SUMMARYReasonable restoration plans for power systems after large-scale power failures are important in both theory and practice. Based on fuzzy data envelopment analysis (DEA), an algorithm for assessing the black-start schemes of power system is proposed in this paper. Depending on the concepts of L-R fuzzy number and a-cut, this algorithm drew important factors from the process of black start as fuzzy input or output indexes and then established a fuzzy computing model. After the black-start schemes were sorted by the relative efficiency values of decision-making units (DMUs), the best one was recommended to dispatchers. The instance of a real power system proves that it is a feasible method.
Summary The BHESS‐BR method, which consists of BHESS reduction and BR iteration, has been used in the complete eigenvalue analysis for power system small signal stability. Despite more efficient than the QR method, the BHESS‐BR method has its numerical stability degrading significantly as the matrix order grows. In order to solve this issue, this paper presents an improved BHESS‐BR method to analyze the power system small signal stability. For improving accuracy, orthogonal similarity transformations are taken to perform column eliminations in both BHESS reduction and BR iteration. Furthermore, a new multiplier tolerance criterion is derived to improve both accuracy and convergence by means of restricting the 2‐norm condition number of similarity transformation matrix. To accelerate the computing speed, row eliminations in the BR iteration are refined so that the occurrences of row spikes are prevented. Test results of three standard systems and three practical systems with up to 4720 state variables demonstrate that the improved BHESS‐BR method is more accurate and robust than the original BHESS‐BR method for the complete eigenvalue analysis of small signal stability in power systems. Because the improvements belong to the scope of algebraic eigenvalue problem, the proposed method can well benefit the small signal stability analysis and offers a new choice for other eigenvalue problems in power systems. Copyright © 2014 John Wiley & Sons, Ltd.
Background: Nitrogen (N) is a limiting factor that determines yield and quality of chrysanthemum. Genetic variation in N use efficiency (NUE) has been reported among genotypes of chrysanthemum. We performed transcriptome analysis of two chrysanthemum genotypes, ‘Nannonglihuang’ (‘LH’, N-efficient genotype) and ‘Nannongxuefeng’ (‘XF’, N-inefficient genotype), under low N (0.4 mM/L N) and normal N (8 mM/L N) treatments for 15 d and N recovery treatment for 12 h (low N treatment for 15 d and then normal N treatment for 12 h) to understand the genetic factors impacting NUE in chrysanthemum. Results: The two genotypes exhibited contrasting responses to different N treatments. N-efficient genotype ‘LH’had significant superiority in agronomic traits, N accumulation and glutamine synthase (GS) activity, under normal N and low N treatments. Transcriptome analysis revealed that low N treatment promoted root growth and increased the expression of partial N uptake genes, genes related to auxin, abscisic acid, and gibberellin signal transduction in roots of ‘LH’. N recovery treatment increased the expression of genes related to the cytokinin signal transduction in roots of ‘LH’. The expression of NRT2-1, AMT1-1, Gln1, genes related to gibberellin (GID1B, GID2, GAI) and cytokinin signal transduction (AHK2, AHK3, AHK4, ARR4, ARR5, ARR9) in roots of ‘LH’ was higher than that in ‘XF’ under different N treatments, suggesting that the genes related to N metabolism and hormone (auxin, abscisic acid, gibberellin, and cytokinin) signal transduction in roots of ‘LH’ were more sensitive to different N treatments than those of ‘XF’. The network analysis also identified hub genes like bZIP43, bHLH93, NPF6.3, IBR10, MYB62, PP2C, PP2C06 and NLP7, which may be the key regulators of N-mediated response in chrysanthemum and play crucial roles in enhancing NUE and resistance to low N stress in the N-efficient chrysanthemum genotype. Conclusion: This study unravels key factors of regulating NUE in chrysanthemum at the genetic level, and could be useful for genotype improvement and breeding of high NUE chrysanthemum genotypes.
In the regional active distribution network where the Distributed Generation (DG) penetration rate is getting higher and higher. When a high-resistance ground fault occurs in a heavy-load line, the traditional current differential protection has very low sensitivity, the protection may refuse to act. And the power differential protection has the voltage dead zone. In addition, the T-type branch will further reduce the sensitivity of the traditional differential protection. In order to solve the problems, this paper proposes a new principle of double-K differential protection with voltage vector compensation. The principle can flexibly adjust the braking zone range by setting two parameters, and then introduce the voltage vector to compensate the operating point, which effectively improves the protection sensitivity in the case of high-resistance ground fault occurs in a heavy-load line, and there is no voltage dead zone. Simulation shows that the principle can greatly improve the reliability of protection.
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