Using Effective Generator Impedance for Forced Oscillation Source Location

Locating the sources of forced low-frequency oscillations in power systems is an important problem. A number of proposed methods demonstrate their practical usefulness, but many of them rely on strong modeling assumptions and provide poor performance in certain cases for reasons still not well understood. This paper proposes a systematic method for locating the source of a forced oscillation by considering a generator's response to fluctuations of its terminal voltages and currents. It is shown that a generator can be represented as an effective admittance matrix with respect to low-frequency oscillations, and an explicit form for this matrix, for various generator models, is derived. Furthermore, it is shown that a source generator, in addition to its effective admittance, is characterized by the presence of an effective current source thus giving a natural qualitative distinction between source and nonsource generators. Detailed descriptions are given of a source detection procedure based on this developed representation, and the method's effectiveness is confirmed by simulations on the recommended testbeds (eg. WECC 179-bus system). This method is free of strong modeling assumptions and is also shown to be robust in the presence of measurement noise and generator parameter uncertainty.Comment: 13 page

Using Passivity Theory to Interpret the Dissipating Energy Flow Method

Despite wide-scale deployment of phasor measurement unit technology, locating the sources of low frequency forced oscillations in power systems is still an open research topic. The dissipating energy flow method is one source location technique which has performed remarkably well in both simulation and real time application at ISO New England. The method has several deficiencies, though, which are still poorly understood. This paper borrows the concepts of passivity and positive realness from the controls literature in order to interpret the dissipating energy flow method, pinpoint the reasons for its deficiencies, and set up a framework for improving the method. The theorems presented in this paper are then tested via simulation on a simple infinite bus power system model.Comment: Submitted to PESGM1

Network Topology Invariant Stability Certificates for DC Microgrids with Arbitrary Load Dynamics

DC microgrids are prone to small-signal instabilities due to the presence of tightly regulated loads. This paper develops a decentralized stability certificate which is capable of certifying the small-signal stability of an islanded DC network containing such loads. Utilizing a novel homotopy approach, the proposed standards ensure that no system eigenmodes are able to cross into the unstable right half plane for a continuous range of controller gain levels. The resulting "standards" can be applied to variety of grid components which meet the specified, but non-unique, criteria. These standards thus take a step towards offering plug-and-play operability of DC microgrids. The proposed theorems are explicitly illustrated and numerically validated on multiple DC microgrid test-cases containing both buck and boost converter dynamics

Influence of injected metoprolol and high-dosage statin therapy on some markers of early myocardial remodeling in acute coronary syndrome

Aim of the study was to evaluate of the effect of intravenous metoprolol tartrate administered before percutaneous coronary intervention (PCI), in combination with long-term use of high-dose atorvastatin, on dynamic changes in biochemical and ultrasound markers, as well as on the outcomes of early myocardial remodeling in patients with ST-segment elevation acute myocardial infarction (MI). Material and methods. A prospective randomized clinical trial included 136 patients with MI. The terms of the study were 35 ± 5 (from 30 to 40) days from the moment of admission to the hospital. The first group (control) included patients who received standard interventional and drug treatment at the hospital and outpatient post-infarction stages. The second group (exposure) included individuals who received a single intravenous injection of metoprolol tartrate before PCI, followed by a switch to oral metoprolol succinate on a systemic basis. These patients, as well as in the first group, regularly received all components of the basic drug therapy, including atorvastatin at a dose of 80 mg per day for one month from the onset of MI. On the 1st-2nd day of MI and a month later, plasma levels of biochemical biomarkers were assessed in patients; on the 1st, 10th day and one month later, ultrasound markers were evaluated using echocardiography. Upon the follow-up clinical outcomes of post-infarction myocardial remodeling were analyzed. Results. We confirmed that the use of a single intravenous injection of metoprolol tartrate (5–15 mg) in acute myocardial infarction before PCI against the background of high-dose atorvastatin (80 mg/day) for one month from the onset of myocardial infarction demonstrated convincing efficacy in relation to the prevention of early myocardial remodeling, which we assessed by the dynamics of ultrasound markers, as well as by the plasma activity of all three key biochemical markers in comparison with the control group of patients. Conclusions. The use of a single intravenous injection of metoprolol tartrate in the acute phase of MI against the background of high-dose atorvastatin for one month from the onset of MI is a highly effective pharmacological method for preventing the formation of early postinfarction myocardial remodeling

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements