Summary Object detection in crowded scenes involves various difficulties, such as small objects, occluded objects, and insufficient features. Existing models for crowded object detection often focus on only one detection difficulty, and they are too large to be applied in practice. To address the diverse challenges of object detection in crowded scenes, we construct a lightweight crowded object detector called MBB‐YOLO, which contains several modules for comprehensive improvement. To improve the network's ability to extract fine‐grained features, we use SPD‐Conv and the proposed MS‐Conv to replace the strided convolution in the network. An bi‐branch multi‐scale convolution attention (BMCA) module is proposed to aggregate multi‐scale contextual information. We also propose boundary‐NMS to better identify proposal boxes from different objects, which reduces suppression errors caused by object occlusion. MBB‐YOLO achieves 87.6% AP and an inference speed of 78.8 FPS on the CrowdHuman dataset, which surpasses other mainstream lightweight object detectors.

The maximum current carrying capacity of a power cable (Ampacity) is determined by the thermal characteristics of the cable components and surrounding medium in which they are buried. Power cable ampacity calculations are based on typical standard tables defined with predetermined parameters. In realtime, the environment of installation plays significant role in cable current carrying capacity. This paper presents FEM approach to determine the maximum current capacity within the safe operating limits of the cable by modeling electro-magnetic heat transfer. The study includes complex thermo-electric coupling and heat transfer in different zones surrounding the cable and its effect on the conductor operating temperature. The results show the difference between the proposed approach and standard calculations and improvements to accurate rating of the cables.

Nowadays, medium frequency transformers have gained growing attention in modern power system. Higher power density, which is realized by increasing the operating frequency, leads to the reduction of the magnetic components size. Along with it, cooling surface is consequently reduced which results in high thermal stress. Careful attention must be paid on the loss mechanisms and thermal analysis of a medium frequency transformer at the design stage. This paper develops an equivalent thermal circuit of an oil-immersed medium frequency transformer to predict its temperature profile. Thermal resistance, capacitance and the losses generated in the core and winding are carefully estimated. Two oil-immersed shell-type transformer prototypes with specifications as 5kW, 500/5000V, 5kHz, interleaved winding construction have been developed and built for verification purpose. Loss and temperature measurements have been performed to verify the presented framework. The accuracy of the proposed thermal model is benchmarked and corroborated through experimental measurements as well as FEM-CFD study with good agreement.

A medium/high-power conversion system, using power electronic (PE) converter in conjunction with a medium/high-frequency transformer, has many desirable effects suitably oriented for modern power system architecture. Switching at high frequency results in lesser volume of magnetics but induces higher loss density. Thus design and characterization of a medium-frequency (MF) high-power (HP) transformer has significant ramification on its performance and application. Thermal management of a MF HP transformer is one of key aspects for its characterization. In this paper, an equivalent thermal model of a multi-layer concentrated winding is derived. Core and copper losses are carefully estimated. Thermal resistance and capacitance are accurately calculated. Time-domain response of proposed thermal network is obtained using Heun's method (Modified Euler) and validated with PLECS. Effects of temperature change on thermal properties of material and coolant (transformer oil) are also discussed. Furthermore, accuracy of said thermal network is corroborated through FEM-CFD study of a 10kW, 0.5/2.5kV, 1kHz natural oil-cooled transformer. Close agreement between analytical and simulation results is observed which substantiates proposed thermal model in terms of accuracy and efficacy of computation.