This paper proposes an improved fast charging strategy for electric vehicles (EVs) by considering available battery capacity. According to previous research and battery experiment reports, the energy capacity of batteries is not fixed, and it can decrease temporarily depending on the magnitude of charging or discharging power. This paper addresses the decreased capacity in proportion to the magnitude of the charging power which leads to a reduction in the driving range. For effective and practical use for EV users, the change in battery capacity is expressed through an equation, and a new state of charged indicator is proposed. To improve the conventional charging method that uniformly supplies power regardless of the battery capacity, this paper proposes an optimal charging strategy injecting constant power. The proposed charging strategy provides an optimal charging power reference to minimize costs considering charged energy, charging time, and usable energy loss based on billing system of EV charging. To verify the effectiveness of the proposed charging method, the optimal charging power reference for each battery is calculated based on capacity and characteristics, and the total cost is compared. The results show that the performance of the proposed charging strategy is effective in minimizing both the reduced battery capacity and economic burden on EV users.

This study proposes an energy management system (EMS) for stable operation of isolated microgrid which is composed of diesel generators, wind turbines, photovoltaic generation systems and battery energy storage systems (BESS). In the EMS, a power dispatch control is proposed in order to minimise diesel operation. There is also a state-of-charge (SOC) control to allow continuous use of the BESS. By dispatching the scheduled power of the diesel generators, the SOC can be regulated within its limits. A simulation model for isolated microgrid was developed using DIgSILENT Power Factory® software. To verify the performance of the proposed EMS, case studies are performed using practical data of Dukjuk Island in Korea.

In South Korea, the existing diesel generators are being replaced with renewable energy sources (RESs) in several stand-alone microgrids. However, their reliability and stability are not still guaranteed by fluctuations of the system caused by RESs, arising from unpredictable changes in environmental factors. Moreover, since the inertia that is originally provided by the diesel synchronous generators is reduced, the overall system becomes highly sensitive to frequency variations. As a result, the installation of RESs must be well planned while considering the upper limit of their installed capacity. In this paper, a new method for evaluating the maximum penetration capacity of photovoltaic (PV) generators to ensure the stable operation of a microgrid is proposed. For the analytical approach, two frequency stability indexes, which are the minimum instantaneous frequency and the quasi-steady-state (QSS) frequency after a disturbance, are used. The capacity of PV to be installed is limited by considering the characteristics of other generators. In addition, the efficiency of the energy storage system (ESS) is also analyzed to determine the optimal capacity of both PV and ESS. The effectiveness of the proposed method is firstly proven through the mathematical analysis. Then, case studies on a practical stand-alone microgrid in South Korea are carried out using a time-domain simulation based on the DIgSILENT PowerFactory^® software.

Currently, the total generator capacity installed in most ships is greater than the required capacity. In addition, due to new environmental regulations, various auxiliary gears are required to avoid breaking the law. Therefore, the internal environments of ships, such as their machine rooms, have become narrower, making creating space more important than ever before. This paper provides a method for optimizing generator capacity through an analysis of total load data in order to avoid overestimating the generator capacity. In addition, an actual situation in which the generator capacity is determined by the number of cylinders is considered. Three practical case studies with different possible combinations of generators and varying capacities are presented. Therefore, this method can secure space and reduce weight, which can be beneficial in many ways. Additionally, since it does not require various types of data, this information can be used for already built ships or those that will be made in the future.

기후 위기 등의 다양한 문제에 대처하기 위하여 신재생에너지원 기반 분산전원 계통의 수용율이 증가함에 따라 전통적인 계통의 구성 및 운영과 많은 다른 특성들을 가지게 되었다. 신재생에너지원 기반 분산전원의 출력변동은 동기발전기의 투입율이 줄어든 상황에서 전력계통에 관성저하 문제를 일으킬 수 있다. 전력계통의 관성이 낮을 경우, 급격한 주파수 변동은 계통 내의 기기들에 대하여 문제를 일으킬 수 있을 뿐만 아니라, 저주파수 부하 차단 등의 이벤트를 발생시켜 계통의 연속적인 사고를 야기할 수 있는 원인이 될 수 있다. 본 논문에서는 국내 전력계통 내 관성확보를 위한 동기조상기 설치를 위한 경제성 편익 분석을 위한 해외사례를 검토하였다. 아울러, 동기조상기의 신규설치 및 전환에 대한 단위 비용을 산정하여 국내 편익 분석을 위한 기초를 마련하고 그 비용을 해외사례와 비교 분석하였다.