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Super agile imaging mode can effectively solve the contradiction between short transit time and various imaging tasks, and can significantly improve the satellite observation efficiency. The premise of its on-orbit implementation is to greatly improve the attitude control ability of satellite platform. In order to satisfy the requirement of super agile attitude maneuver control for multi-target imaging task, an "attitude planning + moving horizon tracking" control scheme for rigid satellite using reaction wheels is designed. Based on the analysis of the performance requirement of attitude control for multi-target imaging task, two methods of attitude determination in the stages of attitude maneuver and stable control are proposed. The control model of the rigid satellite is established, and the super agile attitude maneuver trajectory is designed based on the three-stage planning method, then the moving horizon optimization tracking control method is proposed to realize the super agile attitude maneuver control. The effectiveness of the proposed control scheme is demonstrated by numerical simulation.

The spontaneous imbibition of water into the matrix and gas-filled fractures of unsaturated porous media is an important phenomenon in many geotechnical applications. Previous studies have focused on the imbibition behavior of water in the matrix, but few works have considered spontaneous imbibition along fractures. In this work, a new fractal model, considering the water losses from the fracture to the matrix, was established to predict the sorptivity of rough-walled fracture. A fractal model, considering the fractal dimension of tortuosity, was modified to estimate the sorptivity of the matrix. Both of the models have a time exponent α and can be simplified to the classical Lucas–Washburn (L–W) equation with α = 0.50. To verify the proposed models, quantitative data on the imbibition of water in both the matrix and the fracture of unsaturated sandstone were acquired by neutron radiography. The results show that the motion of the wetting front in both the matrix and the fracture does not obey the L–W equation. Both theory and experimental observations indicate that fracture can significantly increase spontaneous imbibition in unsaturated sandstone by capillary action. Compared with the classical L–W equation, the models proposed in this study offers a better description of the dynamic imbibition behavior of water in unsaturated fractured sandstone and, thus, more reliable predictions of the sorptivity of the matrix and the fracture. Moreover, a new method to estimate the time exponent of rough-walled fracture in sandstone was also provided.

The system inertia and the primary frequency modulation capacity are decreased by the reduction of the traditional conventional unit start-up capacity as the rapid development of wind power. The active power disturbance is increased after system frequency change rate. It is indispensable to study the inertia compensation and primary frequency modulation methods provided by wind turbines. A fuzzy adaptive virtual frequency modulation control strategy for wind power is proposed by analyzing the frequency modulation characteristics of wind turbines. Firstly, the mathematical model of wind power participation in frequency modulation and the frequency response model of the high proportion system is established. Secondly, analyzing the frequency change characteristics of the system after the disturbance, and establishing the wind power fuzzy control rules for the shortcomings of insufficient fixed parameter control, the stability of the fuzzy control rule parameters are analyzed by the root locus method. Finally, the effectiveness of the fuzzy control is verified by simulation, and the system stability is improved.

Aiming at the characteristics of the large-scale power electronic equipment access in modern power system, the inertia is continuously reduced. Based on the stability graph theory, the inertia evaluation method for power electronic system is proposed and designed. The method derives the relationship between inertia and active power from the second-order rocking equation model of the power system. Then, based on the output equivalence principle, the equivalent model of the new energy generation system is established by the synchronous machine rocking model. Further, the combination is stable. The graph method identifies the equivalent inertia of the wind farm and the fan based on the active power of the grid connection point. The simulation and measured tests show that the inertia estimated by this method can effectively adapt to the evaluation of the equivalent inertia of the wind farm, thus significantly improving the level of inertia assessment of the power system.

In this paper, a non-along track imaging mode for remote sensing of satellite is introduced, and a ground experiment verification method is proposed, the feasibility of the control scheme is verified by mathematical simulation and physical experiment. The control requirements of satellite attitude in the non-along track imaging process are analyzed, based on the quaternion feedback control method proposed by Bong Wie, the attitude maneuver control law satisfying various constraints is given. By constructing a small three axis air bearing table control system and camera imaging system, the non-along track imaging scheme is verified. The experimental results show that the pointing control accuracy is better than 0.05 ° , the tracking accuracy of attitude angular velocity is better than 0.005 ° /s, and the imaging result of non-along track is good.

In order to solve the voltage over-limit problem of distributed photovoltaic(PV) connected to string lines, it is feasible to fully utilize the reactive power regulation ability of PV systems to adjust the line's voltage. In this paper, based on analyzing the mechanism of the point of interconnection(POI) of PV systems voltage over-limit and the voltage sensitivity of low-voltage string lines, a reactive power voltage control strategy named Q(U, P) was proposed, which is based on the POI voltage and the active power of PV. This control strategy inherits the advantages of Q(U) and cosφ(P) control strategies, determines the reactive power reference value by detecting the POI voltage and active power output of the PV systems. The simulation results show that the proposed control strategy satisfies the grid voltage within the rated range, the total absorbed amount of reactive power is lower and the active and reactive loss of grid are less than the existing control strategies.