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Active Power Control Strategy for a Virtual Synchronous Machine Under Overload Conditions
Geon Heo,Yongsoon Park,Kyungkyu Lee,Hoseon Ryu 전력전자학회 2023 ICPE(ISPE)논문집 Vol.2023 No.-
Virtual synchronous machine(VSM) enhances the frequency stability of the power grid by emulating properties of the conventional synchronous machine through a voltage source inverter. However, the output active power of the inverter sometimes may exceed its rated power limit during the response of emulated synchronous machine’s properties such as the inertial response and the droop control. This paper presents an active power limiting strategy to prevent the VSM from overloading. When the active power of the VSM approaches its power limit, the VSM turns into the overload-limiting mode and its internal frequency is actively adjusted to limit the output power rapidly. The feasibility and performance of the proposed power-limiting strategy are validated with simulation and experimental results. Furthermore, the effectiveness of the proposed method is demonstrated by on-site tests, conducted at an actual microgrid.
클래시 오브 클랜 오토 프로그램의 악성 행위 분석을 통한 모바일 게임 보안 위협에 관한 연구
허건일(Geon Il Heo),허청일(Cheong Il Heo),김휘강(Huy Kang Kim) 한국정보보호학회 2015 정보보호학회논문지 Vol.25 No.6
모바일 게임 시장 규모와 인구가 증가하고 동시에 모바일 게임의 생명주기가 크게 길어지면서 PC 기반 온라인게임에서 나타났던 오토 프로그램 문제가 모바일 게임에서 그대로 재현되고 있다. 사용자들은 오토 프로그램 실행을 위해 안티 바이러스 프로그램의 경고를 무시하거나 심지어 안티 바이러스 프로그램을 삭제하기 때문에, 오토 프로그램이 게임 관련 기능 외에 악성 행위를 수행할 경우 게임 이용자들은 위협에 무방비로 노출될 수 있다. 본 논문에서는 장기간 대규모의 사용자를 확보하고 있는 대표적인 모바일 게임인 클래시 오브 클랜의 오토 프로그램 7종을 대상으로 악성 행위 유무를 분석하고, 이를 바탕으로 향후 발생 가능한 보안 위협과 대응방안을 제시하였다. 높은 인기를 가진 특정 모바일 게임의 오토 프로그램들을 일괄 분석함으로써 개발 플랫폼, 동작 방식 등 오토프로그램의 최신 동향을 파악하였고, 향후 오토 프로그램의 변화 양상 예측 및 잠재적 위협을 사전에 차단할 수 있는 방안을 제시하였다. Recently, the size of the mobile game market and the number of mobile game users are growing. Also, as the mobile game’s life cycle is increasing at the same time, auto program issue reappears which has been appeared in PC online games. Gamers usually tend to ignore warning messages from antivirus programs and even worse they delete antivirus program to execute auto programs. Therefore, mobile game users are easily compromised if the auto program performs malicious behaviors not only for the original features. In this paper, we analyze whether seven auto programs of “clash of clans” which has a lot more users for a long time perform malicious behaviors or not. We forecast the possible security threats in near future and proposed countermeasures based on this analysis. By analyzing auto programs of highly popular mobile game of today, we can acquire the knowledge on auto program’s recent trend such as their development platform, operating mode, etc. This analysis will help security analysts predict auto program’s evolving trends and block potential threats in advance.
허건(Geon Heo),하종은(Jong-Eun Ha) 제어로봇시스템학회 2015 제어·로봇·시스템학회 논문지 Vol.21 No.1
In this paper, we present an algorithm for the analysis of poses while playing table-tennis using action recognition. We use Kinect as the 3D sensor and 3D skeleton data provided by Kinect for further processing. We adopt a spherical coordinate system and feature selected using k-means clustering. We automatically detect the starting and ending frame and discriminate the action of tabletennis into two groups of forehand and backhand swing. Each swing is modeled using HMM(Hidden Markov Model) and we used a dataset composed of 200 sequences from two players. We can discriminate two types of table tennis swing in real-time. Also, it can provide analysis according to similarities found in good poses.
위암 환자에서 da Vinci<SUP>®</SUP> Surgical System을 이용한 위절제술의 초기 경험
허건웅(Geon-Ung Heo),김민찬(Min-Chan Kim),정갑중(Ghap-Joong Jung),최석렬(Seok Reyol Choi) 대한외과학회 2009 Annals of Surgical Treatment and Research(ASRT) Vol.76 No.5
Purpose: To assess the feasibility of the da Vinci<SUP>®</SUP> surgical system in performing gastrectomies for gastric cancer. Methods: Between 31 December 2007 and 30 June 2008, twenty patients underwent robotic gastrectomies using the da Vinci<SUP>®</SUP> surgical system for gastric cancer. Retrospectively, clinicopathologic and postoperative surgical outcomes were retrieved from the Stomach Cancer Database at Dong-A University Medical Center. Results: Two patients with serosa invasion required conversion to laparotomy. Seventeen robotic distal gastrectomies and one robotic total gastrectomy were performed. Most patients underwent D1+β or D2 lymph node dissection. The average number of retrieved lymph nodes was 41. Mean operative time was 271 minutes. Estimated blood loss was 30 ml and mean postoperative hospital stay was 5.1 days. No postoperative complications were reported. Conclusion: While application of robotic technology for gastric cancer is technically feasible, problems of long operative times and extremely high costs remain. More randomized studies comparing long-term surgical outcomes between robotic, conventional open, and laparoscopic surgery are needed.