Ethyl levulinate (EL) is a highly promising biomass fuel and additive, and the production of EL using yieldrich biomass is beneficial to the industrialized largescale production of EL. In this article, we studied the effects of sulfuric acid dosage, reaction time, reaction temperature and substrate concentration on the yield of EL using ultralow concentration sulfuric acid catalyzed cellulose, and optimized the EL production process by using response surface BoxBehnken model to study the effects of various factors on the yield of EL, and obtained the optimal process conditions for EL production from ultralow concentration sulfuric acid catalyzed cellulose: sulfuric acid dosage 0.5%, reaction temperature 204 °C, reaction time 240 min, substrate concentration 29 g/L reaction, the actual average yield of EL was 66.70%, with a relative error of 3.25% from the theoretical prediction. GCMS analyzed the distribution of alcoholysis products of ultralow concentration sulfuric acidcatalyzed cellulose under different reaction times, and proposed possible reaction pathways, the results of which can provide reference and reference for the alcoholysis conversion of cellulosic biomass.

The characteristics of zero moment of inertia of modular multilevel converter, it can not support the frequency fluctuation of AC power grid, so that the overall inertia of AC/DC hybrid system decreases, affecting the dynamic performance and stability of the system. Therefore, an improved powervoltage droop control combined with a virtual synchronous machine technology of coordinated control strategy, in the case of de voltage stability of ac power grid frequency adjustment, at the same time, reasonable allocation of power between the converter, in the case of without communication system to establish effective energy management system. In order to verify the feasibility and effectiveness of the proposed control strategy, a comparative test was conducted with the traditional double closedloop control. The results show that the proposed control strategy effectively solves the dynamic performance and stability problems of the system caused by low inertia and under damping.

Deep borehole heat exchangers (DBHE) is currently recognized as the most environmentally friendly way to exploit geothermal energy. The deep Ushaped borehole heat exchanger is a new type of DBHE which is being explored. Heat extraction capacity and influence radius are the important problems in the process of popularizing this technology. Based on the measured parameters of ground temperature and thermophysical properties, the heat extraction capacity and influence radius of the 2 500 m deep Ushaped borehole heat exchanger are analyzed by the way of insitu test and numerical simulation in Caotan area of Xi'an. The results show that the sustainable heat extraction power of the heat exchanger in 30 years is closed to 750 kW, with an average linear meter of 144 W; The attenuation degree and range of wall rock temperature increase with the increase of heat extraction power; The influence radius of the deep Ushaped borehole heat exchanger are different at different depths, and the deep stratum is larger than the shallow stratum as a whole; The influence radius of the 2 500 m deep Ushaped borehole heat exchanger with the heat extraction rates of 750 kW can greater than 100 m after work for 30 years, and there is a certain degree of thermal interference between the inlet well and outlet well of the Deep Ushaped borehole exchanger.

The virtual power plant technology provides a new path for userside demand response to enhance the potential of distributed energy consumption and fill the blind area of grid dispatching. In order to guide users to participate in power dispatching, a virtual energy storage model including smart home load and building phasechange energy storage system with combined cooling and heating was constructed based on the incentive demand response power purchase agreement, and the schedulable margin of various resources was quantitatively analyzed; Taking user response characteristics as an indicator, using entropy weight method to evaluate the dynamic response performance of various user loads, setting the dynamic response priority of virtual energy storage participating in dispatching; taking the maximum benefit of virtual power plants as the goal, comprehensively considering resource power purchase costs, electric heating Based on factors such as balance, a terminal virtual power plant optimal scheduling model that integrates distributed power sources and smart community incentive response loads is proposed, and an improved light optimization algorithm is used to solve the model. The results verify the effectiveness of the proposed method.

In response to the challenge posed by the limited accuracy of traditional fault diagnosis methods in wind turbine gearbox applications due to the complex and variable operational conditions and the presence of significant noise, the MTFSwin Transformer wind turbine gearbox fault diagnosis model is proposed. Initially, the onedimensional vibration time series signal is transformed into a twodimensional feature map with correlated temporal information using the Markov Transition Field (MTF) graph encoding method. Subsequently, this feature map is employed as the input for the Swin Transformer model, which utilizes a selfattention mechanism for automatic feature extraction. This process culminates in the classification of various fault types. The results demonstrate a fault diagnosis accuracy of 99.48%, affirming the effectiveness and superiority of the proposed method.

In order to further improve the efficiency and reliability of the local power grid in the process of fault recovery, this paper proposes an island partition strategy of local power grid with distributed generation based on improved GSAGWO algorithm. Firstly, the optimalworst method is used to evaluate the load to obtain the load weight value, so as to determine the priority of island division of important load restoration under local power grid fault. Secondly, combined with the load priority, the load level weight coefficient is determined, and the objective function model of island division of local power grid with distributed generation is constructed. Then, in order to obtain better objective function solution results, chaotic reverse learning and genetic annealing algorithm (GSA) are introduced to improve the grey wolf optimization algorithm (GWO) to improve the optimization performance of the algorithm. Finally, the modified IEEE 69 node is taken as an example for simulation analysis. The improved GSAGWO algorithm is used to solve the local distribution network fault model, and a better islanding result is obtained. The example analysis shows that the strategy proposed in this paper can accurately realize the optimal strategy of island division under local grid fault, ensure the restoration of power supply of important loads, and verify the effectiveness and superiority of the strategy.

In order to reduce the influences of renewable energy power fluctuations on power systems, an energy storage configuration optimization method considering renewable energy power probability distribution is proposed in this paper. Firstly, calculate and count the renewable energy power fluctuations at different time scales, and determine the probability distribution characteristics of renewable energy power. Secondly, according to the probability distribution characteristics and the gridconnected index of renewable energy, the configuration optimization model of energy storage considering the renewable energy timescale and power fluctuation is set up. Thirdly, based on the given constraints and time scale, calculate the minimum energy storage charging and discharging power where the fluctuations meet any set probability levels, thereby determining the rated power, capacity and initial state of the energy storage. At last, through calculation and analysis using the data measured from a 50 MW photovoltaic power station, the method is proved to be correct and effective. This method only compensates the fluctuated power that does not meet the fluctuation index, and has no impact on the power that has already satisfied.

With the high penetration of renewable energy and electronic equipment, the problem of wideband oscillation in power systems is becoming increasingly prominent, which has become a key factor restricting the efficient consumption of renewable energy. A wideband phasor measurement method is proposed and the corresponding device is developed to satisfy the requirements of wideband oscillation mitigation and protection in power systems with renewable energy. Based on the windowed discrete Fourier transform and three peak interpolation, this device can measure multi –mode wideband phasor of multiple voltages and currents. Besides, the amplitude and phase of high frequency phasor are compensated based on the linear regression, which effectively improves the measurement accuracy of the device while ensuring the dynamic response speed. Finally, the measurement performance of the developed device was verified by experimental testing with testers and realtime digital simulation, and the device can provide support for ensuring the safety and stability of power systems and the consumption of renewable energy.

The integrated energy system (IES) planning and optimization faces multiple challenges such as high volatility of new energy sources and large uncertainty of output. In view of this, this paper proposes a twostage capacitycost planning and optimization method for integrated energy systems considering scenery uncertainty. Firstly, Latin hypercube sampling is applied to generate the base wind and solar scenarios set, and the scenarios are reduced based on the improved kmeans algorithm. Secondly, a multiobjective optimization model is constructed with the lowest operating cost, optimal carbon emission reduction, and optimal pollutant emission reduction; finally, the system capacitycost twostage planning and optimization solution strategy is proposed, and a business park in the south is selected for the planning simulation. The simulation example shows that the twostage planning model of integrated energy system constructed in this paper can ensure the economy of system and environmental protection at the same time, and meet the multiple energy demands of users.

The wind turbines are subjected to continuous wind loads during their whole service life and are inevitably resisted earthquake action. In this paper, a large megawatt wind turbine is taken as the research object to simulate and analyze its deformation and mechanical responses under the conditions of normal operation, earthquake during shutdown and earthquake during operation. The results show that the deformation of wind turbine increases with the increase of tower height, and the horizontal displacement of the wind turbine under the earthquake is obviously less than that under the wind turbine operation state. With the increase of earthquake level, the horizontal displacement of the wind turbine is gradually increased. The deformation shape of the wind turbine remains unchanged, and the deformation of tower top is large. The influence of the wind turbine operating load on structural deformation response is significantly greater than that of small and medium earthquake actions. Meanwhile, the deformation response of the wind turbine under the combined action of operating load and earthquake is significantly greater than that under the separate action of two loads. In the structural design of the wind turbine, it is necessary to consider the coupling effect of the operating state and the earthquake. The stress response at the top of the tower is the largest, and its crosssection should be checked in the design.