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 non-contact method for simultaneously measuring the current and voltage change rates by Rogowski coils. The dv/dt measurement capability is achieved based on electric field coupling, which is incorporated into the state-of-the-art Rogowski coil based current sensing solutions. The application of the proposed method for power semiconductor devices is demonstrated by a case study of an IGBT switching circuit. The Rogowski coils are integrated with a Printed Circuit Board (PCB) and fit with the IGBT module terminals. The comparable results from high-performance commercial instruments verify the di/dt and dv/dt measurement accuracy of the presented compact and cost-effective solution. 

A Non-contact Method for Simultaneous Measurement of di/dt and dv/dt

This paper presents an improved thermal analysis method focusing on the long-term profiles of power modules. A shift-invariant dictionary method is developed to extract the critical atoms to sparsely represent time series signals. Then the temperature response of the power module can be approximated by a sparse linear combination of basis functions. The performance of the proposed method is compared with the convolution method, the result indicates that the transient junction temperature of the power module can be predicted with less computational effort. The simulation and experimental results also prove that the proposed method can effectively reconstruct the thermal behavior, exhibits good predictive capability and is suitable for temperature prediction under long time scales.

Transient Thermal Modeling of Power Semiconductors for Long-Term Load Profiles

An active two-terminal inductor device with a controllable inducitance based on an inductance value input L_I. A processor system PRS executes an algorithm which controls a power converter PCV with controllable electric switches connected to the two external terminals A, B along with a fixed value inductor component L1. Based on sampling of at least a voltage or a current in connection with the inductor component L1, the algorithm controls the power converter PCV to provide a resulting inductance across the external terminals A, B which serves to match the inductance value input L_I.

A two-terminal active inductor device

Although various machine learning-based methods have been proposed for condition monitoring in power elec-tronics, they are challenging to be implemented in practice due to the accuracy, data availability, computation burden, explainability, etc. Physics-informed machine learning (PIML) has been emerging as a promising direction where the above challenges can be mitigated by incorporating domain knowledge. In this paper, we propose a PIML- based parameter estimation method for a DC-DC Buck converter, as an exemplary application of PIML in power electronics. By seamlessly integrating a deep neural network and the converter physical model, it can estimate multiple component parameters simultaneously with high accuracy and robustness, while based on a limited dataset. It expects to provide a new perspective to tailor existing ML tools for power electronic applications.

Physics-informed Machine Learning for Parameter Estimation of DC-DC Converter

This paper presents the degradation testing and failure mechanisms analysis of metalized film capacitors used for AC filtering in MW power converters. Based on more than 2,800 hours of accelerated testing under accelerated AC voltage, temperature, and AC current, various electro-thermal parameter data are recorded. The results reveal that capacitance values have negligible reduction until the testing samples catastrophically fail. The capacitor hot spot temperature and case temperature are measured along the testing, which are increasing. The observations provide a new perspective on the possible failure mechanisms and condition monitoring of film capacitors in AC filtering applications.

Huai Wang

Papers

A Non-contact Method for Simultaneous Measurement of di/dt and dv/dt

Transient Thermal Modeling of Power Semiconductors for Long-Term Load Profiles

A two-terminal active inductor device

Physics-informed Machine Learning for Parameter Estimation of DC-DC Converter

Accelerated degradation testing and failure phenomenon of metalized film capacitors for AC filtering