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 …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

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.

Ultracapacitors: Why, How, and Where is the Technology

http://ieeexplore.ieee.org/iel5/5610941/5624686/05624745.pdf

Power electronics

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.

/pdf/light-emitting-diodes-ubzde6g9qc.pdf

Light-emitting diodes

Faraday shields are widely used in high-frequency transformers to conduct the common-mode (CM) current to the ground. They are normally located in the high magnetomotive force (MMF) region, where severe eddy currents are induced and contribute considerable magnetic field losses. In this article, an analytical procedure is presented for the magnetically-induced loss in Faraday shields. It is originally derived from shields of foil conductors. Then, it is extended to different shields with round and Litz wire, and different configurations, e.g., multilayer shields, interleaved windings, and coaxial transformers. It is verified by the finite element method (FEM) and experimental results in six case studies. Moreover, the criteria to determine the losses of Faraday shields is given and a design procedure is presented to reduce the shield losses at a certain level while keeping the functionality. Finally, a case study is provided to verify the shield design procedure on a 100-kHz transformer.

https://vbn.aau.dk/ws/files/335746742/FaradayTpel2019_M.pdf

The Faraday Shields Loss of Transformers

Many efforts have been made to improve the single-phase power converters with active capacitive DC-link. The purpose is to reduce the overall DC-link energy storage and to achieve a reliable and cost-effective capacitive DC-link solution. A few review papers have already discussed the existing capacitive DC-link solutions, but important aspects of the topology assessment, such as the total energy storage, overall capacitive energy buffer ratio, cost, and reliability are still not available. This paper proposes a generic topology derivation method of single-phase power converters with capacitive DC-links, which derives all existing topologies to our best knowledge, and identify a few new topologies. A reliability-oriented design process is applied to compare the cost of different solutions with the lifetime target of 10 years and 35 years, respectively. It reveals that the most cost-effective solutions varies with the lifetime target.

A generic topology derivation method for single-phase converters with active capacitive DC-links

Improvement in the efficiency of distribution generation (DG) inverters is a concern and challenge for researchers across the globe. To address the concern an inverter control technique is developed. Inverters have issues with voltage regulation and harmonics when operating in the grid-connected (GC) and stand-alone (SA) mode. This paper proposes a control strategy capable of operating DGs in both SA and GC environments. The GC operation of the inverter is achieved by the current control mode and the SA control features a voltage control loop capable of overcoming the drawbacks due to load shedding or load switching. Besides, the harmonics due to various conditions of transition and load switching are eliminated by adapting a harmonic elimination pulse width modulation (PWM) scheme. To enhance the performance of the inverter and eliminate the problem of flexibility associated with conventional and offline switching angle calculations in the PWM technique, a Bio-Inspired Intelligent algorithm is adapted. The developed system is verified for various reduced total harmonic distortions (THD) by performing simulations and experiments. The results depict that the output voltage is regulated for varying load conditions, and the THD is observed to be 2.4% under varying load conditions.

Stand-Alone Operation of Distributed Generation Systems With Improved Harmonic Elimination Scheme

This paper investigates the power loss imbalance in Modular Multilevel Converters (MMCs) with Nearest Level Modulation (NLM) resulting from the low switching frequency operation and the parameter mismatch. The imbalance might pose a challenge to the cooling system design as well as the reliability of the MMC. To address this problem, a submodule-level power loss balancing control (PLBC) is proposed. Compared with the normal control strategy without the thermal balancing, this method is able to decrease the degree of power loss imbalance among submodules (SMs) to at least half without deteriorating the performance of the converter efficiency and the capacitor voltage ripple. The effectiveness of the proposed control is validated by simulations.

/pdf/submodule-level-power-loss-balancing-control-for-modular-25al4p74a2.pdf

Submodule Level Power Loss Balancing Control for Modular Multilevel Converters

With the revolution of renewable energy, the power system is being more complicated and integrated with more and more power electronics, which is referred to as the “power electronized” power system. In this case, the analysis, control, and operation of the entire power system should tone with the energy-paradigm transition pace. This paper thus explores challenges in power electronized power systems and highlights the stability issue. It serves to spark inspiration on potential solutions to these issues. As one of the solutions to cope with the interconnection of power converters with multi-synchronous generator systems, the virtual inertia concept is discussed in this paper. The impact of highly aggregated power electronic-based power systems is presented. More importantly, prospective solutions considering multiple timescales for the enhancement of power electronized power systems are briefed. A case study is exemplified in this paper to further highlight the analysis and discussion.

Huai Wang

Papers

The Faraday Shields Loss of Transformers

A generic topology derivation method for single-phase converters with active capacitive DC-links

Stand-Alone Operation of Distributed Generation Systems With Improved Harmonic Elimination Scheme

Submodule Level Power Loss Balancing Control for Modular Multilevel Converters

On Power Electronized Power Systems: Challenges and Solutions