• Journal of international Conference on Electrical Machines and Systems
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• v.1 no.4
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• pp.425-433
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• 2012

As the demand for electric power increases rapidly and the amount of fossil fuels decreases year by year, making use of renewable resources seem very necessary. However, due to the discontinuous nature of renewable resources and the hierarchical topology of existing grids, power quality and grid stability will deteriorate as more and more distributed generations (DGs) are connected to the grids. It is a good idea to combine local utilization, local consumption, energy storage and DGs to form a grid-friendly micro grid, these micro grids can then assembled into an intelligent power system - the smart Grid. It can optimize power flow and integrate power generation and consumption effectively. Most importantly, the power quality and grid stability can be improved greatly. This paper depicts how the smart grid addresses the current issues of a power system. It also figures out the key technologies and expectations of the smart grid.

• International Journal of Contents
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• v.6 no.3
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• pp.15-18
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• 2010

Grid system is based on the Grid Security Infrastructure (GSI). GSI uses user's proxy to guarantee availability among multi-trust domains. Since grid system has been developed focusing on availability, GSI provides authentication and authorization performed by systems, but there are lacks of privacy consideration. For this reason, some researchers decide to use their own cluster system and do not want to use public grid systems. In this paper, we introduce a new privacy enhanced security mechanism for grid systems. With this mechanism, user can participate in resource allocation and authorization to user's contents more actively. This mechanism does not need to change previous middleware and minimize the computational overheads.

• Journal of international Conference on Electrical Machines and Systems
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• v.1 no.2
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• pp.70-78
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• 2012

Due to the variable nature of renewable energy resources and power demand by consumers, it is difficult to operate a power system installed with only one type of renewable energy resource. Grid-based renewable generation may be the only solution to overcome this problem. The conventional approach based on a low-voltage converter with power frequency transformer is commonly employed for grid connection of offshore renewable energy systems. Because of the heavy weight and large size of the transformer, the system can be expensive and complex in terms of installation and maintenance. In this paper, an 11-kV series connected H-bridge (SCHB) multilevel voltage source converter (VSC) is proposed to achieve a compact and light direct grid connection of renewable energy systems. This paper presents the design, simulation and analysis of a five level (5L)-SCHB and an eleven level (11L)-SCHB VSC for 11-kV grid-based renewable energy systems. The performance, cost, modulation scheme and harmonic spectra of the converter are analyzed.

• Journal of Electrical Engineering and Technology
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• v.13 no.1
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• pp.114-123
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• 2018

Recently, as one of the countermeasures to reduce carbon dioxide($CO_2$) for global warming problems, operation methods in micro-grid systems replacing diesel generator with renewable energy sources including wind power(WP) and photovoltaic(PV) system have been studied and presented in energetic manners. However, it is reported that some operation problems in micro-grid systems without diesel generator for carbon-free island are being occurred when large scaled WP systems are at start-up. To overcome these problems, this paper proposes an operation strategy in micro-grid systems by adapting control devices such as CVCF(constant voltage constant frequency) ESS(energy storage system) for constant frequency and voltage regulation, load control ESS for balancing demand and supply and SVC(static-var compensator) for reactive power compensation. From the simulation results based on the various operation scenarios, it is confirmed that the proposed operation strategy in micro-grid systems without diesel generators is a useful tool to perform a stable operation in micro-grid systems without diesel generator and also make a contribution to reduce carbon dioxide in micro-grid systems.

• Proceedings of the Korea Society for Industrial Systems Conference
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• 2003.05a
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• pp.3-7
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• 2003

For high performance Grid environments, an efficient GIS(Grid Information Service is required In the Metacomputing Directory Service(MDS) of the Glogus middleware, the Lightweight Directory Access Protocol(LDAP), which is a distributed directory service protocol, is used. The LDAP GIS differs from general purpose LDAP directories in that most of the LDAP operations are write in Grid environments. To get an efficient design of the GIS, it is thus required to analyze the performance of the LDAP system in the context of Grid environments. This paper presents the result of a performance analysis of LDAP systems. The main objective of the evaluation is to see the performance scalability of the LDAP system in the Grid environment where the write operations prevails. Based on these results, we suggest directions of an efficient LDAP-based GIS for a high performance Grid.

• Journal of international Conference on Electrical Machines and Systems
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• v.2 no.3
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• pp.306-312
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• 2013

Doubly fed induction generator (DFIG) systems widely used globally are highly sensitive to the grid disturbance due to the structure that the stator is connected to the grid. In the past, when a grid fault occurs in order to prevent a system, generators are separated from the grid regardless of the fault duration time. Recently, however, the grid connection standards(Grid Code)says that for the failures removed within a certain time, the generator remains operation without separating from the grid. This paper proposes a new flux tracking LVRT(Low-Voltage Ride Through) control based on system modeling equations. The validity of the proposed strategy has been demonstrated by computer simulations.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.8
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• pp.1059-1065
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• 2013

Doubly Fed Induction Generator(DFIG) systems occupy the largest proportion of worldwide wind energy generation market. DFIG systems are very sensitive to grid disturbances especially to voltage dips due to the structure of the stator connected to grid. In the past, when a grid fault occurs generators are separated from grid(trip method) in order to protect the systems. Nowadays, due to the growing penetration level of wind power, many countries have made some requirements that wind turbines are required to have Low Voltage Ride Through(LVRT) capability during grid faults. In this paper, a flux tracking LVRT control strategy based on system modeling equations is proposed. The validity of the proposed strategy is verified through computer simulations.

• KEPCO Journal on Electric Power and Energy
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• v.2 no.2
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• pp.233-244
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• 2016

Smart grid is called it as a system of systems. There are diverse types of systems in smart grid environment. Therefore, one of key factors to achieve smart grid successfully is interoperability among diverse systems. To secure interoperability, smart grid operating system should be developed complied with standards in terms of the data representation and communication. Common Information Model (CIM) and OLE Process for Control - Unified Architecture (OPC-UA) are the representative international standards in smart grid domain. Each standard defines data representation and communication by providing common information model and the unified architecture. In this paper, we explain a smart grid platform that we have developed to comply with CIM and OPC-UA standards for secure interoperability among numerous legacy systems.

• International Journal of Contents
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• v.6 no.2
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• pp.10-13
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• 2010

For applications that are grid enabled, the grid can offer a resource balancing effect by scheduling grid jobs on machines with low utilization. When jobs communicate with each other, the internet, or with storage resources, an advanced scheduler could schedule them to minimize communications traffic or minimize the distance of the communications. We propose an intelligent load distribution algorithm to minimize communications traffic and distance of the communications using genetic algorithm. The experiments show the proposed load redistribution algorithm performs efficiently in the variance of load in grid environments.

• The Transactions of the Korean Institute of Power Electronics
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• v.24 no.2
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• pp.111-119
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• 2019

In this study, constant power generation (CPG) algorithms are introduced for whole range power point tracking in photovoltaic systems. Currently, maximum power point tracking (MPPT) algorithm is widely used for high-power photovoltaic systems. However, MPPT algorithm cannot flexibly control such systems according to changing grid conditions. Maintaining grid stability has become important as the capacity of grid-connected photovoltaic systems is increased. CPG algorithms are required to generate the desired power depending on grid conditions. A grid-connected photovoltaic system is configured, and CPG algorithms are implemented. The performances of the implemented algorithms are compared and analyzed by experimental results.