HBMO Based Output Feedback Damping Controller for STATCOM

The aim of this paper is to investigate a novel approach for output feedback damping controller design of the static synchronous compensator (STATCOM) in order to enhance the damping of power system low frequency oscillations (LFO). The design of output feedback controller is considered as an optimization problem according to the time domain-based objective function solved by a honey bee mating optimization (HBMO) algorithm that has a strong ability to find the most optimistic results. To validate the accuracy of results a comparison with genetic algorithm (GA) has been made. The effectiveness of the proposed controller are tested and demonstrated through eigenvalue analysis and nonlinear time-domain simulation studies over a wide range of loading conditions. The simulation study shows that the designed controller by HBMO performs better than GA in finding the solution.U ovome radu istražene su metode za sintezu regulatora prigušenja za statički sinkroni kompenzator (STATCOM) u svrhu povećanja prigušenja nisko frekvencijskih oscilacija u energetskim sustavima. Sinteza regulatora je razmatrana kao optimizacijski problem u vremenskoj domeni koji je riješen pomoću HBM algoritma optimizacije (eng. Honey bee mating) koji ima svojstvo pronalaska najoptimističnijeg rezultata. U svrhu provjere rezultata napravljena je usporedba s rješenjem koje daje genetski algoritam. Efikasnost predloženog regulatora testirana je uz pomoć analize svojstvenih vrijednosti i nelinearnih simulacija u vremenskoj domeni za različite uvjete. Simulacijski rezultati pokazuju da se korištenjem regulatora s HBM optimizacijom postižu bolji rezultati nego korištenjem genetskog algoritma

The risk factors and laboratory diagnostics for post renal transplant tuberculosis: A case-control, country-wide study on definitive cases

Background. Tuberculosis (TB) is an important cause of morbidity and mortality in renal transplant recipients and, because of its infrequency and the lack of medical awareness, it is usually misdiagnosed. This study was carried out to determine frequency and weight of multiple risk factors for post kidney transplantation TB. Methods. A total of 44 cases (0.3), out of 12,820 patients from 12 major kidney transplantation centers in Iran from 1984 to 2003, were compared with 184 healthy transplant subjects who were transplanted by the same surgical team. Results. The mean age of cases and controls was 37.7 (13-63) and 35.6 (8-67) years (P=0.3), respectively. The mean duration of pre-transplantation hemodialysis was 30.3 (3-168) months in cases and 18.2 (1-180) months in controls (P=0.03). A positive past history of TB was detected in 2 cases and 1 control (P=0.3). The mean doses of initial and maintenance immunosuppressive drugs in cases and controls were not significantly different. A total of 25 cases (56.8) and 60 controls (32.6) had rejection before diagnosis of TB (P=0.004; OR=2.7, CI95: 1.3-5.6). Conclusions. To our knowledge, this is the first study that demonstrated an increase in the risk of post-transplant TB by increasing the duration of pre-transplant hemodialysis and the number of post-transplant rejection episodes as 2 immunocompromised states. Further study is needed to clarify our new findings, specifically in relation to different immunosuppressive regimens. © 2008 Wiley Periodicals, Inc