Accurate condition monitoring of wind turbines is crucial to the safe and stable operation of wind turbines and the improvement of economic benefits. However, affected by the divergence in the distribution of operating data of different wind turbines, the existing condition monitoring methods have the problem of difficulty in taking into account the accuracy and efficiency in the application scenario of multiple wind turbines. BDA can shorten the data distance and reduce the data distribution divergence. Therefore, this paper propose a multiwind turbine condition monitoring method based on balanced distribution adaptive transfer learning. Firstly, the mutual information method based on Copula entropy is used to mine the key influencing parameters of the wind turbine condition; then, a wind turbine condition monitoring model is established based on the GRU model and SPRT method; wind turbine operation data distribution assimilation model based on BDA is constructed, and used for multiwind turbine condition monitoring. Results show that the proposed method can effectively save the modeling cost and calculation cost, and can significantly improve the monitoring efficiency on the premise of ensuring the monitoring accuracy of the operating state of multiple wind turbines.

In order to improve the efficiency of geothermal energy extraction in the hightemperature zone at the bottom of the well, a jettype coaxial borehole heat exchanger is constructed for horizontal geothermal well extraction. Based on the finite volume method, a threedimensional numerical simulation model of the horizontal section near the bottom of the well is established, and the flow and temperature fields of the Outsidein and insideout type (OI), Insideout type (IO), and Jet inlet (IOI) coaxial borehole heat exchangers are compared and analyzed, so as to reveal the mechanism of the injection heat exchanger to strengthen the heat transfer. The results showed that the use of the IOI type heat exchanger increased the turbulent kinetic energy of the fluid and formed vortices, which improved the efficiency of geothermal heat extraction. By comparing the heat extraction performance, it was found that the Nusselt number increased with the increase of mass flow rate, and the Nusselt number of IOI type was higher than the other two by 18.33%~32.48% and 5.33%~18.84%, and the friction coefficient decreased with the increase of mass flow rate; under the same mass flow rate, the thermal enhancement factor of IOI type heat exchanger was higher than the other two by 9.13%~13.58%, 3.61%~10.24%, and the average extraction temperature and average extended metre heat exchange are always the highest among the three. The results provide a theoretical basis for the efficient extraction of coaxial borehole heat exchanger in horizontal geothermal wells.

The output of wind, solar and other renewable energy sources is highly variable and stochastic, which poses a great challenge for the flexibility of the system. Therefore, a hybrid energy storage joint planning method for power systems that balances economy and flexibility is proposed. First, the flexibility requirements of the source and load sides are assessed from the perspective of power balance; then, a twolayer planning model that coordinates the flexibility retrofit of thermal power units and the hybrid energy storage is established, with three types of flexibility resources as the planning objects, namely, thermal power unit flexibility retrofit, Vanadium Redox flow Battery, and pumped storage. Using the upper and lower layer models, the scheme is iteratively optimized to obtain the optimal hybrid energy storage configuration scheme that balances economy and flexibility; secondly, an an improved whale algorithm based on inverse learning is adopted to optimize the planning model, and the validity of the model is verified by simulation. Finally, a case study is carried out using historical data from a certain region in Inner Mongolia Eastern to validate the effectiveness of the proposed method.

The doubly fed induction generator, operating in electric mode, has a certain inertia supporting capacity to the power grid, but the supporting capacity is limited, and the rotor is out of control during the lowvoltage crossing of the power grid. In this paper, a kind of rotor stability control technology is proposed when voltage sags in power system. Firstly, a flywheel is attached to the rotor shaft of a doubly fed fan to increase the inertia of the system and stabilize the speed of the rotor. Secondly, voltage compensation is used to reduce the back electromotive force of the rotor side and stabilize the rotor current when the voltage of the power grid falls, the simulation model of the system is built in MATLAB/Simulink platform, and the results show that the antimutation ability of the rotor speed of the doublyfed fan is improved by 20% by adopting the rotor stability control technology, the rotor current drop value is reduced by 45%, which verifies the validity and reliability of the proposed rotor stability control technique.

In this paper, in order to study the dynamics of the model turbine with driven motion at different yaw angle operating condition, a wind turbine model based on elasticity is established. Under the condition of turbulent flow, the driven motion state of the model wind turbine is realized with irregular rotation, and the wake distribution characteristics and energy characteristics of the wind turbine are studied. The results show that when the yaw angle is 0°, the wake of the driven wind turbine is obviously smaller than that of the fixed wind turbine, and the turbulent kinetic energy is greater than that of the fixed wind turbine because of the multifreedom rotational motion of the driven wind turbine. With the increase of yaw Angle, the distribution of wake and turbulent kinetic energy of wind turbine appears radial deviation, and the deviation direction is opposite to the direction of yaw Angle rotation, and the wake and turbulent kinetic energy decreases with the increase of yaw Angle. With the increase of yaw Angle, the average output power of forced and fixed wind turbines decreases, and the average output power of forced wind turbines is smaller than that of fixed wind turbines.

In the design of highpower directdrive wind turbines, this paper proposes to design axial flux permanent magnet generators as highpower half directdriven wind turbines to address the issues of large radial dimensions and high maintenance costs in the later stage. Taking the 2 MW semi direct drive axial flux permanent magnet generator as the research object, the parameter design principle and method are studied. By exploring the influence of different pole pairs on the output performance of the generator, the optimal scheme of the generator meeting the design goal is determined. The 3D finite element method is used to analyze the air gap flux density, voltage, current waveform, output power, loss and efficiency of the generator under noload and rated load conditions, and verify the correctness of the electromagnetic design of the generator. The efficiency of the generator can reach 97.79%, which has the advantages of low loss and high efficiency. By comparing with generators in the existing research, it is concluded that the radial size of the MW half directdriven axial flux permanent magnet generator proposed in this paper is significantly reduced, and it has better performance than the existing radial flux structure highpower semi direct drive permanent magnet generator in terms of axial dimension and cogging torque.

The analysis and mastery of the inner law of the fluctuation characteristics of wind power output is conducive to improving the prediction accuracy of wind power output, thus guiding the power grid scheduling department to reasonably arrange the power generation plan and improve the economy of system operation. To characterize the probability density distribution of wind power output fluctuations, two adaptive bandwidth kernel density estimation models are developed by modifying the fixed bandwidths obtained from the empirical method and the unbiased crossvalidation method. Then, the above two models are combined and optimized, and finally the probability density distribution model of wind power output fluctuation based on hybrid adaptive kernel density estimation (HAKDE) is established. A variety of probability density distribution models were used to fit the fluctuations of wind power output at different spatial and temporal scales in a province in North China. The results show that the fitting effect of the HAKDE model is the best, which verifies the effectiveness of the HAKDE model.

A transfer learningbased early fault warning method for offshore wind turbine bearings is established to address the problems of varying operating conditions of offshore wind turbines and many false alarms for early fault warning of turbine bearings. The method uses the shorttime Fourier transform to extract the timefrequency domain features of the vibration signals, which are normalised to form pre processed samples. The objective function of the convolutional autoencoder is supplemented with a support vector data description regular term and a maximum mean discrepancy regular term to constrain the feature distribution while obtaining the common features center of the bearings in normal state under different operating conditions. The Euclidean distance between the online sample features and the common feature center is calculated to construct bearing health indicator sequence, and the ADF(Augmented DickeyFuller)test is introduced to perform stationarity analysis and capture the sequence mutation points, which finally realize the early fault warning of bearings in offshore wind turbines. The validation on the XJTUSY bearing dataset showed that the proposed method has fewer false alarms, high accuracy and better detection stability.

To investigate the combustion characteristics of a blended fuel consisting of bituminous coal, miscellaneous wood pellets, and oil sludge, thermogravimetric analysis is conducted on the blended fuel to analyze its combustion behavior. The FWO method is employed for kinetic analysis of the blended fuel. The results show that the combustion process of bituminous coal is primarily fixed carbon combustion, while the combustion process of miscellaneous wood pellets is more complex and exhibits the best combustion performance, with a comprehensive combustion characteristic index as high as 1.93×10⁻⁷. Cofiring with miscellaneous wood pellets effectively enhances the combustion performance of bituminous coal. When bituminous coal and miscellaneous wood pellets are blended in a mass ratio of 1:4, the ignition temperature of the blended fuel decreases by 35% compared to bituminous coal alone. The comprehensive combustion characteristic index increases by 7.2% compared to miscellaneous wood pellets. The most probable function for the cofiring of bituminous coal and miscellaneous wood pellets is [ln (1x)]⁻³/⁴. When the blending ratio of miscellaneous wood pellets reaches 45%, the appropriate addition of oil sludge can improve the combustion performance of the fuel. The most probable function for the combustion reaction of the blended fuel consisting of all three components is [ln (1x)]². When the blending ratios of bituminous coal, miscellaneous wood pellets, and oil sludge are 40:40:20 and 45:45:10, respectively, the corresponding activation energies of the blended fuel are significantly lower than those of other blending ratios, and the comprehensive combustion characteristic index is approximately 1.5 times that of pure bituminous coal.

Aiming at the problem that the complex coordination relationship of the sendingend power grid with high proportion of new energy and pumped storage combined power generation may lead to insufficient new energy consumption capacity, an energy balance optimization control method of the new energy sendingend power grid based on variable speed pumped storage is proposed. Firstly, the operating characteristics of variable speed pumped storage units are studied, and the active and reactive power output characteristics of variable speed pumped storage units based on frequency converter control are analyzed. Secondly, the variable speed pumping is used to analyze the improvement of new energy generation capacity, and the energy balance optimization model of the new energy sending end power grid is established. Then, the quantum particle swarm optimization algorithm is improved, and the energy balance optimization control algorithm of the new energy sending end power grid is proposed. Finally, with reference to the delivery mode of new energy base in a certain area of Northwest China, a typical scenario of variable speed pumped storage power station and conventional pumped storage power station cooperating with new energy is constructed. The improved new energy consumption capacity of variable speed pumped storage power station and conventional pumped storage power station is compared. The simulation results show that the energy balance optimization control method of the sending end power grid based on variable speed pumped storage can improve the utilization rate of new energy and play a significant role in improving the level of renewable energy consumption.