Effect of DFIG control parameters on small signal stability in power systems.

The doubly-fed induction generator (DFIG) with virtual inertia control and reactive damping control gives a renewable energy generation system inertia and damping characteristics similar to those of a thermal power plant, and the parameters of the control strategy have a direct impact on the small-signal stability of the system. This paper firstly introduces the operating characteristics and control strategies of DFIG-based damping control and virtual inertia control, establishes a small-signal model of the control-based DFIG integrated interconnected system, and investigates the effects of virtual inertia and reactive damping values on the small-signal stability of the system; then, the maximum damping ratio of the interval oscillation mode in small disturbance analysis is taken as the optimization objective, and the control parameters are the optimization variables. An optimization method of inertia and damping parameters is established for improving the small disturbance stability of the system. The results show that the optimization procedure could improve the damping ratio of the interval oscillation mode while ensuring the system frequency. The effects of virtual inertia and reactive damping values on the small signal stability of the system are investigated, and an optimal allocation model and method for virtual inertia used to improve the small disturbance stability of the system is proposed.

[Impact of CHA2DS2 VASc score on substrate for persistent atrial fibrillation and outcome post catheter ablation of atrial fibrillation].

OBJECTIVE: To explore if CHA2DS2 VASc score can predict substrate for persistent atrial fibrillation ( AF) and outcome post catheter ablation of AF. METHODS: From January 2011 to December 2012,116 patients underwent catheter ablation of persistent AF in our department and were enrolled in this study. CHA2DS2VASc score was calculated as follows: two points were assigned for a history of stroke or transient ischemic attack and age ≥ 75 and 1 point each was assigned for age ≥ 65, a history of hypertension, diabetes,recent cardiac failure, vessel disease, female. Left atrial geometry ( LA) was reconstructed with a 3.5 mm tip ablation catheter with fill-in threshold 10 in CARTO system. The mapping catheter was stabled at each endocardial location for at least 3 seconds for recording. The electrogram recordings at each endocardial location were analyzed with a custom software embedded in the CARTO mapping system. Interval confidence level (ICL) was used to characterize complex fractionated atrial electrograms (CFAEs) . As the default setting of the software, ICL more than or equal to 7 was considered sites with a highly repetitive CFAEs complex. CFAEs index was defined as the fraction of area of ICL more than or equal to 7 to the left atrial surface. The CFAEs index and outcome of catheter ablation among different CHA2DS2VASc groups were compared. RESULTS: Of the 116 patients, CHA2DS2VASc was 0 in 33 patients, 1 in 31 patients and ≥ 2 in 52 patients. Left atrial surface ((121.2 ± 18.9) cm2, (133.6 ± 23.8) cm2, (133.9 ± 16.1) cm2, P = 0.008), left atrial volume ((103.6 ± 24.8) ml, (118.3 ± 27.8) ml, (120.9 ± 20.9) ml, P = 0.005) and CFAEs index (44.6% ± 22.4%, 54.2% ± 22.2%, 58.7% ± 23.1%, P = 0.023) increased in proportion with increasing CHA2DS2VASc. ICLmax, ICLmin and CFAEs spatial distribution were similar among the three groups. During the mean follow-up of (13 ± 8) months, the recurrence rate were 36.4%, 35.5%, 55.8% among the three groups (P = 0.025). CONCLUSION: A high CHA2DS2VASc score is associated with extensive AF substrate and higher recurrence rate post catheter ablation of persistent AF.

Percutaneous treatment with drug-eluting stent vs bypass surgery in patients suffering from chronic stable angina with multivessel disease involving significant proximal stenosis in left anterior descending artery.

BACKGROUND: The aim of the present study was to compare the effects of drug-eluting stents (DES) and coronary artery bypass grafting (CABG) in patients suffering from chronic stable angina with multivessel disease, involving significant proximal stenosis in the left anterior descending artery (LAD). METHODS AND RESULTS: All consecutive patients suffering from chronic stable angina with multivessel disease involving significant proximal LAD stenosis underwent DES implantation (n=600) or CABG (n=709) at our institution. At 2 years, the unadjusted mortality was significantly lower in the DES group than in the CABG group (2.2% vs 5.2%, P=0.004), but the adjusted risk of death was similar (odds ratio (OR) 0.74, 95%CI 0.28-1.97, P=0.555). Furthermore, both the adjusted rate of nonfatal myocardial infarction and cerebrovascular events was also comparable. However, the unadjusted and adjusted risk of major adverse cardiac cerebrovascular events in the DES was significantly higher than in the CABG (13.3% vs 9.6%, OR 2.71, 95%CI 1.56-4.74, P<0.001), which is probably attributed to the higher subsequent revascularization rate after DES implantation. CONCLUSIONS: DES showed comparable long-term mortality for the treatment of multivessel disease involving significant proximal stenosis in LAD in comparison with CABG.