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

The smart transformer (ST), a solid-state-based transformer with control and communication functionalities, determines the voltage of the low voltage (LV) network. Due to the similar control purpose, the classic multiple feedback loop (multiloop) voltage control strategies widely utilized in the uninterruptible power supply (UPS) application, can be considered for the control of ST LV converter. However, a fundamental difference between ST and UPS is the presence in LV grid of distributed generation integrated through power electronics interfaces and the dimension of the supplied grid. Emerging issues like stability and harmonic oscillations challenge the safe operation of the ST-fed grid. In order to explore the problems associated with the grid-converter-based devices, the impacts of the grid converters on various multiloop voltage control strategies have been studied in this paper. Optimal multiloop strategy has been found to offer stable operation to a ST-fed distribution grid under various conditions. Case studies in a CIGR E benchmark grid and experimental results are provided to verify the correctness of the theoretical analyses.

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Stability Assessment of Voltage Control Strategies for Smart Transformer-Fed Distribution Grid

The stability of a converter synchronized to the grid voltage through a phase-locked loop (PLL) is negatively affected by the presence of another converter with the same synchronization principle operating nearby, especially under weak grid conditions. However, while weak grids are critical for PLL-based converters, virtual synchronous machines (VSMs) are instead suitable for such applications. In fact, it can be proven that the robust stability of a VSM is enhanced when it is connected to a weaker grid. Recent studies have investigated the parallel operation between VSMs, but the parallel operation between a VSM and a PLL-based converter has not yet been properly addressed in the literature. In this paper, this topic is investigated by means of eigenvalue analysis, showing the positive effects on the stability of a PLL-based converter due to the presence of a synchronverter operating nearby. The model of the system under study is obtained adopting the component connection method (CCM), and time-domain simulations as well as experimental results using a power hardware-in-the-loop (PHIL) test bench are reported to demonstrate the validity of the performed analysis.

Analysis of the Parallel Operation Between Synchronverters and PLL-Based Converters

This chapter contains sections titled: Introduction Filter Topologies Design Considerations Practical Examples of LCL Filters and Grid Interactions Resonance Problem and Damping Solutions Nonlinear Behaviour of the Filter Summary References

Grid Filter Design

The rapid increase in current harmonics in the AC systems due to large introduction of solid state power switching devices is deteriorating the power quality Consequently the interest in active filters is growing However for their correct operation it is imperative to know the harmonic parameters such as magnitude and phase Hence many algorithms have been developed to detect the harmonics The frequency-domain-based algorithms (generally adopting the Fourier Transform) request high computation resources The time-domain techniques work on the instantaneous values of signals, therefore they request fewer calculations By these reasons, the time-domain algorithms are frequently used in active filter control In this work, a review of principal time-domain methods is carried out Also, their principal problems are indicated and the possible solutions and improvements are proposed The analysis is validated by experimental results obtained with digital signal processor TMS320C6713

Comparison of Voltage Harmonic Identification Algorithms for Three-Phase Systems

In microgrid systems one or more inverters should be grid-forming in order to control the voltage during island mode operation. Usually the voltage regulation is operated controlling the capacitor voltage of the LCL filter interconnected between the converter and the load. In the present paper a cascade control is proposed for a Three-Level Neutral Point Clamped (3L-NPC) inverter where the voltage and the current at the output of the LCL filter are used as state variables instead of the capacitor voltage and the converter-side current. Instability issues inherent in the control of the filter output voltage are solved using a Virtual Resistor (VR) active damping method. The proposed control strategy allows loads voltage control eliminating the error due to the voltage drop on load-side inductance of the LCL filter. Since the filter output voltage and current measurements are required anyway, in order to perform the active and reactive power control based on droop control techniques, the proposed control scheme provides also a number reduction of the measurements sensors compared with the classical implementation of the hierarchical control. Simulation results, considering two different operating scenarios, validate the proposed control strategy.

Marco Liserre

Papers

Stability Assessment of Voltage Control Strategies for Smart Transformer-Fed Distribution Grid

Analysis of the Parallel Operation Between Synchronverters and PLL-Based Converters

Grid Filter Design

Comparison of Voltage Harmonic Identification Algorithms for Three-Phase Systems

Voltage control of microgrid systems based on 3lnpc inverters with LCL-filter in islanding operation