Dynamic Optimization Algorithms for Baseload Power Plant Cycling under Variable Renewable Energy

The growing deployment of variable renewable energy (VRE) sources, such as wind and solar, is mainly due to the decline in the cost of renewable technologies and the increase of societal and cultural pressures. Solar and wind power generation are also known to have zero marginal costs and fuel emissions during dispatch. Thereby, the VRE from these sources should be prioritized when available. However, the rapid deployment of VRE has heightened concerns regarding the challenges in the integration between fossil-fueled and renewable energy systems. The high variability introduced by the VRE as well as the limited alignment between demand and wind/solar power generation led to the increased need of dispatchable energy sources such as baseload natural gas- and coal-fired power plants to cycle their power outputs more often to reliably supply the net load. The increasing power plant cycling can introduce unexpected inefficiencies into the system that potentially incur higher costs, emissions, and wear-and-tear, as the power plants are no longer operating at their optimal design points. In this dissertation, dynamic optimization algorithms are developed and implemented for baseload power plant cycling under VRE penetration. Specifically, two different dynamic optimization strategies are developed for the minute and hourly time scales of grid operation. The minute-level strategy is based on a mixed-integer linear programming (MILP) formulation for dynamic dispatch of energy systems, such as natural gas- and coal-fired power plants and sodium sulfur batteries, under VRE while considering power plant equipment health-related constraints. The hourly-level strategy is based on a Nonlinear Multi-objective dynamic real-time Predictive Optimization (NMPO) implemented in a supercritical pulverized coal-fired (SCPC) power plant with a postcombustion carbon capture system (CCS), considering economic and environmental objectives. Different strategies are employed and explored to improve computational tractability, such as mathematical reformulations, automatic differentiation (AD), and parallelization of a metaheuristic particle swarm optimization (PSO) component. The MILP-based dynamic dispatch framework is used to simulate case studies considering different loads and renewable penetration levels for a suite of energy systems. The results show that grid flexibility is mostly provided by the natural gas power plant, while the batteries are used sparingly. Additionally, considering the post-optimization equivalent carbon analysis, the environmental performance is intrinsically connected to grid flexibility and the level of VRE penetration. The stress results reinforce the necessity of further considering and including equipment health-related constraints during dispatch. The results of the NMPO successfully implemented for a large-scale SCPC-CCS show that the optimal compromise is automatically chosen from the Pareto front according to a set of weights for the objectives with minimal interaction between the framework and the decision maker. They also indicate that to setup the optimization thresholds and constraints, knowledge of the power system operations is essential. Finally, the market and carbon policies have an impact on the optimal compromise between the economic and environmental objectives

Advancement and analysis of Gauss pseudospectral transcription for optimal control problems

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2007.Includes bibliographical references (p. 195-207).As optimal control problems become increasingly complex, innovative numerical methods are needed to solve them. Direct transcription methods, and in particular, methods involving orthogonal collocation have become quite popular in several field areas due to their high accuracy in approximating non-analytic solutions with relatively few discretization points. Several of these methods, known as pseudospectral methods in the aerospace engineering community, have also established costate estimation procedures which can be used to verify the optimality of the resulting solution. This work examines three of these pseudospectral methods in detail, specifically the Legendre, Gauss, and Radau pseudospectral methods, in order to assess their accuracy, efficiency, and applicability to optimal control problems of varying complexity. Emphasis is placed on improving the Gauss pseudospectral method, where advancements to the method include a revised pseudospectral transcription for problems with path constraints and differential dynamic constraints, a new algorithm for the computation of the control at the boundaries, and an analysis of a local versus global implementation of the method. The Gauss pseudospectral method is then applied to solve current problems in the area of tetrahedral spacecraft formation flying. These optimal control problems involve multiple finite-burn maneuvers, nonlinear dynamics, and nonlinear inequality path constraints that depend on both the relative and inertial positions of all four spacecraft. Contributions of this thesis include an improved numerical method for solving optimal control problems, an analysis and numerical comparison of several other competitive direct methods, and a greater understanding of the relative motion of tetrahedral formation flight.by Geoffrey Todd Huntington.Ph.D

Institutions and land-use planning. The adoption of the land-use act "LOUGA" by local authorities in the autonomous region of Galicia, north-west of Spain

Durante los últimos 25 años, la región de Galicia aprobó tres leyes que regulan el uso del suelo (1985, 1997 y 2002) y que trataban de controlar el desorden territorial de buena parte del territorio. Sin embargo, después de estos 25 años, muchos municipios siguen sin tener un plan y sólo el 12% tienen un plan aprobado con respecto a la última ley del suelo (LOUGA) después de casi 10 años de vigencia. Esta investigación tiene como objetivo entender por qué unos pocos municipios han decidido adaptarse a la LOUGA mientras que la mayoría parecen reacio a hacerlo. El enfoque teórico para comprender esta falta de aplicación de la ley es la literatura institucional. En la literatura institucional hay cuatro grandes tipos de corrientes: el institucionalismo racional, el histórico, el sociológico y el discursivo. Se consideran para cada uno de ellos las fuentes de cambio y resistencia institucional. Como buena parte de ellos se centra más en la resistencia al cambio que en analizar los cambios, se elabora un modelo de cambio institucional basado en el concepto de contradicción institucional, con el que se pretende entender tanto la aprobación de la LOUGA como la adopción y la no adopción de la misma por parte de los municipios. Los resultados de la investigación indican que el concepto de contradicción institucional es útil para entender tanto la aprobación de la LOUGA como el patrón de difusión que ha tenido en los municipios. La LOUGA se aprobó por un cambio legislativo a nivel estatal y los municipios que se adaptaron lo hicieron no por mandato legal, sino porque la LOUGA creaba inseguridad jurídica a la hora de conceder licencias dada la obsolescencia de sus planes. Sin embargo, la dirección y objetivos que finalmente tomaron tanto la LOUGA como los diferentes planes aprobados, sólo se explica por la influencia de otras fuentes de cambio institucional y el papel de la agencia. En cuanto a las razones de resistencia hay que mencionar los efectos redistributivos que tiene cualquier cambio institucional. Los municipios que no iniciaron los trámites son aquellos que o bien no tienen apenas actividad urbanística, o bien en su mayoría tienen planes muy expansivos aprobados de acuerdo a la ley de 1997. El coste político de retirar derechos de edificación que concedieron plane