• Journal of Power Electronics
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• v.19 no.4
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• pp.835-845
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• 2019

This paper presents a robust-optimal control strategy to improve the output-voltage error-tracking and control capability of a DC-DC boost converter. The proposed strategy employs an optimized Fractional-order Proportional-Integral (FoPI) controller that serves to eliminate oscillations, overshoots, undershoots and steady-state fluctuations. In order to significantly improve the error convergence-rate during a transient response, the FoPI controller is augmented with a pre-stage nonlinear error-modulator. The modulator combines the variations in the error and error-derivative via the signed-distance method. Then it feeds the aggregated-signal to a smooth sigmoidal control surface constituting an optimized hyperbolic secant function. The error-derivative is evaluated by measuring the output-capacitor current in order to compensate the hysteresis effect rendered by the parasitic impedances. The resulting modulated-signal is fed to the FoPI controller. The fixed controller parameters are meta-heuristically selected via a Particle-Swarm-Optimization (PSO) algorithm. The proposed control scheme exhibits rapid transits with improved damping in its response which aids in efficiently rejecting external disturbances such as load-transients and input-fluctuations. The superior robustness and time-optimality of the proposed control strategy is validated via experimental results.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.17 no.3
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• pp.158-165
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• 2005

In order to analyze incompressible two-phase flow, Level Set method was applied on pseudo-compressibility formulation. Level Set function is defined as a signed distance function from the phase interface, and gives the information of the each phase location and the geometric data to the flow. In this study, Level Set function transport equation was coupled with flow conservation equations, and owing to pseudo-compressibility technique we could solve the resultant vector equation iteratively. Two-phase flow analysis code was developed on general curvilinear coordinate, and numerical tests of bubble dynamics and surging wave problems demonstrate its capability successfully.

• Archives of Plastic Surgery
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• v.45 no.2
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• pp.165-170
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• 2018

Background To present the outcomes of the tarsal switch procedure using an anterior approach to correct severe ptosis with poor levator muscle function (<4 mm) with absent or poor Bell's phenomenon. Methods This retrospective case series included 11 patients with severe neurogenic or acquired myogenic palpebral ptosis. All patients underwent the tarsal switch procedure through an anterior approach from 2012 to 2015. Margin reflex distance (MRD1 and MRD2) and the palpebral fissure were evaluated preoperatively and postoperatively. Data were compared using the Wilcoxon signed-rank test. P-values <0.05 were considered to indicate statistical significance. Results Surgery was performed on 18 eyelids (11 patients). The median age at surgery was 57 years (range, 29-86 years). Four patients had unilateral ptosis and seven had bilateral ptosis. Nine patients had myogenic ptosis and two had neurogenic ptosis. Postoperatively, the chin-up position improved in all patients. The MRD1 increased statistically significantly, from 0 mm preoperatively to 1.0 mm postoperatively (P=0.001). The MRD2 decreased statistically significantly, from 4.5 mm preoperatively to 3.0 mm postoperatively (P=0.001). The palpebral fissure did not change (4.0 mm preoperatively to 4.0 mm postoperatively) (P=0.13). Conclusions The tarsal switch procedure through an anterior approach is an effective alternative for correcting severe ptosis, especially neurogenic or acquired myogenic ptosis. This procedure can be performed with minimal risk of ocular surface exposure and provides stable outcomes.