Fuzzy logic damping controller for FACTS devices in interconnected power systems

Fuzzy controllers are designed for flexible AC transmission systems (FACTS) in interconnected power systems. Two typical FACTS devices, a static synchronous compensator (STATCOM) and a unified power flow controller (UPFC), are used as examples to show that FACTS devices with well-designed fuzzy controllers can significantly improve the dynamic behavior of interconnected power systems.published_or_final_versio

Effect of hydraulic system models on power system transient stability analysis

The dynamic models of hydraulic system used in power system transient stability analysis are presented. The dynamic characteristic of turbines and conduits are studied in detail. Different models taking elastic or rigid water-hammers into consideration are established. Together with the conventional models of the power system, the power system transient stability analytical software is improved. Using the updated software, the dynamic process of Three Gorges power station and the power system interconnected with it is analyzed for disturbance. The effect of different hydraulic system models in transient stability is compared and discussed.link_to_subscribed_fulltex

Study on the effect of hydraulic system models on power system dynamic stability analysis

The dynamic models of hydraulic system used in power system dynamic stability analysis are presented. Different models considering elastic or rigid-hamming are established. Together with the conventional models of the power system, the power system dynamic stability analytical software is improved. Using the updated software, the low frequency oscillation of the Three Gorges power station and the power system interconnected with it is analyzed. The effect of different hydraulic system models on dynamic stability are compared and discussed.link_to_subscribed_fulltex

Appication of unified power flow controller in interconnected power systems-modeling, interface, control strategy and case study,”

Abstract-In this paper, a new power frequency model for unified power flow controller (UPFC) is suggested with its dc link capacitor dynamics included. Four principal control strategies for UPFC series element main control and their impacts on system stability are discussed. The main control of UPFC series element can be realized as a combination of the four control functions. The supplementary control of UPFC is added for damping power oscillation. The integrated UPFC model has then been incorporated into the conventional transient and small signal stability programs with a novel UPFC-network interface. Computer tests on a 4-generator interconnected power system show that the suggested UPFC power frequency model and the UPFC-network interface method work very well. The results also show that the suggested UPFC control strategy can realize power flow control fairly well and improve system dynamic performance significantly

Birth weight predicts response to vaccination in adults born in an urban slum in Lahore, Pakistan.

BACKGROUND: Substantial evidence exists linking small size at birth to later-life susceptibility to chronic disease. Evidence is also emerging that some components of immune function may be programmed in early life. However, this evidence is limited and requires confirmation. OBJECTIVE: We investigated the association between size at birth and response to vaccination in a cohort of 257 adults (mean age: 29.4 y; 146 men) born in an urban slum in Lahore, Pakistan, during 1964-1978. DESIGN: A single dose of Vi polysaccharide vaccine for Salmonella typhi and 2 doses of rabies vaccine were given to each subject. Antibody titers were measured in prevaccination serum samples (Vi) and in postvaccination samples (Vi and rabies). RESULTS: The mean birth weight of the subjects was 3.24 kg; 14% of the subjects had low birth weights (<2.5 kg). Vaccine responses were not consistently associated with contemporary variables (month of study, sex, current age, or indicators of wealth). Response to typhoid vaccination was positively related to birth weight (anti-Vi immunoglobulin G: r = 0.138, P = 0.031; anti-Vi immunoglobulin M: r = 0.197, P = 0.034). Response to the rabies vaccine was not significantly associated with birth weight. CONCLUSIONS: These findings add to a growing body of evidence suggesting that components of the immune system may be permanently programmed by events in early life. The contrasting effects on typhoid and rabies responses suggest that antibody generation to polysaccharide antigens, which have greater B cell involvement, is compromised by fetal growth retardation

Revaccination does not improve an observed deficit in antibody responses in Pakistani adults born of a lower birth weight.

We have previously shown that the generation of antibodies to a polysaccharide vaccine (Typhim Vi) is compromised in Pakistani adults born of a lower birth weight. To assess whether this represents a true B-cell-dependent deficit, we revaccinated subjects with a second dose of the same vaccine and with a polysaccharide-protein conjugate vaccine to a different polysaccharide antigen (conjugated Haemophilus influenzae type b (Hib) vaccine). Anti-Vi IgG levels remained positively correlated with birth weight (p=0.0284) but no associations were observed between anti-Hib IgG levels and size at birth. These findings indicate that small size at birth results in a poor antibody response to vaccination with a polysaccharide antigen vaccine in adulthood, even following a second dose of the vaccine. No such association was observed in response to a polysaccharide-protein conjugate vaccine indicating an early-life programming effect on the generation of antibodies during a B-cell-dependent immune response

Early-life and contemporaneous nutritional and environmental predictors of antibody response to vaccination in young Gambian adults.

Recent research links nutritional exposures early in life with alterations in functional immunity that persist beyond childhood. Here we investigate predictors of antibody response to polysaccharide vaccines in a cohort of Gambian adults with detailed records from birth and early infancy available. 320 adults were given a single dose of a Vi polysaccharide vaccine for Salmonella typhi and a 23-valent capsular polysaccharide pneumococcal vaccine. Anti-Vi antibody levels and antibodies against 4 pneumococcal serotypes (1, 5, 14 and 23F) were measured in serum samples collected at baseline and then 14 days following vaccination and compared to data available from birth and early infancy. Post-vaccination antibody titres to serotype 14 of the pneumococcal vaccine were negatively associated with rate of growth from birth to three months of age, infant weight at 12 months of age and season of birth, but no other associations were observed with early-life exposures. The strongest predictor of antibody levels was pre-vaccination antibody titres, with adult height and serum neopterin levels at time of vaccination also implicated. The current study does not support the hypothesis that nutritional exposures early in life consistently compromise antibody response to polysaccharide vaccines administered in young adulthood