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      • KCI등재

        고전압 이용을 위한 다중인접 기준벡터 불연속변조기법 기반의 다이오드 클램핑 멀티레벨 LLC 공진형 컨버터

        송민섭,조인호,이재범,류준형 한국철도학회 2021 한국철도학회논문집 Vol.24 No.3

        본 논문에서는 철도차량 추진 또는 보조전원시스템과 같은 높은 입력 전압을 이용하는 전력 변환 시스템에 적합한 다이오드 클램핑 멀티레벨 LLC 공진형 컨버터를 제안하였다. 높은 전압을 갖는 입력 dc-link 단의 직렬 연결된 커패시터들의 전압 편차를 제거하기 위해 기존 AC/DC 혹은 DC/AC 시스템에 적용된 다중인접 기준벡터 불연속 변조기 법을 DC/DC 컨버터에 적합하게 변형하여 적용하였다. 제안하는 멀티레벨 공진형 컨버터는 주파수 스윕형의 기존 2레벨 시스템과 다르게 동작 주파수를 공진점에 고정한 채 Full-Bridge 스위칭 스택을 통해 공진 탱크로 입력되는 전압의 크기를 변조하는 방식으로 출력 정전압 제어를 수행한다. 동작 주파수를 고정함에 따라 수동 소자의 설계가 용이하고 단일 전력변환 stage 만으로 넓은 동작 범위에서 안정적인 동작이 가능하다. 본 논문에서는 새롭게 제안된 멀티레벨 공진형 컨버터의 제어 알고리즘과 동작 특성을 상세하게 분석하였고, 시뮬레이션을 통해 검증하였다. In this paper, a diode-clamped multi-level LLC resonant converter suitable for power conversion systems using high input voltages such as propulsion systems or auxiliary power systems of railway vehicles is proposed. To remove the voltage deviation of the capacitors connected in series at the input dc-link terminal with high voltage, the multineighboring reference vector discontinuous PWM for the AC/DC or DC/AC system was modified and applied appropriately to the DC/DC conversion system. Unlike the existing 2-level system that sweeps the operating frequency for constant output voltage control, the proposed multi-level resonant converter modulates the magnitude of the voltage input to the resonant tank through the full-bridge switching stack while the operating frequency is fixed at the resonant point. By fixing the operating frequency, it is easy to design a passive element, and stable operation over a wide operating range is possible with only a single power conversion stage. In this paper, the control algorithm and operating characteristics of the newly proposed multi-level resonant converter were analyzed in detail and verified through simulation.

      • KCI등재

        Non-isolated Bidirectional Soft-switching SEPIC/ZETA Converter with Reduced Ripple Currents

        송민섭,손영두,이광현 전력전자학회 2014 JOURNAL OF POWER ELECTRONICS Vol.14 No.4

        A novel non-isolated bidirectional soft-switching SEPIC/ZETA converter with reduced ripple currents is proposed andcharacterized in this study. Two auxiliary switches and an inductor are added to the original bidirectional SEPIC/ZETA componentsto form a new direct power delivery path between input and output. The proposed converter can be operated in the forward SEPICand reverse ZETA modes with reduced ripple currents and increased voltage gains attributed to the optimized selection of duty ratios. All switches in the proposed converter can be operated at zero-current-switching turn-on and/or turn-off through soft currentcommutation. Therefore, the switching and conduction losses of the proposed converter are considerably reduced compared withthose of conventional bidirectional SEPIC/ZETA converters. The operation principles and characteristics of the proposed converterare analyzed in detail and verified by the simulation and experimental results.

      • KCI등재

        Earnings Announcements, Analyst Forecasts, and Trading Volume

        송민섭 서울대학교 경영연구소 2013 Seoul Journal of Business Vol.19 No.2

        Empirical evidence shows that a significant proportion of analysts issue their forecasts at the time of an earnings announcement (Ivković and Jegadeesh 2004). These forecasts are commonly regarded as analyst interpretations of earnings news contained in the announcement (Schipper 1991). Although analytical studies suggest that market reaction to news from earnings announcement could be affected by analysts’ interpretation information (Kim and Verrecchia 1994, 1997), the vast majority of previous research has ignored whether and how these analysts’ interpreting forecasts affect the market reaction to the earnings announcements. Our empirical results show that sensitivity of trading volume reaction to earnings announcements is increasing in the number of announcement period analyst forecasts. The sensitivity of trading volume reaction is greater when there is small analyst forecast dispersion. We also find that stock return sensitivity is also increasing with the number of analyst forecasts. In general, our results suggests that analysts’ interpretation help disseminate new information contained in earnings announcement to the market.

      • KCI등재

        How Does Prior Information Affect Analyst Forecast Revisions?

        송민섭 한국증권학회 2008 Asia-Pacific Journal of Financial Studies Vol.37 No.6

        This study investigates how observable prior information affects individual analysts’ earnings forecast revisions. Following Stickel (1990), it first examines how new information observed by Korean analysts and uncertainty in the analysts’ current forecast affect the analysts’ forecast revision. Then, this study extends the prediction model by examining how characteristics of new information (positive vs. negative change in consensus forecast) and the characteristics of the analysts’ current forecast (higher vs. lower than the mean forecast) affect their forecast revision. The empirical results show that the individual analyst revision, the change in consensus forecast, and the cumulative stock returns are positively related whereas the revision and the deviation of the analyst’s current forecast from the consensus forecast are negatively related. Results also show more sensitive reactions to consensus change when analysts observe a negative consensus change. In addition, analysts’ reaction to a negative consensus change is greater when their current forecast is greater than the prior mean forecast. These results suggest that analysts learn from market expectation changes and incorporate new information into their new forecasts.

      • KCI등재후보

        Information Content of Analyst Forecast Revisions

        송민섭 한국회계정책학회 2008 회계와 정책연구 Vol.13 No.2

        This study investigates information content of analyst forecasts by examining the relationship between analyst forecast revisions and abnormal stock returns around the announcement dates of analyst forecast revision. Empirical results show that both monthly consensus revisions and individual forecast revisions are positively related to abnormal stock returns. In addition, abnormal stock returns are concentrated around the months of consensus revisions or around dates of individual analyst forecast revisions, implying that stock return reflect new information from forecast revisions immediately. This evidence suggests that analyst forecast contains information content.

      • KCI등재

        Infliximab Treatment for Refractory Kawasaki Disease in Korean Children

        송민섭,이상범,손세정,오진희,윤경림,한지환,김철호 대한심장학회 2010 Korean Circulation Journal Vol.40 No.7

        Background and Objectives: This was a multicenter study to evaluate the usefulness of the tumor necrosis factor-alpha (TNF-α) blocker infliximab for treatment of Korean pediatric patients with refractory Kawasaki disease (KD). Subjects and Methods: Data from 16 patients throughout Korea who were diagnosed with refractory KD and received infliximab were collected retrospectively. Results: Complete response to therapy with cessation of fever occurred in 13 of 16 patients. C-reactive protein (CRP) concentrations decreased following infliximab infusion in all 14 patients in whom it was measured before and after treatment. There were no infusion reactions or complications associated with infliximab except in 1 case with acute hepatitis occurring during treatment followed by calculous cholecystitis 4 months later. Fifteen patients had coronary artery (CA) abnormalities before infliximab therapy. Three had transient mild dilatation and 9 had CA aneurysms,with subsequent normalization in 4 patients, persistent mild dilatation in 3, persistent aneurysm in 2, and there were 3 cases (2 with CA aneurysm, 1 with mild CA dilatation) without follow-up echocardiography. Conclusion: The results of this study suggest that infliximab may be useful in the treatment of refractory KD, and it appears that there is no significant further progression of CA lesions developing after infliximab treatment. Multicenter trials with larger numbers of patients and long-term follow-up are necessary to assess the clinical efficacy and safety of infliximab in refractory KD.

      • 국내 발전소별 바텀애시를 잔골재 대체재로 사용한 모르터의 특성에 대한 실험적 연구

        송민섭,장재봉,조봉석,김재환,김용로,김무한 대한건축학회 2003 대한건축학회 학술발표대회 논문집 - 계획계/구조계 Vol.23 No.1(구조계)

        With the advance in industrial development and modern living comfort, the demand for electricity throughout the country is ever increasing. Also the annual consumption of coal by coal-fired power plants is increasing. The amount of ash produced in 2000 is estimated to be about 4.5 million tons. The disposal of this huge amount of ash introduces serious environmental problems. Fly ash among the ash produced is used in building industries as a substitute to cement in concrete and the concrete thus produced is said to be lighter and stronger. But bottom ash among the ash produced is not used because of its poor properties. But encouraging the use of bottom ash as a construction material is a sensible method of utilization as it avoids the problems and costs associated with disposal and provides an alternative aggregate source. This study is aimed at using bottom ash as an alternative fine aggregate source to provide a solution to disposal and insufficient fine aggregate for the production of concrete. So properties of bottom ash produced in power plants were estimated due to the difference of bottom ash produced in each plant. And mortar strength was estimated as basic data to use bottom ash in building industries.

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