高次谐波大回旋太赫兹振荡器多模工作特性

设计了一支可工作于4~9次谐波的大回旋太赫兹振荡管,借助于三维粒子模拟,研究了设计的大回旋振荡管注-波互作用机理、高次谐波工作特性、谐波模式间竞争等关键特性。结果表明,通过调节磁场强度,可以在多个相邻谐波处连续激发振荡,实现频率为240 GHz到460 GHz之间的太赫兹波辐射,最大辐射功率为19kW。同时研究了第7、8和9次谐波模式之间的竞争,讨论了实现稳定注-波互作用和高次谐波状态下单模工作的方法。此外,论文还对不同谐波状态下的欧姆损耗功率进行了研究。

大功率半导体技术现状及其进展

介绍了现代硅基大功率半导体器件的历史演变和新型器件结构的研究进展,以及宽禁带半导体材料和器件的现状;阐述了国内大功率半导体器件在轨道交通、直流输电和新能源汽车等领域的研发进展和应用现状;最后讨论了大功率半导体技术面临的技术挑战和发展趋势。

Cascaded Multilevel Inverter Based Power and Signal Multiplex Transmission for Electric Vehicles

Power&signal multiplex transmission(P&SMT)is a technique that uses power electronic circuits for communication signal transmission.In this paper,a three-phase cascaded multilevel inverter-based P&S MT system is proposed.The proposed method can transmit communication signals without using a Controller Area Network bus,thereby reducing the wiring cost of the conventional electric vehicle(EV)communication system.The designed system can achieve motor speed regulation and battery balance discharging for EVs.With the combined pulse width modulation scheme and frequency shift keying method,both power and communication signals are transmitted successfully in a simulation model implemented in Matlab/Simulink.By evaluating the bit error rate of the transmitted signal,the maximum signal rate of the proposed system is determined as 600 bit/s.

IGBT模块的热设计概述

对IGBT模块的热特性和热设计进行概述,介绍IGBT模块的热阻抗网络模型及其与封装材料热性能及尺寸的关系;从芯片和模块封装材料、结构等方面讨论模块的热设计要点,并阐述传统IGBT模块及新型压接式IGBT模块的热设计。

The History and Development of IGBT

In this paper,IGBT history is briefl y reviewed and IGBT chip technology is discussed in detail,especially for soft punch through,carrier injection enhancement and trench technologies.Concurrently with the improvements in chip technology,there has been rapid development of the packaging technology which will be discussed in this paper.Some suggested technologies of IGBT in the future are presented to conclude the paper.

Press-pack IGBTs for HVDC and FACTS

The popularity of insulated gate bipolar transistors(IGBTs)for use in high-voltage direct current(HVDC)transmission and flexible AC transmission systems(FACTS)is increasing.Unfortunately,for these applications wire-bond IGBT technology has a number of shortcomings,such as insufficient current ratings for the most powerful schemes,and inability to fail to short-circuit.Press-pack IGBT technology,conversely,offers increased current ratings,and an inherent short-circuit failure mode,making it a more attractive choice for HVDC and FACTS.However,the design and manufacture of these devices requires a comprehensive understanding of the unique technical challenges,which differ markedly from those for wirebond modules or traditional pressure contact devices.Specific challenges include providing a high degree of mechanical protection for the IGBT chip against normal operating stresses.Furthermore,it is essential to achieve uniform contact pressure across each chip surface to ensure optimum performance.To achieve this,manufacturers have designed products that use rigid copper electrodes manufactured to tighter tolerances than for other pressure contact devices,such as thyristors,and products that use compliant electrodes,incorporating spring assemblies.Dynex is in the advanced stages of development of press-pack IGBT technology with demonstrated robust solutions for the technical challenges outlined in this paper.Design success has been achieved through the use of state-of-the-art simulations in conjunction with a long history of manufacturing expertise for bipolar and IGBT products.Finally,multiple press-pack IGBT variants are currently undergoing evaluation tests prior to product release.

Thermal Management of Electrified Propulsion System for Low-Carbon Vehicles

An overview of current thermal challenges in transport electrification is introduced in order to underpin the research developments and trends of recent thermal management techniques.Currently,explorations of intelligent thermal management and control strategies prevail among car manufacturers in the context of climate change and global warming impacts.Therefore,major cutting-edge systematic approaches in electrified powertrain are summarized in the first place.In particular,the important role of heating,ventilation and air-condition system(HVAC)is emphasised.The trends in developing efficient HVAC system for future electrified powertrain are analysed.Then electric machine efficiency is under spotlight which could be improved by introducing new thermal management techniques and strengthening the efforts of driveline integrations.The demanded integration efforts are expected to provide better value per volume,or more power output/torque per unit with smaller form factor.Driven by demands,major thermal issues of high-power density machines are raised including the comprehensive understanding of thermal path,and multiphysics challenges are addressed whilst embedding power electronic semiconductors,non-isotropic electromagnetic materials and thermal insulation materials.Last but not least,the present review has listed several typical cooling techniques such as liquid cooling jacket,impingement/spray cooling and immersion cooling that could be applied to facilitate the development of integrated electric machine,and a mechanic-electric-thermal holistic approach is suggested at early design phase.Conclusively,a brief summary of the emerging new cooling techniques is presented and the keys to a successful integration are concluded.

Impact of design and process variation on the fabrication of SiC diodes

We have studied the influence of design and process variations on the electrical performance of SiC Schottky diodes. On the design side, two design variations are used in the active cell of the diode（segment design and stripe design）. In addition, there are two more design variations employed for the edge termination layout of the diodes, namely, field limiting ring（FLR） and junction termination extension（JTE）. On the process side, some diodes have gone through an N;O annealing step. The segment design resulted in a lower forward voltage drop（VF） in the diodes and the FLR design turned out to be a better choice for blocking voltages, in the reverse bias.Also, N;O annealing has shown a detrimental effect on the diodes’ blocking performance, which have JTE as their termination design. It degrades the blocking capability of the diodes significantly.

A Study of the Truncated Square Pyramid Geometry for Enhancement of Super-hydrophobicity

Super-hydrophobic surfaces are quite common in nature,inspiring people to continually explore its water-repellence property and applications to our lives.It has been generally agreed that the property of super-hydrophobicity is mainly contributed by the microscale or nanoscale(or even smaller)architecture on the surface.Besides,there is an energy barrier between the Cassie-Baxter wetting state and the Wenzel wetting state.An optimized square post micro structure with truncated square pyramid geometry is introduced in this work to increase the energy barrier,enhancing the robustness of super-hydrophobicity.Theoretical analysis is conducted based on the wetting transition energy curves.Numerical simulation based on a phase-field lattice Boltzmann method is carried out to verify the theoretical analysis.The numerical simulation agrees well with the theoretical analysis,showing the positive significance of the proposed micro structure.Furthermore,another novel micro structure of rough surface is presented,which combines the advantages of truncated pyramid geometry and noncommunicating roughness elements.Theoretical analysis shows that the novel micro structure of rough surface can effectively hinder the Cassie-Baxter state to Wenzel state transition,furthefly enhancing the robustness of the surface hydrophobicity.

Thermal Analyses of Power Electronics Integrated with Vapour Chamber Cooling

Insulated gate bipolar transistor(IGBT)power module is used for power switching transistor devices in the power supply and motor control circuits in both hybrid electric vehicles and electric vehicles.The target of heat flux of IGBT is continuously increasing due to the demand for power rating improvements and miniaturisation.Without suitable efficient cooling technolo-gies,excessively high temperature and uneven temperature distribution can cause high thermal stress,eventually leading to severe module failures.Therefore,highly efficient cooling solutions are highly required.Vapour chamber with phase change can provide quick heat transfer and low temperature gradient.This study proposes a new IGBT structure integrated with vapour chamber.The tests and simulation results indicate that the thermal and thermo-mechanical performances of IGBT integrated with vapour chamber are better than those of the IGBT with copper baseplate module.The thermal resistance between the junction and heat sink is reduced from 0.25 to 0.14°C/W,and the temperature uniformity is greatly improved due to the phase change in the vapour chamber.The simulation also investigates the thermal stress distribution,deformation and thermal fatigue lifespan of IGBT power electronics module.A reduction of 21.8%in thermal stress and an increase of 9%in lifespan of Sn-3.5Ag solder are achieved.