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

The Passivity-Based Control (PBC) has been adopted in LCL-filtered Grid-Tied Inverters (GTI). However, the inaccurate mathematic model of control object will lead to a steady state error, when using the conventional PBC controller. In this paper, a modified PBC controller by using Dynamic Damping Injection (DDI) for LCL-filtered GTI is proposed to eliminate the steady state error. Furthermore, the state observer is used to reduce the number of sensors. A simulation platform is built in MATLAB/Simulink, and a 3-kW experimental device is developed with the control hardware of dSPACE DS1202 to verify the correctness and effectiveness of proposed control method.

A Modified PBC Controller Using Dynamic Damping Injection for LCL-Filtered Grid-Tied Inverter with Zero Steady State Error

In this paper, the power losses of three-level active neutral-point-clamped (3L-ANPC) inverters fully utilizing silicon-carbide (SiC) MOSFETs are studied and compared under three typically modulation schemes (i.e., the outer mode, inner mode, and full mode). Double-pulse tests (DPTs) are performed on a 3L-ANPC inverter prototype to evaluate the switching losses of SiC MOSFETs. The overall conversion losses subject to the three modulation schemes are investigated considering device junction temperatures. Accordingly, loss distributions among SiC devices are obtained, and the devices subject to the most significant electro-thermal stresses are identified. A power-loss comparison exhibits a comparable loss performance between the outer-mode and inner-mode modulation methods, while the full-mode loss characteristic is quite dependent on its loading condition. Finally, the theoretical finding presented in this work are validated through experimental measurements of the conversion efficiencies.

Loss Analysis of SiC-based Three-Level Active Neutral-Point-Clamped Inverters under Different Modulation Schemes

Single-stage power factor correction (PFC) solutions for low power LED applications are facing challenges of how to achieve lower cost, higher efficiency and longer lifetime. Mainly focusing on efficiency improvement, this paper proposes a single-stage bridgeless buck-boost converter with DC split configuration to minimize conduction losses. Secondly, two inductors in the proposed topology are alternately working in discontinuous conduction mode (DCM) when connecting to AC side, and working in continuous conduction mode (CCM) when connecting to DC side. The inductor in CCM helps filter switching frequency ripple, while the inductor in DCM allows the converter to utilize simple single loop control scheme in order to achieve output current regulation and near unity power factor (PF). Thirdly, harmonic injection is applied to further reduce output current ripple. A tradeoff between PF and lower output current ripple is given. Experimental validations are presented with 12.5 W prototypes to verify the theoretical analyses.

Single-stage Bridgeless Buck-boost PFC Converter with DC Split for Low Power LED applications

For modular multilevel converters (MMCs), reducing the design margin while fulfilling the reliability target in the design stage is challenging. To address this challenge, a system-level power loss evaluation is essential. Although many studies have discussed the power loss calculation of the MMC, most of them focus on the power losses of semiconductor devices while ignoring the impact of capacitors, arm inductors, and ac transformers. Therefore, this paper proposes a system-level power loss evaluation for MMCs from the perspective of reliability assessment. The power loss model covers switching devices, capacitors, and inductors. All the power loss calculation is starting from the active/reactive-power set points of the converter at the point of common coupling (PCC), where the converter is connected to the AC grid. The leakage inductance of the ac transformer is also considered. In addition, in order to meet the needs of long-term reliability assessment, the proposed power loss calculation is computation-efficient and easy to update parameters. The theoretical analysis has been verified by a full-scale MMC in simulations and a down-scale platform by experiments.

/pdf/system-level-power-loss-evaluation-of-modular-multilevel-3tjri2en1g.pdf

System-Level Power Loss Evaluation of Modular Multilevel Converters

The knowledge of DC-DC converter parameters is essential to both of the health condition estimation and controller tuning for better performance of DC-DC converters. This paper proposes a parameter identification method for DC-DC power converters by taking advantage of its dynamic characteristics, which is non-invasive, computation efficient and without additional hardware compared to existing methods. The application of the proposed method for a buck converter is presented here. Firstly, the modelling method of buck converter with an accurate solving method is described. Then, the particle swarm optimization algorithm (PSO)is introduced for parameter identification. Finally, experiments are performed to verify the feasibility and effectiveness of the proposed method.

Huai Wang

Papers

A Modified PBC Controller Using Dynamic Damping Injection for LCL-Filtered Grid-Tied Inverter with Zero Steady State Error

Loss Analysis of SiC-based Three-Level Active Neutral-Point-Clamped Inverters under Different Modulation Schemes

Single-stage Bridgeless Buck-boost PFC Converter with DC Split for Low Power LED applications

System-Level Power Loss Evaluation of Modular Multilevel Converters

Parameters Identification of Buck Converter Based on Dynamic Characteristics