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

A predictive control of buck converter to achieve fast transient response is presented. The methodology is based on using the output capacitor current and instantaneous output voltage to predict the output voltage at the end and mid of a switching cycle to determine the state of the main switch. Two switching criteria, one for switching on and one for switching off the main switch, will be formulated. The operating principles of the control method and all possible cases in the operation will be discussed. The proposed control method has been verified with experimental results of a 50W, 12V/5V buck converter prototype. The controller is realized by analogue devices. The steady-state and transient response to large-signal disturbances will be discussed.

Predictive control of buck converter using nonlinear output capacitor current programming

This paper proposes a fast and robust open-circuit fault diagnosis method without additional sensors for cascaded H-bridge multilevel converters (CHBMCs). The method is based on the error between the actual input-side voltage and the estimated one, with one detection threshold and 2n comparators in n cascaded H-bridges. Benefit from the simple design of the fault location, spike elimination, and parameter estimation, with the lower implementation burden, the single and multiple faults in arbitrary positions are accurately identified within a fundamental cycle, and the diagnostic robustness is guaranteed under different transient changes. In view of the low complexity, the proposed scheme can be easily applied to the CHBMCs with arbitrary modules. The experimental results from a CHBMC prototype verify the effectiveness of the proposed method under different operating conditions and fault scenarios.

A Voltage-Based Multiple Fault Diagnosis Approach for Cascaded H-Bridge Multilevel Converters

Interleaved power factor correction (PFC) is widely used circuit topology due to good efficiency and power density for single-switch boost PFC. As the differential mode (DM) electromagnetic interference (EMI) noise magnitude depends upon the input current ripple, this research details a comprehensive study of DM EMI filter design for interleaved boost PFC with the aim of minimizing the component size. It is also demonstrated that the different numbers of interleaved stages and switching frequency influence the filter attenuation requirement and, thus, the EMI filter size. First, an analytical model is derived on the basis of the Norton equivalent circuit model for the differential mode noises of interleaved boost PFC within the frequency range of 9–500 kHz. The derived model can help identify the proper phase shifting among the interleaved boost converters in order to minimize the considered differential mode noises at the filter design frequency. So, a novel phase-shift method is developed to get a minimized attenuation required by a filter in Band B. Further, a volume optimization of the required DM filter was introduced based on the calculated filter attenuation and volumetric component parameters. Based on the obtained results, unconventional and conventional phase shifts have demonstrated a good performance in decreasing the EMI filter volume in Band B and Band A, respectively. A 2-kW interleaved PFC case study is presented to verify the theoretical analyses and the impact of phase-shifting on EMI filter size.

Differential Mode Noise Estimation and Filter Design for Interleaved Boost Power Factor Correction Converters

In power electronic-based power systems (PEPS), challenges are arising such as how to ensure a reliable power system, although increasingly efforts have been made to enhance the reliability of power electronics at the component-level and converter-level. Existing methods for single converter reliability analysis might not be scalable for system-level reliability analysis in power systems. Thus, this paper presents a general concept on the reliability analysis in PEPS to curb the arising issues. The concept considers the individual reliability matrices and more importantly, takes the complicated interactions and cross coupling-effects among multiple converters into account and thereby improve the reliability of next generation power systems. This will be beneficial for power system operators, end-users and the average electrical consumer with the possibility to decrease the costs related to component failures, maintenance and also system downtime as a result of advancing the system reliability.

Reliability Analysis of Power Electronic-based Power Systems

The lifetime prediction of LED lighting system is important to guide the designers to fulfill the design specifications and to benchmark the cost-competitiveness of different lighting technologies. Currently, the lifetime of LED system is usually predicted from the source part and the driver part separately, and then the thermal design is also optimized independently. In practice, the LED source and driver are usually compacted in a single fixture. The heat dissipated from LED source and driver will be coupled together and affect the heat transfer performance, which may degrade the whole system and accelerate the failure. In this paper, a new thermal model concerning the thermal coupling is proposed with Finite Element Method (FEM) simulation for parameter acquirement. The proposed model has a better estimation of the thermal stresses of key components in the LED lamps and therefore an improved lifetime prediction of the LED systems. Moreover, with a given lifetime requirements, this method can be used to guide the thermal design of the LED system. A case study of an outdoor lighting application is then demonstrated by both FEM simulations and experimental verifications in this digest.

Huai Wang

Papers

Predictive control of buck converter using nonlinear output capacitor current programming

A Voltage-Based Multiple Fault Diagnosis Approach for Cascaded H-Bridge Multilevel Converters

Differential Mode Noise Estimation and Filter Design for Interleaved Boost Power Factor Correction Converters

Reliability Analysis of Power Electronic-based Power Systems

Lifetime prediction of LED lighting systems considering thermal coupling between LED sources and drivers