Huai Wang

Bio: Huai Wang is an academic researcher from Aalborg University. The author has contributed to research in topics: Capacitor & Power electronics. The author has an hindex of 38, co-authored 328 publications receiving 7480 citations. Previous affiliations of Huai Wang include Yangtze University & City University of Hong Kong.

Impact of Space Vector Modulation Strategies on the Reliability of Impedance-Source Inverters

Abstract: Comparisons of different modulation strategies for Z-source/quasi-Z-source inverters (ZSI/qZSI) focused on voltage gains, switching losses, inductor current ripples, and harmonics. However, Pulse Width Modulation (PWM) strategies can affect voltage/current stresses and power losses on power devices. Therefore, thermal loading of the ZSI/qZSI inverters may be redistributed, and thus, the inverter lifetime may be affected. Hence, this paper evaluates the impact of three Space Vector Modulation (SVM) strategies on the qZSI reliability. More specifically, the maximum current stresses, power losses, thermal stresses, and the number of cycles to failure of the power switches are benchmarked. The evaluation enables identifying the most appropriate modulation strategy for Z-source inverters to achieve better performances in terms of efficiency and reliability. Simulation and experimental tests validate the theoretical analysis and comparison.

Degradation Analysis of Planar Magnetics

Abstract: This paper presents the degradation testing results of a type of planar transformer under accelerated thermal conditions The likely failure mechanisms are an-alyzed Thermal-related degradation models and lifetime models are obtained based on certain end-of-life criteria and assumptions

Simplified Estimation of the Junction Temperature Fluctuation at the Output Frequency for IGBT Modules in Modular Multilevel Converters

Abstract: Thermal modeling of modular multilevel converters (MMCs) are of interest for reliability-oriented component sizing. However, conventional analytical thermal modeling is difficult to consider an inherent thermal unbalance in MMCs, while a time-domain simulation is challenging to process one-year mission profiles in reliability evaluation. This paper proposes a thermal modeling method for IGBT modules in MMCs based on simplified equivalent power loss profiles. It compromises the accuracy and computation time. A derived analytical equation quantifies the modeling error and the level of simplification for periodic power loss profiles related to the ac output frequency of MMCs. The theoretical results have been verified by both simulations and experiments.

Reliability Evaluation and Optimization of Capacitor Bank

Abstract: Capacitors are widely used in power electronic converters to buffer the pulsation power, filter the harmonics and support voltage for stable operation. For these applications where single capacitor can not fulfill the voltage rating or capacitance requirements, capacitor bank is always used as the energy buffer by connecting several capacitors in parallel for larger capacitance, or in series for higher voltage rating. With more stringent constrains on volume for high power density applications, the thermal coupling effect becomes more severely which accelerates a portion of cells aging, therefore, reliability should be considered into the design phase. In this paper, considering the uneven temperature distribution in an ultra-compact capacitor bank, the lifetime of each cell is estimated at the beginning to reveal the reliability issue. Aiming to extend the lifetime of the capacitor bank with cost constraint, optimization solutions are proposed from the two aspects: rated lifetime allocation, and thermal loading distribution of each cell which are the significant factors to the lifetime. Simulation and experiment are conducted to verify the accuracy of the proposed solutions.

Integrin α6-Targeted Molecular Imaging of Central Nervous System Leukemia in Mice

Abstract: Central nervous system leukemia (CNS-L) is caused by leukemic cells infiltrating into the meninges or brain parenchyma and remains the main reason for disease relapse. Currently, it is hard to detect CNS-L accurately by clinically available imaging models due to the relatively low amount of tumor cells, confined blood supply, and the inferior glucose metabolism intensity. Recently, integrin α6-laminin interactions have been identified to mediate CNS-L, which suggests that integrin α6 may be a promising molecular imaging target for the detection of CNS-L. The acute lymphoblastic leukemia (ALL) cell line NALM6 stabled and transfected with luciferase was used to establish the CNS-L mouse model. CNS-L-bearing mice were monitored and confirmed by bioluminescence imaging. Three of our previously developed integrin α6-targeted peptide-based molecular imaging agents, Cy5-S5 for near-infrared fluorescence (NIRF), Gd-S5 for magnetic resonance (MR), and 18F-S5 for positron emission tomography (PET) imaging, were employed for the molecular imaging of these CNS-L-bearing mice. Bioluminescence imaging showed a local intensive signal in the heads among CNS-L-bearing mice; meanwhile, Cy5-S5/NIRF imaging produced intensive fluorescence intensity in the same head regions. Moreover, Gd-S5/MR imaging generated superior MR signal enhancement at the site of meninges, which were located between the skull bone and brain parenchyma. Comparatively, MR imaging with the clinically available MR enhancer Gd-DTPA did not produce the distinguishable MR signal in the same head regions. Additionally, 18F-S5/PET imaging also generated focal radio-concentration at the same head regions, which generated nearly 5-times tumor-to-background ratio compared to the clinically available PET radiotracer 18F-FDG. Finally, pathological examination identified layer-displayed leukemic cells in the superficial part of the brain parenchyma tissue, and immunohistochemical staining confirmed the overexpression of the integrin α6 within the lesion. These findings suggest the potential application of these integrin α6-targeted molecular imaging agents for the accurate detection of CNS-L.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Ultracapacitors: Why, How, and Where is the Technology

Abstract: The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

Light-emitting diodes

Abstract: Light-Emitting Diodes. (Monographs in Electrical and Electronic Engineering.) By A. A. Bergh and P. J. Dean. Pp. viii+591. (Clarendon: Oxford; Oxford University: London, 1976.) £22.