Modular multilevel converters(MMCs)have limited ability to withstand overcurrent.Additionally,the complex characteristics of faults make it extremely difficult to reliably identify the fault area within a short period...Modular multilevel converters(MMCs)have limited ability to withstand overcurrent.Additionally,the complex characteristics of faults make it extremely difficult to reliably identify the fault area within a short period.In this paper,the waveform of the transient current component is transformed into multiple intersecting curves in an alternative coordinate system,utilizing the principle of coordinate mapping.The internal and external faults are identified by determining the range of angles between the current waveforms and the time axis based on the intersecting regions of the curves.Subsequently,a unit protection scheme based on the transient current coordinate mapping interval is proposed.Finally,a modular multi-level converter-high voltage direct current(MMC-HVDC)system is built using PSCAD/EMTDC to validate the proposed scheme.The simulation results show that the proposed protection scheme is insensitive to factors such as current fluctuations caused by noise and distributed capacitive currents.In addition,it shows high robustness against fault resistance.展开更多
We show that there exists an underlying manifold with a conformal metric and compatible connection form, and a metric type Hamiltonian （which we call the geometrical picture）, that can be put into correspondence wit...We show that there exists an underlying manifold with a conformal metric and compatible connection form, and a metric type Hamiltonian （which we call the geometrical picture）, that can be put into correspondence with the usual Hamilton-Lagrange mechanics. The requirement of dynamical equiva- lence of the two types of Hamiltonians, that the momenta generated by the two pictures be equal for all times, is sufficient to determine an expansion of the conformal factor, defined on the geometrical coordinate representation, in its domain of analyticity with coefficients to all orders determined by functions of the potential of the Hamiltonian-Lagrange picture, defined on the Hamilton-Lagrange coordinate representation, and its derivatives. Conversely, if the conformal function is known, the potential of a Hamilton-Lagrange picture can be determined in a similar way. We show that arbi- trary local variations of the orbits in the Hamilton-Lagrange picture can be generated by variations along geodesics in the geometrical picture and establish a correspondence which provides a basis for understanding how the instability in the geometrical picture is manifested in the instability of the the original Hamiltonian motion.展开更多
基金supported by the Tianshan Talent Training Program(No.2022TSYCLJ0019)the National Key R&D Program of China(No.2021YFB1507000)+1 种基金the Excellent Doctoral Research and Innovation Project of Xinjiang University(No.XJU2022BS094)the Natural Science Foundation of Xinjiang Uygur Autonomous Region Sponsored Programs(No.2022D01C662).
文摘Modular multilevel converters(MMCs)have limited ability to withstand overcurrent.Additionally,the complex characteristics of faults make it extremely difficult to reliably identify the fault area within a short period.In this paper,the waveform of the transient current component is transformed into multiple intersecting curves in an alternative coordinate system,utilizing the principle of coordinate mapping.The internal and external faults are identified by determining the range of angles between the current waveforms and the time axis based on the intersecting regions of the curves.Subsequently,a unit protection scheme based on the transient current coordinate mapping interval is proposed.Finally,a modular multi-level converter-high voltage direct current(MMC-HVDC)system is built using PSCAD/EMTDC to validate the proposed scheme.The simulation results show that the proposed protection scheme is insensitive to factors such as current fluctuations caused by noise and distributed capacitive currents.In addition,it shows high robustness against fault resistance.
文摘We show that there exists an underlying manifold with a conformal metric and compatible connection form, and a metric type Hamiltonian （which we call the geometrical picture）, that can be put into correspondence with the usual Hamilton-Lagrange mechanics. The requirement of dynamical equiva- lence of the two types of Hamiltonians, that the momenta generated by the two pictures be equal for all times, is sufficient to determine an expansion of the conformal factor, defined on the geometrical coordinate representation, in its domain of analyticity with coefficients to all orders determined by functions of the potential of the Hamiltonian-Lagrange picture, defined on the Hamilton-Lagrange coordinate representation, and its derivatives. Conversely, if the conformal function is known, the potential of a Hamilton-Lagrange picture can be determined in a similar way. We show that arbi- trary local variations of the orbits in the Hamilton-Lagrange picture can be generated by variations along geodesics in the geometrical picture and establish a correspondence which provides a basis for understanding how the instability in the geometrical picture is manifested in the instability of the the original Hamiltonian motion.
