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With the considerable demand for distributed renewable energy and the significant increase of generalised DC loads, such as IT equipment, DC air-conditioner, electric vehicle, the traditional AC distribution network is no longer efficient. Driven by the rapid development of power electronics technology, the AC/ DC hybrid system is an effective way for large capacity AC/DC sources and loads efficient integrated. To ensure the stable operation of AC/DC hybrid system, the grounding mode analysis is necessary, which is the precondition for overvoltage analysis, lightning arrester configuration, and protection design. To select grounding mode of AC/DC hybrid system, the detailed system structure scheme is first determined considering the factors such as integrated object, reliability requirement, capacity of sources and loads, and converter type. Then the main connection scheme is selected considering the principle of line insulation, economy, and reliability. Based on the system structure and main connection scheme, a suitable grounding mode is selected for the AC/DC hybrid system with various distributed renewable energy, by weighing various factors such as power supply reliability, protection sensitivity, insulation level, and personal safety.

The morphology of high-voltage cable sealing layer has an important impact on the sealing characteristics. Aiming at the measurement problem of high-voltage cable sealing layer morphology, this paper uses a lattice laser to irradiate the target to form a laser lattice on the surface of the target, and then obtains the target image with a binocular polarization camera. The polarized light is used to overcome the influence of metal reflected flare, and then a pair of target images are matched. Then the parallax of each point is calculated. Finally, these points are used to reconstruct the point cloud to obtain the three-dimensional(3D) shape of lead sealing layer. The method in this paper provides a method for the measurement of the 3D shape of lead sealing layer, which is of great significance for the quality control of lead sealing layer.

Lead has good corrosion resistance and sealing property, which is often used in cable lead sealing process and various processes. In the production process, there may be small defects in the lead products, which may affect the quality of the products. Therefore, it is of great economic significance to inspect them to ensure their reliability. Due to the variety of lead products, the use of traditional ultrasonic detection is limited, and laser ultrasound has the ability to detect all kinds of surface samples. However, when the inner defect size of lead products is submillimeter or smaller, the echo signal-to-noise ratio(SNR) is low, so the traditional laser ultrasonic technology is difficult to locate the defects. In this paper, the synthetic aperture focusing (SAFT) technology is applied to the laser ultrasonic detection of lead internal defects. The minimum defect identification ability and resolution ability of laser ultrasonic combined with SAFT are studied, which provides reference for practical application.

Based on the incremental power flow equation, the influence of VDCOL controller parameters on voltage stability factor VSF was studied by sensitivity analysis method, and the mathematical relationship between the two was obtained for the first time. Based on the analytical relationship, the quantitative relationship between VDCOL control parameters and voltage stability factor VSF was made clear, which lays a mathematical and theoretical foundation for the controller parameters tuning. Taking CIGRE standard DC system parameters as typical parameters, the relation curve between VDCOL control parameters and VSF was obtained. Combined with the relation curve, the influence of VDCOL parameters on the system voltage stability was further expounded, and some useful conclusions were obtained. The simulation analysis shows that the method and conclusions obtained in this paper are correct and effective, and have important theoretical guidance and practical significance on the design and operation of the system.

The effective calculation of transient power angle is the basis of on-line identification of synchronous generator parameters in time domain. In view of the shortcomings and difficulties of the existing methods of measuring transient power angle, a method for calculating transient power angle of synchronous generator is proposed in this paper. In this method, according to the real-time data of current and voltage sampled by generator terminal, the instantaneous initial phase angle of transient current and voltage signal is calculated by using the sinusoidal representation method of transient signal based on Hilbert transformation. By using the change of current phase angle at generator terminal, the angle change between rotor axis d and stator phase a flux axis is obtained, and then the transient power angle of generator is obtained. In this paper, a simulation model is built on MATLAB/Simulink platform to verify the effectiveness of the proposed method, and the measured data of a large hydropower station are used to verify the effectiveness of the proposed method. The results show that the high estimation accuracy in a short transient time can be obtained by this method.

This paper designs a new AC & DC hybrid power supply system for data centres, which includes photostatic power generation, wind power generation, solar thermal power generation, storage power systems, and different types of loads. According to the above-mentioned, the paper first presents the reliability evaluation indicators and analysis methods applicable to the new AC & DC hybrid power supply system for data centres, which are for solving the problem of the reliability evaluation under uncertain parameters and load parameters of the new data centre power supply system. The paper describes the new power supply system reliability indicators and evaluation methods in detail. The problem of the power supply reliability in the new AC & DC hybrid power supply system in the data centre is analysed in a targeted manner by adopting actual examples, then it is verified that the power supply reliability of the new AC & DC hybrid power supply system can perfectly meet the qualification of the A-class data centre power supply. The reliability of assessment index and analysis methods presented here will be two simple and superior analysing tools.

Synthetic Aperture Focusing (SAFT) is one of the methods to improve the spatial resolution in laser ultrasound. However, the research on laser ultrasonic SAFT technology is mainly focused on block or plate samples. In order to study the detection capability of laser ultrasonic SAFT technology on the samples with curved surface, a finite element simulation model of curved surface samples with sub millimeters internal defects is established. And then the laser ultrasound field is obtained through numerical simulation. At last the SAFT algorithm was performed to image the defects in the samples. The results show that laser ultrasonic SAFT technology can image curved surface samples with sub millimeters internal defects. The results provide a reference for the practical application of laser ultrasonic SAFT technology.

Synthetic Aperture Focusing (SAFT) is one of the methods to improve the spatial resolution in the traditional acoustics field. Its basic principle is to combine a series of small-aperture sensors to replace a large-aperture sensor in order to improve the detection lateral resolution. However, the practical detection results will be affected by noise. In this paper, the time-domain B-scan signal is obtained by establishing a physical model of a lead sample containing defects and computing with finite element method. Then, the influence of noise with different signal-tonoise ratio(SNR) on SAFT imaging results is studied. The results show that SAFT algorithm has better anti-noise performance, and can still obtain good results even when the SNR is low.

Under the rapid development of power electronics technology, AC/DC hybrid power supply can be used to comprehensively solve the demand for source and supply.The article takes the first comprehensive demonstration project of the dual-stage AC-DC hybrid system based on multi-function power electronic transformer cluster in China as the research object.A distributed renewable energy system simulation platform with AC/DC hybrid is established in the hardware RTDS to simulate and analyze the fault characteristics under different conditions.Based on the fault characteristics and the principle of protection division, in order to ensure that the ranges between the protection zones overlap each other and cover the entire AC-DC distribution network,This paper studies the specific protection zones and configurations for the industrial park system, and has developed a comprehensive protection configuration plan.