It is a promising technology to store CO2 by hydrate formation in seafloor sediments. In this paper, the evolution process of CO2 hydrate formation promoted by amino acids in natural sand system was studied by hydrate formation test in a visible reactor. The experimental results showed that the formation rate and amount of CO2 hydrates in 8 mmol/L Lmethionine solution were significantly higher than those in deionized water system; The natural sand with medium particle size had the best promotion effect on the formation of CO2 hydrate, and a large amount of CO2 hydrates were generated in it, which effectively filled the gap between natural sands; Secondly, a lot of CO2 hydrates were also generated in small size natural sand; The effect of large particle size natural sand on promoting the formation of CO2 hydrate was not obvious, and no obvious CO2 hydrate formation was found inside, only a small amount of CO2 hydrates was observed on the inner wall of the reactor.

With the advancement of the "dual carbon" goal, the scale and capacity of randomly fluctuating new energy connected to the power grid are increasingly increasing, seriously affecting the safe and stable operation of the power grid. This paper proposes a power grid voltage security and stability control strategy based on time series convolutional residual network and Pelican optimization algorithm for the problem of voltage stability control in large disturbance faults. Firstly, taking advantage of the advantages of low loss of temporal convolutional information, wide receptive field, and strong deep feature extraction ability of residual networks, a voltage stability prediction model based on temporal convolutional residual networks is constructed, mapping the relationship between sensitive node voltage temporal features and voltage stability; Secondly, a voltage stability control model is constructed to output control strategies, and the Pelican optimization algorithm is utilized to solve the control model with its fast convergence speed and strong search ability, resulting in the optimal measures for machine and load shedding actions. Finally, after simulation and verification, the experimental results show that the proposed method improves the accuracy of voltage safety and stability prediction in the power grid, and improves the safe and stable operation level of the power grid after faults through the optimal voltage stability control strategy.

Aiming at the longterm operation of the mediumdeep coaxial borehole heating system which has issues of cold accumulation in rocksoil and decrease in the heat extraction capacity of the system, in this research, a numerical heat transfer model for MDGSHPs was established, the governing equations were discretized based on the finite difference method, and the accuracy of the model was verified with experimental data. This research separately studied the effects of heat storage temperature (Tin) and flow rate of hot water injection (G) on BHE heat extraction rate (Q), system energy consumption(W) and the coefficient of system performance (CSP) in the next heating period. The results show that the first step to realize heat storage is to determine the threshold value for the temperature of heat storage water. Below the threshold, heat storage will not be achieved, and the threshold temperature for this study is 50 °C. After operating for 500 hours, when the inlet water temperature increases from 50 °C to 80 °C, Q, W and CSP increase by 54.41 kW, 8.96 kW and 0.17. Furthermore, when the flow rate of hot water injection increases from 1 kg/s to 7 kg/s, the growth rate of Q, W and CSP are 7.71%, 6.34% and 1.19%. Therefore, a small flow rate with high temperature of heat storage water is recommended during the heat storage period which will improve heat storage effect and reduce energy consumption. This study provides a theoretical basis for heat storage in MDGSHPs.

Since the output voltage level of a range of green renewable energy sources is low, it is necessary to use Boost converter to increase the voltage level in the process of grid connection. A high gain Boost converter is proposed which not only achieves high voltage gain but also extends the circuit structure to meet higher boost requirements. Firstly, the operating principle and switching device stress of the proposed converter are theoretically analyzed, and the design method of the device parameters is given; then the boosting capability of the converter is comparatively studied, and the influence of nonideal devices on the voltage gain is analyzed; finally, the correctness and feasibility of the theoretical analysis are fully verified through the combination of simulation model building and experimental prototype.

Integrated energy system is an important means to improve the permeability of distributed new energy and enhance the flexibility of terminal energy consumption. In view of the shortcomings of existing technologies in the modeling of external energy characteristics of multienergy systems and the research of multisystem interaction strategies, this paper proposes a coordinated control method of integrated energy system based on virtual energy storage, and constructs threelayer energy architecture in terms of building layer, agent layer and distribution network layer based on multiagent technology.Based on the interactive architecture, the virtual energy storage model describing the external characteristics of the system is used as the interactive interface to quantitatively analyze and control the virtual energy storage of agents which regulates multi energy distributed resources, such as multi buildings, grid connected energy storage, micro gas turbine, etc. Furthermore, according to the system spatial scope, the hierarchical expansion and progressive analysis are carried out to build a multiagent based integrated energy system coordinated control strategy. The decisionmaking goal is to maximize the resource endowment of the building, park and other comprehensive energy systems so as to meet the energy demand as much as possible and realize autonomous operation.

As the interface of microgrid photovoltaic power generation system, inverter control strategy directly affects the stability of gridconnected system. The stability of gridconnected inverter is easily affected by the internal and external parameters of the system, especially when the gridconnected inverter adopts LCL filter, the design and operation conditions of the system become more and more complex. In this paper, an active disturbance rejection control strategy based on weighted average current is proposed to solve the disturbance problem of highorder gridconnected inverter system. Firstly, based on the WACC control principle, the system is reduced from third order to first order. At the same time, the internal and external disturbances of the inverter system are regarded as generalized disturbances of a single structure, and the control law is used to adjust the parameters of the closedloop system. Finally, the effectiveness of the control strategy is verified by simulation and experiment.

In order to calculate the time history response of wind turbine structure more accurately, the influence of wind shear, tower shadow and mountain environment was considered. Based on Kaimal selfpower spectrum and crosspower spectrum, the harmonic superposition method was used to simulate fluctuating wind speed. The spatial three dimensional non stationary wind field simulation method with wind direction correlation was established by using turbulence coherence model. Taking 2 MW wind turbine of a wind farm as an example, the correctness of the simulation method is verified and compared with the simulation results without considering the correlation of wind direction. The results from statistical analysis of simulated data and comparison with target spectrum demonstrated the accuracy and accuracy of the presented method, the simulation of threedimensional nonstationary fluctuating wind field can be realized. The results from statistical analysis of simulated data and comparison with target spectrum demonstrated accuracy of the presented method, and considering the correlation of wind direction can improve the simulation coincidence, which proves the necessity of simulation method.

This paper studied the simulation of methanol synthesis from CO2 and green hydrogen, and proposed an indicator of the energy storage density of CO2. Then influences of multiple variables on the performance indicators were analyzed. The results show that the systematic energy efficiency and energetic yield of methanol increase with the increase in the electrolysis efficiency, per pass CO2 conversion rate, electrolysis pressure, and initial CO2 pressure. However, these indicators decrease with the increase in the methanol synthesis pressure. The variations of the energy storage density of CO2 with these variables are opposite to the systematic energy efficiency and energetic yield. The electrolysis efficiency and per pass CO2 conversion rate are the sensitive and key variables of this process. Under the optimal conditions, the systematic energy efficiencies based on the higher and lower heating values are 68.0% and 59.6%, respectively, the energy storage density of CO2 is 6.07 kWh/kg, and the energetic yield of methanol is 0.108 kg/(kW·h), indicating the powertomethanol system using CO2 as feedstock is unsatisfactory in term of systematic energy efficiency, but has significant advantage in the energy storage density.

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.

Lignin is one of the main components of biomass and can be converted into renewable fuels and chemicals by catalytic hydrodeoxygenation. Extensive fundamental research has been conducted based on lignin model compounds and heterogeneous catalytic systems. However, the hydrodeoxygenation of lignin model compounds with high selectivity remains a significant challenge due to their intricate molecular structures, which are featured with hydroxyl and methoxyl groups connected to the phenyl ring, leading to diverse reaction pathways. In this paper, the factors affecting the selectivity of the product were reviewed comprehensively. First, the reaction mechanisms and pathways involved in the hydrodeoxygenation of lignin model compounds were stated. Next, the factors influencing the selectivity of the products were summarized from two aspects. One aspect is focused on the hydrodeoxygenation catalysts, including catalyst components, promoters, supports, and preparation methods; the other is associated with the reaction conditions, including reaction temperature, hydrogen pressure, time, and solvents.