Multiterminal hybrid HVDC systems,combining the advantages of conventional and flexible DC systems,are considered important development trends for future power networks.With the ability to suppress DC fault current,hy...Multiterminal hybrid HVDC systems,combining the advantages of conventional and flexible DC systems,are considered important development trends for future power networks.With the ability to suppress DC fault current,hybrid HVDC systems eliminate the requirement of current limiting reactors at both ends of DC lines.Thus,non-unit protection based on line boundaries is no longer applicable.In this paper,a non-unit protection scheme in cooperation with converter control is proposed to ensure protection speed,reliability,and sen-sitivity for multiterminal hybrid HVDC systems without line boundaries.In the proposed protection scheme,the protection criterion based on the transient energy of the DC voltage and the direction criterion based on the travelling wave are used to identify whether the fault occurs on the DC line.When the fault is detected as a DC-line fault,the relevant converter station is quickly blocked.After a specified hold-off duration,the converter station interfacing with multiple DC lines is prioritized for restart,while the remaining converter stations are restarted once the DC voltage is stabilized.Simulations based on PSCAD/EMTDC validate the feasibility of the proposed protection scheme and its superiority over competing approaches.展开更多
In this paper, we first give the definition of possibly non-unital function system, which is a characterization of the self-adjoint subspace of the space of continuous functions on a compact Hausdorff space with the i...In this paper, we first give the definition of possibly non-unital function system, which is a characterization of the self-adjoint subspace of the space of continuous functions on a compact Hausdorff space with the induced order and norm structure. Similar to operator system case, we define the unitalization of a possibly non-unital function system. Then we construct two possibly non-unital operator system structures on a given possibly non-unital function system, which are the analogues of minimal and maximal operator spaces on a normed space. These two structures have many interesting relations with the minimal and maximal operator system structures on a given function system.展开更多
An analytical method of fault characteristic for the HVDC system based on frequency response characteristics of boundary elements is presented here.The computational formulas of transfer function and input impedance a...An analytical method of fault characteristic for the HVDC system based on frequency response characteristics of boundary elements is presented here.The computational formulas of transfer function and input impedance are deduced using the distributed parameter model of HVDC transmission line,and the amplitude-to-frequency-characteristics of the transfer function and input impedance are analyzed.Based on the amplitude-to-frequency difference between internal and external faults,a non-unit protection method for VSC-HVDC transmission line is presented.Using the current ratio of high-to-low-frequency,this protection method can distinguish internal from external fault.The presented algorithm only uses local-end current,has high operation speed,and is easy to implement.Simulations on a±200 kV VSC-HVDC system are conducted to demonstrate the validity and feasibility of the developed protection method.展开更多
基金supported by the National Natural Science Foundation of China(No.52207088)the Natural Science Foundation of Hebei Province(No.E2024202184).
文摘Multiterminal hybrid HVDC systems,combining the advantages of conventional and flexible DC systems,are considered important development trends for future power networks.With the ability to suppress DC fault current,hybrid HVDC systems eliminate the requirement of current limiting reactors at both ends of DC lines.Thus,non-unit protection based on line boundaries is no longer applicable.In this paper,a non-unit protection scheme in cooperation with converter control is proposed to ensure protection speed,reliability,and sen-sitivity for multiterminal hybrid HVDC systems without line boundaries.In the proposed protection scheme,the protection criterion based on the transient energy of the DC voltage and the direction criterion based on the travelling wave are used to identify whether the fault occurs on the DC line.When the fault is detected as a DC-line fault,the relevant converter station is quickly blocked.After a specified hold-off duration,the converter station interfacing with multiple DC lines is prioritized for restart,while the remaining converter stations are restarted once the DC voltage is stabilized.Simulations based on PSCAD/EMTDC validate the feasibility of the proposed protection scheme and its superiority over competing approaches.
文摘In this paper, we first give the definition of possibly non-unital function system, which is a characterization of the self-adjoint subspace of the space of continuous functions on a compact Hausdorff space with the induced order and norm structure. Similar to operator system case, we define the unitalization of a possibly non-unital function system. Then we construct two possibly non-unital operator system structures on a given possibly non-unital function system, which are the analogues of minimal and maximal operator spaces on a normed space. These two structures have many interesting relations with the minimal and maximal operator system structures on a given function system.
基金supported in part by the Science and Technology Project Funds through Grid State Corporation(Grant No.SGSNKYOOKJJS1501564)the National Science Foundation of China(Grant No.51477131).
文摘An analytical method of fault characteristic for the HVDC system based on frequency response characteristics of boundary elements is presented here.The computational formulas of transfer function and input impedance are deduced using the distributed parameter model of HVDC transmission line,and the amplitude-to-frequency-characteristics of the transfer function and input impedance are analyzed.Based on the amplitude-to-frequency difference between internal and external faults,a non-unit protection method for VSC-HVDC transmission line is presented.Using the current ratio of high-to-low-frequency,this protection method can distinguish internal from external fault.The presented algorithm only uses local-end current,has high operation speed,and is easy to implement.Simulations on a±200 kV VSC-HVDC system are conducted to demonstrate the validity and feasibility of the developed protection method.
