Application of thyristor controlled phase shifting transformer excitation impedance switching control to suppress short-circuit fault current level

Short-circuit fault current suppression is a very important issue in modern large-interconnected power networks. Conventional short-circuit current limiters, such as superconducting fault current limiters, have to increase additional equipment investments. Fast power electronics controlled flexible AC transmission system(FACTS)devices have opened a new way for suppressing the fault current levels, while maintaining their normal functionalities for steady-state and transient power system operation and control. Thyristor controlled phase shifting transformer(TCPST) is a beneficial FACTS device in modern power systems, which is capable of regulating regional powerflow. The mathematical model for TCPST under different operation modes is firstly investigated in this study. Intuitively, the phase shifting angle control can adjust the equivalent impedance of TCPST, but the effect has been demonstrated to be weak. Therefore, a novel transformer excitation impedance switching(EIS) control method, is proposed for fault current suppressing, according to the impedance characteristics of TCPST. Simulation results on IEEE 14-bus system have shown considerable current limiting characteristic of the EIS control under various fault types. Also, analysis of the timing requirement during fault interruption, overvoltage phenomenon, and ancillary mechanical support issues during EIS control is discussed,so as to implement the proposed EIS control properly for fast fault current suppression.

Distributionally Robust Optimal Reactive Power Dispatch with Wasserstein Distance in Active Distribution Network

The uncertainties from renewable energy sources(RESs)will not only introduce significant influences to active power dispatch,but also bring great challenges to the analysis of optimal reactive power dispatch(ORPD).To address the influence of high penetration of RES integrated into active distribution networks,a distributionally robust chance constraint(DRCC)-based ORPD model considering discrete reactive power compensators is proposed in this paper.The proposed ORPD model combines a second-order cone programming(SOCP)-based model at the nominal operation mode and a linear power flow(LPF)model to reflect the system response under certainties.Then,a distributionally robust optimization(WDRO)method with Wasserstein distance is utilized to solve the proposed DRCC-based ORPD model.The WDRO method is data-driven due to the reason that the ambiguity set is constructed by the available historical data without any assumption on the specific probability distribution of the uncertainties.And the more data is available,the smaller the ambiguity would be.Numerical results on IEEE 30-bus and 123-bus systems and comparisons with the other three-benchmark approaches demonstrate the accuracy and effectiveness of the proposed model and method.

Anionic MOF derived Bimetallic Ni_(x)Co_(y)@Nano-porous carbon composites toward strong and efficient electromagnetic wave absorption

Metal-organic frameworks (MOFs) derived metallic nanoparticles embedded nano-porous carbon (NPC)composites have shown to be promising microwave absorbing materials. Although MOF precursors withdiverse compositions and morphologies have been extensively investigated, anionic MOFs are rarelyexplored for this utility. In addition to the metal sites and ligands on the MOF framework, the guestcounter-cations in the void provide supplementary parameters to tune the capability of microwaveabsorption. Herein, we applied an anionic NixCoy-MOF featuring N-rich ligands and hierarchical porousstructures as a precursor for microwave absorption. The obtained dielectric-magnetic Ni_(x)Co_(y)@NPCcomposites with rich N dopants and multiple hetero-interfaces promote the microwave attenuationcapability through enhanced dipole/interfacial relaxation. The synergistic effects of magnetic loss andconduction loss induced by metallic nanoparticles (NPs) and porous graphitic layers further facilitate themicrowave dissipation. More significantly, impedance matching can be effectively improved by tuningthe Co/Ni amount in the precursors to realize the modulation of electromagnetic parameters. Conse-quently, Ni@NPC exhibits the optimal electromagnetic wave (EMW) absorption with minimum reflectionloss of 66 dB at only 2 mm and broad effective absorption band covering 4.56 GHz at a thin thickness of2.07 mm, making this material promising absorber for EMW elimination.