Three-phase current-limiting droop controlled inverters operating in parallel

A new current-limiting droop controller is proposed in this paper for three-phase inverters operating in parallel. Droop control is employed to ensure the proportional power sharing between the parallel inverters while an inherent current-limiting property is achieved through the control design. The current limitation is mathematically proven using nonlinear analysis of the closed-loop system which leads to the boundedness of each inverter current under a threshold value at all times. Furthermore, small-signal analysis is performed to examine the closed-loop system stability of two parallel inverters equipped with the proposed controller. The example of two parallel inverters is further exploited to validate the proposed controller through Matlab/Simulink simulation results

Factors associated with disease evolution in Greek patients with inflammatory bowel disease

BACKGROUND: The majority of Crohn's disease patients with B1 phenotype at diagnosis (i.e. non-stricturing non-penetrating disease) will develop over time a stricturing or a penetrating pattern. Conflicting data exist on the rate of proximal disease extension in ulcerative colitis patients with proctitis or left-sided colitis at diagnosis. We aimed to study disease evolution in Crohn's disease B1 patients and ulcerative colitis patients with proctitis and left-sided colitis at diagnosis. METHODS: 116 Crohn's disease and 256 ulcerative colitis patients were followed-up for at least 5 years after diagnosis. Crohn's disease patients were classified according to the Vienna criteria. Data were analysed actuarially. RESULTS: B1 phenotype accounted for 68.9% of Crohn's disease patients at diagnosis. The cumulative probability of change in disease behaviour in B1 patients was 43.6% at 10 years after diagnosis. Active smoking (Hazard Ratio: 3.01) and non-colonic disease (non-L2) (Hazard Ratio: 3.01) were associated with behavioural change in B1 patients. Proctitis and left-sided colitis accounted for 24.2%, and 48.4% of ulcerative colitis patients at diagnosis. The 10 year cumulative probability of proximal disease extension in patients with proctitis and left-sided colitis was 36.8%, and 17.1%, respectively (p: 0.003). Among proctitis patients, proximal extension was more common in non-smokers (Hazard Ratio: 4.39). CONCLUSION: Classification of Crohn's disease patients in B1 phenotype should be considered as temporary. Smoking and non-colonic disease are risk factors for behavioural change in B1 Crohn's disease patients. Proximal extension is more common in ulcerative colitis patients with proctitis than in those with left-sided colitis. Among proctitis patients, proximal extension is more common in non-smokers

Serum folate, homocysteine and colorectal cancer risk in women: a nested case–control study

Accumulating evidence suggests that folate, which is plentiful in vegetables and fruits, may be protective against colorectal cancer. The authors have studied the relationship of baseline levels of serum folate and homocysteine to the subsequent risk of colorectal cancer in a nested case–control study including 105 cases and 523 matched controls from the New York University Women's Health Study cohort. In univariate analyses, the cases had lower serum folate and higher serum homocysteine levels than controls. The difference was more significant for folate (P < 0.001) than for homocysteine (P = 0.04). After ad'justing for potential confounders, the risk of colorectal cancer in the subjects in the highest quartile of serum folate was half that of those in the lowest quartile (odds ratio, OR = 0.52, 95% confidence interval, CI = 0.27–0.97, P-value for trend = 0.04). The OR for the highest quartile of homocysteine, relative to the lowest quartile, was 1.72 (95% CI = 0.83–3.65, P-value for trend = 0.09). In addition, the risk of colorectal cancer was almost twice as high in subjects with below-median serum folate and above-median total alcohol intake compared with those with above-median serum folate and below-median alcohol consumption (OR = 1.99, 95% CI = 0.92–4.29). The potentially protective effects of folate need to be confirmed in clinical trials. © 1999 Cancer Research Campaig

Grid-supporting three-phase inverters with inherent RMS current limitation under balanced grid voltage sags

In this paper, a novel nonlinear droop control method is proposed for three-phase grid-supporting inverters that rigorously guarantees limited RMS value of the inverter current and closed-loop system stability under both normal grid conditions and balanced voltage sags. Contrary to the traditional dq frame approaches which align the inverter output voltage with the d axis, the proposed controller aligns the inverter current with the d axis resulting in the desired current limitation and detailed closed-loop system stability conditions. Inspired by the recently presented state-limiting PI controller and using nonlinear invariant set theory, it is rigorously proven that the RMS value of the inverter current is always limited below a given value, even during transients or faults, without requiring additional adaptive saturation units, as commonly applied in conventional approaches. Furthermore, analytic conditions for the controller parameter selection are provided to ensure asymptotic stability for the entire closed-loop grid supporting inverter for the first time without depending on particular values of the filter and line parameters. To verify the effectiveness of the proposed controller compared to existing current-limiting control methods, extensive simulation and experimental results of a three-phase inverter are provided under a normal grid and under different balanced voltage sag scenarios

Growth and feed efficiency of sea bass (Dicentrarchus labrax) juveniles reared in different stocking densities and feeding levels

National audienc

Deep sedation for endoscopic retrograde cholangiopacreatography

Sedation and analgesia comprise an important element of unpleasant and often prolonged endoscopic retrograde cholangiopacreatography (ERCP), contributing, however, to better patient tolerance and compliance and to the reduction of injuries during the procedure due to inappropriate co-operation. Although most of the studies used a moderate level of sedation, the literature has revealed the superiority of deep sedation and general anesthesia in performing ERCP. The anesthesiologist’s presence is mandatory in these cases. A moderate sedation level for ERCP seems to be adequate for octogenarians. The sedative agent of choice for sedation in ERCP seems to be propofol due to its fast distribution and fast elimination time without a cumulative effect after infusion, resulting in shorter recovery time. Its therapeutic spectrum, however, is much narrower and therefore careful monitoring is much more demanding in order to differentiate between moderate, deep sedation and general anesthesia. Apart from conventional monitoring, capnography and Bispectral index or Narcotrend monitoring of the level of sedation seem to be useful in titrating sedatives in ERCP

Do stocking density and feed reward level affect growth and feeding of self-fed juvenile European sea bass?

Survival, growth, nitrogen (N) and phosphorus (P) budgets and feeding behaviour were studied in groups of sea bass, Dicentrarchus labrax L., that fed using self-feeders with different feed reward and maintained at different densities (up to 35 kg m(-3) or 500 fish tank(-1)). The experiment was conducted in 500-1 indoor tanks under ambient conditions of light and temperature during two successive years. In the first year (experiment I), fish (5.5 +/- 0.1 g) were separated into five groups according to stocking density (50, 200 or 500 fish tank(-1)) and reward (R=0.6 g trigger(-1)) level: 50:R, 200:R, 200:4R, 500:R and 500:10R. Both increases in stocking density and in feed reward affected negatively all the studied parameters concerning growth and feed efficiency (FE). In the second year (experiment II), the experiment was repeated with fish of similar weight (5.3 +/- 0.0 g), which were held under the following four feeding protocols: 50:0.5R, 50:R, 500:0.5R and 500:R. The lowest feed reward fish groups presented better tendencies in growth and feed efficiency independent of stocking density. Survival was high in all feeding regimes in both experiments, but at high density (500 fish tank(-1)), some mortalities (<4%) were observed. Also in both experiments, feeding rhythm was affected by stocking density, but not by reward levels. Thus, although fish presented a typical diurnal activity, they restricted their feed demands at the first and late hours of daylight (08:00-09:00 and 19:00 h) when held in the lowest stocking density, while in high density they did not

Modeling of DC-Side Dynamics in PV/Battery Grid-forming Inverter Systems

The DC-side dynamics of two-stage grid-forming (GFM) inverters are often neglected or oversimplified in power system studies, although they play a vital role in stability. Detailed models for the primary source and power converter are not practical for complexity reasons, leading usually to DC side representations that omit critical aspects such as the operational limits. To bridge this gap between accuracy and simplicity, this paper proposes for the first time an equivalent model for the DC side dynamics of GFM systems that captures all important dynamics and limits in a simple formulation. The model supports either batteries or photovoltaic arrays as a primary source and is easily parameterizable with minimal information, thus proving a useful tool for grid stability studies. Time-domain simulations validate the proposed equivalent model