Controlled islanding is an important measure to ensure the stability of power system and avoid largescale power outages. However, the traditional researches method that regard the splitting surface determination as a single objective optimization problem neglect the stability of isolated subsystem. Therefore, a control islanding strategy considering the stability of subsystem with new energy is proposed in this paper. Firstly, the initial islanding surface with the minimum powerflow disruption is obtained based on the electrical connections and power flow distribution between nodes. Then considering the electrical coupling connectivity of key nodes and the penetration of new energy, the final islanding surface is searched in the neighborhood search space of the initial solution, to improve the stability of the isolated network subsystem after splitting. Finally, the proposed method is analyzed based on the New England 39bus system, and the simulation results validate the effectiveness and advancement of the method.

According to the different conditions of photovoltaic resources, ongrid price, initial total investment and light abandonment rate in various regions of China, a photovoltaic economic evaluation model is constructed to analyze the ongrid situation of photovoltaic power generation parity in various regions and calculate the minimum ongrid price and the maximum initial total investment that meet the benchmark yield in each region. The results show that there are obvious regional differences in China's photovoltaic economy. Considering the abandonment of light, a total of 15 regions in the country cannot achieve grid parity access, but most of them are close to parity access. Some regions with high photovoltaic economy can achieve parity with a price of 0.05 CNY/(kW·h) below the benchmark price. The research results of this paper are helpful to the investment decisionmaking of photovoltaic projects and the formulation of relevant policies.

In view of the large number of rocksocketed demand of offshore wind power foundation in China, horizontal loading characteristics and pilerock integrated failure mode of large diameter rocksocketed monopile foundation are studied by combining physical model test and numerical simulation method, and the analysis of the influences of bedrock strength, pile foundation diameter, wall thickness and rocksocketed depth on the horizontal bearing capacity of rocksocketed pile is carried out. The research shows that the flexural capacity of pile increases with the increase of bedrock strength. The failure mode of shallow bedrock of rocksocketed pile foundation follows passive wedge failure mode, while the failure mode of deep bedrock follows rotating failure mode. The horizontal bearing capacity of pile foundation can be improved with the increase of bedrock strength, pile diameter and depth of rock socketed, but the pile thickness has little effect on it. Critical depth of rocksocketed pile is found to improve the horizontal bearing capacity of rocksocketed pile. Pile diameter and overburden thickness have little effect on critical depth of rocksocketed pile, while bedrock strength is sensitive to its change.

It is difficult to control and predict the solidification process and the morphology of phase transition interface in sealed directional solidification. The directional solidification (DS) process model of solargrade polysilicon is solved by analytic method, and a high precision mathematical model of solidification process is obtained. The solidification height, instantaneous solidification rate and melt temperature distribution can be calculated from the easily measured heat dissipation temperature and solidification time. By solving the Poisson equation, a 3D model of phase transition interface was established. It is revealed that the heat flow rate q value on the side wall of the melt is the key factor to influence the interface morphology, which provided quantitative analysis basis for solidification process control. The large size (0.90 m × 0.90 m × 0.35 m) ingot casting experiments were carried out using 3303 industrial silicon as raw material in YITIPV vacuum ingot furnace. For the geometrically symmetric phase transition interface, the maximum deviation between the mathematical model and the experimental curve is 4.43%; for the irregular phase transition interface, the maximum deviation is 8.68%, and the solidification process model is modified according to the experimental results. The prediction accuracy and reliability of the 3D phase transition interface model were verified by detecting the parameters such as impurity content, resistivity and minority carrier lifetime, and comparing the typical phase transition interface morphologies of the four ingots.

An improved virtual synchronous generator (VSG) control strategy for multiinverter parallel system is proposed in this paper to suppress the circulating current caused by the impedance difference of transmission lines between PV microgrid inverters in islanded mode. Firstly, based on the traditional VSG control block diagram, each inverter counteracts the power loss on the transmission line by introducing the line power feedback, so as to improve the active and reactive power sharing accuracy, reduce the output voltage drop, and improve power quality. Then, the synchronous controller is introduced to reduce the instantaneous current and suppress the instantaneous circulating current between the multiinverter parallel system. Finally, the effectiveness of the proposed control strategy is verified by simulation and experiment.

In order to reduce external interference and ensure safe and stable power operation, a research on intelligent control of largescale wind power generation based on MQWaveNet for smart new energy is proposed. By constructing a smart new energy largescale wind turbine model, calculating the captured wind energy and blade tip speed values, adjusting the speed of the generator, and obtaining the optimal power coefficient. Input parameters such as air pressure, wind direction, and wind speed into a wavelet neural network, and obtain power values for the hidden layer and output layer based on the weights between layers; Combining multi view quantiles to form an MQWaveNet model, calculate the power generation prediction results for each quantile and clarify the temporal characteristics of wind power generation. Using Lyapunov function estimation, calculate the transformation and control vector of the sliding mode surface for wind power generation, reach the sliding mode surface within the range of multiple quantiles, and achieve intelligent and stable control of the wind power generation state. Through experiments, it has been proven that the studied model can improve the antiinterference ability of wind turbines and ensure the intelligent and stable operation of equipment.

To improve the fragmentation rate , particle size uniformity, and stability of straw micropulverization, a composite pulverizing method of moving and fixed cutter impact shear was proposed for the physical properties of straw, and a curved serrated blade pulverizing cutter was designed. The main factors affecting the pulverizing performance of straw and the way of fragmentation were clarified through the analysis of the shear mechanics of straw, the analysis of impact dynamics, and the mechanical analysis of pulverizing moving cutter. Based on EDEM numerical simulation, the effects of the serrated blade and smooth blade cutters on the pulverizing performance of straw were compared and analyzed. The simulation results show that when pulverizing corn straw with a moisture content of 20%, the number of connective keys of the serrated blade is 16.76% less than that of the smooth blade, the particle motion speed is increased by 15.9%, the total energy of particles is increased by 25.05%, and the impact force on the pulverizing chamber wall is reduced by 33.69% , and has a smoother working condition and lower energy consumption.

The instability of power generation in photovoltaic power generation system is difficult to avoid, and its instability will cause a great burden on the energy storage system, of which the impact on the service life of the battery is the most serious. Based on extended Kalman Filter (EKF) to achieve supercapacitor state of charge (SOC) estimation, according to the realtime photovoltaic output power and SOC of the supercapacitor, a new controllable topology is controlled to achieve hybrid energy storage of supercapacitor and battery, so as to alleviate the sudden change of battery charging voltage. In MATLAB/Simulink, the simulation model is constructed, the results show that the error of EKF estimating SOC is within 4%, and the fluctuation of the input voltage of the battery is significantly suppressed under the hybrid energy storage strategy, which can effectively reduce the impact of photovoltaic output instability on battery service life.

With the increase in the penetration rate of gridconnected wind power and the continuous expansion of the scale of wind farms, the integration of wind power into the grid will have a significant impact on the power quality and power dispatching of the regional power grids. In order to study the macroscopic dynamic response characteristics of wind farms under large disturbances, it is very important to carry out dynamic equivalent modeling of wind farms. Aiming at the research on dynamic equivalent modeling of wind farms, this paper briefly introduces the current mainstream wind turbine types and their model structures. Then, the reduced order method, the singlemachine equivalent method and the multimachine equivalent method of the equivalent modeling methods are compared and elaborated, and the calculation of equivalent parameters and the equivalent value of the collector network are summarized. Finally, the existing challenges in equivalent modeling of wind farms are summarized, and the future research directions are prospected.

Biomass pyrolysis can produce pyrolysis carbon and pyrolysis oil, of which the pyrolysis carbon is rich in surface functional groups and pore structures, while the pyrolysis oil contains a variety of components that can undergo redox reactions, which can be used for the preparation of fuel cell electrode materials and fuels, respectively. In this article, the working conditions of using wood pyrolysis oil as alkaline fuel cell fuel were optimized, and wood activated carbon (AC) and three types of wood pyrolysis carbon composite electrodes (AC/Fe, AC/Mn and AC/Fe/Mn) were prepared from wood pyrolysis carbon with K2CO3 activation and metal loading, furthermore the electrodes were analyzed using Fourier transform infrared spectroscopy, scanning electron microscopy, and electrochemical workstation. The microstructure, surface properties and electrochemical activity of the materials were analyzed by Fourier transform infrared spectroscopy and an electrochemical workstation. The results indicated that the optimal wood pyrolysis oil mass fraction and environmental temperature were 30% and 60 °C, respectively, when AC was used as the cathode electrode, at this point the current reached 3.10 mA; under the optimized conditions, the currents for AC/Fe, AC/Mn and AC/Fe/Mn were 8.02, 12.57, 15.25 mA, which were 159%, 305% and 392% higher than that of AC, respectively; under the optimized conditions, when AC/Fe/Mn was used as the cathode electrode and 12 mL of wood pyrolysis oil was added as the fuel, the fuel cell constructed from wood pyrolysis products could work continuously for 408.6 min with a total discharge capacity of 40.61 mAh.