Kyebyung Lee

Smart storage system for seamless transition of customers with intermittent renewable energy sources into Microgrid

This paper challenges a seamless transition of the customers comprising conventional distributed energy resources with the intermittent renewable energy sources into a Microgrid to provide high power quality and enhance the local reliability and the rate of using the renewable energy. Firstly, several problems which have to be solved in the customers are specified from the requirements needed for the microgrid operation. Secondly, the smart storage system which is able to solve these problems is introduced. The smart storage system is located at the point of common coupling and plays a key role for stable operation of the microgrid. The performance of the smart storage system proposed in this paper is verified in the computer simulation using PSCAD/EMTDC. The case study results show that the microgrid is an appropriate way to maintain high power quality and to enhance the local reliability and the rate of using renewable energy in the customers considered.

A New Assessment for the Total Harmonic Contributions at the Point of Common Coupling

A new method to determine the total harmonic contributions of several customers and the utility at the point of common coupling is presented. The proposed method can quantify the individual harmonic impact of each suspicious harmonic source at the point of common coupling. The individual harmonic impact index is then used to assess the total harmonic contribution of each harmonic source. This index can be calculated by the results processed from instantaneous harmonic voltage and current phasor values. The results demonstrate the performance of the proposed method in terms of steadystate accuracy and response to time-varying operating conditions. The proposed index can be used for billing purposes to control harmonic distortion levels in power systems.

Optimal Placement of Distributed Generation Units Considering Voltage Sags

This paper presents a method for determining the optimal placement of distributed generation units considering voltage sags. In general, the existing methods for distributed generation placement do not consider power quality problems such as voltage sags. In this paper, a novel method based on both genetic algorithm and voltage sag assessment is proposed for determining the placement of distributed generation unit. In the proposed method, the optimal placement is determined to minimize voltage sag effects and system losses.

Interface composition and reduced railway model to verify the effect of supercapacitor applied to railway system

As the importance of the improvement of energy efficiency is constantly increasing, a study has been done on the implementation of an energy storage system, to improve load efficiency, on the railway which has relatively large regenerative energy. The pre-existing regenerative energy not only has a low efficiency but also increases the catenary, which has a possibility to create problems in the electrical device voltage, during the regeneration process. In this paper, the improvement of the efficiency and stabilization of the catenary voltage by the implementation of an energy storage device is being discussed. The composition of the interface, control strategy and reduced railway model for simulation are being proposed.

Utilization of energy storage system based on the assessment of area of severity in Islanded microgrid

This paper proposes a method to utilize an energy storage system (ESS) based on the assessment of an area of severity (AOS) to voltage sag. The AOS is defined as a set of the fault positions that can cause voltage sags at many buses simultaneously. The assessment of AOS helps to determine an optimal location of ESS installation to minimize the expected sag frequency (ESF) at concerned buses. The ESS has the ability not only to play traditionally known roles but also to mitigate voltage sag impact on renewable energy sources (RES) in the islanded microgrid. Accordingly, using the proposed method the ESS has additional features to prevent the operation failure of RESs and improve the stability of the microgrid. In order to verify the presented method, a case study was conducted on the sample microgrid system that is modified from an IEEE 57-bus system.

Method to Estimate Expected Sag Frequency Considering the Operating Condition of Power System

This paper deals with the assessment of voltage sags regarding the variation of system operating conditions. In general, voltage sag assessment is performed by assuming the constant operating condition throughout the year. However, the assumption can lead to assessment errors in case of considerable changes of system operation condition. This paper presents a method to estimate ESF(expected sag frequency) considering the operating conditions according to the changes of power demand throughout the year.

Establishment of Preventive Measures against Faults Based on the Area of Severity to Voltage Sags

This paper presents an effective approach for establishing countermeasures against voltage sags based on the concept of area of severity. In order to apply preventive measures against faults such as lightning arrester, overhead earth wires and so on, it is important to find optimal points for installing the preventive measures. The optimal points can be determined by the calculation of the area of severity(AOS) to voltage sags and the expected sag frequency per unit length of line. In this paper, an effective method to find optimal points to apply countermeasures against voltage sags is addressed with case studies.

Method to Select Optimal Device for Mitigating Voltage Sag Based on Voltage Sag Assessment

This paper presents a method to select optimal device for mitigating voltage sags. The method is based on economic evaluation and voltage sag assessment involving sag duration as well as magnitude. The economic evaluation is performed by using the operation cost and economic benefit of the mitigation devices. The optimal device can be determined from the values of NPV (net present value) which is widely accepted in cost-benefit analysis. The proposed method can help sensitive customers to select optimal mitigation device. In this paper, the case study considering two sensitive customers was performed by using the proposed method.