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 paper investigates the reliability of power electronic converters employed for different applications in a dc power system employing a mission profile based reliability approach. The power electronic converter reliability depends on its loading profile, which induces thermal stresses on the failure-prone components, hence, limiting the converter lifetime. The loading profile of different converters in a power system is relevant to the mission profiles (including environmental and operational conditions), which can be controlled by a power management strategy. Moreover, the battery converter sizing in a renewable based power system may affect the power flow through the converters, and hence, its loading profiles. Therefore, this paper studies the impact of mission profile, power management strategy, and battery converter capacity on the reliability of different converters. The obtained results are presented through numerical analysis.

/pdf/mission-profile-based-power-converter-reliability-analysis-4lmct0mbl0.pdf

Mission Profile Based Power Converter Reliability Analysis in a DC Power Electronic Based Power System

This letter proposes a simplified converter-level on-state voltage measurement circuit for power semiconductor devices, without an external power supply and self-power circuit. It has a reduced component count and circuit complexity, and retains the plug-and-play feature, comparable measurement accuracy, and dynamic response as recently reported methods. A proof-of-concept prototype is developed and tested for a three-phase inverter application.

A Simplified On-State Voltage Measurement Circuit for Power Semiconductor Devices

This letter proposes a two-terminal active inductor concept with minimum apparent power processed by the auxiliary circuits, which are implemented by power semiconductor switches and passive elements. It has the same level of convenience as a passive inductor with two power terminals only. Compared with a conventional inductor with the same equivalent inductance and current rating, the energy storage requirement of the inductor can be reduced significantly, as well as the weight and volume. The auxiliary circuit in the active inductor processes both partial voltage and partial current, with the lowest apparent power rating compared to existing solutions. A case study for the dc-link filter inductor in a three-phase diode-bridge rectifier is discussed. Proof-of-concept experimental results are given to verify the functionality and effectiveness of the proposed active inductor.

/pdf/a-two-terminal-active-inductor-with-minimum-apparent-power-uqeu356m4j.pdf

A Two-Terminal Active Inductor With Minimum Apparent Power for the Auxiliary Circuit

A novel concept for reduction of dc-link capacitors is proposed in this paper. It is based on introducing a voltage compensator connected in series with the dc bus line. The compensator processes the ripple voltage and reactive power only and thus can be implemented with switches and capacitors of low voltage ratings. The overall required energy storage is reduced, allowing the replacement of electrolytic capacitors by alternatives with longer lifetime and comparable or reduced volume and cost. A general theory that illustrates the proposed concept is presented. The theoretical predictions are favorably verified by simulations and experiments.

Study of a new technique to reduce the dc-link capacitor in a power electronic system by using a series voltage compensator

This chapter discusses the modeling and control methods for basic DC-DC converters by three specific case studies. It covers both the frequency-domain control methods and time-domain control methods. Specifically, the voltage mode control of a Buck converter, current mode control of a Boost converter, and a unified second-order boundary control of a Buck-Boost converter are presented. The analysis methods and control schemes can be extended to other DC-DC converter applications.

Huai Wang

Papers

Mission Profile Based Power Converter Reliability Analysis in a DC Power Electronic Based Power System

A Simplified On-State Voltage Measurement Circuit for Power Semiconductor Devices

A Two-Terminal Active Inductor With Minimum Apparent Power for the Auxiliary Circuit

Study of a new technique to reduce the dc-link capacitor in a power electronic system by using a series voltage compensator

Modeling and Control of DC-DC Converters