Luís Seca

Provision of Inertial and Primary Frequency Control Services Using Offshore Multiterminal HVDC Networks

This paper addresses the problem of providing frequency control services, including inertia emulation and primary frequency control, from offshore wind farms connected through a multiterminal HVDC network. The proposed strategy consists of a cascading control mechanism based on dc voltage regulation at the onshore converters and frequency regulation at the offshore converters. The control scheme involves only local measurements and actions avoiding security and reliability issues of control structures based on remote information. The effectiveness of the proposed strategy is illustrated in a test system that consists of two nonsynchronous areas linked by a multiterminal HVDC grid where two offshore wind farms are also connected.

Electric vehicles participating in frequency control: Operating islanded systems with large penetration of renewable power sources

This paper addresses the problematic of operating isolated networks with large penetration of intermittent renewable power sources, as well as the benefits that electric vehicles might bring to these systems. A small islands network was used as case study and a 100% renewable dispatch for a valley period, only with hydro and wind generation, was tested in a dynamic simulation platform developed in Eurostag. Two distinct wind speed disturbances were simulated and, for both, the impact in the networks frequency was evaluated considering two different situations: electric vehicles only in charging mode and electric vehicles participating in primary frequency control. It was assumed the existence of 575 electric vehicles in the island. The impact of having electric vehicles performing primary frequency control in the expected batteries state of charge was also evaluated.

Importance of Manchester Triage in acute myocardial infarction: impact on prognosis

Background Fast and effective diagnosis of patients with acute myocardial infarction (AMI) in the Emergency Department (ED) is needed. Manchester Triage (MT) is based on identification of the patients main complaint, establishing, through decision flowcharts, a target-time for first observation. This study aimed to evaluate the impact of MT on short-term mortality in AMI and detect potential improvements, and to analyse high-risk groups: diabetic patients, women and older patients. Methods 332 consecutive patients (69.0+13.6 years mean age; 34.9% women) with final diagnosis of AMI were assessed in the ED using MT. Data were analysed according to demographics and risk groups, as well as several AMI parameters, admission duration and intrahospital mortality (IHM). Independent predictors of mortality were determined. Results 82.8% of patients met the ideal goal of ≤10 min target-time for a first observation (ITTFO). This was higher (95%) in typical presentations (‘chest pain’), versus 52% in other flowcharts; p<0.01. Patients ≥70 years old were less frequently screened with ITTFO ≤10 min (76.2% vs 90.0% in those under 70; p=0.001) or the ‘chest pain’ flowchart (66.9% vs 77.5%; p=0.031). IHM was 13.3%. Triage with ≤10 min ITTFO and the ‘chest pain’ algorithm seems to predict a lower mortality (0.33 OR; 95% CI 0.17 to 0.63; p=0.0005 and 0.49 OR; 95% CI 0.24 to 1.03; p=0.056). Conclusion MT proved to be an effective system. Patients with typical AMI presentation, ST elevation myocardial infarction and less than 70 years old are protected by MT, with lower ITTFO and better short-term survival.

Impact of Routine Fractional Flow Reserve Evaluation During Coronary Angiography on Management Strategy and Clinical Outcome: One-Year Results of the POST-IT.

Background—Penetration of fractional flow reserve (FFR) in clinical practice varies extensively, and the applicability of results from randomized trials is understudied. We describe the extent to which the information gained from routine FFR affects patient management strategy and clinical outcome. Methods and Results—Nonselected patients undergoing coronary angiography, in which at least 1 lesion was interrogated by FFR, were prospectively enrolled in a multicenter registry. FFR-driven change in management strategy (medical therapy, revascularization, or additional stress imaging) was assessed per-lesion and per-patient, and the agreement between final and initial strategies was recorded. Cardiovascular death, myocardial infarction, or unplanned revascularization (MACE) at 1 year was recorded. A total of 1293 lesions were evaluated in 918 patients (mean FFR, 0.81±0.1). Management plan changed in 406 patients (44.2%) and 584 lesions (45.2%). One-year MACE was 6.9%; patients in whom all lesions were deferred had a lower MACE rate (5.3%) than those with at least 1 lesion revascularized (7.3%) or left untreated despite FFR⩽0.80 (13.6%; log-rank P=0.014). At the lesion level, deferral of those with an FFR⩽0.80 was associated with a 3.1-fold increase in the hazard of cardiovascular death/myocardial infarction/target lesion revascularization (P=0.012). Independent predictors of target lesion revascularization in the deferred lesions were proximal location of the lesion, B2/C type and FFR. Conclusions—Routine FFR assessment of coronary lesions safely changes management strategy in almost half of the cases. Also, it accurately identifies patients and lesions with a low likelihood of events, in which revascularization can be safely deferred, as opposed to those at high risk when ischemic lesions are left untreated, thus confirming results from randomized trials. Clinical Trial Registration—URL: http://www.clinicaltrials.gov. Unique identifier: NCT01835808.

Coordinated management of distributed energy resources in electrical distribution systems

Current electrical distribution systems are facing significant challenges due to the widespread deployment of Distributed Energy Resources (DER), particularly the integration of variable Renewable Energy Sources (RES). This requires a change in the paradigm of distribution grids from a purely passive perspective into fully active networks within the smart grid vision. This new paradigm involves new control and management architectures as well as advanced planning methods and operational tools for distribution systems exploiting a smart metering infrastructure. This infrastructure will enable leveraging data from smart meters and short-term forecasts of load demand and RES in order to manage the distribution system in a more efficient and cost-effective way, thus enabling large scale integration of RES. Future tests to be carried out in a new, state of the art laboratory environment will bring additional added-value to the validation of the proposed concepts and tools.

Estimation of the flexibility range in the transmission-distribution boundary

The smart grid concept increases the observability and controllability of the distribution system, which creates conditions for bi-directional control of Distributed Energy Resources (DER). The high penetration of Renewable Energy Resources (RES) in the distribution grid may create technical problems (e.g., voltage problems, branch congestion) in both transmission and distribution systems. The flexibility from DER can be explored to minimize RES curtailment and increase its hosting capacity. This paper explores the use of the Monte Carlo Simulation to estimate the flexibility range of active and reactive power at the boundary nodes between transmission and distribution systems, considering the available flexibility at the distribution grid level (e.g., demand response, on-load tap changer transformers). The obtained results suggest the formulation of an optimization problem in order to overcome the limitations of the Monte Carlo Simulation, increasing the capability to find extreme points of the flexibility map and reducing the computational effort.

An innovative strategy for power system restoration using utility scale wind parks

This paper presents an innovative Power System Restoration (PSR) that exploits the flexibility offered by large offshore wind parks, in particular with HVDC connection with Voltage Source converter (VSC) technology, to support restoration following a black out in a typical transmission grid. Restoration sequences comparing different strategies in a VHV AC network with conventional generation (thermal units and hydro units) were implemented for two cases: with and without the participation of a large offshore wind farm in the restoration plan. In order to evaluate the benefit of using Utility scale Wind Parks to support PSR, a typical transmission network with all its models (including HVDC link with DC converter) was implemented in EUROSTAG simulation platform.

Mitral regurgitation during a myocardial infarction – New predictors and prognostic significance at two years of follow-up

Aims: Ischemic Mitral Regurgitation (MR) has early prognostic impact in Myocardial Infarction (MI). Its medium-term importance, especially of mild MR, has not been established. Purpose: to determine new clinical/analytical predictors of MR in MI-patients and establish its prognostic value during two-year follow-up [endpoints: mortality, decompensated heart failure (dHF)].Methods and Results: 796 patients admitted for MI (age 68.8±13.4, 63.2% males, 44.6% STEMI). Data: Admission analytical study, risk scores, coronariography, pre-discharge echocardiogram. Patients followed for two years. Clinical/analytical predictors of pre-discharge MR assessed. Predictive model for presence of pre-discharge MR included GRACE for intra-hospital mortality [IHM](OR=1.008, p<0.001), glomerular filtration rate (GFR)[OR=0.993, p=0.048], admission haemoglobin (OR=0.84, p=0.003). In univariate analysis, moderate-severe MR predicted 2-year mortality (OR=3.32, p<0.001), but not dHF. Two year mortality rate was proportional to severity of pre-discharge MR. Mild MR (vs. no MR) associated with higher risk for 2-year mortality (OR=2.04, p=0.014) and re-admission for dHF (OR=2.55, p=0.001). Predictive model for 2-year mortality included MR severity (OR=1.42, p=0.033) and GRACE for IHM (OR=1.023, p<0.001).Conclusion: GRACE score for IHM, GFR and admission haemoglobin independently predicted risk for pre-discharge MR. MR, including its milder form, was an independent predictor of 2-year mortality, adding prognostic power to GRACE score.

The challenges of estimating the impact of distributed energy resources flexibility on the TSO/DSO boundary node operating points

Abstract The increasing penetration of renewable energy sources characterized by a high degree of variability and uncertainty is a complex challenge for network operators that are obligated to ensure their connection while keeping the quality and security of supply. In order to deal with this variable behavior and forecast uncertainty, the distribution networks are equipped with flexible distributed energy resources capable of adjusting their operating point to avoid technical issues (voltage problems, congestion, etc.). Within this paradigm, the flexibility that, in fact, can be provided by such resources, needs to be estimated/forecasted up to the transmission network node (primary substation) and requires new tools for TSO/DSO coordination. This paper addresses this topic by developing a methodology capable of finding the flexibility area while taking into account the technical grid constraints. The proposed approach is based on the formulation of a single optimization problem which is run several times, according with the expected precision for the flexibility area estimation. To each optimization problem run, a different objective function belonging to a family of straight lines is assigned. This allows exploring the active and reactive power flow limits at the TSO/DSO boundary nodes – which define the flexibility area. The effectiveness of the proposed model has been evaluated on two test networks and the results suggest a step forward in the TSO/DSO coordination field. Nevertheless, further investigations to study the effect of assets with discrete control nature (e.g., on load tap changers – OLTC, capacitor banks) on the occurrence of disjoint flexibility areas should be carried.

Predição do risco de evento cerebrovascular após um enfarte agudo do miocárdio

INTRODUCTION Patients with coronary artery disease (CAD) are at increased risk of stroke. The aim of this study was to analyze the prognostic accuracy of selected clinical and laboratory variables in stroke risk prediction following discharge after myocardial infarction (MI). METHODS We analyzed 404 consecutive patients (aged 68.1±13.7 years; 63.4% male; 37.4% with diabetes) without previous stroke who were discharged in sinus rhythm after being admitted for MI. The following data were collected: cardiovascular risk factors, admission blood glucose (BG), HbA1c, creatinine, peak troponin levels; glomerular filtration rate (GFR) by the MDRD formula; maximum Killip class; GRACE score for in-hospital and 6-month mortality; and extent of CAD. Patients were followed for two years and each variable was tested as a possible predictor of cerebrovascular events (stroke or transient ischemic attack [TIA]). RESULTS During follow-up, 27 patients were admitted for stroke or TIA. The presence of diabetes, hypertension, dyslipidemia and previously known CAD, type of MI (STEMI vs NSTEMI) and extent of CAD did not predict cerebrovascular risk. The following variables were associated with higher stroke risk: GFR <60ml/min/m(2) (p=0.029, OR 2.65, 95% CI 1.07-6.55); maximum Killip class >1 (p=0.025, OR 2.71, 95% CI 1.10-6.69); GRACE in-hospital mortality >180 (p=0.001, OR 4.09, 95% CI 1.64-10.22); admission BG >140 mg/dl (p=0.001, OR 5.74, 95% CI 1.87-17.58); GRACE 6-month mortality >150 (p=0.001, OR 4.50, 95% CI 1.80-6.27); and peak troponin >42ng/ml (p=0.032, OR 2.64, 95% CI 1.06-6.59). Logistic regression analysis produced a model with the predictors GRACE 6-month mortality >150 (OR 3.26; p=0.014) and admission BG >7.7mmol/l (OR 4.09; p=0.017) that fitted the data well (Hosmer-Lemeshow: p=0.916). DISCUSSION/CONCLUSIONS In patients with MI, variables known to be predictors of in-hospital mortality, including admission BG, renal function, acute heart failure and GRACE score, were found to be useful predictors of stroke during 2-year follow-up. While both GRACE score for 6-month mortality >150 and admission BG >7.7 mmol/l were independent predictors of stroke, CV risk factors, previously known CAD, and extent of CAD assessed by coronary angiography did not improve stroke risk prediction. This study highlights the need for even more aggressive secondary prevention in patients most at risk.