Nonlinear programming

About: Nonlinear programming is a research topic. Over the lifetime, 19486 publications have been published within this topic receiving 656602 citations. The topic is also known as: non-linear programming & NLP.

Computer-Aided Design and Optimization of High-Efficiency LLC Series Resonant Converter

Abstract: High conversion efficiency is desired in switch mode power supply converters. Computer-aided design optimization is emerging as a promising way to design power converters. In this work a systematic optimization procedure is proposed to optimize LLC series resonant converter full load efficiency. A mode solver technique is proposed to handle LLC converter steady-state solutions. The mode solver utilizes numerical nonlinear programming techniques to solve LLC-state equations and determine operation mode. Loss models are provided to calculate total component losses using the current and voltage information derived from the mode solver. The calculated efficiency serves as the objective function to optimize the converter efficiency. A prototype 300-W 400-V to 12-V LLC converter is built using the optimization results. Details of design variables, boundaries, equality/inequality constraints, and loss distributions are given. An experimental full-load efficiency of 97.07% is achieved compared to a calculated 97.4% efficiency. The proposed optimization procedure is an effective way to design high-efficiency LLC converters.

Structural damage detection based on static and modal analysis

Abstract: The present paper describes an approach for structural damage assessment that has its basis in methods of system identification. Response of a damaged structure differs from predictions obtained from an analytical model of the original structure, where the analytical model is typically a finite-element representation. The out- put error approach of system identification is employed to determine changes in the analytical model necessary to minimize differences between the measured and predicted response. Structural damage is represented by changes in element stiffness matrices resulting from variations in geometry or material properties of the structure during damage. Measurements of static deflections and vibration modes are used in the identification procedure. The identification methodology is implemented for representative structural systems. Principal shortcomings in the proposed approach and methods to circumvent these problems are also discussed. of obtaining poor results. These difficulties are clearly evi- denced by the results obtained. Smith and Hendricks8 follow a similar approach using two different identification methods to identify the stiffness matrix based on the minimum deviation approach and using eigenmodes as experimental data. Similar difficulties are re- ported in their work. The entries of the stiffness matrix corre- sponding to the damaged members do show considerable vari- ations. However, entries corresponding to undamaged members are also affected, thereby making the damage detec- tion process more uncertain. The analysis of changes in the stiffness matrix is typically cumbersome, may not always yield correct answers, and does not permit the determination of the extent of damage. This paper presents an approach that is designed to circum- vent the problems just discussed. The output error method or structural identification9 is used, wherein the analytical model is refined to minimize the difference between the predicted and measured response of the structure. Iterative nonlinear pro- gramming methods are employed to determine a solution to the unconstrained optimization problem. Damage is repre- sented by reduction in the elastic extensional and shear moduli of the element, and those are designated as the design varia- bles of the problem. The use of static structural displacements as the measured response is a departure from the standard practice of using eigenmodes alone for the identification pro- blem. Numerical evidence clearly indicates that when eigen- modes alone are used for identification, the location and ex- tent of damage predicted by the optimization approach is dependent on the number of modes used to match the measured and the predicted response. Higher modes are diffi- cult to determine and measure, and the use of static displace- ments obtained by a loading that simulates higher modes is proposed as a solution to this problem. The paper also presents an implementation of the proposed damage assessment strategies, with special focus on problems of practical significance. In this context, the use of incomplete modal or static displacement information in the identification problem is discussed. Further, the approach of treating the modulus of each structural element as an independent design variable results in a large dimensionality problem. This results in significant computational costs when using a gradient-based nonlinear programming algorithm for function minimization. The use of a reduced set of dominant design variables and the construction of equivalent reduced-order models for damage assessment are explored with some success.

Optimal operation solutions of power systems with transient stability constraints

Abstract: The computation of an optimal operation point in power systems is a nonlinear optimization problem in functional space, which is not easy to deal with precisely, even for small-scale power systems. On the other hand, the emergence of competitive power markets makes optimal power flow (OPF) with transient stability constraints increasingly important because the conventionally heuristic evaluation for the operation point can produce a discrimination among market players in the deregulated power systems. Instead of directly tackling this tricky problem, in this paper, OPF with transient stability constraints (OTS) is equivalently converted into an optimization problem in the Euclidean space via a constraint transcription, which can be viewed as an initial value problem for all disturbances and solved by any standard nonlinear programming techniques adopted by OPF. The transformed OTS problem has the same variables as those of OPF in form, and is tractable even for the large-scale power systems with a large number of transient stability constraints. This paper also derives the Jacobian matrices of the transient stability constraints and gives two computation algorithms based on the relaxation scheme. The numerical simulation verified the effectiveness of the proposed approach.

Real-Time Optimization Model for Dynamic Scheduling of Transit Operations

Abstract: A new transit operating strategy is presented in which service vehicles operate in pairs with the lead vehicle providing an all-stop local service and the following vehicle being allowed to skip some stops as an express service. The underlying scheduling problem is formulated as a nonlinear integer programming problem with the objective of minimizing the total costs for both operators and passengers. A sensitivity analysis using a real-life example is performed to identify the conditions under which the proposed operating strategy is most advantageous.