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The realization of fault location method based on traveling wave natural frequency depends on the extraction of traveling wave natural frequency. When the fault occurs on the power system with one or more nodes, there will be multiple reflections at the discontinuous wave impedance, which makes it difficult to extract the natural frequency principal component that represents the fault distance in the spectrum. Upon this foundation, a traveling wave natural frequency extraction method based on PSO and VMD is proposed in this paper. Firstly, PSO algorithm was used to calculate the envelope entropy of VMD at different parameters, and to select the optimal parameter combination corresponding to the minimum envelope entropy. Then, the fault traveling wave is decomposed by VMD based on the optimal parameter combination, and to extract principal components of natural frequency by analyzing spectrum. Finally, the simulation model of T-type transmission line is built to verify the reliability of this method. The simulation results show that this method can effectively suppress the influence of spectrum aliasing, accurately extract the natural frequency principal component including fault information, and the ranging error is small.

A large number of distributed generators access to low resistance grounding system may have great influence on the fault characteristics of single phase ground. In view of low resistance ground active distribution network, the connection mode of Inverter-interfaced Distributed Generators (IIDG) is discussed comprehensively based on operation safety and protection requirements. The equivalent model of IIDG and simplified zero sequence network model of low resistance grounding system contain multi-IIDG for single phase ground fault are established. The amplitude and phase characteristics of zero sequence current in single phase grounding fault of the system and the characteristics of high-resistance ground fault are analyzed. Simulative results by MATLAB/Simulink verifies the correctness of the analysis results of fault characteristics. The conclusions could be provided as reference for solving the grounding protection of system with high penetration of distributed generator.

Dynamics is one of the fundamentally important aspects of all space tether research. This paper derives the dynamic equations of electrodynamic tether system (EDT) in stationkeeping phase using Newton’s laws. This paper further analyzes the tether system motion rules under electrodynamic drag, gravity induced force, and tether tension. Numerical simulation of electrodynamic tether system in station-keeping phase is calculated using an approach that combines the central difference method, fourth-order Runge-Kutta method, and predictor-corrector method, among others. The simulation results show that the motion of electrodynamic tether in stationkeeping phase not only contains librations caused by the motion of endmass, but also contains vertical and longitudinal vibrations of tether. If the motion of endmass is ignored, it is much similar to the vibration of cable with two immovable pinned-supports, in which the mid-span has the largest amplitude of vibration. Based on this, the main satellite and the endmass at both ends of tether can be treated as immovable pinned-supports when the tether vibration and tension of electrodynamic tether system in impermanency are investigated.

A rigid - flexible coupling dynamic model is established for full reflection of the coupling between deformation of flexible body and large angle maneuver. Considering uncertainties of the flexible spacecraft a traditional PD controller and an adaptive attitude adjustment controller are designed to solve the attitude adjustment problem of the rigid-flexible coupling spacecraft based on Lyapunov method. These two controllers are compared in simulation analyses; results show that compared with the traditional PD controller, the adaptive controller can effectively suppress the influence of disturbance torques, with higher precision and better robustness, and be able to fulfill the important demand of attitude adjustment for the rigid-flexible coupling spacecraft.

A new control strategy is proposed, which integrates input shaping technique with feedback control for vibration reduction of rigid-flexible spacecraft. This strategy could ensure the achievement of attitude maneuver and the suppression of appendages vibration simultaneously. Considering the absence of the knowledge of modal variables of flexible appendages and the presence of external disturbances, a feedback controller which only requires spacecraft attitude and angular velocity measurement is designed. Combined with the feedback controller, a robust multiple mode input shaper is designed to enhance the system performance. This input shaper requires the eigenvalues of the whole close loop system, rather than the natural frequency and damping ratio of the flexible appendages. Simulation results show that the presented control strategy reduces the system response time and suppresses the vibration of the appendages successfully during the attitude maneuver. In addition, it can provide strong robustness to system parameter uncertainties.