We report a regime of ion beam sputtering that occurs for sufficiently steep slopes. High slopes propagate over large distances without dissipating the steepest features. Both the propagation velocity and the dynamically selected slope are universal, independent of the details of the initial shape of the surface. The resulting behavior can be understood as the propagation of a shock front that self-selects a stable slope, as has been previously observed in thin-film fluid flows. Experiments confirm predictions of the theory. An important implication of the propagative behavior at high surface slopes is that a pattern can be fabricated at a large length scale and, through uniform ion irradiation, reduced to a smaller length scale while preserving, or even sharpening, the sharpest features.

In this paper, we propose a novel control algorithm for improving steady-state (quasi-static) voltage stability by use of an embedded voltage source converter (VSC) based high voltage direct current (HVDC) system. In this paper, the terms "steadystate" and "quasi-static" are used interchangeably. By embedded HVDC, we refer to a meshed AC system with all HVDC terminals connected within the same AC grid. The sensitivity between VSC control input and the voltage stability margin is introduced. Based on this sensitivity, the proposed control algorithm jointly satisfies system-wide voltage stability margin as well as local voltage magnitude requirements. The proposed approach is to first migrate the entire system to have sufficient voltage stability margin, and then to correct any voltage magnitude violation while keeping that stability margin. A contour-based visualization of the VSC capability space for maintaining system voltage stability is introduced, which can effectively illustrate how the singular value sensitivity (SVS) based control achieves both the local and global voltage stability requirements. The efficacy of the proposed algorithm is shown via case studies on a 6-bus and 118-bus system with and without static VAR compensation.Index Terms-High voltage direct current (HVDC) transmission control, power system stability, voltage source converter (VSC), voltage stability.

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In this paper, a novel approach to incorporate voltage source converter-based embedded HVDC for improving power system economic dispatch efficiency is proposed. An analytical formulation is presented to quantify the economic benefits of embedded HVDC by modeling its flow control as an injection-extraction pair in the economic dispatch of the transmission grid. A computationally efficient algorithm is proposed to rank the potential locations of such embedded HVDC. The algorithm is based on expected economic dispatch cost reduction weighted by the historical line shadow prices. The use of a distribution of historical data as a means of weighting also allows for incorporation of diurnal and seasonal influences on congestion patterns. Numerical case studies using the proposed method of locating the embedded HVDC suggest promising results in choosing the location of improved flow control devices.Index Terms-Mixed ac/dc, security-constrained economic dispatch (SCED), transmission planning, voltage source converter (VSC) HVDC, wind curtailment.

In this paper the concept of targeted conversion of AC lines to DC lines is proposed for improved securityconstrained economic dispatch by incorporating the converted line into the formulation to improve flow pattern control and relieve flow constraints on both the converted line and the remaining AC system. The proposed model treats the flow on the converted line as an independent control variable for the operator to utilize. It is shown that the introduction of this additional control variable significantly decreases the dispatch cost through congestion relief. Wind curtailment due to transmission congestion, is also shown to be significantly relieved. The technical feasibility of the implementation, combined with the economic benefits, suggests that targeted conversion of AC lines to DC lines a promising approach to best utilizing transmission grid for maximized social welfare. Illustrative examples on a 24-bus system demonstrate the technical feasibility and economic benefits for renewable energy resources by use of the proposed conversion.