The interface between nanofillers and matrix plays a key role in determining the properties of nanocomposites, but the interfacial characteristics of nanocomposites such as molecular structure and interaction strength are not fully understood yet. In this work, the interfacial features of a typical nanocomposite, namely epoxy resin (EP) filled with boron nitride nanosheet (BNNS) are investigated by utilizing molecular dynamics simulation, and the effect of surface functionalization is analyzed. The radial distribution density (RDD) and interfacial binding energy (IBE) are used to explore the structure and bonding strength of nanocomposites interface. Besides, the interface compatibility and molecular chain mobility (MCM) of BNNS/EP nanocomposites are analyzed by cohesive energy density (CED), free volume fraction (FFV), and radial mean square displacement (RMSD). The results indicate that the interface region of BNNS/EP is composed of three regions including compact region, buffer region, and normal region. The structure at the interfacial region of nanocomposite is more compact, and the chain mobility is significantly lower than that of the EP away from the interface. Moreover, the interfacial interaction strength and compatibility increase with the functional density of BNNS functionalized by CH₃–(CH₂)₄–O– radicals. These results adequately illustrate interfacial characteristics of nanocomposites from atomic level.

Space charges accumulate easily at insulation interface of cable accessories, which cause different electric field distribution and aging characteristics compared to single-layered cable. To explore the space charge behavior in double-layered insulation of cable accessories, a one-dimensional (1D) axisymmetric model for bipolar charge transport is built in this work, in which the effects of temperature gradient and electric field gradient in the radial direction are considered. Then the influences of electric field/temperature gradient and interface position on transport behavior of space charges are investigated. The simulation results suggest that the charges accumulate easily at the interface, which severely reduce the electric field in the inner layer of insulation and further inhibit the injection and migration processes of charges. The charge density at the interface increases with temperature and voltage, which accelerates the decay of the charge injection, furthers the interface charges to reach the dynamic equilibrium state quickly. The charge density at the interface and the electric field distribution are closely related to the interface position, and the electric field is more uniform when XLPE occupies the 1/3 to 1/2 inner part of the whole insulation.

This paper introduces an improved rotor braking protection circuit configuration and the corresponding self-adaptive control strategy to enhance the low voltage ride-through (LVRT) capability of the doubly-fed induction generator (DFIG). The proposed protection circuit consists of a crowbar circuit and a series rotor braking resistor array, which guarantees the safe operation of wind generators under the LVRT. Moreover, to adapt the proposed protection and further enhance the performance of the improved configuration, a corresponding self-adaptive control strategy is presented, which regulates the rotor braking resistor and protection exiting time automatically through calculating the rotor current in the fault period. The LVRT capability and transient performance of the DFIG by using the proposed method is tested with simulation. Compared with the conventional crowbar protection or the fixed rotor braking protection, the proposed protection and the control strategy present several advantages, such as retaining the control of the rotor side converter, avoiding repeated operation of the protection and accelerating the damping of stator flux linkage during a grid fault.

The deep interdependence between electrical and natural gas system has great influence on the security of multi-carrier energy (MCE) systems. The large-scale access to distribution generation (DG) of clean energy makes it necessary to investigate the effects of uncertainties on the safe and stable operation of MCE systems. However, the existing probabilistic energy flow analysis for MCE systems pays little attention to the difference between the correlation of various DG during calculating the energy flow. Therefore, this paper investigates the probabilistic energy flow considering the uncertainties and correlations of various DG. A framework of MCE systems considering various coupling units including power to gas (P2G) and energy hub is initially proposed. For this, the Monte Carlo simulation (MCS) method based on Latin hypercube sampling (LHS) and Nataf transformation is specially designed to calculate the energy flow for each sample. The energy flow calculation method is composed of three-phase AC/DC alternating iteration method and improved Newton node mesh method considering the control mode of compressors. Finally, the test system containing improved IEEE123-node system and NGS48-node system have verified the accuracy of the proposed probabilistic energy flow calculation method.

Voltage sag is a significant problem that affects the quality of power, and some researches have been performed on this theme. The characteristic of load is an important factor affecting the voltage sag, which is rarely studied. This paper investigates the influence of dynamic characteristics of induction motor on voltage sag caused by short circuit fault. The analytic expression of induction electromotive force is derived by space vector method. The mechanism of amplitude and waveform changes caused by dynamic load characteristics of induction motor are analyzed. The results indicate that the voltage at the load terminal of the induction motor is higher than that at the static load during the sag. Besides, the voltage sag waveform is not in rectangular shape. The static load terminal voltage returns to normal value quickly, while the voltage at the load terminal of the induction motor needs about 200 ms after the fault is removed. Induction motors can reduce the magnitude of voltage sags caused by short circuit faults, but will extend the duration. At the same time, the bigger the induction motor capacity is, the longer the voltage recovery time after sag is.