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.

In order to solve the problem of incomplete utilization of waste heat in traditional solar thermal storage liquid air energy storage systems (LAESS) and further improve the roundtrip efficiency of the system, a liquid air energy storage system (LAESSO) coupled with solar thermal storage and a dual Organic Rankine Cycle on the basis of the LAESS system is developed. The thermodynamic model of the coupled system is established, and the influence of key parameters on system performance is analyzed. The results show that the net output power of subsystems ORC1 and ORC2 is 1 296 kW and 6 695.83 kW under typical operating conditions; the round trip efficiency of the new system can reach 117.63%; the exergy efficiency is 38.97%; and the energy efficiency is 28.88%, which are 12.58%, 2.35%, and 1.21% higher than those of the reference system, respectively. In addition, the system provides domestic hot water at a temperature of 364.15 K to the users, achieving cogeneration efficacy. Sensitivity analysis of key parameters shows that when the liquefaction pressure (compressor outlet pressure) increases from 15 MPa to 18 MPa and the liquefaction temperature (throttle inlet air temperature) rises from 93.15 K to 113.15 K, the air liquefaction rate, roundtrip efficiency, and exergy efficiency decrease with the increase of liquefaction pressure, and the increase of liquefaction pressure and temperature is not conducive to the system performance; however, when the exhaust pressure increases from 5.3 MPa to 7.7 MPa, the roundtrip efficiency and the exergy efficiency increases. The research results can provide some theoretical support for the liquidaircoupled solar system.

In order to improve the efficiency of CO2 cycle system for electric vehicle, a transcritical CO2 system with regenerator and gas injection in the middle was constructed. The effects of Tgo, Pg, Pm, B, AT on EER, Qe and To were studied by simulation. The results show that Pgo and Pm,opt makes the EER reach the maximum value, and the relationship between the Popt and the Tgo. An increase in To can degrade system performance, The performance of the system can be improved by increasing the amount of gas injection in the middle and the superheat of the regenerator, which can increase the EER by 15.64% and 6.07%, respectively, and the cooling capacity by 27.88% and 4.78%. The increase of the superheat of the regenerator will lead to the increase of the discharge temperature of the compressor, the gas injection in the middle can reduce the discharge temperature of the compressor, when the discharge temperature of the compressor is limited, the optimization ability of the regenerator to EER and cooling capacity can be increased by 203% and 173.87%. Compared with the basic transcritical CO2 system, the optimized system can increase the EER and cooling capacity by 18.38% and 35.03%.

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.

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 freezing and icing environment, the field tests of 2 MW wind turbine blades by aerothermal antiicing/deicing method is carried out to verify the antiicing/deicing effect and energy consumption. Firstly, this paper analyzes the complex process of blade surface icing and then its icing distribution on the surface of NACA64618 airfoil is simulated. Secondly, the blade active aerothermal antiicing/deicing system for 2 MW wind turbine is constructed in the field demonstration project. Finally, three tests are finished with the help of the panoramic infrared thermal imaging detection, including the static deicing test, static antiicing test and production test with antiicing, and then evaluate blade antiicing/deicing effect and heating energy consumption. The test results show that the blade surface begins to melt and fall off after continuous heating for 2 hours when the ice thickness is 30 mm and the heating control temperature is 50 °C, and the heating energy consumption power is less than 50 kW, which can provide a reference for the design of engineering application system of aerothermal antiicing and deicing of wind turbine blade.

In order to explore the fatigue performance of the wind turbine foundation with embedded ring when the blade mass is imbalanced, the additional load is derived by reconstructing the blade mass imbalance model of the wind turbine, a singlepoint simulation of the pulsating wind velocity spectrum is done based on the harmonic synthesis method theory to calculate the basic operating load such as the aerodynamic load of the wind turbine, the finite element model of the wind turbine bladetowerfoundation integration is established with the actual engineering as an example, and the structural selfresonance characteristics and the load response under the combined action of the basic operating load and the additional load are calculated. The results show that the deepening of the imbalanced quality of the wind turbine blades will lead to the intensification of the stress concentration phenomenon and the increase of the stress amplitude of the basic structure, which in turn will affect the fatigue performance and fatigue life of the structure. and the force characteristics of the concrete in the structure will be greatly affected, followed by the steel cage, and the foundation embeddedring is the smallest.

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.

With the increasing connection of renewable energy power plants (REPPs), there are some problems that power frequency distance protection criterion cannot identify grid faults. Therefore, this paper focuses on the extraction algorithm of power frequency and protection criteria in the device, and analyzes the adaptability of distance protection algorithms from different manufacturers with high proportion of renewable energy power plants. Regarding the power frequency extraction algorithm, the aperiodic component characteristics of the shortcircuit current provided by different renewable energy power plants were explored. The error of Fourier algorithm caused by the influence of harmonic was further derived. For the protection criteria, the adaptability of directional circle, polygon, phase comparison, and power frequency variation distance protection was compared and analyzed, and the distance protection criteria that can be well applied to high proportion of renewable energy power plants were clarified.

Largescale wind power grid integration increases the uncertainties of system operation. It is urgent to use rapidly adjustable resources to smooth the power imbalance caused by wind power and load fluctuation and consider the impact of spinning reserve calling process on the system power flow. Firstly, the probability distribution model of wind power and load prediction error is analyzed. Then, the optimal dispatching model of power system with N1 network security opportunity constraint and spinning reserve opportunity constraint is established, and the unit output is optimized with the goal of minimizing the total dispatching cost. Finally, the Benders decomposition method based on the identification method of active integer variables is used to deal with the N1 network security constraints to improve the solving efficiency. Using the modified IEEE30node test system, it is verified that the proposed model can guarantee the reserve availability, economy and safety of the system, and fully excavate the fast adjustable capacity of pumped storage.