new-generation STATCOM

This paper deals with the development and implementation of a current-source-converter-based static synchronous compensator (CSC-STATCOM) applied to the volt-ampere-reactive (VAR) compensation problem of coal mining excavators. It is composed of a +/- 750-kVAR full-bridge CSC with selective harmonic elimination, a low-pass input filter tuned to 200 Hz, and a Delta/Y-connected coupling transformer for connection to medium-voltage load bus. Each power semiconductor switch is composed of an asymmetrical integrated gate commutated thyristor (IGCT) connected in series with a reverse-blocking diode and switched at 500 Hz to eliminate 5th, 7th, 11th, and 13th current harmonics produced by the CSC. Operating principles, power stage, design of dc link, and input filter are also described in this paper. It has been verified by field tests that the developed STATCOM follows rapid fluctuations in nearly symmetrical lagging and leading VAR consumption of electric excavators, resulting in nearly unity power factor on monthly basis, and the harmonic current spectra in the lines of CSC-STATCOM at the point of common coupling comply with the IEEE Std. 519-1992

Is Carotid Atherosclerosis More Important in Patients with Mitral Annular Calcification than in Those without?

It has been suggested that mitral annular calcification (MAC) may be a manifestation of generalized atherosclerosis. However, how the incidence and extent of coronary artery disease (CAD) are affected by the coexistence of carotid atherosclerosis (CAS) in patients with versus without MAC have not yet been studied. We studied 101 patients with echocardiographic MAC and 52 controls without MAC to investigate the clinical impact of CAS on the frequency and severity (defined as the number of obstructed vessels) of CAD in patients with MAC. Carotid Doppler ultrasonographic examination was performed on all patients before coronary angiography. In patients with both MAC and CAS, the incidences of CAD and multivessel disease (greater than or equal to 2 vessel or left main coronary artery disease) were significantly higher than in the control group with CAS alone (91% versus 68%, P = 0.008 and 76% versus 44%, P = 0.004, respectively). On the other hand, among study and control patients without CAS, although the frequencies of CAD and multivessel disease were higher in patients with MAC, interestingly, the differences were not statistically significant (37% versus 58% and 15% versus 26%, respectively, P>0.05 for both). Stepwise multiple logistic regression analysis revealed that CAS (P<0.001), MAC (P<0.01) and, to a limited extent hypertension (P = 0.054), were independent predictors for the presence of CAD. In conclusion, the coexistence of CAS is more important in patients with MAC than in those without as it provides valuable information about the incidence and severity of underlying CAD. In cases with MAC but without CAS, MAC could be caused by factors other than atherosclerosis.WoSScopu