• Journal of Broadcast Engineering
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• v.15 no.6
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• pp.868-875
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• 2010

AT-DMB was developed to raise the transmission rate of existing T-DMB with backward compatability. The transmission and hierarchical video service technique were legislated as Korean TTA standards, and other application service techniques including data services are being developed for the commercial service. In this paper, we consider the power of transmission power level of signals in Advanced Terrestrial Digital Multimedia System according to the constellation ratio. And we propose a new scheme for normalization of transmission signal power level in AT-DMB system. Adopting this scheme, the signal power level of hierarchical modulated signal can be uniform in AT-DMB system both for B Mode and Q Mode.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.7
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• pp.863-871
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• 1999

While Logic Based Expert System (LBES) has a merit of rapid and complete inference, it also has a defect of huge knowledge base. Hierarchical LBES (HLBES) replaces the assertion time inference of LBES with the multi-level logic minimization procedure, and it guarantees smaller knowledge base comparing with LBES. This paper has two contributions. The one is proposing so-called fact-minimization procedure which reduces not only the number of facts or measured events but also the size of knowledge base dramatically. The other contribution is application of HLBES and the proposed fact-minimization to the fault diagnosis of power system. The application is successfully performed in the example with the transmission system which takes 72 goals and 352 facts.

• Proceedings of the KIEE Conference
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• 2000.07a
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• pp.397-399
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• 2000

This paper presents a method for assessing reliability indices of transmission system. Because successful operation of electric power under the deregulated electricity market depends on transmission system reliability management, quantity evaluation of transmission system reliability is very important. The key point idea is based on that the reliability level of transmission system is equal to reliability level difference of between composite power system(HLII) and generation system(HLI). It is sure that risk indices of reliability of composite power system are larger than those of generation system. It is the reason that composite power system includes uncertainties and capacity limit of transmission lines. The characteristics and effectiveness of this methodology are illustrated by the case study using MRBTS.

• Journal of Power Electronics
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• v.18 no.6
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• pp.1791-1804
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• 2018

To achieve a fast dynamic response and to solve the multi-objective control problems of the output currents, capacitor voltages and system constraints, this paper proposes a deadbeat and hierarchical predictive control with space-vector modulation (DB-HPC-SVM) for five-level nested neutral point piloted (NNPP) converters. First, deadbeat control (DBC) is adopted to track the reference currents by calculating the deadbeat reference voltage vector (DB-RVV). After that, all of the candidate switching sequences that synthesize the DB-RVV are obtained by using the fast SVM principle. Furthermore, according to the redundancies of the switch combination and switching sequence, a hierarchical model predictive control (MPC) is presented to select the optimal switch combination (OSC) and optimal switching sequence (OSS). The proposed DB-HPC-SVM maintains the advantages of DBC and SVM, such as fast dynamic response, zero steady-state error and fixed switching frequency, and combines the characteristics of MPC, such as multi-objective control and simple inclusion of constraints. Finally, comparative simulation and experimental results of a five-level NNPP converter verify the correctness of the proposed DB-HPC-SVM.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.05a
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• pp.52-53
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• 2014

The Work Breakdown Structure (WBS) is a primary tool which provides a framework that defines clear scope of all deliverables throughout the project life cycle. Once the WBS is established in projects, it should allow project team members to measure and manage work performances by the WBS; further, it should provide a reference point when any work scope needs to be redefined. Based on the project information in the Progress and Performance Measurement System (PPMS) of UAE's Barakha Nuclear Power Plant (BNPP) projects, an attempt was made to develop a new WBS which provides hierarchical and systematical decomposition of the total work scope of NPP construction projects while avoiding from the preexistence concept in Korean NPP projects that the WBS is a combination of Physical Breakdown Structure (PBS) and Functional Breakdown Structure (FBS). The unique features of the new WBS are as follows: (1) defined the definition of each level of the WBS, (2) subdivided the WBS into 5 hierarchical levels, and (3) adopted globally used general coding structure. The new WBS provides a basic hierarchical structure for the project scope and can be used as a basic tool for schedule control, performance measurement, project status monitoring, and communication among project participants. In addition, by putting the Work Package (WP) under the WBS, the Earned Value Management System (EVMS) per WP can be utilized for the project.

• KIEE International Transactions on Power Engineering
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• v.4A no.2
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• pp.91-99
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• 2004

This paper illustrates a tie line constrained equivalent assisting generator (TEA G) model considering forced outage rates of transmission systems for reliability evaluation of interconnected power systems. Interconnections between power systems can provide improved levels of reliability. It is expected that the TEAG model developed in this paper will prove useful in the solution to problems related to the effect of transmission system uncertainties in the reliability evaluation of interconnected power systems. The characteristics and concept of this TEAG considering transmission systems are described in detail by sample studies on a simple test system.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1172-1173
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• 2008

At the moment, the control ability of wind farms is a prime research concern for the grid integration of large wind farms, due to their required active role in the power system. As more wind turbines are installed, the power from wind energy will start to replace conventional generation units and its influence on power systems cannot be neglected. Besides, because of the intermittent nature of wind the output power of wind turbines fluctuates according to wind speed variation. Especially an isolated power system with small capacity such like Jeju needs more systematic solutions and regulations(grid code). This paper presents the idea of approach for centralized operating wind farm strategy to regulate the wind farm power production to the reference power ordered by the system operator. The doubly fed induction generator(DFIG) can control active and reactive power in feasible range. So wind farm comprised of DFIG has the possibility of a controllable component in the power system. The presented wind farm control has a hierarchical structure with both a wind farm control level and a wind turbine control level.

• Journal of Communications and Networks
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• v.13 no.4
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• pp.319-326
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• 2011

Beamforming techniques have been successfully utilized for traffic channels in order to solve the interference problem. However, their use for control channels has not been sufficiently investigated. In this paper, a (semi-) centralized beamforming strategy that adaptively changes beam patterns and controls the total transmit power of cells is proposed for the performance enhancement of the common channel in hierarchical cell structure (HCS) networks. In addition, some examples of its practical implementation with low complexity are presented for two-tier HCS networks consisting of macro and pico cells. The performance of the proposed scheme has been evaluated through multi-cell system-level simulations under optimistic and pessimistic interference scenarios. The cumulative distribution function of user geometry or channel quality has been used as a performance metric since in the case of common control channel the number of outage users is more important than the sum rate. Simulation results confirm that the proposed scheme provides a significant gain compared to the random beamforming scheme as well as conventional systems that do not use the proposed algorithm. Finally, the proposed scheme can be applied simultaneously to several adjacent macro and pico cells even if it is designed primarily for the pico cell within macro cells.

• Proceedings of the KIEE Conference
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• 1998.07c
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• pp.997-999
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• 1998

An operationally secure power system is one low probability of blackout or equipment damage. The power system is needed to maintain a designated security level at minimum operating cost. The inclusions of security make power system problem complex. But, because security and optimality are normally conflicting requirement, the separate treatments of both are inappropriate. So, a unified hierarchical formulation is needed. In this paper, the overview of security constrained optimal power flow (SCOPF) is presented and an introduction of parallel distributed formulation to SCOPF is also presented.

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.3
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• pp.238-248
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• 2016

In this study, an automatic command mode transition strategy of direct power control (DPC) is proposed for permanent magnet synchronous generators (PMSGs) medium-voltage (MV) offshore wind turbines (WTs). Benchmarking against the control methods are performed based on a three-level neutral-point-clamped (NPC) back-to-back type voltage source converter (VSC). The ramping rate criterion of complex power is utilized to select the switching vector in DPC for a three-level NPC converter. With a grid command and an MPPT mode transition strategy, the proposed control method automatically controls the generated output power to satisfy a grid requirement from the hierarchical wind farm controller. The automatic command mode transition strategy of DPC is confirmed through PLECS simulations based on Matlab. The simulation result of the automatic mode transition strategy shows that the proposed control method of VOC and DPC achieves a much shorter transient time of generated output power than the conventional control methods of MPPT and VOC under a step response. The proposed control method helps provide a good dynamic performance for PMSGs MV offshore WTs, thereby generating high quality output power.