International Core Journal of Engineering
Boya Century Publishing Limited,正常發行
選擇卷期
- 期刊
Overcurrent and power-angle instability will occur in the converter controlled by virtual synchronous generator (VSG), when the grid voltage drops rapidly, a low voltage ride-through (LVRT) strategy using voltage amplitude command dynamic calibration is proposed. When the grid voltage drops rapidly, the voltage amplitude of the converter port is used as the voltage command value of the VSG in a short time, making the inner voltage potential of VSG can respond to the grid voltage drops rapidly. In order to reduce the influence of large voltage fluctuation of converter port on dynamic calibration of voltage amplitude command, a sliding filter is designed to extract the voltage amplitude of the converter port; the selection principle of dynamic calibration voltage is analyzed, the constraints of VSG output current amplitude and power-angle stability are considered, VSG power command is designed based on phasor diagram analysis method under grid voltage drops.Simulation results verify the effectiveness of the proposed control strategy.
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The connector plays an important role in the composite sandwich wall panel. The selection of the connector is a factor affecting the strength and thermal performance of the composite sandwich wall panel. The type, thermal conductivity and position arrangement of connectors at home and abroad are systematically summarized, and the future development of connectors is prospected.
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The superconducting current limiter plays an important role in limiting the short-circuit current. Therefore, a 500kV iron-core saturated superconducting current limiter (SCSFCL) model was built and its impedance characteristics were analysed. By setting different short circuit faults and then setting different ground resistance at the fault point, different data can be obtained. Finally, the data are summarized. The installation of SCSFCL will not cause the misoperation of current differential protection. In the case of faults in the area, the difference current size at both ends of the line is less affected and the probability of protection rejection is small.
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Taking the factors affecting the escape route of the river treatment project during the flood period as the research object, the 42 influencing factors of the flood period escape route of the river treatment project were obtained through the literature analysis method and expert interview method, and the ISM (explanatory structure model) was used to analyze the interrelationship between the influencing factors, divide the hierarchy, draw the hierarchical topology map, and propose the flood period management strategy of the river treatment project according to the analysis results, It provides reference for the safety management of construction enterprises of river treatment projects.
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New Energy vehicles refer to those which adopt new power systems and are driven entirely or mainly by new energy sources, including plug-in hybrid (including the program) cars, electric vehicles and fuel cell vehicles, and so on. Safety design is very important in the development of new energy vehicle, especially the safety of high pressure system. However, due to the complex structure of its high-voltage system, more lines, the probability of fire accidents also greatly increased. Therefore, how to improve the safety of new energy vehicles is an urgent problem to be solved. In this paper, the existing high-voltage system fault diagnosis and analysis, and put forward the corresponding safety protection measures, in order to provide a reference for the new energy vehicle safety research and development.
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Because the change values of luminous signals and electrical signals of different gases are different, different gases can be identified by analyzing the characteristic signals of gases. The response curve of the gas sensor is divided into three stages: response stage, steady state and recovery stage. The article mainly introduces the severe ml algorithms and the infrared feature vector design for gas discrimination and concentration measurement with an ultrasonically catalyzed MOX sensor. Compared with optical sensors, Ultrasonically catalyzed MOX sensor, as a low-cost and low-power sensor, meets the requirements of wireless sensor networks used in home automation and environmental monitoring.The overall accuracy of KNN(K- nearest neighbor) algorithm under the third scheme is 59.84%, the overall accuracy of scheme 2 is close to that of scheme 3, and the overall accuracy of scheme 1 is the lowest. The average classification accuracy of RF (Random Forest) model for three gases with different concentrations is 0.84, 0.90, 0.91 and 0.92, respectively. Using ML technology can improve the classification efficiency of gases with different concentrations, which is the trend of gas sensor data classification in the future. The prediction accuracy of the CNN-LSTM (Convolutional Neural Network-Long Short Term Memory) algorithm in mixed gases is significantly better than that of the individual LSTM algorithm and other ML algorithms. Taking into account accuracy, efficiency, and complexity, the proposed algorithm is suitable for applications where concentration mutations may occur, such as continuous monitoring applications or chemical source localization, with a wider range of application scenarios.
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Inspired by the effect of thermal shock on rock failure, an innovation concept of drilling with liquid nitrogen is presented to improve the drilling efficiency in hard and high temperature formation. The main objective of this paper is to investigate the effect of rapid thermal shock on surface mechanical propertied and analyses the feasibility through theoretical and experimental methods. Base on the calculation results, it indicated that the tensile stress only occurred close to the surface, while the interior region was under compressive stress. Time and heat transfer coefficient, which have threshold values, are the key parameters for surface crack growth. Then hardness test experiment was carried out and the results showed the subcritical crack growth did not occurred, but average reduction in hardness, maximum load and yield limit reached 13.18%, 13.00% and 15.74% respectively after being cooled by liquid nitrogen for 5 seconds. The conclusion drawn that drilling with liquid nitrogen is a promising technology, even if the thermal stress is not sufficient to form a crack on the surface of the rock alone, the transient thermal shock is also conducive to reduce the penetration resistance of the bits and improve the rate of penetration, especially in high temperature wells. The new innovation technology of liquid nitrogen assisted drilling shows great potential in improving geothermal drilling efficiency and subsequent research should continue.
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In order to improve the accuracy of nitrate nitrogen detection, this paper proposes a method for rapid determination of nitrate nitrogen in water based on UV visible absorption spectroscopy. The experimental subjects were the absorption spectra of sodium nitrate standard solution with a concentration range of 0.1~20mg L-1. The principal component analysis method PCA (Principal Component Analysis) was used to find the appropriate number of principal components. Use Support Vector Regression (SVR) to fit the absorbance and sample concentration at characteristic wavelengths, and establish a regression model for nitrate nitrogen. The root mean square error (RMSE) is used as the evaluation indicator for the model. The experiment found that the RMSE of the mixed prediction model established using PCA-SVR modeling method was 0.00779mg L-1, and its modeling effect was better than SPA-SVR, achieving rapid and accurate measurement of nitrate nitrogen.
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This study focuses on TF card slots and examines the research status of automated assembly for TF card slots. By analyzing the assembly process of TF card slots, a TF card slot automated assembly line is designed. The assembly line includes automatic screening and feeding of the base, automatic feeding and pressing of the male-female spring, automatic feeding of the buckle, visual inspection of the product, and overall performance testing. The key technologies of automated assembly equipment are analyzed and researched.
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In this paper, the stability of the elevation slope of a large section tunnel cavity under the influence of excavation disturbance is studied based on the fifth standard of National Highway 208 from Jinzhong to Changzhi section, Zihong No. 1 tunnel project. A sensitive analysis of tunnel elevation stability under single factor was carried out by FLAC-3D software to simulate the effect of different slope angles and different slope heights on the stability of tunnel elevation slopes. The results show that the slope stability decreases with the increase of slope angle when the slope angle varies from 15° to 45°. When the slope height varies from 20m to 40m, the stability of tunnel elevation slope decreases with the increase of slope height. In large section tunnel construction, the simulation is done by step-by-step excavation according to the construction sequence. The stability coefficient of tunnel opening slope gradually decreases under the influence of excavation disturbance, and the minimum value is 1.07. The stability coefficient of tunnel opening slope gradually increases to 1.13 with the completion of support.