A Study on the Regulating and Equalizing Neutral Point Voltage of a Three-Level Inverter for Self-Commutated Static Var Compensator

SVC(Static Var Compensator)s play important roles in larger and more complex electric power system. Rapid and continuous reactive power compensation by SVC contributes to voltage stabilization, power oscillation damping, overvoltage suppression, minimization of transmission losses and so on. Harmonic contents of the three level inverter are less than those of two level inverter at the same switching frequency and blocking voltage of the switching device is half of the DC-link voltage. So three level inverter topology is generally used in realizing high performance, high voltage AC drive system. Multi level inverters connected in series are suitable for high voltage system because of their circuit structure. They are capable of reducing harmonic components in the AC source side current without requiring high frequency switching. However, the main problem of multi level inverters without independent DC voltage sources is the unbalance of DC capacitor voltage. Problems in using SVC are the voltage unbalance at each stage of DC capacitor. And, equalizing DC capacitor voltages is required to ensure the even sharing of voltage stress in the power devices, and to compensate reactive power accurately. In this paper, a simple SVPWM(Space Vector Pulse Width Modulation) method for neutral point balancing of three level inverter is proposed. By using the new PWM strategy, voltage vector selection is easily done like that of two level inverter. And the neutral point voltage control by changing the sequence of voltage vector is easy to implement. Instantaneous power vector theory which expresses the instantaneous apparent power vector can be applied for controlling reactive power. The validity of the proposed method is confirmed by simulation studies and experiments.List of figures iii List of tables vi Abstract vii 기호설명 ix 제 1 장 서 론 1 1.1 연구배경 1 1.2 연구목적 및 내용 3 제 2 장 무효전력보상장치의 종류와 특징 6 2.1 무효전력보상장치원리 6 2.2 콘덴서 조정형 무효전력보상장치 10 2.3 리액터 조정형 무효전력보상장치 16 2.4 자려식 무효전력보상장치 25 2.5 무효전력제어방식 33 2.5.1 dq 좌표방식 33 2.5.2 VQ 벡터제어방식 35 2.5.3 순시전력 지령값에 의한 무효전력제어 41 2.5.3.1 벡터도 41 2.5.3.2 무효전력제어 49 제 3 장 멀티레벨 인버터를 이용한 SVC의 중성점 전위변동 제어 53 3.1 멀티레벨 인버터를 이용한 SVC의 원리 53 3.2 3레벨 인버터의 구성과 스위칭 패턴 58 3.3 3레벨 인버터의 중성점 전위변동 메카니즘해석 61 3.3.1 단펄스 제어 61 3.3.2 해석의 일반화 70 3.4 멀티레벨 인버터의 중성점 변동 억제방식 80 3.4.1 외부 DC 전원의 공급과 위상제어 81 3.4.2 용량이 다른 콘덴서 부가법 81 3.4.3 스위칭각의 변조법 83 제 4 장 새로운 중성점 전위제어 알고리즘 85 4.1 3레벨 인버터의 SVPWM 스위칭법 85 4.2 스위칭 순서 결정법에 의한 SVPWM 스위칭법 88 제 5 장 실험결과 고찰 99 5. 실험장치 99 5.1.1 주회로 100 5.1.2 제어회로 102 5.2 스위칭 순서 결정법에 의한 중성점 변동고찰 107 5.3 순시전력 지령값에 의한 무효전력제어 검토 116 제 6 장 결 론 124 참고문헌 12

A Case Report of Primary Cardiac Lymphoma : Diagnosis by Transvenous Biopsy under Transesophageal Echocardiographic Guidance

Primary cardiac lymphomas diagnosed antemortem are extremely rare. We present a case of primary cardiac lymphma diagnosed antemortem by transvenous biopsy under transesophageal echocardiographic guidance. The patient who was a 62 years old male presented with facial edema, dyspnea on exertion and syncope. The chest X-ray film showed double contour at right cardiac border and the ECG showed marked sinus bradycardia. Transesophageal echocardiography (TEE), chest computed tomography (CT) and magnetic resonance imaging (MRI) showed intracardiac tumor of right atrium, invasing interatrial septum and inlets of superior and inferior vena cava and lateral wall of right atrium. Abdominopelvic CT and bone scan failed to show any extracardiac location. Transvenous biopsy confirmed the diagnosis of malignant lymphoma (diffuse large cell, B cell type). After chemotherapy was begun, the tumor makedly shrunk and symptoms resolved. Primary cardiac lymphoma is extremely rare and almost uniformly fatal, but this case showed that early diagnosis and intensive chemotherapy might contribute to a better prognosis for patients with malignant lymphoma of the heartope

Serum phosphorus levels are associated with carotid intima-media thickness in asymptomatic postmenopausal women

Objective: Serum phosphorous is a significant risk factor for increased carotid intima-media thickness. Increased thickness of the carotid intima is a known cause of cardiovascular disease. Coronary heart disease is a significant cause of mortality and morbidity in postmenopausal women. This study aimed to compare the relationship between serum phosphorous concentration and carotid intima-media thickness in healthy asymptomatic postmenopausal women. Methods: A retrospective review of the medical records from a health checkup center in Gangnam Severance hospital between March 2007 and September 2017 was conducted. We examined asymptomatic postmenopausal female patients with age range between 56 and 66 (N = 361) who underwent measurement of carotid intima-media thickness by B-mode ultrasonography. The physiological variables analyzed included mean blood pressure, body mass index, renal function (serum creatinine and estimated glomerular filtration rate), cholesterol levels (total cholesterol, triglyceride, and high- and low-density lipoprotein), serum phosphorous, calcium, electrolytes, diabetic status, hypertension, and albumin. Results: Pearson correlation test showed that carotid intima-media thickness was significantly associated with age (r = 0.192, P < 0.001), mean blood pressure (r = 0.116, P = 0.029), diastolic blood pressure (r = 0.146, P = 0.029), serum phosphorous (r = 0.134, P = 0.012), and lactate dehydrogenase (r = 0.106, P = 0.047). On the basis of age-adjusted multivariate linear regression analysis, carotid intima-media thickness was significantly correlated with serum phosphorous levels (β = 0.273, P = 0.022) in asymptomatic menopausal women. Increased carotid intima-media thickness (cut-off 1.5 mm) was detected, although serum phosphorous was within the normal range (2.8-4.5 mg/dL). Conclusions: Serum phosphorus concentration is significantly associated with carotid intima-media thickness in asymptomatic menopausal women.ope

Clinical and Hospital Factors Affecting Treatment with Primary Prevention Implantable Cardioverter-Defibrillators in Ischemic Cardiomyopathy Patients

Purpose: Implantable cardioverter defibrillators (ICD) are the standard of care for primary prevention (PP) in patients with ischemic cardiomyopathy (ICM). However, PP ICD implantation is underused in Asian countries. This study investigated ICD implantation rates and factors associated with appropriate PP ICD implants for ICM. Materials and methods: In this prospective multicenter observational registry (ADVANCE-ICM registry), ICM patients who were eligible for PP ICD were screened and enrolled. Factors associated with appropriate ICD implantation, including hospital and clinical factors, were investigated. Results: Of the 1453 ICM patients eligible for PP ICD [1111 male; median age, 71.0 (61.0-78.0) years], only 76 (5.2%) patients underwent ICD implantation. Among hospital factors, a non-monetary incentive for referral (72.4% vs. 52.9%, p=0.001) and total hospital system score (6.0 vs. 5.0, p=0.013) were higher in the ICD than in the no-ICD group. In multivariate analysis, total hospital system score [odds ratio (OR), 1.28; 95% confidence interval (CI), 1.10-1.50] was an independent factor for predicting ICD implantation, along with clinical factors, including high New York Heart Association class (≥III: OR, 7.29; 95% CI, 2.97-17.87) and younger age (<70 years: OR, 2.14; 95% CI, 1.30-3.53). Conclusion: PP ICD implantation for ICM patients is underused in Korea. Hospital factors were important for improving PP ICD implantation rate, suggesting that new screening and referral systems for ICM patients would improve the PP ICD implantation rate (Clinical trial registration No. NCT03590925).ope

VILLONODULAR SYNOVITIS OF THE TEMPOROMANDIBULAR JOINT : A CASE REPORT

Villonodular synovitis, also called pigmented villonodular synovitis, is the benign lesion with the characteristic of locally aggressive proliferation of mononuclear histiocyte and giant cell. Typically it involves single joint, especially about 80% of disease occurs in the knee joint. Villonodular synovitis of the temporomandibular joint is very rare disease. Differential diagnosis includes synovial chondromatosis and tumors of the temporomandibular joint. Optimal treatment consists of complete excision of the mass and removal of the synovium including adjacent affected bony structures. This is a case report of villonodular synovitis developed in the temporomandibular jointope

Long-term Clinical Outcomes and Prognostic Factors After Endovascular Treatment in Patients With Chronic Limb Threatening Ischemia

Background and objectives: Endovascular therapy (EVT) first strategy has been widely adopted for the treatment of chronic limb threatening ischemia (CLTI) patients in real-world practice. This study aimed to investigate long-term outcomes of CLTI patients who underwent EVT and identify prognostic factors. Methods: From the retrospective cohorts of a Korean multicenter endovascular therapy registry, 1,036 patients with CLTI (792 men, 68.8 ± 9.5 years) were included. The primary endpoint was amputation-free survival (AFS) defined as the absence of major amputation or death. Secondary endpoints were major adverse limb events (MALE; a composite of major amputation, minor amputation, and reintervention). Results: Five-year AFS and freedom from MALE were 69.8% and 61%, respectively. After multivariate analysis, age (hazard ratio [HR], 1.476; p<0.001), end-stage renal disease (ESRD; HR, 2.340; p<0.001), Rutherford category (RC) 6 (HR, 1.456; p=0.036), and suboptimal EVT (HR, 1.798; p=0.005) were identified as predictors of major amputation or death, whereas smoking (HR, 0.594; p=0.007) was protective. Low body mass index (HR, 1.505; p=0.046), ESRD (HR, 1.648; p=0.001), femoropopliteal lesion (HR, 1.877; p=0.004), RC-6 (HR, 1.471; p=0.008), and suboptimal EVT (HR, 1.847; p=0.001) were predictors of MALE. The highest hazard rates were observed during the first 6 months for both major amputation or death and MALE. After that, the hazard rate decreased and rose again after 3-4 years. Conclusions: In CLTI patients, long-term outcomes of EVT were acceptable. ESRD, RC-6, and suboptimal EVT were common predictors for poor clinical outcomes. Trial registration: ClinicalTrials.gov Identifier: NCT02748226.ope

Sex-based Approach for the Clinical Impact of the Increased Hemoglobin on Incident AF in the General Population

Background and objectives: Although the adverse cardiovascular effect of anemia has been well described, the effect of polycythemia on the incident atrial fibrillation (AF) remain unclear. The objective of this study is to identify the association between increased hemoglobin and incident AF. Methods: This was a retrospective-cohort study with 434,269 subjects who underwent national health examinations from the Korean National Sample Cohort. We estimated the risk of incident AF according to hemoglobin-based four-categories. Results: During 3.9-year of follow-up, polycythemia group showed higher incidences of AF (hazard ratio[HR] with 95% confidence interval[CI], 1.50 [1.28-1.76] and 1.69 [1.13-2.56]; in men and women, respectively) than normal hemoglobin group (each p<0.001). In the normal hemoglobin and polycythemia groups, a 1 g/dL increase in hemoglobin level was associated with increased risks of incident AF (1.12 [1.07-1.17] and 1.18 [1.10-1.26] in men and women, each p<0.001). To investigate the specific hemoglobin concentration related to greater AF incidence, we analyzed the sensitivity/specificity of different hemoglobin levels: ≥16.0 g/dL in men and ≥14.5 g/dL in women showed the highest Youden's index, with c-indices of 0.83 and 0.82, respectively. Kaplan-Meier cumulative-event curves according to these specific hemoglobin levels (≥16.0 g/dL in men and ≥14.5 g/dL in women) also showed consistent results in both sexes (each p<0.05). Conclusions: Even in the Korean general population, increased hemoglobin was significantly associated with higher rate of incident AF. Especially, subjects with hemoglobin levels ≥14.5 g/dL in women and ≥16.0 g/dL among men were associated with increased risk of incident AF.ope

Prevalence and risk factors for secondary hypertension among young Korean men

Screening for secondary hypertension (HTN) is recommended for early-onset HTN. However, there have been few studies on secondary HTN in young adults. We aimed to investigate the prevalence and risk factors for secondary HTN in young male military personnel. In this retrospective cross-sectional study, hypertensive men (age, 19-29 years) were identified using the electronic medical records (EMR) database between 2011 and 2017. Among them, patients with secondary HTN were confirmed through a review of the EMR. Using clinical characteristics and laboratory findings, independent predictors associated with secondary HTN were identified by binary logistic regression analysis. Secondary HTN was confirmed in 140 of 6373 participants (2.2%). Overall, the most common causes were polycystic kidney disease (n = 47, 0.74%) and renal parenchymal diseases (n = 24, 0.38%). The independent predictors of secondary HTN were abnormal thyroid function test (TFT) (odds ratio [OR]: 9.50, 95% confidence interval [CI]: 4.84-19.45, P < 0.001), proteinuria (≥ trace) (OR: 6.13, 95% CI: 2.97-12.99, P < 0.001), hematuria (≥ trace) (OR: 4.37, 95% CI: 2.15-9.01, P < 0.001), severe HTN (≥ 180/110 mmHg) (OR: 3.07, 95% CI: 1.42-6.65, P = 0.004), and non-overweight (OR: 3.03, 95% CI: 1.69-5.26, P < 0.001). However, there were no significant differences in the family history of HTN, headache, total cholesterol, and diabetes between patients with primary and secondary HTN. Therefore, to ensure cost-effectiveness, screening for secondary HTN in young hypertensive men should be performed selectively considering abnormal TFT, proteinuria, hematuria, severe HTN, and non-overweight.ope

Nonsustained atrial tachycardia in 24-hour Holter monitoring: a potential cardiac source of embolism in acute ischemic stroke

Background: Whether nonsustained atrial tachycardia (NSAT) has a causative role similar to paroxysmal atrial fibrillation (AF) in ischemic stroke is unclear. We investigated the clinical and imaging features of ischemic stroke patients with NSAT to demonstrate that these patients would have a higher proportion of embolic strokes. Methods: We retrospectively reviewed ischemic stroke patients who underwent Holter monitoring and selected patients with NSAT. The clinical and imaging characteristics were compared between patients with and without NSAT, and the risk factors for embolic stroke were evaluated. Moreover, the images of the selected patients were analyzed according to the Trials of Org 10172 in Acute Stroke Treatment classification. Results: From a total of 1,051 patients who had 24-hour Holter monitoring, 681 patients were selected for the study. Among the selected patients, NSAT was detected in 243 patients. The patients with NSAT had a significantly higher proportion of imaging findings suggestive of cerebral embolism compared with patients without NSAT (27% vs. 14%, P<0.001). Moreover, the presence of NSAT was a statistically significant factor associated with imaging findings suggestive of cerebral embolism in the univariate (OR, 2.22; 95% CI, 1.51-3.27; P<0.001) and multivariate (OR, 2.26; 95% CI, 1.53-3.34; P<0.001) analyses. The patients with NSAT had a significantly older age at diagnosis, higher proportion of female sex, higher proportion of hypertension, lower proportion of smokers, higher CHA2DS2-VASc score, and higher left atrium index value compared with patients without NSAT. Conclusions: The embolic pattern of acute ischemic stroke in patients with NSAT was frequently observed and shared clinical characteristics of AF rather than those of atherosclerosis. As NSAT may be a potential source of cardiac embolism, we suggest a more intensive search for modifiable risk factors such as AF in ischemic stroke in patients with NSAT.ope

Comparison of two different doses of single bolus steroid injection to prevent atrial fibrillation recurrence after radiofrequency catheter ablation

PURPOSE: Steroids may play a role in preventing the early recurrence of atrial fibrillation (AF) after radiofrequency catheter ablation (RFCA). However, optimal doses and route of steroid delivery have not yet been determined. This study evaluated the effect of two different doses of a single bolus injection of steroids on AF recurrence after RFCA. MATERIALS AND METHODS: Of 448 consecutive AF patients who underwent RFCA, a single steroid bolus was injected into 291 patients. A low-dose steroid group (n=113) received 100 mg of hydrocortisone and a moderate-dose steroid group (n=174) received 125 mg of methylprednisolone. We used propensity-score matching to select patients as follows: control (n=95), low-dose (n=95), and moderate-dose steroid groups (n=97). RESULTS: Pericarditis developed in 1 (1.1%) control patient, 2 (2.1%) low-dose patients and 0 moderate-dose patients. Maximum body temperature and C-reactive protein were significantly decreased in the moderate-dose steroid group compared to the other groups (p<0.01). The number of patients of early AF recurrence (≤3 months) did not differ among three groups. Early recurrence was 24 (25%) in the control, 24 (25%) in the low-dose and 25 (26%) in the medium-dose groups (p=0.99). Compared with control group, low-dose or moderate-dose steroid treatment did not effectively decrease mid-term (3-12 months) AF recurrence [22 (23%) vs. 23 (24%) vs. 18 (19%); p=0.12]. CONCLUSION: A single injection of moderate-dose steroid decreased inflammation. However, single bolus injections of low-dose or moderate-dose steroids were not effective in preventing immediate, early or midterm AF recurrence after RFCA.ope