefficient compensation of state of charge(SOC)and voltage is designed,which can adaptively adjust a power characteristic curve according to the sampling period,so as to ensure precise distribution of load power while minimizing voltage deviation.Considering the stability of the system under communication anomaly,a non-communication backup control based on Metropolis acceptance criterion is proposed,which only uses internal data to adaptively adjust the droop coefficient.In addition,a gradual smooth handover strategy is designed through gradient coefficient to optimize control stability under communication anomaly.Finally,effectiveness and correctness of the proposed control strategy are verified by mathematical analysis and RTDS/DSP hardware-in-the-loop experiments.
基金supported by the National Natural Science Foundation of China for Distinguished Young Scholars(No.52025071)the Joint Funds of the National Natural Science Foundation of China(No.U1866205)。
文摘At present,electrode line impedance supervision(ELIS)based protection is widely used to detect faults on grounding electrode lines,which are indispensable elements of high-voltage direct current(HVDC)systems.The existing theoretical analysis of measured impedance is based on lumped line model and the threshold value is generally set according to engineering experience,which have caused the dead zone problem and even accidents.Therefore,a study on measured impedance of ELIS-based protection and its threshold value selection method is carried out to solve this problem.In this study,the expressions of measured impedance under normal operation and fault conditions are deduced based on rigorous and accurate line model.Based on the expressions,the characteristics of the measured impedance are calculated and analyzed.With the characteristics of the measured impedance,the applicability of the protection with the traditional threshold value is further discussed and the distribution of the dead zone can be located.Then,the method to calculate the threshold value of ELIS-based protection is proposed.With a proper threshold value selected by the proposed method,the dead zone of ELIS-based protection is effectively eliminated,and the protection can identify all types of faults even with large transition resistances.Case studies on PSCAD/EMTDC have been conducted to verify the conclusion.
基金supported by the National Science Foundation(NSF)(No.2306098)。
文摘Transmission expansion planning(TEP)addresses the intricate task of optimizing new transmission infrastructure within an existing grid to meet system objectives.As a critical strategy in power system development,TEP significantly influences the long-term efficiency,reliability,and scalability of the network,with enduring effects on overall system performance.This paper explores the application of unconventional high surge impedance loading(HSIL)lines as a cost-effective alternative to conventional extra high-voltage(EHV)transmission lines.By optimizing the geometry of subconductors,HSIL designs could achieve higher power delivery capacities while operating at reduced voltage levels,addressing the increased demand for sustainable energy infrastructure.Two 500 kV HSIL line configurations are analyzed for their feasibility in replacing the conventional 765 kV transmission lines for the TEP to integrate the large-scale wind energy sources located in far remote areas.The analysis is carried out within the 23-bus EHV test system.This study reveals that both HSIL line configurations successfully meet the technical constraints of the TEP problem,ensuring reliable system operation even under contingency conditions.Therefore,the HSIL lines offer significant cost savings due to infrastructure and accessories at reduced voltage levels with much smaller right of way(ROW)than conventional counterparts.This underscores the potential of unconventional HSIL lines to contribute to more sustainable and cost-effective grid planning strategies for integrating large-scale renewable energy sources.
文摘This paper gives an insight on the effect of transmission line temperature variations, resulting from loading and weather conditions changes, on a power system＇s steady state and dynamic performance. The impact of dynamic load models on system stability is also studied. The steady-state and dynamic stability simulation results of a 39 bus system for constant line impedance （the traditional simulation practice） are compared to the results with estimated, but realistic, temperature varied line impedances using PSLF （positive sequence load flow） software. The modulated line impedances will affect the thermal loading levels and voltage profiles of buses under steady state response, while the dynamic results will show improved damping in electro-mechanical oscillations at generator buses.
文摘In this paper,an improved load sharing strategy is proposed for distributed generation units(DGs)connected in a microgrid.Conventional frequency and voltage droop control result in unacceptable active and reactive power sharing.The proposed method formulates a suitable algorithm for load sharing in the islanded microgrid.The feeder power loss and the line impedance voltage drops are minimized so as to regulate the voltage at the point of common coupling(PCC)at its nominal value.The desired DG output voltages are calculated and a linear relationship is obtained between the shared active and reactive powers and the DG output voltages.A master DG controller sets the frequency which is followed by other DG units.The reference powers for the DG units are adjusted so as to maintain the rated PCC voltage.The proposed strategy is verified taking into account the DG ratings,unequal line impedance drops,feeder losses,change in system impedance and effect of DG local loads and formulates an improved power sharing strategy that also facilitates PCC voltage regulation under variable loading conditions.Simulation and experimental results are presented to verify the effectiveness of the proposed method.
