Three-phase voltage-source converters (VSCs) are commonly used as power flow interface in AC/DC hybrid power systems. The AC power grid suffers from unpredictable shortcircuit faults and power flow fluctuations, causing undesirable grid voltage dips. The voltage dips may last for a short time or a long duration, and vary the working conditions of VSCs. Due to their nonlinear characteristics, VSCs may enter abnormal operating mode in response to voltage dips. In this paper, the transient response of three-phase VSCs under practical grid voltage dips is studied and a catastrophic bifurcation phenomenon is identified in the system. The converter will exhibit an irreversible instability after the dips. The expanded magnitude of AC reactive current may cause catastrophic consequence for the system. A full order eigenvalue analysis and a reduced order mixed-potentialtheory based analysis are adopted to reveal the physical origin of the large-signal instability phenomenon. The key parameters of the system are identified and the boundaries of instability are located. The bifurcation phenomenon and a set of design-oriented stability boundaries in some chosen parameter space are verified by cycle-by-cycle simulations and experimental measurement on a practical grid-connected VSC prototype.

Hereditary gingival fibromatosis (HGF) is a rare, benign disorder characterized by slowly progressive fibrous overgrowth of the gingiva. To date, two loci have been mapped in familial cases with autosomal dominant non-syndromic HGF: GINGF (MIM 135300) on chromosome 2p21-p22 and GINGF2 (MIM 605544) on chromosome 5q13-q22. Of the two loci, only SOS1 (son of sevenless one, MIM 182530) gene underlying GINGF locus has been identified. Ascertainment of a large Chinese family has allowed the mapping of a novel locus to 2p22.3-p23.3, GINGF3. Haplotype construction and analysis localized the new locus to an 11.4-cM interval between markers D2S2221 (telomeric) and D2S1788 (centromeric). The maximum two-point limit of detection (LOD) score of 3.45 (theta=0) and multipoint LOD score of 5.00 for marker D2S390 strongly supported linkage to this region. Thus, this genetic interval is distal to and does not overlap with the previously described locus, GINGF, on 2p21-p22.

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