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Recent studies have shown the potential benefits of grid-forming (GFM) converters and their capability of stabilizing a power system with high penetration of power electronics-based generation. A crucial aspect of any GFM converter control strategy will be the handling of fault-ride through (FRT) scenarios, which converters for generation sources will face regularly in the field. In this article, an FRT strategy for GFM converters is proposed, which respects the converter hardware limitations (i.e., current limitations) while maintaining GFM behavior even during “protective” operating modes. The FRT strategy addresses both symmetrical and asymmetrical faults and is compliant with recently proposed draft grid codes requirements published by the British system operator NGESO. The issues related to FRT of GFM converters are first discussed in detail, then a proper strategy is presented and its effectiveness is demonstrated by means of an extensive power-hardware-in-the-loop measurement campaign, showing its efficacy even against severe fault conditions.

Grid inverters need a synchronization algorithm to connect with the grid which is often a phase-locked loop (PLL). Conventionally, small-signal models are used to tune such PLL and to assess stability in steady state; however, they can misjudge the dynamic behaviors, in particular, during large phase perturbation due to grid faults. To address this issue, a more accurate model of PLL-based synchronization of the grid inverter with second-order approximation terms valid not only for the steady state but also for phase transients has been developed in this paper. Stability criterion based on the developed model has been proposed to assess the harmonic stability during phase perturbations. The model accuracy and the effectiveness of the stability criterion have been comprehensively evaluated and validated by simulation and experiments.

State-of-the-art grid-connected converters can be classified as “grid-following,” meaning that they require a dedicated synchronization unit in order to inject active and reactive currents into the grid. Recently, other converter control concepts have been proposed in the literature, such as the synchronverter, which can instead achieve synchronization without a dedicated unit and, within its physical limitations, make the converter behave as an ideal voltage source. Since it should be expected that the grid-connected converters having different control philosophies will coexist for many years, in this article, the interaction among the converters operating nearby are addressed. First, the component connection method (CCM) technique is introduced, as a means for obtaining the state-space representation of a complex system with several units operating nearby. Due to the complexity of the grid and the difficulty in obtaining its exact representation, $\mu $ -analysis is adopted in this article for assessing the robust stability of the converter under different operating conditions, according to a defined set of plant uncertainties. Simulation results and experimental tests in a laboratory environment by means of a power hardware-in-the-loop (PHIL) test bench are performed to demonstrate the validity of the presented analysis.

The increasing penetration of converter-based generation in many power systems around the world has sparked a discussion about how to operate these power systems with the usual levels of efficiency, reliability and cost-effectiveness. Current grid-following converter-based generators have proven to run stably in parallel to one another, even if there are thousands of them connected in a power system, and even in very small isolated power systems with extremely low system inertia. Discussions around the necessity of additional converter performance, usually under the ‘grid-forming’ and ‘Virtual Synchronous Machines’ concepts, have recently been transferred from the academic sphere to national and international industry fora. Formal discussions have started in Great Britain, in Germany and at ENTSO-E level. However, there is still a lot of uncertainty about the real and not simulated performance of grid-forming converters, whilst the needs case for requiring this radically different control method has not been adequately justified. With the present paper we raise key questions that will serve towards an objective discussion about power system needs, grid infeed technologies and their interaction.

Neonatal subcutaneous fat necrosis (SCFN) is a transient, generally benign panniculitis that presents within several weeks of life and occurs mostly in term or post-term newborns who have a history of intrauterine or perinatal distress. It is usually a self-limited condition. Hypercalcemia is a rare but serious complication of SCFN and needs prolonged follow-up. The etiopathogenesis of both subcutaneous fat necrosis in newborn and the resultant hypercalcemia is poorly understood. We describe a classic presentation of SCFN that led to a severe hypercalcemia refractory to standard treatment. This case shows how a single dose of neridronic acid was safe and effective in managing severe hypercalcemia unresponsive to conventional therapy without hypocalcemic rebounds.

Recent studies have shown the importance of considering the synchronization mechanism of a grid-connected converter in its stability assessment. Moreover, it is often taken for granted that synchronization units of grid-connected converters operating nearby may interact with each other, but this topic has not yet been deeply investigated in the literature. In this paper, the interaction between synchronization units of grid-connected converters is investigated by means of impedance-based analysis. A multiple-inputs multiple-outputs analysis is required and a stability margin is introduced, based on the calculation of the norm of the equivalent grid impedance and equivalent output admittance of the converter. The sensitivity of the stability margin to parameter variations (e.g., grid impedance, bandwidth of the synchronization loop of each converter) is assessed by means of Monte Carlo simulations. Time-domain simulations as well as experimental results in a laboratory environment using a power hardware-in-the-loop test bench are performed so as to validate the presented frequency-domain analysis.

Recent studies have shown how synchronization units of converters operating nearby may interact with each other, affecting the stability of the system. Synchronverters are able to self-synchronize to the grid without the need of a dedicated unit because they can reproduce the power synchronization mechanism of synchronous machines. Recently, the robust stability of a synchronverter has been investigated by means of structured singular values (commonly called $\mu$ -analysis). In this paper, $\mu$ -analysis is performed to investigate how the robust stability of a synchronverter is affected by the presence of another converter of the same type operating in parallel. It is demonstrated that the parallel operation of synchronverters reduces their robust stability and a possible solution is proposed, based on the implementation of virtual impedances in the control algorithm. An accurate state-space model of the system under study is developed by adopting the component connection method and the robust stability analysis is validated against time-domain simulations in MATLAB/Simulink/PLECS and experimental results with a power-hardware-in-the-loop test bench.

Synchronverters have gained interest due to their capability of emulating synchronous machines, offering self-synchronization to the grid. Despite the simplicity of the control structure, the adoption of an LCL filter makes the overall model complex again, posing questions regarding the tuning of the synchronverter and its robustness. The multi-inputs multi-outputs (MIMO) formulation of the problem requires multivariable analysis. In this paper, the effects of control parameter and grid conditions on the stability of the system are investigated by means of structured singular values (or $\mu$ -analysis). A step-by-step design procedure for the control is introduced based on a linearized small-signal model of the system. Then, the design repercussions on the stability performance are evaluated through the performed robustness analysis. The developed linearized model is validated against time-domain simulations and laboratory experiments. These have been carried out using a power hardware-in-the-loop test bench, which allows as to test the synchronverter under different grid conditions. As a conclusion, this paper offers a simple guide to tune synchronverters but also a theoretical solid framework to assess the robustness of the adopted design.

Grid converters synchronized by phase-locked loops (PLLs) could suffer from stability problems, especially being connected to a weak grid or high penetration of converters. The existing literature assesses the stability of the paralleled PLL-synchronized converters at the same point of common coupling (PCC) using identical control and system parameters. However, in an actual grid, the parameters of grid converters are normally different due to different manufacturers. In this regard, this article aims to study the stability indices and margins of two PLL-synchronized converters with different parameters, particularly with different PLL bandwidths and power injections. The main purpose of this article is to provide a general design guidelines of PLL bandwidths of two converters (can be extended to two wind/solar farms) for stable operation in practical grids. The state-space model of the PLL-synchronized converter based on the component connection method is developed and eigenvalue-based analysis is used to investigate the interactions between the two converters. Moreover, the stability borders of two PLL-synchronized converters using different PLL bandwidths and power setpoints are studies. Monte Carlo simulations and experimental results are provided to validate the effectiveness of the developed model and theoretical analysis.

The potentials of grid-forming (GFM) converters in stabilizing a power system with high penetration of power electronics-based generation have been recently investigated. Due to their intrinsic behaviour of voltage source behind impedance, a crucial aspect of any GFM converter control strategy will be the handling of fault-ride through (FRT) scenarios. This paper proposes a FRT strategy for GFM converters, which respects the converter hardware limitations (i.e. current limitations) even under sever fault conditions, while maintaining GFM behavior before, during, and after the fault. The presented strategy addresses both symmetrical and asymmetrical faults, and is compliant with recently proposed draft grid codes requirements published by the British system operator NGESO. The issues related to FRT of GFM converters are first discussed in detail, and a comprehensive overview on the solutions proposed in the literature is reported. Then a proper strategy is presented, and its effectiveness is demonstrated by means of simulations and Power-Hardware-in-the-Loop (PHIL) measurements in a laboratory environment.

In the last decade, the concept of grid-forming (GFM) converters has been introduced for microgrids and islanded power systems. Recently, the concept has been proposed for applications in wider and interconnected transmission networks, and several control structures have thus been developed, giving rise to discussions about the characteristics and the functionalities of such converters. In this paper, an overview of control schemes for GFM converters is provided. By identifying the main subsystems in respect to their functionalities, a generalized control structure is derived and different solutions for each of the main subsystems composing the controller are analyzed and compared. Subsequently, several selected open issues and challenges regarding GFM converters, i. e., angle stability, fault ride-through (FRT) capabilities, and transition between islanded to grid-connected modes are discussed. Perspectives on challenges and future trends are lastly shared.

Early detection of chronic obstructive pulmonary disease (COPD) exacerbations using telemonitoring of physiological variables might reduce the frequency of hospitalization.To evaluate the efficacy of home monitoring of lung mechanics by the forced oscillation technique and cardiac parameters in older patients with COPD and comorbidities.This multicenter, randomized clinical trial recruited 312 patients with Global Initiative for Chronic Obstructive Lung Disease grades II to IV COPD (median age, 71 yr [interquartile range, 66-76 yr]; 49.6% grade II, 50.4% grades III-IV), with a history of exacerbation in the previous year and at least one nonpulmonary comorbidity. Patients were randomized to usual care (n = 158) or telemonitoring (n = 154) and followed for 9 months. All telemonitoring patients self-assessed lung mechanics daily, and in a subgroup with congestive heart failure (n = 37) cardiac parameters were also monitored. An algorithm identified deterioration, triggering a telephone contact to determine appropriate interventions.Primary outcomes were time to first hospitalization (TTFH) and change in the EuroQoL EQ-5D utility index score. Secondary outcomes included: rate of antibiotic/corticosteroid prescription; hospitalization; the COPD Assessment Tool, Patient Health Questionnaire-9, and Minnesota Living with Heart Failure questionnaire scores; quality-adjusted life years; and healthcare costs. Telemonitoring did not affect TTFH, EQ-5D utility index score, antibiotic prescriptions, hospitalization rate, or questionnaire scores. In an exploratory analysis, telemedicine was associated with fewer repeat hospitalizations (-54%; P = 0.017).In older patients with COPD and comorbidities, remote monitoring of lung function by forced oscillation technique and cardiac parameters did not change TTFH and EQ-5D. Clinical trial registered with www.clinicaltrials.gov (NCT 01960907).

The stability of a converter synchronized to the grid voltage through a phase-locked loop (PLL) is negatively affected by the presence of another converter with the same synchronization principle operating nearby, especially under weak grid conditions. However, while weak grids are critical for PLL-based converters, virtual synchronous machines (VSMs) are instead suitable for such applications. In fact, it can be proven that the robust stability of a VSM is enhanced when it is connected to a weaker grid. Recent studies have investigated the parallel operation between VSMs, but the parallel operation between a VSM and a PLL-based converter has not yet been properly addressed in the literature. In this paper, this topic is investigated by means of eigenvalue analysis, showing the positive effects on the stability of a PLL-based converter due to the presence of a synchronverter operating nearby. The model of the system under study is obtained adopting the component connection method (CCM), and time-domain simulations as well as experimental results using a power hardware-in-the-loop (PHIL) test bench are reported to demonstrate the validity of the performed analysis.

The synchronization of grid converters through phase-locked loop (PLL) could cause stability issues especially when the penetration of grid converters is high. Most of the works in the literature consider all the grid converters with identical system parameters. In contrast, this paper aims at studying the stability issues of two PLL-synchronized grid converters with different PLL bandwidths and power injections and revealing the interactions between two converters caused by the band-width and power differences. Moreover, the relationship between power injection and PLL bandwidth of the grid converter is investigated. For these studies, a state-space model based on the component connection method (CCM) is developed, which is scalable for the power system with large numbers of grid converters. Eigenvalue-based analysis is carried out to study the grid converters’ interactions as well as power/bandwidth relation under various scenarios. Experimental results are given to validate the effectiveness of the model and theoretical analysis.

Serum biomarkers of myocardial damage are commonly used in babies after perinatal asphyxia. We present a case report of a persistently troponin I elevation without evidence of clinical or instrumental signs of myocardial ischaemia in a baby with perinatal asphyxia. When the blood was mixed with polyethylene glycol we found that the troponin I levels were falsely elevated due to interfering antibodies. This case shows that analytical errors may still occur despite modern immunoassay systems and underlines the need for further investigations to identify false-positive values in case of disagreement between clinical conditions and laboratory values.

Early-onset sepsis (EOS) is responsible for an important fraction of neonatal morbidity and mortality all over the world. The aim of this study was to assess whether presepsin (P-SEP) can be a more accurate biomarker of EOS compared with pro-calcitonin (PCT) and C-reactive protein (CRP). Consecutive preterm neonates (

Virtual Synchronous Machines (VSMs) have been proposed during the last decade as possible solutions for integrating the increasing amount of power electronics-based grid connected converters in the utility grid. One of their main characteristics is the ability to self-synchronize themselves to the main grid without the need of a dedicated unit, since they can reproduce the power synchronization mechanism of a synchronous machine (SM). Different control strategies have been proposed in the literature based on the aforementioned principle. The aim of this work is to provide a generalized formulation of a power synchronization based (PSB) control algorithm, outlining the different loops constituting the control and to give an overview of the solutions proposed in the literature. Similarities along with advantages and drawbacks of each formulation are highlighted in the paper and time-domain simulation in MATLAB/SimulinkIPLECS are performed to compare the performance of the different solutions.

During the last decade virtual synchronous machines (VSMs) have been intensively investigated and plenty of control strategies have been proposed as possible implementations. Some of the proposed control strategies aim to reproduce the inertia of a synchronous machine (SM), but rely on a dedicated unit for the synchronization to the main grid. However, one of the most appealing features of a SM is its ability to self-synchronize itself to the grid thanks to the intrinsic power synchronization mechanism. The Synchronous Power Control (SPC) is among the control strategies proposed in the literature based on the power synchronization mechanism. In this paper, the aforementioned control is deeply investigated. Its concept is first introduced and a small-signal model of an SPC-based grid connected converter is developed. Subsequently, a comprehensive parameter sensitivity analysis is performed in order to identify the effects of control parameters variations on the eigenvalues of the system under different grid conditions. Time-domain simulations in MATLAB/Simulink/PLECS confirm the validity of the developed frequency-domain model.

It has been recently demonstrated that synchronization units of converters operating nearby may interact with each other affecting the stability of the system. Synchronverters have gained interest from the research community due to their capability of emulating the behaviour of synchronous machines (SMs), therefore being able to self-synchronize themselves to the grid without the need of a dedicated unit. However, parallel operation of synchronverters has not yet been properly investigated in literature. In this paper this topic is investigated by means of eigenvalue analysis. An accurate model of the system under study is developed by adopting the component connection method (CCM) technique, which allows to easily obtain the state-space representation of a complex system. It is demonstrated that the stability of the synchronverter could be negatively affected by the presence of another synchronverter operating in parallel, unless proper measures are taken. The developed frequency-domain model is validated against time-domain simulations in MATLAB/Simulink/PLECS and experimental results with a power-hardware in the loop (PHIL) test bench.

Aim: To assess the electrocardiography and echocardiography changes during therapeutic hypothermia and rewarming period in encephalopathic infants with long-term adverse neurological outcome. Methods: Prospective multicentre longitudinal study. We included 64 consecutive infants with moderate or severe hypoxic ischaemic encephalopathy undergoing therapeutic hypothermia who had 18–24 month-outcome data. We analysed electrocardiography and heart rate changes before, during and after therapeutic hypothermia. Superior vena cava flow, left ventricular cardiac output and stroke volume were studied using echocardiography during and immediately after therapeutic hypothermia. An abnormal outcome was defined as death or moderate/severe disability at 18–24 months. Results: Neonates with higher superior vena cava flow pre-rewarming had significantly higher odds of documented long-term adverse outcome when compared to newborns with good outcome (OR 1.57; 95%CI, 1.1–1.78; p = 0.01 after adjustment). QTc and RR intervals were significantly longer at 12, 24, 36 and 48 h in infants with good outcome compared with those with adverse outcome (p < 0.001). During therapeutic hypothermia, infants with poor outcome had a higher heart rate at 12, 24, 36, 48, 60 h after birth compared with those with good outcome (p < 0.001). From 36 h on, heart rate gradually increased and RR and QTc intervals progressively shortened with values back to normal after rewarming. Conclusions: Infants with hypoxic ischaemic encephalopathy who have adverse neurological outcome show a preferential cerebral blood flow redistribution during therapeutic hypothermia. Infants with poor outcome have higher heart rate and shorter RR and QTc intervals during therapeutic hypothermia.

Robots have the potential to support care and independence of older adults. The ENRICHME project is developing an integrated system composed of a robot, sensors and a networking care platform, aiming at assisting older adults with MCI in their home environment. This paper reports findings of the tests performed on a sample of MCI users and their caregivers, with the first version of the ENRICHME system, in a controlled environment.

Interactions between power electronic converters are typically investigated by means of impedance-based model analysis. The effects of the PLL are usually neglected, but recent studies have shown the importance of including those effects for stability analysis purposes. This paper focuses on the investigation of interactions between synchronization units of converters operating in parallel. The impedance-based approach is used for the investigation in the frequency-domain. The converters are supposed to share the same point of common coupling (PCC) and the characteristic of the grid at the connection point is crucial for determining the effects of the interactions between the operating units. In order to isolate the effects of the synchronization, the converters is modeled as a current sources, whose reference currents are calculated using the angle detected by their PLLs. Time-domain simulations are performed as well as experimental laboratory tests in order to validate the presented analysis.

Evidence of clinical benefit and cost-effectiveness from daily symptom and simple telemonitoring in COPD is unproven. The CHROMED study explored the effect of telemonitoring in older people with COPD and significant co-morbidity who performed daily forced oscillation measurements via RESMON PRO DIARY to identify early physiological change associated with an exacerbation. Six centres in 5 countries randomised 312 people to 9 months telemonitoring (154) or daily symptom questionnaires (158). Each day the monitored group recorded symptoms, pulse, BP, oxygen saturation and airway resistance and reactance. An alert was generated if results exceeded pre-determined parameters and the participant was contacted by their local clinical centre to consider additional treatment. Baseline characteristics were evenly matched: mean age 71 years, FEV1 1.3L (50% predicted) and SGRQ score 49. 61% of subjects had 2+ exacerbations and 42% had been hospitalised in the previous year. Time to first hospitalisation did not differ albeit the monitoring group had fewer hospitalisations (79 vs 103; p=ns) and days in hospital (329 vs. 650; p=ns). However, subjects hospitalized with an AE COPD in the previous year (n=128) had a lower hospitalisation rate (p

CHROMED (clinical trials for elderly people with multiple diseases, www.chromed.eu) is an EU-funded project involving 9 partners from 7 European countries aimed at evaluating the impact of a new home care approach to reduce costs and improve quality of life in elderly patients with COPD and comorbidity. The trial involves 300 patients with a prior history of exacerbations randomly assigned to a monitoring or observational arm. Monitored patients performed daily self-assessment of lung mechanics with a FOT (Forced Oscillation Technique) device (RESMON PRO DIARY, Restech srl, Italy) and completed a symptom diary card on touchscreen device (HOME PATIENT MONITOR, EBM srl, Italy). Any detected worsening in lung mechanics generated an alert triggering a phone interview directed at verifying the patient's status and optimizing treatment. By the end of March 2015, 70 monitored patients had completed the trial resulting in 16198 measurements with an adherence of 90.1%. Based on lung mechanics, 311 worsening events were detected, resulting in 0.65±0.3 alerts/patient/month. At least one major symptom (dyspnea, sputum purulence and volume) was reported in 70% of events and 41% were associated with an exacerbation according to diary cards (Seemungal et al., Am J Respir Crit Care Med 1998). A total of 77 exacerbations were confirmed during the phone interview and treated, but 48% of them were not associated with an exacerbation defined by diary cards only. These results suggest that a significant percentage of exacerbations cannot be identified by diary cards only. Self-assessment of lung mechanics using FOT provides complementary information which can be useful to manage COPD patients at home.