• Journal of Power Electronics
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• v.1 no.2
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• pp.65-70
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• 2001

Transmission System Operators are governed by operational security standards that are applied in real time. During system disturbances, the System Operators must rely on the installed protection and control equipment, prior to human intervention. New power electronic solutions bring rapid and repeatable responses to disturbances, which will help System Operators to guarantee a stable system. Last year, Alstom completed the world's first competitively bid STATCOM to support the voltage on National Grid's 400kV network that supplies London and the Southeast from the north of the UK. It is rated ${\pm}75MVAr$ and forms part of a Static Var System (SVS) with a total rating of 0 to 225MVAr. This paper will describe the reasons for its size, location, its chain-link configuration and give examples of its operating performance. The paper will also describe the features that allow this STATCOM to deliver much more than reactive compensation in support of a wider transmission service objective, as system conditions require.

• Proceedings of the KIEE Conference
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• 2000.07a
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• pp.322-324
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• 2000

This paper introduces the concepts of UML(Unified Modeling Language) and the applying this technique for implementing voltage stability analysis program. Conventional function-oriented software development methodologies are inadequate to support further maintenance and enhancement. To overcome drawbacks of these methodologies, this paper proposes applying object-oriented technology for voltage stability evaluation software development. In this paper, a modal analysis approach, a steady-state voltage stability evaluation method, is used and UML is applied to the analysis and design for software development.

• Korean Chemical Engineering Research
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• v.61 no.3
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• pp.341-347
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• 2023

In PEMFC, PtCo/C alloy catalysts are widely used because of good performance and durability. However, few studies have been reported on the durability of carbon supports of PtCo/C evaluated at high voltages (1.0~1.5 V). In this study, the durability of PtCo/C catalysts and Pt/C catalysts were compared after applying the accelerated degradation protocol of catalyst support. After repeating the 1.0↔1.5V voltage change cycles, the mass activity, electrochemical surface area (ECSA), electric double layer capacitance (DLC), Pt dissolution and the particle growth were analyzed. After 2,000 cycles of voltage change, the current density per catalyst mass at 0.9V decreased by more than 1.5 times compared to the Pt/C catalyst. This result was because the degradation rate of the carbon support of the PtCo/C catalyst was higher than that of the Pt/C catalyst. The Pt/C catalyst showed more than 1.5 times higher ECSA reduction than the PtCo/C catalyst, but the corrosion of the carbon support of the Pt/C catalyst was small, resulting in a small decrease in I-V performance. In order to improve the high voltage durability of the PtCo/C catalyst, it was shown that improving the durability of the carbon support is essential.

• Journal of Power Electronics
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• v.9 no.6
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• pp.854-865
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• 2009

Super-lift dc-dc converters are a series of advanced step-up dc-dc topologies that provide high voltage transfer gains by super-lift techniques. This paper presents a developed graphical modelling method for super-lift converters and gives a thorough analysis with a consideration of the effects caused by parasitic parameters and diodes' forward voltage drop. The general guidelines for constructing and deriving graphical models are provided for system analysis. By applying it to examples, the proposed method shows the advantages of high convenience and feasibility. Both the circuit simulation and experimental results are given to support the theoretical analysis.

• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.3
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• pp.153-160
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• 2018

Recent trends in high-power-density applications have highlighted the importance of designing power converters with high-frequency operation. However, conventional LLC resonant converters present limitations in terms of high-frequency driving due to switching losses during the turn-off period. Switching losses are caused by the overlap of the voltage and current during this period, and can be decreased by reducing the switch voltage. In turn, the switch voltage can be reduced through a series connection of four switches, and additional circuitry is essential for balancing the voltage of each switch. In this work, a three-level LLC resonant converter that can operate at high frequency is proposed by reducing switch losses and balancing the voltages of all switches with only one capacitor. The voltage-balancing principle of the proposed circuit can be extended to n-level converters, which further reduces the switch voltage stress. As a result, the proposed circuit is applicable to high-input applications. To confirm the validity of the proposed circuit, theoretical analysis and experimental verification results from a 350 W-rated prototype are presented.

• Journal of Power Electronics
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• v.9 no.4
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• pp.643-653
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• 2009

Voltage-controlled voltage source inverter (VCVSI) based distributed generation systems (DGS) using renewable energy sources (RES) is becoming increasingly popular as grid support systems in both remote isolated grids as well as end of rural distribution lines. In VCVSI based DGS for load voltage stabilization, the power angle between the VCVSI output voltage and the grid is an important design parameter because it affects not only the power flow and the power factor of the grid but also the capacity of the grid, the sizing of the decoupling inductor and the VCVSI. In this paper, the steady state modeling and analysis in terms of power flow and power demand of the each component in the system at the different values of maximum power angle is presented. System design considerations are examined for various load and grid conditions. Experimental results conducted on a I KVA VCVSI based DGS prove the analysis and simulation results.

• Proceedings of the KIEE Conference
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• 2003.11b
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• pp.43-46
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• 2003

In this paper, a novel rotor flux estimation method of an induction motor using support vector machine(SVM) is presented. Two veil-known different flux models with respect to voltage and current are necessary to estimate the rotor flux of an induction motor. The theory of the SVM algorithm is based on statistical teaming theory. Training of SVH leads to a quadratic programming(QP) problem. The proposed SVM rotor flux estimator guarantees the improvement of performance in the transient and steady state in spite of parameter variation circumstance. The validity and the usefulness of Proposed algorithm are throughly verified through numerical simulation.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.53 no.1
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• pp.67-72
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• 2004

This paper addresses the bidding strategies of generating firms in a competitive market where the firms are provided with payment for generating reactive power. Reactive support for voltage control is an integral and critical part of power system operations. Since reactive support is unbundled in a competitive market under open access transmission, it is treated as one of ancillary services. The operation costs and opportunity costs for reactive support are compensated by payment to the firms, hence their bidding strategies will be affected. The opportunity costs are evaluated from the foregone profits of a generator in making sales in real power market by providing reactive support instead of real power. Game theory approach is used to analysis the transaction strategies of real power by the bimatrix method in this paper. Through computing the Nash equilibrium in a sample system, an incentive of a generator for improving the reactive generating capacity is found to be effective and the variations of the profits are analyzed as the demand power factor changes.

• Proceedings of the KIEE Conference
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• 1999.11b
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• pp.181-183
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• 1999

As one of ancillary services, voltage support and reactive power service should be compensed properly for its contribution. In this paper, a cost-based reactive power planning is presented. which minimizes the total cost of reactive power support of generators and VAR compensation facility installation. Reactive power support of generator is evaluated by the opportunity costs of reduced energy sale considering the varying SMP(system marginal price) in power market, Gradient projection method is applied to solve this reactive power planning using IEEE14 bus system.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.2
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• pp.70-78
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• 2005

In this paper, a novel rotor flux estimation method of an induction motor using support vector regression(SVR) is presented. Two well-known different flux models with respect to voltage and current are necessary to estimate the rotor flux of an induction motor. Training of SVR which the theory of the SVR algorithm leads to a quadratic programming(QP) problem. The proposed SVR rotor flux estimator guarantees the improvement of performance in the transient and steady state in spite of parameter variation circumstance. The validity and the usefulness of proposed algorithm are throughly verified through numerical simulation.