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Insulator faults are an important factor in causing outages and accidents in power transmission lines. In response to problems related to inefficient insulator positioning, limited robustness of insulator defect feature extraction methods, and the scarcity of defective insulator samples leading to poor classifier generalization, a method for insulator defect detection and recognition based on vision big-model transfer learning and a stochastic configuration network (SCN) is proposed. First, data augmentation methods, such as Mosaic and Mixup, are employed to mitigate overfitting in the YOLOv7 network. Second, StyleGanv3 adversarial generative networks are used to augment the dataset of defective insulators, which enhances dataset diversity. Third, a vision big-model transfer learning method based on DINOv2 is introduced to extract features from insulator images. Finally, an SCN classifier is used to determine the status of insulators. Experimental results demonstrate that the applied data augmentation methods effectively mitigate overfitting. YOLOv7 accurately detects insulator positions, and the use of the DINOv2 feature extraction method increases the accuracy of insulator defect recognition by 28.6%. Compared with machine learning classification methods, the SCN classifier achieves the highest accuracy improvement of 17.4%. The proposed method effectively detects insulator positions and recognizes insulator defects.

Analysis of the short-circuit characteristics of SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) is very important for their practical application. This paper studies the SiC MOSFET short-circuit characteristics with an improved test setup under different conditions. A high-current Si insulated gate bipolar transistor is used as a circuit breaker in the test circuit rather than the usual short-circuit test conducted without a circuit breaker. The test platform with a circuit breaker does not influence the calculation results regarding the short-circuit withstand time and energy, but the SiC MOSFET will switch off after failure in a very short time. In addition, the degree of failure will be limited and confined to a small area, such that the damage to the chip will be clearly observable, which is significant for short-circuit failure analysis.

The voltage balancing problem of dc-link capacitors in multilevel diode-clamped converters limits their applications in industry under some operational conditions. Virtual vector PWM (VVPWM) can attain the capacitor voltage balancing under all operational conditions but it increases the complexity and computation burden by increasing the number of triangular regions for higher levels as compared to conventional space vector PWM (CSVPWM). In order to solve the dc-link voltage balancing problem in four-level diode-clamped converter, a simplified virtual vector PWM (SVVPWM) algorithm is proposed in this paper. The pair of new virtual vectors is defined in such a way that the space vector diagram of four level converter is transformed into three level space vector diagram that lessens the complexity and computation burden by decreasing the number of triangular regions. The balancing of capacitor voltages can be achieved by using proposed SVVPWM algorithm for the whole range of modulation index load power factor. Steady state and dynamic performance of the SVVPWM algorithm is verified through the simulations and experiments.

This paper presents system-level efficiency evaluation of the suitable isolated dc/dc converters in input-series-output-parallel power electronics transformers (PET) applied for medium-voltage dc systems and provides engineering insights into the design of PETs from a system perspective. To this end, three candidates-a single-stage dual active bridge (DAB) converter, a boost converter plus a DAB with a constant boost output voltage, and a boost converter plus a DAB with a constant DAB voltage gain-are selected and evaluated from a system-level aspect. Comprehensive system-level efficiency comparisons are done with the chosen candidates, considering numbers of normal and hot standby submodules, different working conditions, rated voltages and power of the PET, switching frequencies, and commercial devices. Analysis with detailed loss breakdowns clearly shows the distribution of losses and elaborates the profound reasons behind the efficiency differences. In the comparison, the boost and DAB with a constant boost output voltage have higher or similar efficiency than the other two candidates, verified by simulation and experimental results. Considering its advantages in redundancy in the PET, the boost and DAB with constant boost output voltage are a preferable choice for submodules in input-series-output-parallel PETs.

In urban rail transit, there is a large number of harmonics brought by diode rectifiers, and shunt active power filters (APFs) are an effective method of harmonics rejection. Traditional shunt APFs work with a dedicated DC link leading to complexity, while those with a common DC bus but using non-isolated topologies bring serious problems of zero-sequence circulating current (ZSCC), which introduce losses and provoke poor quality. Consequently, this paper first analyzes the limitations of traditional non-isolated APFs on modulation radio. Based on the analysis, this paper put forward a novel isolated APF with a common DC link based on existing diode rectifiers in urban rail transit, which realizes braking energy recovery as an additional function. To this end, harmonics brought by diode rectifiers are reduced while rejecting ZSCC. Meanwhile, braking energy can feedback to the city grid with lower harmonics. Finally, simulation and experiment using a 1-kW prototype converter verify the feasibility and validity of the proposed converter on harmonics suppression and braking energy recovery.

Nickel is an excellent ohmic-contact metal on 4H-SiC. This paper discusses the formation mechanism of nickel ohmic contact on 4H-SiC by assessing the electrical properties and microstructural change. Under high-temperature annealing, the phase of nickel-silicon compound can be observed with X-ray diffraction, and the contact resistance also changes. A comparative experiment was designed to use X-ray diffraction and energy-dispersive spectroscopy to clarify the difference of ohmic-contact material composition and elemental analysis between samples prepared using pulsed laser annealing and rapid thermal annealing. It is found that more Ni2Si and carbon vacancies formed at the interface in the sample prepared using pulsed laser annealing, resulting in a better ohmic-contact characteristic.

Multiphase machines are gaining increasing popularity because of their distinct advantages over three-phase counterparts, such as reduced per phase power rating, improved reliability and increased degrees of freedom. This paper overviews the development history of multiphase machines and drive techniques in Section II. Three kinds of drive algorithms, including Field-Oriented Control (FOC), Direct Torque Control (DTC) and Model Predictive Control (MPC), are introduced in Section III. Then two types of fault-tolerant methods are compared in Section IV, which are the Vector Space Decomposition (VSD) strategy and Optimal Current Control (OCC) method. Furthermore, different types of existing multiphase converter topologies are listed in Section V, and various kinds of multiphase PWM methods are discussed in Section VI. Finally, based on the review, developing trends of multiphase drive techniques are forecasted.

DC collection network offers an attractive alternative to AC network for photovoltaic, as it avoids the charging current issues and reduces the size and weight. Variable voltage gain DC/DC converters play an important role in DC collection network. Two topologies suitable for photovoltaic DC collection are studied. Boost and LLC converter and active clamp isolated full-bridge boost converter are two converters with high and variable voltage conversion ratio suitable for the photovoltaic system. This work investigates the two converters comprehensively. The topologies are analysed so as to summarise and compare the characteristic of the converters. Soft switching condition is compared to help extend the zero voltage switching range. Voltage and current stress of the two converters are calculated. Loss comparison is made with the theoretical analysis. Advantages and disadvantages are summarised to get a deep insight into their application field.

In recent years, the urban rail transit has a great development in many cities of China. It is important to keep the DC transit grid strong and the power transmitted/power transmission high quality. During the process of rail operation, braking energy leads to a wide range of load oscillation for the traction and city grid, which cannot be absorbed inside the rail transit system. In this study, a novel architecture of urban rail transit power supply based on power electronics transformer braking energy feedback is put forward. Based on the circle grid, the topology adds an inverter to LLC series resonant converter to carry the power from 1500 V DC traction grid to 1180 V AC. Analysis together with simulation on the topology and control strategy is made on the basis of MATLAB/Simulink. Process of braking energy feedback and transmission of energy are illustrated with simulation. By paralleling the three-phase H bridge and braking energy feedback device, double direction of the power flow is ensured. As a consequence, the power quality increases and harmonics reduce. The energy can be used more efficiently to achieve better effects on energy conservation.

By operating at much higher frequencies, power electronic transformers (PETs) offer many advantageous features consisting of high power density, high efficiency and diverse functionalities. But the trade-off between the operating frequency and the conversion efficiency limits the further development of PETs. Nevertheless, with the advancements on SiC-MOSFET devices, this limitation can be overcome due to the higher blocking voltage utilisation factor and lower on-state losses of SiC devices. The potential applications of the proposed SiC-based PET are railway traction for electric multiple units (EMUs), interfacing electric vehicles, marine propulsion, etc. This paper focuses on a SiC-based three-stage AC to DC PET, which employs an input series and output parallel (ISOP) configuration. By synthetically comparing some typical topologies of PETs, their merits and demerits are summarised. By minutely analysing requirements and rigorously calculating, the design of the high power medium-frequency transformer (MFT) is presented. By operating simulations of topological structures of the proposed PET on the basis of MATLAB/Simulink, control strategies including phase-shift control and voltage balancing control are described. Simulations with prototype model are provided to demonstrate the operation of the PET.

The article discusses the Arch-I-Scan Project, which aims to use artificial intelligence to automate the identification and classification of ancient Roman pottery, specifically terra sigillata (stamped clay) tableware. It mentions the potential for AI to democratize the recording process, allowing non-specialists to contribute to archaeological data collection and analysis.