Ruben Ramos

Control design of a STATCOM with Energy Storage System for stability and power quality improvements

This paper presents a robust control scheme for a STATic Synchronous COMpensator (STATCOM) coupled with a Battery Energy Storage System (BESS) for improving the dynamic oscillations damping and the transmission power quality in electric power systems. The presented STATCOM/BESS controls both reactive and active power injection/absorption to/from the power system. It is investigated the performance of a Supplementary Damping Controller (SDC) added to the reactive power control scheme. The SDC is designed by a robust control technique structured in the form of linear matrix inequalities (LMIs). The main objectives, from the application viewpoint, are the improvements of the damping of oscillations in tie-lines (precisely, voltage and active power flow oscillations which are related to the presence of inter-area oscillations mode), and also, the minimization of their peak values during transients. The tests were realized in a two-area four-machine power system, and the results show the proposed control scheme presents a good performance for several different operating points.

An analysis of the potential impacts of electromechanical oscillations on the stability and power quality of distributed generation systems

The paradigm that distribution networks are free from problems related to electromechanical oscillations (due to their mainly passive nature and relatively large resistances) is about to change with the increase in the number of small generators connected to them. This paper shows a real situation in which the connection of a few small generators in the distribution network can significantly deteriorate the damping in the system response to small perturbations. The effects of the system response on the power quality across the network are also discussed. The analyzed system is located within the state of Sao Paulo, Brazil, having 3 feeders (comprising 57 kilometers of cables) and 32 buses distributed along these feeders. The need for an adequate assessment of the oscillations and their impacts over power quality is pointed out. It is shown that conventional PSSs can be a simple, cheap, and effective solution to keep the power quality standards as the number of generators entering the grid increases.

Effects of acute autonomic modulation on atrial conduction delay and local electrograms duration in paroxysmal atrial fibrillation

UNLABELLED Slowed atrial conduction may contribute to reentry circuits and vulnerability for atrial fibrillation (AF). The autonomic nervous system (ANS) has modulating effects on electrophysiological properties. However, complex interactions of the ANS with the arrhythmogenic substrate make it difficult to understand the mechanisms underlying induction and maintenance of AF. AIM To determine the effect of acute ANS modulation in atrial activation times in patients (P) with paroxysmal AF (PAF). METHODS AND RESULTS 16P (9 men; 59±14years) with PAF, who underwent electrophysiological study before AF ablation, and 15P (7 men; 58±11years) with atrioventricular nodal reentry tachycardia, without documentation or induction of AF (control group). Each group included 7P with arterial hypertension but without underlying structural heart disease. The study was performed while off drugs. Multipolar catheters were placed at the high right atrium (HRA), right atrial appendage (RAA), coronary sinus (CS) and His bundle area (His). At baseline and with HRA pacing (600ms, shortest propagated S2) we measured: i) intra-atrial conduction time (IACT, between RAA and atrial deflection in the distal His), ii) inter-atrial conduction time (interACT, between RAA and distal CS), iii) left atrial activation time (LAAT, between atrial deflection in the distal His and distal CS), iv) bipolar electrogram duration at four atrial sites (RAA, His, proximal and distal CS). In the PAF group, measurements were also determined during handgrip and carotid sinus massage (CSM), and after pharmacological blockade of the ANS (ANSB). AF was induced by HRA programmed stimulation in 56% (self-limited - 6; sustained - 3), 68.8% (self-limited - 6; sustained - 5), and 50% (self-limited - 5; sustained - 3) of the P, in basal, during ANS maneuvers, and after ANSB, respectively (p=NS). IACT, interACT and LAAT significantly lengthened during HRA pacing in both groups (600ms, S2). P with PAF have longer IACT (p<0.05), a higher increase in both IACT, interACT (p<0.01) and electrograms duration (p<0.05) with S2, and more fragmented activity, compared with the control group. Atrial conduction times and electrograms duration were not significantly changed during ANS stimulation. Nevertheless, ANS maneuvers increased heterogeneity of the local electrograms duration. Also, P with sustained AF showed longer interACT and LAAT during CSM. CONCLUSION Atrial conduction times, electrograms duration and fractionated activity are increased in PAF, suggesting a role for conduction delays in the arrhythmogenic substrate. Acute vagal stimulation is associated with prolonged interACT and LAAT in P with inducible sustained AF and ANS modulation may influence the heterogeneity of atrial electrograms duration.

A Mixed Procedure Based on Classical and Modern Control to Design Robust Damping Controllers

A systematic mixed procedure based on classical and robust control techniques is proposed in this work for the design of robust low-order damping controllers. The procedure formally guarantees a robust performance index for the system in closed-loop by employing a minimum performance index associated with a robust control technique. The mixed approach aims at providing an acceptable and easy-to-use robust design procedure as well as controllers with a simple and typical structure. Besides, a great variety of mathematical tools for the analyses and design of control systems may be employed in the overall procedure. The tests and results have shown that the overall procedure is suitable for the oscillation problem in power systems and that the resulting controllers are robust and effective in the damping of low-frequency electromechanical oscillations.

Simultaneous coordinated design of PSS and TCSC damping controller for power systems

This paper presents a simultaneous coordinated design of PSS-type and TCSC supplementary damping controllers for electric power systems. Such controllers are designed by means of a systematic methodology based on robust control. The adopted technique is an extension of a previously presented methodology. The design procedure is structured in the form of linear matrix inequalities (LMIs). The controllers are obtained by means of a numerical solution of the LMIs describing the control problem. Possible undesirable interactions between the PSS-type damping controllers and the TCSC damping controller are avoided by using the multimachine model in the design stage. The proposed technique ensures that the designed controllers fulfill various practical requirements of the oscillation damping problem in power systems. The minimum damping ratio is used as performance index for the system in closed loop. The proposed controllers were simultaneously designed and they have provided a coordinated control action and a satisfactory performance for the power system, as shown in the results

Does admission NT-proBNP increase the prognostic accuracy of GRACE risk score in the prediction of short-term mortality after acute coronary syndromes?

Background: NT-proBNP has prognostic implications in heart failure. In acute coronary syndromes (ACS) setting, the prognostic significance of NT-proBNP is being sought. We studied short-term prognostic impact of admission NT-proBNP in patients admitted for ACS and in association with GRACE risk score (GRS). Methods and Results: We studied 1035 patients admitted with ACS. Patients were divided in quartiles according to NT-proBNP levels on admission: Q1 <180 pg/ml; Q2 180–691 pg/ml; Q3 696–2664 pg/ml; Q4 2698–35 000 pg/ml. Groups were compared in terms of short-term all-cause mortality. Patients with higher NT-proBNP had worst GRS on admission. They also received less aggressive treatment. In-hospital mortality was 0.8%, 3.0%, 5.8% and 12.8% (P<0.001) and 30-day mortality 1.6%, 4.6%, 6.5% and 16.7% (P<0.001) respectively. In multivariate logistic regression analysis, NT-proBNP is an independent predictor of in-hospital (OR 2.35; 95% CI: 1.12–4.93, P=0.022) and 30-day mortality (OR 2.20; 95% CI: 1.17–4.12, P=0.014). However, NT-proBNP does not add any incremental benefit to GRS for prediction of outcome by ROC curve analysis. Conclusions: NT-proBNP is an independent predictor of in-hospital and 30-day mortality after ACS, independently of left ventricular function, but does not increase the prognostic accuracy of GRS.

Prognostic value of a new cardiopulmonary exercise testing parameter in chronic heart failure: oxygen uptake efficiency at peak exercise — comparison with oxygen uptake efficiency slope

INTRODUCTION A growing body of evidence shows the prognostic value of oxygen uptake efficiency slope (OUES), a cardiopulmonary exercise test (CPET) parameter derived from the logarithmic relationship between O(2) consumption (VO(2)) and minute ventilation (VE) in patients with chronic heart failure (CHF). OBJECTIVE To evaluate the prognostic value of a new CPET parameter - peak oxygen uptake efficiency (POUE) - and to compare it with OUES in patients with CHF. METHODS We prospectively studied 206 consecutive patients with stable CHF due to dilated cardiomyopathy - 153 male, aged 53.3±13.0 years, 35.4% of ischemic etiology, left ventricular ejection fraction 27.7±8.0%, 81.1% in sinus rhythm, 97.1% receiving ACE-Is or ARBs, 78.2% beta-blockers and 60.2% spironolactone - who performed a first maximal symptom-limited treadmill CPET, using the modified Bruce protocol. In 33% of patients an cardioverter-defibrillator (ICD) or cardiac resynchronization therapy device (CRT-D) was implanted during follow-up. Peak VO(2), percentage of predicted peak VO(2), VE/VCO(2) slope, OUES and POUE were analyzed. OUES was calculated using the formula VO(2) (l/min) = OUES (log(10)VE) + b. POUE was calculated as pVO(2) (l/min) / log(10)peakVE (l/min). Correlation coefficients between the studied parameters were obtained. The prognosis of each variable adjusted for age was evaluated through Cox proportional hazard models and R2 percent (R2%) and V index (V6) were used as measures of the predictive accuracy of events of each of these variables. Receiver operating characteristic (ROC) curves from logistic regression models were used to determine the cut-offs for OUES and POUE. RESULTS pVO(2): 20.5±5.9; percentage of predicted peak VO(2): 68.6±18.2; VE/VCO(2) slope: 30.6±8.3; OUES: 1.85±0.61; POUE: 0.88±0.27. During a mean follow-up of 33.1±14.8 months, 45 (21.8%) patients died, 10 (4.9%) underwent urgent heart transplantation and in three patients (1.5%) a left ventricular assist device was implanted. All variables proved to be independent predictors of this combined event; however, VE/VCO2 slope was most strongly associated with events (HR 11.14). In this population, POUE was associated with a higher risk of events than OUES (HR 9.61 vs. 7.01), and was also a better predictor of events (R2: 28.91 vs. 22.37). CONCLUSION POUE was more strongly associated with death, urgent heart transplantation and implantation of a left ventricular assist device and proved to be a better predictor of events than OUES. These results suggest that this new parameter can increase the prognostic value of CPET in patients with CHF.

Impact of body mass index in the results after primary angioplasty in patients with ST segment elevation acute myocardial infarction

Introduction: Obese patients submitted to elective coronary angioplasty have a paradoxical reduction in hospital and long-term mortality. In primary angioplasty setting, the relation with Body Mass Index (BMI) is less studied. Objectives: To evaluate the impact of obesity in the results after ST-segment elevation acute myocardial infarction treated by primary angioplasty. Methods: Study of 539 consecutive patients with ST-segment elevation acute myocardial infarction (STEMI) submitted to primary angioplasty. We evaluated in-hospital, 30-day and one-year all-cause mortality according to BMI: ‘normal’, <25 kg/m2; ‘overweight’, 25–29.9 kg/m2 and ‘obese’, ≥ 30 kg/m2.Results: Obese patients were younger, had more hypertension and hyperlipidemia. There were no differences in previous cardiac history and hospital data. In-hospital mortality was 8.0% for patients with normal BMI, 4.4% for overweight patients and 5.9% for obese patients (P=0.296). At 30 days, 9.6%, 5.2% and 6.9% (P=0.212) and at first year, 11.2%, 5.2% and 6.9% (P=0.064), respectively. Overweight was the only group with decreased risk (OR: 0.44, 95% CI: 0.21–0.90, P=0.015), even after adjustment for confounding variables (OR: 0.37, 95% CI: 0.15–0.95, P=0.038). Conclusions: Overweight patients had a better prognosis after primary angioplasty for STEMI compared with other BMI groups.

Look-ahead based method for selection of preventive control for voltage stability analysis

In recent years, the analysis of voltage stability has become crucial for the proper operation of electrical power systems, especially when it comes to large systems. The need for effective voltage control strategies have been brought to evidence in a considerable number of studies, as power system loads are located farther away from power plants and losses have tended to increase due to heavier power flows over long distance transmission loads. A new methodology for selection of the most effective controls to prevent voltage instability in electrical power systems is developed in this paper. The proposed methodology is fast and suitable for real time operation. It is based on a sensitivity analysis of both a maximum loadability estimate (which is obtained via Look-Ahead method) and the load flow solution with respect to the selected controls. The methodology was successfully tested in two systems: the reduced equivalent model of the southern Brazilian system (represented by a 33-bus model) and the south-southeast Brazilian interconnection (represented by a 65-bus model).

Application of extended participation factors to detect voltage fluctuations in distributed generation systems

The dynamics of distribution systems has been significantly modified by the increasing penetration of distributed generation in distribution grids. Distribution systems, with distributed synchronous generators, may exhibit dynamic characteristics similar to those observed in transmission systems, such as, for example, low-frequency electromechanical oscillations. The impacts related to electromechanical oscillations raise important concerns about the system stability and power quality across the distribution grids. Tools usually employed to analyze such kind of oscillations in transmission systems (such as participation factors, for example), may not be fully appropriate for analyzing this same phenomenon in distribution systems. Due to the aforementioned issues, this work proposes the use of extended participation factors as a tool to detect voltage fluctuations caused by electromechanical oscillations in distributed generation systems. The results of a case study show that, in some cases, the traditional participation factors are not able to detect these fluctuations, while the extended participation factors performed well with respect to this detection.