In order to effectively monitor the abnormal tower vibration and ensure the unit operation safety, a data-knowledge-driven variable condition tower vibration prediction method based on long-short term memory (LSTM) and empirical mode decomposition (EMD)-eXtreme gradient boosting (XGBoost) algorithm step-by-step modeling is proposed. Firstly, the relationship between environmental and operational variables is stripped out based on the analysis of the unit's operating mechanism and the wind turbine SCADA operating parameters that affect tower vibration are identified. Then, the ultra-short term prediction of unit environmental wind speed and operating power is realized based on LSTM, and the unit data knowledge model is established based on the full working condition historical operating data. Finally, Hilbert-Huang transform (HHT) is used to decompose the vibration signal and extract the low frequency vibration of the tower, and build a tower vibration prediction model based on XGBoost algorithm. Through inputting the predictive variables, the prediction results of the tower low frequency vibration are output, and the prediction interval is determined. The results show that, the tower vibration prediction model can effectively predict the tower vibration, determine the tower operation condition, and ensure the smooth operation of the unit.

In recent years, the scale of wind power is growing rapidly, its economic analysis and cost modeling methods are also constantly improving. In order to summarize the existing methods and clarify the follow-up research ideas, the four stages of the whole life cycle of the wind power project are first explained. Then, the cost composition and modeling method of the whole life cycle of wind power projects are introduced, and the differences between onshore and offshore wind farms in this part are compared, and the relationship between life cycle and investment cost is discussed based on the above contents. In order to introduce the benefits of cost investment, the basic economic evaluation indexes and applicability of wind power projects are compared. On this basis, the future development trend is analyzed according to the existing problems, and some suggestions are put forward for the economic evaluation of wind power in different regions and environments. It is hoped that the work of this paper can provide reference for wind power cost modeling and economic evaluation under the new development trend.

Aiming at solving the problems of large number of wind turbine faults, complex fault knowledge relationship, large difference of knowledge expression and low efficiency of knowledge reasoning, a framework of acquisition, expression and reasoning of wind turbine fault knowledge is proposed. Firstly, through the failure mode and effect analysis method based on the fault tree analysis method, the expert knowledge of wind turbine trouble shooting and maintenance is comprehensively obtained and sorted out. Then, with the help of ontology theory, unstructured expert knowledge is expressed structurally to form a knowledge map and displayed visually. Combined with self-defined rules of ontology and causal reasoning model, the query and reasoning of fault causes are realized, which improves the efficiency of knowledge query and reasoning. Finally, the practicability of this method is illustrated by a specific unit fault case. The results of this study can provide a direction for the intelligent development of wind farm's operation and maintenance.

Large number of bolted structures exist in wind turbine equipment, once the bolt hole is defective, it may lead to fracture of the entire matrix and cause major accident, but the current bolt hole defect detection method has the situation of missed detection and misjudgment. Aiming at solving this problem, through investigation, theoretical analysis and physical research, two methods which combine special tooling with probe for bolt hole defect detection are developed, namely the direct beam method and the sector scanning deflection method. Taking the bolt hole of pitch bearing in wind turbine as the research object, the CIVA software is used to simulate the two detection methods, and the rectangular simulated crack can be detected. Experiments were carried out on the defects of rectangular grooves in the actual pitch bearing bolt holes, which showed that the direct beam method could realize the defect detection of bolt hole cracks. The research provides a new method for monitoring the service status of bolt holes, which is beneficial to ensure the safe service of bolted structures.

The wake effect of wind farm is the main factor affecting the performance of wind turbines in the downstream wind farm. The wake effect, load characteristics and fatigue damage of wind turbines in front, middle and rear of an offshore wind farm were quantitatively assessed by FAST.Farm, which is the latest opensource multi-physical field coupling simulation software tool of National Renewable Energy Laboratory (NREL). The results show that, the wind speed decreases and the turbulence intensity increases in turn in the wind farm along the flow direction. The fatigue damage of front-row, middle-row and back-row wind turbines increases with the inflow wind speed. Especially, under the condition of high inflow wind speed, the fatigue damage of the middle-row wind turbines at the blade root and the tower base increases exponentially, and the increase range is obviously higher than that of the front and back row wind turbine. It suggests that the structural strength of wind turbines in the central area should be improved to some extent in wind power pre-development and post-operation and maintenance work.

In view of the high failure rate of the insulated gate bipolar transistor (IGBT) of wind turbine converter and the fact that the failure occurs on a short time scale, a health state assessment method of the IGBT based on dynamic regularization and Park vector centrifugal change rate is proposed. The similarity calculation model is established by using the dynamic regularization algorithm to calculate the minimum regularization distance and waveform similarity of three-phase waveforms to judge the condition of the converter. The centrifugal rate and change rate of Park vector ellipse are used to evaluate the IGBT status and set the evaluation index. Moreover, the practicability is verified by simulation data and operation data, respectively. The results reveal that, these two methods have good practicability, the waveform similarity decreases gradually before the fault occurs, and the change trend of Park vector eccentricity continues to increase, which proves that the two algorithm models can clearly distinguish between normal and abnormal waveforms. Using these two methods can timely feed back of the converter health status, thus to effectively avoid the shutdown or damage of the power electronic system due to the IGBT fault and avoid the property loss caused by equipment fault.

With the increase of the scale of wind farms and the proportion of wind power in energy system, the power grid has higher and higher requirements for the voltage stability of wind farms. The actual operation status of wind farms is focused, and the key issues of the reactive power and voltage control of wind farms are summarized, including how wind turbines adjust the reactive power, how to allocate the reactive power in large scale wind farms, how to maintain the stability of the internal node voltage of wind farms, how to solve the problem of voltage control lag, the transient voltage control strategy under fault conditions, and so on. In view of these issues, the methods and characteristics of reactive power and voltage control technology in wind farms are systematically summarized, and the realization process of reactive power and voltage control technology is expounded from the aspects of the characteristics of wind turbines and reactive power compensation equipment, reactive power and voltage steady-state control, internal node voltage control, model predictive control, and transient control under fault conditions. The research can provide reliable technical means for safe and stable operation of wind farms.

Phase change energy storage technology has the advantages of high heat storage density and constant temperature, so it has great potential for large-scale commercialization. The development of phase change materials is very important to the application of phase change energy storage technology. To solve the problems of poor heat transfer performance and easy leakage of phase change materials, extensive research has been conducted based on the heat transfer enhancement and packaging of phase change materials. The characteristics of thermal energy storage technologies are firstly compared. Then, the classification and properties of phase change materials are summarized. The progress of heat transfer and storge enhancement is discussed from the aspects of increasing heat transfer area, thermal conductivity, melting latent heat and specific heat capacity. The packaging of phase change materials is also discussed. Finally, a prospect for the future development direction of phase change energy storage is made.

Heat transfer fins can be used to improve the operation performance of heat storage tanks using phase change filling material (PCM). Based on the COMSOL software, the effects of annular heat transfer fin's parameters (fin length, fin thickness and fin angle) on charging performance of a double-tube PCM heat storage tank is preliminarily evaluated. The results show that, when the fin length increases from 1.0 m to 1.2 m, the total melting time of the filling material shortens from 8 h to 5 h. When the fin thickness increases from 40 mm to 60 mm, the total melting time of the filling material decreases from 10 h to about 6 h, and the average charging rate increases from 11.3×10⁸ kJ/h to 14.8×10⁸ kJ/h. When the fin angle is –15°, the tank has the shortest total melting time and the maximum average charging rate, which is 14.3×10⁸ kJ/h. For the double-tube PCM tank investigated in this study, the optimal fin angle is -15°. The results can provide basis for the design of double-tube PCM heat storage tanks for CSP plants.

Electric-heat conversion is an effective way to realize local consumption of new energy and help build a clean and low-carbon heating system. To this end, a new heating substation system with new energy consumption capability is designed. The system is based on the traditional heating substation, and the adjustment equipment such as the electric boiler and heat storage tank is added. At the same time, a heating substation dispatch strategy based on the coordinated regulation of flexible resources such as the primary heat source and heat storage tank is proposed to achieve complete consumption of new energy, meet the heat load demand, and obtain the required energy capacity of the heat storage tank. Furthermore, the configuration method of the volume of the heat storage tank and its structural parameters considering the dynamic characteristics of charging is proposed to calculate the volume of hot water injected into the heat storage tank and the volume considering the thickness of the thermocline layer. The inlet and outlet pipe diameters of the heat storage tank determine through the maximum heat charging flow. Appropriate ratio of diameter to height is selected to ensure the ideal temperature stratification characteristics of the heat storage tank. The effectiveness of the proposed method is verified by a simulation example. This method can provide a reference for the local consumption of new energy and the construction of heating substations.