To address the global climate crisis,achieving energy transitions is imperative.Establishing a new-type power system is a key measure to achieve CO_(2) emissions peaking and carbon neutrality.The core goal is to trans...To address the global climate crisis,achieving energy transitions is imperative.Establishing a new-type power system is a key measure to achieve CO_(2) emissions peaking and carbon neutrality.The core goal is to transform renewable energy resources into primary power sources.The large-scale integration of high proportions of renewable energy sources and power electronic devices will dramatically change the operational mechanisms and control strategies of power systems.Existing wind and solar converters mostly adopt the grid-following control mode,which leads to significant challenges in system security and stability as it is insufficient to support the frequency and voltage of the grid.On the other hand,grid-forming control technology(GFM)can provide voltage and frequency support for the system,and thus becomes an effective measure to improve the inertia and damping characteristics of power systems.This paper illustrates the principles,control strategies,equipment types,application scenarios,and project implementation of grid-forming technology.The simulation and analysis based on a renewable-dominated real new-type power system show that GFM can significantly enhance the frequency and voltage support capacity of the power system,improve renewable energy accommodation capacity and grid transmission capacity under weak grid conditions,and play an important role in enhancing the stability and power supply reliability of renewable-dominated new-type power systems.展开更多
This paper reviews the applications of line commutated converter based high voltage direct current transmission(LCC-HVDC)technologies in China,with a special focus on UHVDC technology developed in the last 10 years.Th...This paper reviews the applications of line commutated converter based high voltage direct current transmission(LCC-HVDC)technologies in China,with a special focus on UHVDC technology developed in the last 10 years.The paper examines six specific aspects of areas—voltage increase,capacity upgrade,reliability improvement,engineering design innovation,equipment and materials innovation,and the R&D of next step.Subsequent advances in LCC-HVDC technologies in recent years are also discussed.展开更多
This paper investigates the optimal recovery of Sobolev spaces W_(1)^(r)[-1,1],r∈N in the space L_(1)[-1,1].They obtain the values of the sampling numbers of W_(1)^(r)[-1,1]in L_(1)[-1,1]and show that the Lagrange in...This paper investigates the optimal recovery of Sobolev spaces W_(1)^(r)[-1,1],r∈N in the space L_(1)[-1,1].They obtain the values of the sampling numbers of W_(1)^(r)[-1,1]in L_(1)[-1,1]and show that the Lagrange interpolation algorithms based on the extreme points of Chebyshev polynomials are optimal algorithms.Meanwhile,they prove that the extreme points of Chebyshev polynomials are optimal Lagrange interpolation nodes.展开更多
Based on completely mastering±800 kV transmission technologies,the first±1100 kV direct current(DC)transmission demonstration project is being constructed in China.Combining theoretical analysis and a large ...Based on completely mastering±800 kV transmission technologies,the first±1100 kV direct current(DC)transmission demonstration project is being constructed in China.Combining theoretical analysis and a large number of experiments,the margin of switching overvoltage in converter stations,the configuration scheme and performance of lightning arresters,the shielding angles of ground lines under different geographical conditions,and the maximum air gap of lines have been determined.The switching impulse flashover characteristics of equipotential sphere and typical rod-plane air gaps are also provided.The external insulation is designed differently for light,medium,and heavy pollution areas.For the±1100 kV project,if the 8×1250 mm^(2)conductors are applied,the pole gap is 26 m and the height of the line is 25 m,all the electromagnetic parameters will meet the requirement of international electromagnetic standards.The key design points of±1100 kV converter transformers,smoothing reactors,converter valves,and wall bushings are researched and the 75 mH smoothing reactors,±1100 kV/5000 A converter valves,and±1100 kV/5523 A wall bushings are successfully made.The optimised hierarchical connection modes and coordination control measure of the±1100 kV project are studied and the results can provide sufficient technical support for the demonstration project.展开更多
Connecting the voltage source converters(VSCs) to various types of AC systems results in different operation characteristics and core problems associated with traditional control strategies. Therefore, it is necessary...Connecting the voltage source converters(VSCs) to various types of AC systems results in different operation characteristics and core problems associated with traditional control strategies. Therefore, it is necessary to optimize the control strategies of the VSCs according to the types of AC systems.For the VSCs connected to islanded renewable power plants, a voltage/frequency(V/f) droop control strategy is proposed to damp fluctuations of AC voltage and frequency in the island,which is vital for bipolar VSC control. In addition, a multibranch impedance equivalent method for renewable power plants is proposed, with which large-scale renewable power plants can be modeled accurately in the frequency domain to prevent wide-band oscillation. For the VSCs connected to strong AC systems, smart AC voltage and coordinated frequency transient control strategies are proposed, which can improve AC system transient stability. For the VSCs connected to weak AC systems, the relationship between the system stability and strength is analyzed, and then the control strategy of inner-loop control parameter optimization and outer-loop power limiting(if necessary) is proposed to improve the stability of the allied system. The proposed strategies are verified by both software simulation and field commissioning.展开更多
文摘To address the global climate crisis,achieving energy transitions is imperative.Establishing a new-type power system is a key measure to achieve CO_(2) emissions peaking and carbon neutrality.The core goal is to transform renewable energy resources into primary power sources.The large-scale integration of high proportions of renewable energy sources and power electronic devices will dramatically change the operational mechanisms and control strategies of power systems.Existing wind and solar converters mostly adopt the grid-following control mode,which leads to significant challenges in system security and stability as it is insufficient to support the frequency and voltage of the grid.On the other hand,grid-forming control technology(GFM)can provide voltage and frequency support for the system,and thus becomes an effective measure to improve the inertia and damping characteristics of power systems.This paper illustrates the principles,control strategies,equipment types,application scenarios,and project implementation of grid-forming technology.The simulation and analysis based on a renewable-dominated real new-type power system show that GFM can significantly enhance the frequency and voltage support capacity of the power system,improve renewable energy accommodation capacity and grid transmission capacity under weak grid conditions,and play an important role in enhancing the stability and power supply reliability of renewable-dominated new-type power systems.
基金supported in part by The National Key Technology R&D Program(No.2006BAA02A00).
文摘This paper reviews the applications of line commutated converter based high voltage direct current transmission(LCC-HVDC)technologies in China,with a special focus on UHVDC technology developed in the last 10 years.The paper examines six specific aspects of areas—voltage increase,capacity upgrade,reliability improvement,engineering design innovation,equipment and materials innovation,and the R&D of next step.Subsequent advances in LCC-HVDC technologies in recent years are also discussed.
基金supported by the National Natural Science Foundation of China(Nos.11871006,11671271)。
文摘This paper investigates the optimal recovery of Sobolev spaces W_(1)^(r)[-1,1],r∈N in the space L_(1)[-1,1].They obtain the values of the sampling numbers of W_(1)^(r)[-1,1]in L_(1)[-1,1]and show that the Lagrange interpolation algorithms based on the extreme points of Chebyshev polynomials are optimal algorithms.Meanwhile,they prove that the extreme points of Chebyshev polynomials are optimal Lagrange interpolation nodes.
文摘Based on completely mastering±800 kV transmission technologies,the first±1100 kV direct current(DC)transmission demonstration project is being constructed in China.Combining theoretical analysis and a large number of experiments,the margin of switching overvoltage in converter stations,the configuration scheme and performance of lightning arresters,the shielding angles of ground lines under different geographical conditions,and the maximum air gap of lines have been determined.The switching impulse flashover characteristics of equipotential sphere and typical rod-plane air gaps are also provided.The external insulation is designed differently for light,medium,and heavy pollution areas.For the±1100 kV project,if the 8×1250 mm^(2)conductors are applied,the pole gap is 26 m and the height of the line is 25 m,all the electromagnetic parameters will meet the requirement of international electromagnetic standards.The key design points of±1100 kV converter transformers,smoothing reactors,converter valves,and wall bushings are researched and the 75 mH smoothing reactors,±1100 kV/5000 A converter valves,and±1100 kV/5523 A wall bushings are successfully made.The optimised hierarchical connection modes and coordination control measure of the±1100 kV project are studied and the results can provide sufficient technical support for the demonstration project.
文摘Connecting the voltage source converters(VSCs) to various types of AC systems results in different operation characteristics and core problems associated with traditional control strategies. Therefore, it is necessary to optimize the control strategies of the VSCs according to the types of AC systems.For the VSCs connected to islanded renewable power plants, a voltage/frequency(V/f) droop control strategy is proposed to damp fluctuations of AC voltage and frequency in the island,which is vital for bipolar VSC control. In addition, a multibranch impedance equivalent method for renewable power plants is proposed, with which large-scale renewable power plants can be modeled accurately in the frequency domain to prevent wide-band oscillation. For the VSCs connected to strong AC systems, smart AC voltage and coordinated frequency transient control strategies are proposed, which can improve AC system transient stability. For the VSCs connected to weak AC systems, the relationship between the system stability and strength is analyzed, and then the control strategy of inner-loop control parameter optimization and outer-loop power limiting(if necessary) is proposed to improve the stability of the allied system. The proposed strategies are verified by both software simulation and field commissioning.
