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

The enabling of ac microgrids in distribution networks allows delivering distributed power and providing grid support services during regular operation of the grid, as well as powering isolated islands in case of faults and contingencies, thus increasing the performance and reliability of the electrical system. The high penetration of distributed generators, linked to the grid through highly controllable power processors based on power electronics, together with the incorporation of electrical energy storage systems, communication technologies, and controllable loads, opens new horizons to the effective expansion of microgrid applications integrated into electrical power systems. This paper carries out an overview about microgrid structures and control techniques at different hierarchical levels. At the power converter level, a detailed analysis of the main operation modes and control structures for power converters belonging to microgrids is carried out, focusing mainly on grid-forming, grid-feeding, and grid-supporting configurations. This analysis is extended as well toward the hierarchical control scheme of microgrids, which, based on the primary, secondary, and tertiary control layer division, is devoted to minimize the operation cost, coordinating support services, meanwhile maximizing the reliability and the controllability of microgrids. Finally, the main grid services that microgrids can offer to the main network, as well as the future trends in the development of their operation and control for the next future, are presented and discussed.

Control of Power Converters in AC Microgrids

The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

Ultracapacitors: Why, How, and Where is the Technology

http://ieeexplore.ieee.org/iel5/5610941/5624686/05624745.pdf

Power electronics

Microgrids and Active Distribution Networks offer a potential solution for sustainable, energy-efficient power supply to cater for increasing load growth, supplying power to remote areas, generation of clean power and reduction in emission of greenhouse gases & particulates as per Kyoto protocol.

Microgrids and Active Distribution Networks

Distributed generation (DG) is predicted to play an important role in the electric power system in the near future. It is widely accepted that micro turbine-generation are currently attracting lot of attention to meet users' need in the distributed generation market. In order to investigate the ability of microturbine units in distribution systems, their efficient modeling is required. This paper presents a dynamic model of a micro-turbine generator system. The model is developed in the MATLAB/Simulink and implemented in SimPowerSystems library. The model is built from the dynamics of each part with their interconnections. This simplified model is a useful tool for studying the various operational aspects of micro turbines. The performance of developed model is studied by connecting it to an isolated load.

Modeling and simulation of microturbine based distributed generation system

Distributed Generation (DG) is predicted to play an important role in electric power system in the near future. The insertion of DG system into existing distribution network has great impact on real-time system operation and planning. It is widely accepted that micro turbine generation (MTG) systems are currently attracting lot of attention to meet customers need in the distributed power generation market. In order to investigate the performance of microturbine generation systems their efficient modeling is required. This paper presents a dynamic model of a MTG system, suitable for grid connection/islanding operation. The presented model allows the bidirectional power flow between grid and MTG system. The components of the system are built from the dynamics of each part with their interconnections. The control strategies for both grid connected and intentional islanding operation mode of a DG system are also given.

Dynamic Model of Microturbine Generation System for Grid Connected/Islanding Operation

Distributed generation (DG) offers solution to the ever increasing energy needs by generating energy at the consumer end, in most cases, by means of renewable energy sources. Islanding detection is an important aspect of interconnecting a DG to the utility. This study presents comprehensive review of various islanding detection techniques along with their relative advantages and disadvantages. A broad classification of islanding detection methods (IDMs) is laid out as classical methods, signal processing (SP)-based methods, and computational intelligence-based methods with a focus on SP-based methods and computational intelligence-based methods. The evolution of SP techniques used for islanding detection is presented along with the merits and shortcomings of each technique. Furthermore, the advent of computational intelligence methods based IDMs are discussed along with their merits and demerits. An insight into various islanding methods based on quantitative measures of performance indices such as detection time, detection accuracy, and efficiency are tabulated and presented. Finally, the prospective direction of research for IDMs is also presented.

Comprehensive review of IDMs in DG systems

This paper presents modeling and control of Photovoltaic/fuel cell/supercapacitor hybrid power system for stand-alone applications. The hybrid power system uses solar PV array and fuel cell as the main sources. These sources share their power effectively to meet the load demand. The supercapacitor bank is used to supply or absorb load transients. The main control system comprises of MPPT controller for PV system, a DC-DC boost converter with controller for fuel cell system for power management and inverter controller to regulate voltage and frequency. The stand-alone hybrid system aims to provide quality supply to consumers with a constant voltage and frequency. The modeling and control strategies of the hybrid system are realized in Matlab/Simulink.

https://ijrer.com/index.php/ijrer/article/download/3489/pdf

Power Control of PV/Fuel Cell/Supercapacitor Hybrid System for Stand-Alone Applications

The intentional islanding operation of grid-connected distributed generation systems can greatly improve the reliability and quality of the power supply. The existing control techniques for distributed generation systems are designed to operate either in the grid-connected or islanding modes of operation, thus, not allowing for both modes to be implemented and transitioned between. In this article, a novel scheme for automatic mode switching of a microturbine-based distributed generation system between the grid-connected and islanding modes of operation is proposed. The presented scheme is based on the phase angle estimated by the phase-locked loop. The developed phase-locked loop provides an accurate estimation of the phase angle even under unbalanced conditions. The presented scheme does not negatively affect the distributed generation system or utility operations and can work even under matching distributed generation and load power ratings. In this work, back-to-back converters are used to in...

Dattatraya N Gaonkar

Papers

Modeling and simulation of microturbine based distributed generation system

Dynamic Model of Microturbine Generation System for Grid Connected/Islanding Operation

Comprehensive review of IDMs in DG systems

Power Control of PV/Fuel Cell/Supercapacitor Hybrid System for Stand-Alone Applications

Seamless Transfer of Microturbine Generation System Operation Between Grid-connected and Islanding Modes