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

2 1 The innovative transport systems and the CityMobil project 10 1.1 The research questions 10 2 The state of art in the field of automatic transport systems 12 2.1 Case studies and demand studies for innovative transport systems 12 3 The design and implementation of surveys 14 3.1 Definition of experimental design 14 3.2 Questionnaire design and delivery 16 3.3 First analyses on the collected sample 18 4 Calibration of Logit Multionomial demand models 21 4.1 Methodology 21 4.2 Calibration of the “full” model. 22 4.3 Calibration of the “final” model 24 4.4 The demand analysis through the final Multinomial Logit model 25 5 The analysis of interaction between the demand and socioeconomic attributes 31 5.1 Methodology 31 5.2 Application of Mixed Logit models to the demand 31 5.3 Analysis of the interactions between demand and socioeconomic attributes through Mixed Logit models 32 5.4 Mixed Logit model and interaction between age and the demand for the CTS 38 5.5 Demand analysis with Mixed Logit model 39 6 Final analyses and conclusions 45 6.1 Comparison between the results of the analyses 45 6.2 Conclusions 48 6.3 Answers to the research questions and future developments 52

The European commission

Renewable energy sources like wind, sun, and hydro are seen as a reliable alternative to the traditional energy sources such as oil, natural gas, or coal. Distributed power generation systems (DPGSs) based on renewable energy sources experience a large development worldwide, with Germany, Denmark, Japan, and USA as leaders in the development in this field. Due to the increasing number of DPGSs connected to the utility network, new and stricter standards in respect to power quality, safe running, and islanding protection are issued. As a consequence, the control of distributed generation systems should be improved to meet the requirements for grid interconnection. This paper gives an overview of the structures for the DPGS based on fuel cell, photovoltaic, and wind turbines. In addition, control structures of the grid-side converter are presented, and the possibility of compensation for low-order harmonics is also discussed. Moreover, control strategies when running on grid faults are treated. This paper ends up with an overview of synchronization methods and a discussion about their importance in the control

/pdf/overview-of-control-and-grid-synchronization-for-distributed-2nx31ovpe9.pdf

Overview of Control and Grid Synchronization for Distributed Power Generation Systems

DC and AC Microgrids are key elements to integrate renewable and distributed energy resources as well as distributed energy storage systems. In the last years, efforts toward the standardization of these Microgrids have been made. In this sense, this paper present the hierarchical control derived from ISA-95 and electrical dispatching standards to endow smartness and flexibility to microgrids. The hierarchical control proposed consist of three levels: i) the primary control is based on the droop method, including an output impedance virtual loop; ii) the secondary control allows restoring the deviations produced by the primary control; and iii) the tertiary control manage the power flow between the microgrid and the external electrical distribution system. Results from a hierarchical-controlled microgrid are provided to show the feasibility of the proposed approach.

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Hierarchical control of droop-controlled DC and AC microgrids — a general approach towards standardization

The use of distributed energy resources is increasingly being pursued as a supplement and an alternative to large conventional central power stations. The specification of a power-electronic interface is subject to requirements related not only to the renewable energy source itself but also to its effects on the power-system operation, especially where the intermittent energy source constitutes a significant part of the total system capacity. In this paper, new trends in power electronics for the integration of wind and photovoltaic (PV) power generators are presented. A review of the appropriate storage-system technology used for the integration of intermittent renewable energy sources is also introduced. Discussions about common and future trends in renewable energy systems based on reliability and maturity of each technology are presented

/pdf/power-electronic-systems-for-the-grid-integration-of-4s5cxjhatl.pdf

Power-Electronic Systems for the Grid Integration of Renewable Energy Sources: A Survey

https://publikationen.bibliothek.kit.edu/1000123440/88083137

Impact of smart transformer voltage and frequency support in a high renewable penetration system

The Smart Transformer (ST), which is a power electronics-based transformer, represents an enabling technology for providing new services to the Low Voltage (LV) and Medium Voltage (MV) grid. The 3-stage configuration, with a high frequency transformer and 2 DC links, allows the electrical separation of the LV and MV grids. This leads to the independence of the two grids: any disturbance downstream and upstream can be compensated and mitigated by the ST action, which is the case of the unbalanced load condition of the LV grids. The unbalanced currents demanded by the loads could create unbalanced voltages at the LV side and also unbalanced currents at the MV side of a traditional transformer. This paper presents the improvements achieved by ST implementation in terms of voltage and current balancing: with a proper control of the ST, it provides balanced voltage in the LV grid, demanding a balanced current from the MV grid. This feature increases the power quality in both grids and provides an improved service to the customers.

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Voltage and current balancing in Low and Medium Voltage grid by means of Smart Transformer

/pdf/smart-transformer-large-flexible-transformer-1ga1hx87cc.pdf

Smart transformer/large flexible transformer

With the significant increase in renewable energy sources (RES) and storage elements, power distribution system needs new services for reliable and continuous operation. Smart transformer (ST) based on power electronics, control, and communication has been proposed for improving the performance of power system. However, operational capabilities and applications of ST with RES and energy storage in distribution system are still not explored in detail. In this paper, a new prospective of ST application, dual microgrid (DMG) operation, is proposed. In normal medium voltage (MV) grid operation, the ST supplies power to loads connected to its low voltage side and injects into the MV grid depending upon the available RES and load demand. During the voltage disturbances, the ST feeds power to the sensitive loads connected to the other feeders equipped with the conventional power transformers. In this case, the distribution loads are isolated from the MV utility grid. This ability of the smart transformer to isolate from the utility grid and provide continuous power to the sensitive loads of other feeders has potential to significantly improve the performance of power system as well as ST. With simulation results based on PSCAD/EMTDC software, this paper introduces for the first time an unexplored feature of the smart transformer.

/pdf/a-new-prospective-of-smart-transformer-application-dual-3ulm3t614x.pdf

A new prospective of smart transformer application: Dual microgrid (DMG) operation

In the last decades the voltage regulation has been challenged by the increase of power variability in the electric grid, due to the spread of non-dispatchable generation sources. This paper introduces a Smart Transformer (ST)-based Medium Voltage (MV) grid support by means of active power control in the ST-fed Low Voltage (LV) grid. The aim of the proposed strategy is to improve the voltage profile in MV grids before the operation of On-Load Tap Changer in the primary substation transformer, which needs tens of seconds. This is realized through reactive power injection by the AC/DC MV converter and simultaneous decrease of the active power consumption of voltage-dependent loads in ST-fed LV grid, controlling the ST output voltage. The last feature has two main effects: the first is to reduce the active power withdrawn from MV grid, and consequently the MV voltage drop caused by the active current component. At the same time, higher reactive power injection capability in the MV converter is unlocked, due to the lower active power demand. As result, the ST increases the voltage support in MV grid. The analysis and simulation results carried out in this paper show improvements compared to similar solutions, i.e. the only reactive power compensation. The impact of the proposed solution has been finally evaluated under different voltage-dependence of the loads in the LV grid.

/pdf/smart-transformer-based-medium-voltage-grid-support-by-means-4ohxmtxg8w.pdf

Marco Liserre

Papers

Impact of smart transformer voltage and frequency support in a high renewable penetration system

Voltage and current balancing in Low and Medium Voltage grid by means of Smart Transformer

Smart transformer/large flexible transformer

A new prospective of smart transformer application: Dual microgrid (DMG) operation

Smart transformer-based medium voltage grid support by means of active power control