Eigenvalue and frequency-domain analysis of the intermountain power project and the wscc network
The Western Systems Coordinating Council (WSCC) has several interarea modes of oscillation in the range of 0.3 to 0.8 Hz. The results of an investigation of how various network parameters and operating conditions affect the stability of those modes are presented. Eigenvalue and frequency-domain techniques are used. The study results show that numerous system parameters can have a significant impact on overall network stability. These parameters can include control settings, such as those in HVDC systems or power system stabilizers, or operational parameters, such as scheduled tie-line flows. The results show that careful analysis and tuning of all significant controls in a large network are necessary to ensure overall system stability and satisfactory performance. >
Stability of a Variable-Speed Permanent Magnet Wind Generator With Weak AC Grids
The operation of high-power wind generators with weakened ac grids has historically been difficult because of stability and power quality issues. This paper presents an analytical stability study of a variable-speed directly-driven permanently-excited 2-MW wind generator connected to ac grids of widely varying strength and very weak grids. The generator includes two back-to-back full-scale vector controlled 3-level neutral-point-clamped (NPC) voltage-source-converters (VSC). A 47th order small-signal analytical wind generator model is developed within MatLab, and a summary of the model structure and controls is given. Model verification is demonstrated for fast and slow system variables employing detailed simulation software PSCAD/EMTDC. An eigenvalue stability study for weak ac networks is presented, and qualitative conclusions about inherent system dynamics and stability characteristics are given. These insights are employed to study the design of an ac voltage controller for weak ac networks. Two alternative controller designs are studied for their potential to enhance system robustness to changes in ac grid strength. Testing on the detailed simulator PSCAD/EMTDC is employed throughout to confirm conclusions from analytical studies.
Resonant Auger decay study of C1s -> pi* core-excited OCS
The present work aims at characterizing short-lived C1s((-1)) pi*((1)) core-excited states of the OCS molecule based on the analysis of the vibrational fine structure and lineshape profiles of the high-resolution resonant Auger decay spectra recorded at the excitation energies along the C1s -> pi* resonance in the binding energy region 15-19eV. Very different behavior in terms of lineshape and resonant enhancement is observed for the (A) over tilde, (B) over tilde and (C) over tilde final states. This is explained by (1) the variation in the C-O bond lengths for the states involved in the electronic relaxation and (2) different contributions in terms of Mulliken population to the molecular orbitals determining the electronic character of the corresponding states. Since the final-state geometries are known from a number of previous experiments and ab initio calculations, the geometry of the C1s((-1)) pi*((1)) intermediate states can be predicted in analogy with e.g. the N-2, CO2 and N2O molecules. (C) 2009 Elsevier B.V. All rights reserved. (Less)