• New & Renewable Energy
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• v.1 no.3 s.3
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• pp.35-41
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• 2005

This paper analyses the economics of grid-connected photovoltaic systems. With the 2003 cost of photovoltaic systems, under prevailing capital market conditions, with a system lifetime of 30 years, and under the best climatic conditions, it appears that the cost of production of grid-connected electricity could be of 0.21 US $/kWh, and under medium climatic conditions, European locations, Switzerland, Japan and South Korean could be of 0.28$/kWh. If the lifetime if the system goes up, due to future technological improvements, to a very large value such as 50 years, these costs can be lowered by 10-20%. Competitiveness of grid-connected photovoltaic electricity, while it still cannot be taken for granted, is a possibility, especially if major technological advances further lowers the costs of photo cells and increases their lifetimes.

• Proceedings of the KIPE Conference
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• 2018.11a
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• pp.155-156
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• 2018

This paper presents a control method for grid-connected Active-NPC inverter systems. NPC (Neutral Point Clamped) is widely used in power conversion systems. NPC has a loss of switching elements and voltage imbalance. Active NPC has been proposed to overcome these drawbacks. ANPC changed the neutral diode to IGBT to reduce the switching loss. This paper modeled a grid-connected Acitve-NPC inverter systems and analyzed its performance. DSOGI PLL was used as a phase control method for precise control of grid link voltage. The proposed method is verified by PSIM simulation.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.4 no.6
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• pp.1080-1097
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• 2010

Well organized and easy usable Grid management system is very important for executing various Grid applications and managing Grid computing environment. Moreover, information system which can support Grid management system by providing various Grid environment related information is also one of the most interesting issue in the Grid middleware system area. Effective cooperation between Grid management system and information system can make a novel Grid middleware system. Especially, service oriented architecture based Grid management system is flexible and extensible for providing various type of Grid services. Also, information system based on data mining process which comprises various different kinds of domains such as users, resources and applications can make Grid management system more precise and efficient. In this paper, we propose semantic Grid middleware system which is a combination of Grid management system and semantic information system.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.11
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• pp.2497-2506
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• 2010

Smart power grid is targeting to improve grid operation by integrating existing power IT technologies in the jeju smart grid field test. Real-time two-way communication and interoperability in power grid are essential to smart power grid. Adopting smart grid will increase security vulnerabilities in power grid by increasing the number of wireless sensors and the chances of the external exposure of communication networks. In addition, hackers can cause chaos in the power grid system with eavesdropping and forgery attacks in communication networks. Smart power grid is one of the most important systems in deploying smart grid, and it is important to design security system systematically since smart grid can be seriously damaged when problem occurs. In this paper, local and global smart grid security standard and security vulnerabilities in power grid are reviewed, and 2 level smart grid service model is proposed.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.2
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• pp.317-324
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• 2007

Most conventional hybrid systems using renewable energy sources have been applied for stand-alone operation, but Utility-interface may be an useful and viable option for hybrid systems. Grid-connected operation may have benefits such as reduced losses in power system distribution, utility support in demand side management, and peak load shaving. This paper addresses power control and dynamic performance of a grid-connected PV/wind/BESS hybrid system. At all times the PV way and the wind turbine are individually controlled to generate the maximum energy from given weather conditions. The battery energy storage system (BESS) charges or discharges the battery depending on energy gap between grid invertger generation and production from the PV and wind system. The BESS should be also controlled without too frequently repeated shifts in operation mode, charging or discharging. The grid inverter regulates the generated power injection into the grid. Different control schemes of the grid inverter are presented for different operation modes, which include normal operation, power dispatching, and power smoothing. Simulation results demonstrate that the effectiveness of the proposed power control schemes for the grid-interactive hybrid system.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.12
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• pp.2251-2261
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• 2016

The use of renewable energy sources and energy storage systems is increasing due to new policies in the energy industries. However, the increase in distributed generation hinders the reliability of power systems. In order to stabilize power systems, a virtual power plant has been proposed as a novel power grid management system. The virtual power plant plays includes different distributed energy resources and energy storage systems. We define a core virtual power plant technology related to demand response and ancillary service for the cases of Korea, America, and Europe. We also suggest applications of the proposed virtual power plant to the vehicle-to-grid market for restructuring national power industries in Korea.

• Proceedings of the KIPE Conference
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• 2013.07a
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• pp.244-245
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• 2013

This paper proposes a control algorithm for permanent magnet synchronous generator with a back-to-back three-level neutral-point clamped voltage source converter in a medium-voltage offshore wind power system under unbalanced grid conditions. The proposed control algorithm particularly compensates for the unbalanced grid voltage at the point of common coupling in a collector bus of offshore wind power system. This control algorithm has been formulated based on the symmetrical components in positive and negative rotating synchronous reference frames under generalized unbalanced operating conditions. Instantaneous active and reactive power are described in terms of symmetrical components of measured grid input voltages and currents. Negative sequential component of ac input current is injected to the point of common coupling in the proposed control strategy. The amplitude of negative sequential component is calculated to minimize the negative sequential component of grid voltage under the limitation of current capability in a voltage source converter. The proposed control algorithm makes it possible to provide a balanced voltage at the point of common coupling resulting in the generated power of high quality from offshore wind power system under unbalanced network conditions.

• International Journal of Computer Science & Network Security
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• v.22 no.4
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• pp.1-12
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• 2022

In order to overcome the power fluctuation issues in photovoltaic (PV) smart grid-connected systems and the inverter nonlinearity model problem, an adaptive backstepping command-filter and a double second order generalized Integrators (DSOGI) controller are designed in order to tune the AC current and the DC-link voltage from the DC side. Firstly, we propose to present the filter mathematical model throughout the PV system, at that juncture the backstepping control law is applied in order to control it, Moreover the command filter is bounded to the controller aiming to exclude the backstepping controller differential increase. Additionally, The adaptive law uses Lyapunov stability criterion. Its task is to estimate the uncertain parameters in the smart grid-connected inverter. A DSOGI is added to stabilize the grid currents and eliminate undesirable harmonics meanwhile feeding maximum power generated from PV to the point of common coupling (PCC). Then, guaranteeing a dynamic effective response even under very unbalanced loads and/or intermittent climate changes. Finally, the simulation results will be established using MATLAB/SIMULINK proving that the presented approach can control surely the smart grid-connected system.

• Journal of Korea Society of Industrial Information Systems
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• v.9 no.1
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• pp.77-84
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• 2004

Recently, as the number of entities participating in the Grid system increased, the response time of LDAP system became inadequate. Consequently, we have to design new LDAP that suitable for high performance Grid environments. For this, researches about analysis of performance LDAP system are needed firstly. However, because researches are focused mostly on read operation optimized environments, so these result of researches are not directly applied to high performance Grid environments that write operation occupies most. In this paper, we provide overall results of analysis of performance of LDAP system with respect to number of node, query arrival rate, probability of read and so on. The analysis is based on in analytic performance model by applying the M/M/1 queuing model. Finally, based on the results, we suggest the direction for the design of high performance LDAP system and this research results can be applied as basic materials to design of GIS in high performance Grid environments as well as.

• Journal of Hydrogen and New Energy
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• v.27 no.5
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• pp.547-553
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• 2016

This paper presents the effect of a grid system on the performance of a small Savonius wind turbine installed side-by-side. Turbine performance is compared using three different grid systems; tetrahedral grid having a concentrated circular grid around turbine rotors, the tetrahedral grid having a concentrated rectangular grid around turbine rotors and the symmetric grid having a concentrated tetrahedral grid near the turbine rotor blades and a hexahedral grid. The commercial code, SC/Tetra has been used to solve the three-dimensional unsteady Reynolds-averaged Navier-Stokes analysis in the present study. The Savonius turbine rotor has a rotational diameter of 0.226m and an aspect ratio of 1.0. The distance between neighboring rotor tips keeps the same length of the rotor diameter. The variations of pressure and power coefficient are compared with respect to blade rotational angles and rotating frequencies of the turbine blade. Throughout the comparisons of three grid systems, it is noted that the symmetric grid having a concentrated tetrahedral grid near the turbine rotor blades and a hexahedral grid has a stable performance compared to the other ones.