In order to study the microstructure properties of different regions of welding heat affected zone (HAZ) of 1 000 MPa grade ultra-high strength steel, the samples of test steel at different peak temperatures of thermal cycle were prepared by welding thermal simulation technique, and the impact toughness of different regions of HAZ was studied through Charpy impact tests. The results showed that, in the subcritical region of HAZ (SCHAZ), the intercritical region of HAZ (ICHAZ) and the fine-grained region of HAZ (FGHAZ), the samples had relatively high impact absorption energy, crack propagation energy and dynamic impact toughness, and a large area of fiber region and shear lip formed on the fracture surface. Toughness dimples of different sizes can be seen at the microscopic level. The samples had good impact toughness. In the coarse-grained region of HAZ (CGHAZ), all impact data of the samples sharply decreased, and the fracture showed a macroscopic brittle fracture, almost all of which are radiological regions. At the microscopic level, it showed quasi cleavage fracture characteristics, indicating that the resistance to crack propagation decreased, and the time for stable propagation decreased after crack initiation, and the instability propagation was fast. The impact toughness of the samples deteriorated, and the CGHAZ region was a ductile valley region in HAZ. The results showed that the coarse grains and the coarse M-A island were the main causes of embrittlement in the CGHAZ region. The conclusion lays a theoretical foundation for the selection, development and engineering application of 1 000 MPa grade ultra-high strength steel in hydropower projects.

The efficient drying pre-treatment and gasification resource utilization of sewage sludge is one of the important ways to realize green and sustainable city development. Firstly, the thermogravimetric reactor was used to study the drying kinetics of sludge. Then, the influence of high temperature-low speed flue gas and low temperature-high speed flue gas on the sludge drying process was clarified based on Fluent numerical simulation. Finally, a new type of sludge and biomass co-gasification co-generation system was established by Aspen Plus, and the thermodynamic performance of the system was discussed. The results show that, the drying process of sludge in thermogravimetric reactor can be divided into the ascending stage, the first decreasing stage and the second decreasing stage, and the decreasing stage is the main stage. The water diffusion coefficients of SW-60 and SW-80 ranged from 6.34×10–6 to 3.72×10–5 m²/s and 3.69×10–5 to 2.60×10–4 m²/s, respectively. The drying activation energy of SW-60 and SW-80 was 9.55 kJ/mol and 28.25 kJ/mol, respectively, with the increase of initial moisture content. In the drying bed, the drying efficiency of high temperature-low speed flue gas is about 2.67 times that of low temperature-high speed flue gas. In the co-generation system, as the biomass blending ratio increases, the input heat, air flow, low heating value of syngas, yield of syngas and potential of co-generation all increase. However, the electrical efficiency, thermal efficiency and system efficiency will decrease slowly. When the biomass blending ratio is 20%, the blend of 30% moisture dry sludge and biomass can produce electrical energy potential and thermal energy potential of 0.61 kW·h and 4.212 MJ per kg, respectively.

Aiming at the lack of quantitative standards and assessment methods in the current comprehensive assessment of wind turbine control performance, a quantitative assessment method of control performance based on subspace linear quadratic Gaussian (LQG) is proposed. The subspace matrix method is used to solve the assessment trade-off curve, and the benchmark and assessment index of LQG control performance of wind turbines are established. By taking the turbine retrofitted by adding tower damping and load shedding control as an example of the assessment, the multivariate comprehensive quantitative assessment of pitch control performance before and after retrofitting is carried out by using two kinds of data processing strategies. The results show that, both data processing strategies can obtain accurate and effective quantitative evaluation results, and the proposed evaluation method can realize the comprehensive quantitative evaluation of the optimization effect of control strategies.

To study the coupling and oscillation characteristics of power equipment in microgrid, the energy functions of the wind turbine subsystem, generator and excitation subsystem in the doubly-fed wind turbine are deduced based on the transient energy flow method taking into account the wind speed and the control strategy of the unit. Then, the mechanism of the change of the energy consumption of each subsystem is investigated when the wind speed, the control parameters of the unit and other operational parameters change, and the oscillation characteristics of the unit are analyzed. Finally, the energy change and power oscillation characteristics of the doubly-fed wind turbine when the operation parameters change are analyzed by modeling and simulation on PSCAD/EMTDC platform, and the results are compared with the eigenvalue calculation results to verify the reasonableness of the analysis. At last, the influence mechanism of wind speed change on the oscillation of doubly-fed wind turbine is obtained.

A feedback control strategy based on Kalman filter was proposed to quantitatively study the drive train torsional vibration mitigation of doubly-fed wind turbine, and the control effect of drive train torsional vibration was compared through simulation calculation. Taking the drive train of 7.0 MW doubly-fed wind turbine as the research object, the Kalman filter was used to estimate the twist angle of the drive train, and an additional electromagnetic torque of the generator was designed for torque control based on the estimated torsional speed of low-speed shaft. The load and power generation calculations were compared with virtual damping control and no-damping control over 20 years full life cycle. The results show that, the correlation between the twist angle of the low-speed shaft estimated by the Kalman filter and the actual value can reach 0.99. The key differences between the feedback control based on the Kalman filter, the virtual damping control and the non-damping control are as follows. The equivalent fatigue load of the low-speed shaft of the drive train reduces by 2.11% and 4.89%, respectively. The equivalent fatigue load of the high-speed shaft of the drive train reduces by 1.99% and 4.78%, respectively. The power generation reduces by 200 kW·h and 700 kW·h, respectively. It can be concluded that the Kalman filter has a good estimating effect on the twist angle of drive train, and the designed additional electromagnetic torque based on the estimated torsional speed of low-speed shaft obtained by Kalman filtering has a very good suppression effect on the torsional vibration of the drive train.

The working environment of the ring main unit (RMU) in large solar photovoltaic power plants is complex and variable, faced with harsh environments such as temperature differences and humidity, it is extremely easy to cause operational failures of the ring grid cabinet, which seriously affects the safe and stable connection of solar photovoltaic to transmission lines. Based on the measured temperature and humidity data inside the RMU, utilizing the advantages of ARIMA and RBF model in linear and nonlinear data processing, a temperature and humidity prediction model with ARIMA-RBF weight combination is constructed to dynamically predict the temperature and humidity inside the RMU. The dynamic prediction of temperature and humidity in the actual loop cabinet of a photovoltaic power station is carried out. The prediction results show that, compared with the single model, the ARMI-RBF weight combination model has higher prediction accuracy and better stability. The combined model gives full play to the processing ability of a single model for different characteristics of data through appropriate weighting strategies, and can better evaluate the temperature and humidity state inside the RMU. It can provide a reference for the establishment of a more universal prediction model, and help to reduce the failure caused by long-term operation of the ring cabinet under ultra-mild and humid environment.

For the wind-solar-thermal-storage complementary power generation system without conventional power supply support, coordinated planning of installed capacity is of great significance to improve the operation economy and utilization rate of the power generation system. A two-layer optimal configuration method is proposed. The upper layer determines the installed capacity of the system with the minimum levelized cost of energy and the abandonment rate as the goal. The lower layer aims to maximize the consumption of new energy power generation and solve the problem of power distribution. The system capacity configuration is obtained by iterative optimization. Then, the optimization results are selected through Nash negotiation. Finally, the simulation analysis is carried out with the data of Hexi area in Gansu Province. The results show that, the levelized cost of energy is 0.306 4 yuan under the optimal capacity configuration of the wind-solar-thermal-storage complementary power generation system. The optimal ratio of the installed capacity of the wind farm plus photovoltaic power station to the installed capacity of the photothermal power station is 6:1. Compared with the wind-solar hybrid power generation system with the same installed capacity, the wind-solar-thermal-storage complementary power generation system has higher stability.

Building an efficient and pollution-free power generation system is an effective means to solve the current energy shortage and environmental pollution problems. By taking the C65 micro gas turbine produced by Capstone Company as the core power generation component, and coupling with the thermochemical process of solar powered ammonia decomposition to produce hydrogen, this article achieves multi-energy complementarity between renewable energy and ammonia chemical energy. The organic Rankine cycle is used as the bottom cycle to recover the waste heat from the flue gas generated by the micro gas turbine and generate electricity, achieving cascade energy utilization. A detailed simulation process is constructed in the chemical simulation software Aspen Plus. The results show that the complementary use of solar energy and ammonia has improved the calorific value of the generated hydrogen rich synthesis gas. The output power of the micro combustion engine is 89.95 kW, which is 24.95 kW more than the C65 micro combustion engine in the reference system. The electrical efficiency of the system under design conditions reaches 44.81%, and the thermal efficiency is 47.97%, which are 8.51 percentage points and 9.67 percentage points higher than that of the reference system, respectively. The component having the largest exergy loss in the system is the combustion chamber, accounting for 41.67% of the total damage, followed by the evaporator and regenerator, accounting for 14.31% and 11.15%, respectively. Sensitivity analysis shows that the electrical efficiency and thermal efficiency of the system decrease and increase with the increase of solar energy collection, respectively. The research results provide a reference for a distributed micro turbine power generation system using ammonia gas as fuel and coupled with solar energy.

In order to study the effect of backpacking containing barite powder on the heat transfer efficiency of buried pipe boreholes in plain and mountainous areas of Beijing, a comparative analysis of laboratory experiments and field thermal response experiments was carried out. The quaternary boreholes in plain areas were backfilled with medium sand and the bedrock boreholes in mountainous areas were backfilled with cement mortar. When the specific gravity of medium sand barite powder was 5%, the thermal conductivity of medium sand backfill samples increased by 14%. When 5% barite powder was added to cement mortar, the thermal conductivity increased 7.3%. According to the field thermal response test results, under summer conditions in the same site, the heat transfer rate of a backfilling borehole containing barite powder increased by 2.4 W/m and 3.5% per meter compared with that of the medium-sand backfilling borehole in plain area. The heat transfer rate of cement mortar backfill containing barite powder increased by 2.7 W/m and 3.9% per meter. The numerical simulation model of the quaternary system and bedrock area was established. It was found that the content of barite powder increased to 10% and the heat transfer rate of boreholes increased by about 6.0%. In general, the heat transfer capacity of buried pipe is improved and its sustainability gets better after adding barite powder.

In order to ensure safe operation of secondary cycle and reliability of steam generator, it is of great significance to reduce corrosion of equipment & piping of the cycle in nuclear power plant. With the deepening research on organic amines and the continuous accumulation of operation experience, the industry realized that the metal corrosion in the cycle during plant operation depends mainly on the pH at the operating temperature of locations of the cycle, i.e. pHt. To improve pHt at the locations of the cycle, performance characteristics of the main organic amines and their combinations are analyzed in this paper. Combined with the application experience and actual effects of organic amines at home and abroad, the application strategy of the main organic amines and their combinations are discussed and proposed, and the improvement suggestions are put forward with regard to current amine application status of the secondary cycle in China. Selections of amine or its combination should calculate the pHt at various locations to meet anti-corrosion requirements and evaluate effects on service life of resin beds in the system. Ethanolamine with stronger basicity and low volatility is suitably used in plant in which corrosion product is mainly from drain systems and condensate polishers are in continuous operation. 3-methoxyypropyl with strong basicity and moderate volatility can be used in most plants. Morpholine with weaker basicity and moderate volatility is suitably used in plants in which polishers are not in continuous operations. Dimethylamine and ammonia are suitably used with other amines because of their high volatility. Amine mixture application appears advantages on aspects of the anti-corrosion and service life of the resin beds.