다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

DC-link capacitors are an important part in the majority of power electronic converters which contribute to cost, size and failure rate on a considerable scale. From capacitor users' viewpoint, this paper presents a review on the improvement of reliability of dc link in power electronic converters from two aspects: 1) reliability-oriented dc-link design solutions; 2) conditioning monitoring of dc-link capacitors during operation. Failure mechanisms, failure modes and lifetime models of capacitors suitable for the applications are also discussed as a basis to understand the physics-of-failure. This review serves to provide a clear picture of the state-of-the-art research in this area and to identify the corresponding challenges and future research directions for capacitors and their dc-link applications.

/pdf/reliability-of-capacitors-for-dc-link-applications-in-power-2b0em1025t.pdf

Reliability of Capacitors for DC-Link Applications in Power Electronic Converters—An Overview

This paper presents a single-phase cascaded H-bridge converter for a grid-connected photovoltaic (PV) application The multilevel topology consists of several H-bridge cells connected in series, each one connected to a string of PV modules The adopted control scheme permits the independent control of each dc-link voltage, enabling, in this way, the tracking of the maximum power point for each string of PV panels Additionally, low-ripple sinusoidal-current waveforms are generated with almost unity power factor The topology offers other advantages such as the operation at lower switching frequency or lower current ripple compared to standard two-level topologies Simulation and experimental results are presented for different operating conditions

Control of a Single-Phase Cascaded H-Bridge Multilevel Inverter for Grid-Connected Photovoltaic Systems

In the first part of this paper, three-phase power factor correction (PFC) rectifier topologies with sinusoidal input currents and controlled output voltage are derived from known single-phase PFC rectifier systems and/or passive three-phase diode rectifiers. The systems are classified into hybrid and fully active pulsewidth modulation boost-type or buck-type rectifiers, and their functionality and basic control concepts are briefly described. This facilitates the understanding of the operating principle of three-phase PFC rectifiers starting from single-phase systems, and organizes and completes the knowledge base with a new hybrid three-phase buck-type PFC rectifier topology denominated as Swiss Rectifier. Finally, core topics of future research on three-phase PFC rectifier systems are discussed, such as the analysis of novel hybrid buck-type PFC rectifier topologies, the direct input current control of buck-type systems, and the multi-objective optimization of PFC rectifier systems. The second part of this paper is dedicated to a comparative evaluation of four rectifier systems offering a high potential for industrial applications based on simple and demonstrative performance metrics concerning the semiconductor stresses, the loading and volume of the main passive components, the differential mode and common mode electromagnetic interference noise level, and ultimately the achievable converter efficiency and power density. The results are substantiated with selected examples of hardware prototypes that are optimized for efficiency and/or power density.

The Essence of Three-Phase PFC Rectifier Systems—Part II

This paper shows that versatile stand-alone photovoltaic (PV) systems still demand on at least one battery inverter with improved characteristics of robustness and efficiency, which can be achieved using multilevel topologies. A compilation of the most common topologies of multilevel converters is presented, and it shows which ones are best suitable to implement inverters for stand-alone applications in the range of a few kilowatts. As an example, a prototype of 3 kVA was implemented, and peak efficiency of 96.0% was achieved.

Multilevel Inverter Topologies for Stand-Alone PV Systems

A novel three-phase ac-ac sparse matrix converter having no energy storage elements and employing only 15 IGBTs, as opposed to 18 IGBTs of a functionally equivalent conventional ac-ac matrix converter, is proposed. It is shown that the realization effort could be further reduced to only nine IGBTs in an ultra sparse matrix converter (USMC) in the case where only unidirectional power flow is required and the fundamental phase displacement at the input and at the output is limited to plusmnpi/6. The dependency of the voltage and current transfer ratios of the sparse matrix converters on the operating parameters is analyzed and a space vector modulation scheme is described in combination with a zero current commutation method. Finally, the sparse matrix concept is verified by simulation and experimentally using a 6.8-kW/400-V very sparse matrix converter, which is implemented with 12 IGBT switches, and USMC prototypes.

Novel Three-Phase AC–AC Sparse Matrix Converters

Power density of power electronic converters in different applications has roughly doubled every 10 years since 1970. Behind this trajectory was the continuous advancement of power semiconductor device technology allowing an increase of converter switching frequencies by a factor of 10 every decade. However, today's cooling concepts, and passive components and wire bond interconnection technologies could be major barriers for a continuation of this trend. For identifying and quantifying such technological barriers this paper investigates the volume of the cooling system and of the main passive components for the basic forms of power electronics energy conversion in dependency of the switching frequency and determines switching frequencies minimizing the total volume. The analysis is for 5 kW rated output power, high performance air cooling, advanced power semiconductors, and single systems in all cases. A power density limit of 28 kW/dm3@300 kHz is calculated for an isolated DC-DC converter considering only transformer, output inductor and heat sink volume. For single-phase AC-DC conversion a general limit of 35 kW/dm3 results from the DC link capacitor required for buffering the power fluctuating with twice the mains frequency. For a three-phase unity power factor PWM rectifier the limit is 45 kW/dm3@810 kHz just taking into account EMI filter and cooling system. For the sparse matrix converter the limiting components are the input EMI filter and the common mode output inductor; the power density limit is 71 kW/dm3@50 kHz when not considering the cooling system. The calculated power density limits highlight the major importance of broadening the scope of research in power electronics from traditional areas like converter topologies, and modulation and control concepts to cooling systems, high frequency electromagnetics, interconnection technology, multi-functional integration, packaging and multi-domain modeling and simulation to ensure further advancement of the field along the power density trajectory.

https://www.hpe.ee.ethz.ch/uploads/tx_ethpublications/IEEJ_PowerDensity_Paper_FinalRevised_03.pdf

PWM Converter Power Density Barriers

A novel three-phase AC-DC-AC sparse matrix converter (SMC) having no energy storage elements in the DC link and employing only 15 IGBTs as opposed to 18 IGBTs of a functionally equivalent conventional AC-AC matrix converter (CMC) is proposed. It is shown that the realization effort could be further reduced to only 9 IGBTs (ultra sparse matrix converter, USMC) in case the phase displacement of the fundamentals of voltage and current at the input and at the output is limited to /spl plusmn//spl pi//6. The dependency of the voltage and current transfer ratios of the systems on the operating parameters is analyzed and a space vector modulation scheme is described in combination with a zero current commutation procedure. Furthermore, a safe multi-step current commutation concept is treated briefly. Conduction and switching losses of the SMC and USMC are calculated in analytically closed form. Finally, the theoretical results are verified in Part II of the paper by digital simulations and results of a first experimental investigation of a 10 kW/400 V SMC prototype are given.

Novel three-phase AC-DC-AC sparse matrix converter

This paper presents a novel DC-AC converter for applications in the area of distributed energy generation systems, e.g., solar power systems, fuel-cell power systems in combination with supercapacitor or battery energy storage. The proposed converter is realized using an isolated multicell topology where the total AC output of the system is formed by series connection of several full-bridge converter stages. The DC links of the full bridges are supplied by individual DC-DC isolation stages which are arranged in parallel concerning the dc input of the. total system. Therefore, all switching cells of the proposed converter can be equipped with modern low-voltage high-current power MOSFETs, which results in an improved efficiency as compared to conventional isolated DC-AC converters. Furthermore, the cells are operated in an interleaved pulsewidth-modulation mode which, in connection with the low voltage level of each cell, significantly reduces the filtering effort on the AC output of the overall system. The paper describes the operating principle, analyzes the fundamental relationships which are relevant for component selection, and presents a specific circuit design. Finally, measurements taken from a 2-kW laboratory model are presented.

http://www.initkms.ru/umk/etf/d/A_novel_multi-cell_DA-AC_converter_for...(Ertl_H._etc.).pdf

A novel multicell DC-AC converter for applications in renewable energy systems

A novel life-cycle monitoring and voltage-managing device for dc-link electrolytic capacitors in pulsewidth modulation converters is presented. The system performs online identification of the capacitor's equivalent series resistance (ESR) in order to detect the life-cycle status and permit preventive maintenance. The ESR detection is based on the capacitor's ac losses calculated from voltage/current measurements using a simple low-cost microcontroller. The unit is designed as small printed circuit board located directly at the capacitor's screw terminals in order to simplify the required temperature sensing and to minimize wiring effort. The minimized energy consumption allows a power supply taken out of the capacitor to be tested. Besides life-cycle monitoring, the unit further facilitates energy-efficient voltage balancing for capacitors in series arrangements avoiding any power resistors typically used in balancing circuits. Instead, the unit controls the capacitor voltage by influencing its power consumption. Each individual monitoring unit (one per each power capacitor of the converter) transfers the ESR results to the converter's main controller and receives control commands via a common optoisolated fieldbus. Alternatively, this data transfer is performed using wireless near-field communication leading to a completely autonomous monitoring unit without any wiring for power supply and data transmission.

Hans Ertl

Papers

Novel Three-Phase AC–AC Sparse Matrix Converters

PWM Converter Power Density Barriers

Novel three-phase AC-DC-AC sparse matrix converter

A novel multicell DC-AC converter for applications in renewable energy systems

Life-Cycle Monitoring and Voltage-Managing Unit for DC-Link Electrolytic Capacitors in PWM Converters