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

This letter proposes a hybrid power control concept for grid-connected photovoltaic (PV) inverters. The control strategy is based on either a maximum power point tracking control or a constant power generation (CPG) control depending on the instantaneous available power from the PV panels. The essence of the proposed concept lies in the selection of an appropriate power limit for the CPG control to achieve an improved thermal performance and an increased utilization factor of PV inverters, and thus, to cater for a higher penetration level of PV systems with intermittent nature. A case study on a single-phase PV inverter under yearly operation is presented with analyses of the thermal loading, lifetime, and annual energy yield. It has revealed the trade-off factors to select the power limit and also verified the feasibility and the effectiveness of the proposed control concept.

/pdf/a-hybrid-power-control-concept-for-pv-inverters-with-reduced-4jzbhzcaga.pdf

A Hybrid Power Control Concept for PV Inverters with Reduced Thermal Loading

This study explores the integration issues of next-generation high-penetration photovoltaic (PV) systems, where the grid is becoming more decentralised and vulnerable. In that case, the PV systems are expected to be more controllable with higher efficiency and reliability. Provision of ancillary and intelligent services, such as fault ride-through and reactive power compensation, is the key to attain higher utilisation of solar PV energy. Such functionalities for the future PV inverters can contribute to reduced cost of energy, and thus enable more cost-effective PV installations. To implement the advanced features, a flexible power controller is developed in this study, which can be configured in the PV inverter and flexibly change from one to another mode during operation. Based on the single-phase PQ theory, the control strategy offers the possibilities to generate appropriate references for the inner current control loop. The references depend on system conditions and also specific demands from both system operators and prosumers. Besides, this power control strategy can be implemented in commercial PV inverters as a standardised function, and also the operation modes can be achieved online in predesigned PV inverters. Case studies have verified the effectiveness and flexibilities of the proposal to realise the advanced features.

/pdf/power-control-flexibilities-for-grid-connected-multi-1cnsthjyva.pdf

Power control flexibilities for grid-connected multi-functional photovoltaic inverters

Bond wire fatigue is one of the dominant failure mechanisms in IGBT modules. However, the bond wire lifetime is not easily predictable and measurable to date due to several challenges. To overcome this challenge, this paper proposes a Monte Carlo based analysis method to predict the lifetime consumption of bond wires in a Photovoltaic (PV) inverter under long-term operation. The parameter distributions of IGBTs due to manufacturing variation and the annual stress profiles due to intermittent nature of solar irradiance and ambient temperature are taken into consideration. The proposed method enables a more realistic lifetime prediction with a specified confidence level compared to the state-of-the-art approaches. A study case on IGBT modules in a 10 kW three-phase PV inverter demonstrates the procedure and the results of the analysis. Finally, the lifetime distribution of bond wires permits to estimate the risk of unreliability of a single IGBT in a Photovoltaic (PV) inverter.

/pdf/prediction-of-bond-wire-fatigue-of-igbts-in-a-pv-inverter-3chbs3q6cl.pdf

Prediction of bond wire fatigue of IGBTs in a PV inverter under long-term operation

Review on reliability of supercapacitors in energy storage applications

Power electronics are facing continuous pressure to be cheaper and smaller, have a higher power density, and, in some cases, also operate at higher temperatures. At the same time, power electronics products are expected to have reduced failures because it is essential for reducing the cost of energy. New approaches for reliability assessment are being taken in the design phase of power electronics systems based on the physics-of-failure in components. In this approach, many new methods, such as multidisciplinary simulation tools, strength testing of components, translation of mission profiles, and statistical analysis, are involved to enable better prediction and design of reliability for products. This article gives an overview of the new design flow in the reliability engineering of power electronics from the system-level point of view and discusses some of the emerging needs for the technology in this field.

Huai Wang

Papers

A Hybrid Power Control Concept for PV Inverters with Reduced Thermal Loading

Power control flexibilities for grid-connected multi-functional photovoltaic inverters

Prediction of bond wire fatigue of IGBTs in a PV inverter under long-term operation

Review on reliability of supercapacitors in energy storage applications

New Approaches to Reliability Assessment: Using physics-of-failure for prediction and design in power electronics systems