An Anti-Islanding Method for Single-Phase Inverters Based on a Grid Voltage Sensorless Control

The detection of the islanding condition of a distributed generation (DG) system is crucial for safety reasons, as discussed in the IEEE standards and specifically required by some national codes. Several anti-islanding methods that are resident in the inverter have been investigated and classified as passive (measurement of the natural effects of islanding) or active (based on the measurement of the effects due to transients or harmonics deliberately introduced in the system). In case the power drained by the load matches the power generated by the DG inverter, the effect of islanding is small, and the passive methods fail. However, the active methods, which have been developed to overcome these limits, create disturbances that can interact with those generated by other DG systems. In this paper, a new anti-islanding method is proposed. It exploits the natural sensitivity of a grid-voltage sensorless control to disturbances to highlight the islanding condition. The adopted grid-voltage sensorless control is adapted to a single-phase system with the use of resonant controllers based on the internal model control law: resonant-controller-based observer results. Then, a Kalman-filter-based algorithm is used to detect the islanding condition based on the energy mismatch between the estimated third and fifth harmonics and the real ones. Experimental results support the analysis     

A passivity-based multilevel active rectifier with adaptive compensation for traction applications

The control of a single-phase multilevel H-bridge rectifier suitable for traction applications is considered. Such a converter often presents instability problems making difficult its design and uncertain its behavior. In this paper the use of a passivity-based controller is experimentally investigated. Such a controller achieves stability, unity power factor, good balancing between the two DC links, and satisfactory behavior even in the presence of load changes. A right choice of the damping parameters allows the fulfilling of system requirements in terms of DC-link voltage error and grid current distortion.     

Effect of stocking density on ewes' milk yield, udder health and microenvironment

Three groups of 12 lactating Comisana ewes were housed in separate rooms of the same building that contained straw-bedded pens with total areas of 12, 18 and 24 m2. The ewes were assigned to groups with different stocking densities: high (HSD, 1 m2/animal), medium (MSD, 1.5 m2/animal) or low (LSD, 2 m2/animal). The LSD treatment resulted in lower air concentrations of total microorganisms and coliform bacteria than the other two. Ewes in the LSD group gave greater yields of milk, total protein and fat than those in the other two groups. LSD treatment increased milk casein content and improved clotting time and clot firmness. LSD also resulted in ewes giving milk with lower somatic cell counts and smaller concentrations of mesophiles, psychrotrophs and faecal coliforms than MSD and HSD. Subclinical mastitis occurred in three ewes of the MSD groups and four ewes of the HSD group, while no cases were recorded in the LSD group. These results indicate that stocking density is a critical factor in dairy sheep housing and suggest that a space allocation < 2 m2/animal may adversely affect the performance and health of the lactating ewe.     

Analysis of distorted unbalanced waveforms in inverter drives

A new method is proposed for the analysis of waveforms in a three-phase system when both distortion and unbalance are present. The method makes it possible to obtain the positive and negative-sequence components of each harmonic system present in the three phases. This method provides a way to get information both on the degree of unbalance and on the distortion factors of the waveforms generated by pulsewidth-modulated inverters supplying induction motors     

Genetic algorithm-based design of the active damping for an LCL-filter three-phase active rectifier

Active rectifiers/inverters are becoming used more and more often in regenerative systems and distributed power systems. Typically, the interface between the grid and rectifier is either an inductor or an LCL-filter. The use of an LCL-filter mitigates the switching ripple injected in the grid by a three-phase active rectifier. However, stability problems can arise in the current control loop. In order to overcome them, a damping resistor can be inserted, at the price of a reduction of efficiency. The use of active damping by means of control may seem attractive but it is often limited by the use of more sensors compared to the standard control and also by a complex tuning procedure of the controllers. This paper introduces a new active damping method that does not require the use of more sensors. It consists of adding a filter on the reference voltage for the modulator. The tuning process of this filter is easily done, for a wide range of sampling frequencies, with the use of genetic algorithms. This method is used only for the optimum choice of the parameters in the filter and an on-line implementation is not needed. Thus the resulting active damping solution does not need new sensors or complex calculations. Moreover, in the paper particular attention is devoted to the susceptibility of the system in a high polluting environment.     

Etio-pathogenic considerations on the development of multiple bone cysts in the mandible. Report of a clinical case

A case of a mandibular cyst, missing of wall lining and containing some solid material is described. The histologic examination showed that this material consisted of osteofibrous tissue with regressive phenomena, inflammatory cells and hyperplastic nervous tissue. On the basis of clinical and histologic findings it is suggested to be a solitary cyst and the solid material due to a local response to an injury suffered by the patient who is a sport practitioner.     

A Comparative Analysis of Real-Time Algorithms for Power Signal Decomposition in Multiple Synchronous Reference Frames

The monitoring and rejection of voltage and current harmonics in power electronics applications such as power quality conditioners or distributed generation systems require correct estimation algorithms especially if the harmonic amplitudes are time varying. Power signal decomposition in multiple synchronous rotating reference frames (MSRFs) is considered one of the best solutions. The most commonly employed implementations of this signal transformation are based on phase-locked loops (PLLs), recursive discrete Fourier transforms (RDFT), or discrete Kalman filtering (DKF). In this paper, a rigorous analysis of the performance of these implementations has been carried out. Complete tests have been performed to evaluate the computational burden, the frequency domain response, and the tolerance to low frequency amplitude variations. The results make it possible to select the proper method depending on the requirements of each application.     

Effects of solar radiation and feeding time on behavior, immune response and production of lactating ewes under high ambient temperature

A 6-wk trial was performed with 40 late-lactation Comisana ewes, which were either exposed to or protected from solar radiation and fed either in the morning (EXPM, PROM) or afternoon (EXPA, PROA) during summer in a Mediterranean climate. Behavioral traits of ewes were recorded once per week from 0800 to 2000 h. Rectal temperature (RT) and respiration rate (RR) were measured twice weekly at 1430 h. The phytohemagglutinin (PHA) skin test was performed to induce nonspecific delayed-type hypersensitivity at d 10, 20, and 32 of the experiment. Jugular blood samples were taken from ewes at the beginning and at d 21 and 42 of the experiment. Ewe milk yield was recorded daily. Individual milk samples were analyzed weekly for milk composition, coagulating properties, somatic cell count (SCC) and polymorphonuclear neutrophil leukocyte counts (PMNLC) and every 2 wk for bacteriological characteristics. Solar radiation and the interaction of solar radiation x time of feeding had significant effects on rectal temperatures. EXPM ewes had higher rectal temperatures than EXPA ewes, which in turn exhibited higher RT compared with PROM and PROA ewes. EXP groups also had significantly higher respiration rates than PRO groups. Immune response was lower in EXPM ewes at d 10 and in EXPM, EXPA, and PROM animals at d 20 compared with PROA ewes. Exposure to solar radiation resulted in decreased plasma concentrations of alanine amino-transferase, alkaline phosphatase, potassium, and magnesium, as well as in increased levels of nonesterified fatty acids and aspartate amino-transferase. Milk yield and composition were not changed by exposure to solar radiation and time of feeding, but the EXPM treatment resulted in lower yields of casein and fat and reduced clot firmness compared with the three other treatments. Milk SCC was similar across treatments, but PMNLC was higher in EXPM than in PROM and PROA milk. EXPM animals also had the greatest amounts of total and fecal coliforms and of Pseudomonadaceae as well as the highest number of mastitis related pathogens in their milk. Results suggest that provision of shaded areas can play a major role in helping lactating ewes to minimize the adverse effects of high ambient temperatures on thermal balance and energy and mineral metabolism. Changing the time of feeding to late afternoon may be beneficial to exposed ewes in lowering their heat loads during the warmest hours of the day, thereby reducing the detrimental impact of thermal stress on immune function and udder health.     

Paget disease of the jaws. Review of the subject. Clinical-therapeutic considerations

Clinical and diagnostic findings of Paget's disease of the jaws are reported; up to date etiological and pathogenical hypotheses are presented. Laboratory data of increased P.A. as a marker of disease evolution is pointed out, particularly the relationship increasing hydroxyprolinuria, because the increase of a malignant transformation. Surgery, always modeling, is limited to cases of severe facial dysmorphosis associated or not with the local disturbance due to compression; in any case it is suggested to perform the surgery in the phases of inactivity of disease, to avoid local complications, such as hemorrhage a infection.