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

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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

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

Implementation of ancillary services in photovoltaic systems could facilitate their penetration in power systems. PV converters can be designed to improve grid power quality using power conditioning functionalities. This paper presents a single-phase photovoltaic system which provides grid voltage support at fundamental frequency. The proposed topology is controlled with the droop control technique. Experimental results validate the proposed control.

Droop control of a multifunctional PV inverter

The paper presents a small Wind Turbine System (WTS) improved with voltage compensation functionality. In the WTS the Permanent Magnet Generator (PMG) control is designed to maximize the power output and achieve a smooth torque and power profile. The grid-side converter is controlled in order to maintain constant the voltage for local loads also in presence of grid voltage variations. The proposed control allows to obtain sinusoidal grid currents and high power factor during normal operation conditions while the control of the reactive power injected by the wind turbine system provides voltage support.

Grid voltage support by means of a small Wind Turbine System

Fast change of the irradiance conditions entails failure of the maximum power point tracking (MPPT) algorithm in a photovoltaic system (PVS). In this paper it is proposed the combination of a modified Perturb and Observe (P&O) distributed MPPT and an adaptive algorithm. The MPPT has been tested in case of hard mismatch conditions through simulation showing high performance in terms of efficiency.

Adaptive distributed MPPT algorithm for photovoltaic systems

The dual active bridge topology allows bidirectional power flow and galvanic isolation for DC/DC energy conversion. These features have made it the possible backbone of the future smart transformer for distribution. The different voltage drops and commutation dead-times of the semiconductor switches result in DC-voltage at the transformer terminals. Even small DC-voltage components produce large DC-bias currents as they are only limited by the transformer resistances. The DC-bias degrades the transformer performance by increasing the losses. If the core saturates the resulting current pulses can damage the converter. A typical approach to avoid the DC-bias is placing a capacitor in series with the transformer. This capacitor suffers large current variations, reducing its reliability, and complicates the control. The dual active bridge usually handles the power flow by modifying the phase-shift of the converter square waveforms. In this paper the duty-cycle of the converter waveforms is controlled to cancel the current DC-bias in both transformer sides. A formula relating the reference power and phase-shift is provided for the case of varying duty-cycle waveforms. The implementation with constant sampling frequency and its limitations are explained.

DC-bias cancellation for phase shift controlled dual active bridge

The Smart Transformer (ST) is a solid-state transformer performing not only a voltage step-down function but also energy and information management. With the help of control and communication technology, the ST can increase hosting capacity of renewable energies and provide ancillary services to utility and customers. To better exploit the potential of a ST-fed grid, a proper design of architecture, control scenarios and its corresponding communication network has to be done. This paper aims at giving a better understanding of the functionality of the ST-fed grid and of the associated communication challenges.

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Marco Liserre

Papers

Droop control of a multifunctional PV inverter

Grid voltage support by means of a small Wind Turbine System

Adaptive distributed MPPT algorithm for photovoltaic systems

DC-bias cancellation for phase shift controlled dual active bridge

Control and communication in the Smart Transformer-fed grid