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

DC Solid-State Circuit Breakers (SSCB) play an important role in the protection of DC and hybrid AC/DC systems. As they operate mostly in on-state, the use of wide-bandgap devices, with low conduction losses, is an attractive solution. These devices need to be selected based on the rare occasion of fault breaking, with associated overcurrent and overvoltage intervals. In this work a novel clamping circuit, consisting in its simplified form of Metal-Oxide Varistors and capacitors, is proposed to be used in a DC SSCB. This circuit has the objective to reduce the breaker overvoltage during protection, enabling a lower number of required semiconductors in series and consequent overall reduced losses. An analysis of the idea and operation principle of the system is presented, alongside its stages of operation and defining equations. To evaluate its benefits, the system is compared with one typical passive solution. At the end a scaled prototype is tested, validating the benefits and theoretical analysis of the proposed approach.

Passive Clamping Circuit for Reduced Switch Count in Solid State Circuit Breakers

The DC fault is one of the critical challenges in the High Voltage Multi-Terminal Direct Current (HV-MTDC) grid. The fixed value threshold used in some implementations may be affected by different grid conditions and thus causes errors in the fault detection procedure. This paper offers a two-stage fault detection algorithm based on the integrated Artificial Neural Network (ANN) and Discrete Wavelet Transform (DWT) theory. The main innovations of the proposed method are: 1) Increasing the reliability of the fault detection operation by solving the fixed value threshold problems; 2) Offering high robustness against the wide range of fault resistances; 3) Providing bus protection capability and 4) Setting relays locally, and avoiding the requirement to high-speed communications links. Also, it offers DC fault detection in a short period of time. The performance of the proposed protection scheme has been ascertained via simulations in the MATLAB/Simulink environment. The results prove the robustness of the proposed method against noise disturbance, high resistance fault, and grid parameters variations. 

A Fault Detection Algorithm Based on Artificial Neural Network Threshold Selection in Multi-Terminal DC Grids

Dual-active-bridge-based (DAB-based) input-series output-parallel (ISOP) converters have become increasingly popular due to their promising features made up of the advantages of the modular power electronics and the DAB converter. The modeling of the DAB converter and the DAB-based ISOP converter has been widely explored for control design in order to analyze the stability and improve the performance of the converter itself, such as the voltage balancing and power sharing of DAB submodules. However, the modeling on the impedance of the DAB-based ISOP converter, which can be quite useful for system-level stability analysis and optimization, has not been addressed sufficiently so far. To solve this issue, this article presents comprehensive impedance modeling of the DAB-based ISOP converter, where the output voltage control and the input voltage balancing control are applied to the converter to achieve the equal power sharing of the submodules. The proposed input impedance model and output impedance model of the DAB-based ISOP converter are validated through the frequency-domain sweep in simulation and experiment. With the validated impedance models, the instability phenomenon and the frequency of the main harmonic component in oscillating waveforms can be accurately predicted at the source side and at the load side of the converter respectively.

On the Impedance and Stability Analysis of Dual-Active-Bridge-Based Input-Series Output-Parallel Converters in DC Systems

In order to meet the increased demand for renewable energy sources, high power wind turbine systems of multi-MW range have been commercialized. Among the several topologies for high power WTSs developed in the last few years, the full-scale power converters connected in parallel are widely adopted in commercial products due to advantages of a power scalability and a potentially higher reliability in comparison to other topologies. On the other hand, as the power capacity of a single wind turbine is increasing, the high reliability has become one of the key factor to reduce maintenance and operation cost as well as to ensure the high power security. In many literature work based on the physics-of-failure approach, it has proven that the thermal cycling is the main stress source, which depends on the wind profile. Furthermore, the wind profile shows marked variations over time. Hence, in order for the highly reliable converters, it may be of interest to stabilize the thermal cycling from a control point of view. This paper presents a possibility of circulating reactive power among the parallel converters during wind variations, as losses in the power semiconductors can be modified depending on different reactive powers. Besides, by means of a centralized control via a high-speed communication, the synchronization of parallel converters can be not only achieved but the different reactive power with respect to individual converter can be also controlled properly.

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Reactive Power Control to Improve Reliability of High Wind Power Converters Connected in Parallel

This paper focuses on the harmonic analysis of the Quasi-2-Level Super-Switch (Q2L SS), considering different delay times and the number of steps. The harmonic performance is investigated in-depth using Double Fourier Integral Transformation analysis, simulations, and experiments. According to the analysis, increasing the number of steps facilitates a smoother transition between the negative and positive states of the output voltage. As a result, the harmonic performance of the Q2L SS is significantly improved. On the other hand, an increased number of steps sets the boundaries to the switching frequency and the maximum modulation index. Moreover, multi-step Q2L SS requires more capacitors, which can significantly increase the volume of the converter. The study establishes the ground basis for understanding the Q2L SS operation in the harmonic domain. It can be used for the future research in the domain of Q2L SS and approaches for designing EMI filters for Q2L SS-based converters. 

Marco Liserre

Papers

Passive Clamping Circuit for Reduced Switch Count in Solid State Circuit Breakers

A Fault Detection Algorithm Based on Artificial Neural Network Threshold Selection in Multi-Terminal DC Grids

On the Impedance and Stability Analysis of Dual-Active-Bridge-Based Input-Series Output-Parallel Converters in DC Systems

Reactive Power Control to Improve Reliability of High Wind Power Converters Connected in Parallel

Harmonic Analysis of Quasi-2-Level MV Super-Switch