| Name: | Description: | Size: | Format: | |
|---|---|---|---|---|
| 4.19 MB | Adobe PDF |
Authors
Abstract(s)
As centrais termoelétricas convencionais convertem apenas parte do combustível
consumido na produção de energia elétrica, sendo que outra parte resulta em perdas sob a
forma de calor. Neste sentido, surgiram as unidades de cogeração, ou Combined Heat and
Power (CHP), que permitem reaproveitar a energia dissipada sob a forma de energia
térmica e disponibilizá-la, em conjunto com a energia elétrica gerada, para consumo
doméstico ou industrial, tornando-as mais eficientes que as unidades convencionais
Os custos de produção de energia elétrica e de calor das unidades CHP são
representados por uma função não-linear e apresentam uma região de operação admissível
que pode ser convexa ou não-convexa, dependendo das caraterísticas de cada unidade. Por
estas razões, a modelação de unidades CHP no âmbito do escalonamento de geradores
elétricos (na literatura inglesa Unit Commitment Problem (UCP)) tem especial relevância
para as empresas que possuem, também, este tipo de unidades. Estas empresas têm como
objetivo definir, entre as unidades CHP e as unidades que apenas geram energia elétrica ou
calor, quais devem ser ligadas e os respetivos níveis de produção para satisfazer a procura
de energia elétrica e de calor a um custo mínimo.
Neste documento são propostos dois modelos de programação inteira mista para o
UCP com inclusão de unidades de cogeração: um modelo não-linear que inclui a função
real de custo de produção das unidades CHP e um modelo que propõe uma linearização da
referida função baseada na combinação convexa de um número pré-definido de pontos
extremos. Em ambos os modelos a região de operação admissível não-convexa é modelada
através da divisão desta àrea em duas àreas convexas distintas.
Testes computacionais efetuados com ambos os modelos para várias instâncias
permitiram verificar a eficiência do modelo linear proposto. Este modelo permitiu obter as
soluções ótimas do modelo não-linear com tempos computationais significativamente
menores. Para além disso, ambos os modelos foram testados com e sem a inclusão de
restrições de tomada e deslastre de carga, permitindo concluir que este tipo de restrições aumenta a complexidade do problema sendo que o tempo computacional exigido para a
resolução do mesmo cresce significativamente.
Conventional thermal power plants convert only part the of the energy resulting from fuel consumption in electric power, while a significant part is wasted as heat loss Combined Heat and Power (CHP) units allow to reuse the energy dissipated as heat and make it available for consumption either by domestic or industrial costumers. Electricity and heat production costs of CHP units are represented by a nonlinear function and a feasible operating region that is either convex or non-convex, depending on the unit’s characteristics. For these reasons, modelling CHP units in the context of the Unit Commitment Problem (UCP) has been of particular interest for generation companies that use such units in their operation. The goal of these companies is to decide, among CHP units and conventional thermal units and heat-only units, which should be turned on to meet the electricity or heat demand at minimum cost. In this work, two mixed integer programming models are proposed for solving the UCP with inclusion of CHP units: a nonlinear model that includes the real cost function of CHP units; and a model proposing a linearization of that function through a convex combination of a predefined number of extreme points. In both models, the non-convex feasible operating region of some CHP units is modelled by splitting it into two separate convex regions. Computational experiments performed with both models for multiple instances allowed to verify the effectiveness of the proposed linear model. This model allowed to obtain the optimal solutions achieved by the nonlinear model with significantly lower computational times. Moreover, both models were tested with and without the inclusion of ramp constraints, allowing to conclude tha such constraints increase the complexity of the problem in such a way that the time required solve the problem grows sharply when including these constraints.
Conventional thermal power plants convert only part the of the energy resulting from fuel consumption in electric power, while a significant part is wasted as heat loss Combined Heat and Power (CHP) units allow to reuse the energy dissipated as heat and make it available for consumption either by domestic or industrial costumers. Electricity and heat production costs of CHP units are represented by a nonlinear function and a feasible operating region that is either convex or non-convex, depending on the unit’s characteristics. For these reasons, modelling CHP units in the context of the Unit Commitment Problem (UCP) has been of particular interest for generation companies that use such units in their operation. The goal of these companies is to decide, among CHP units and conventional thermal units and heat-only units, which should be turned on to meet the electricity or heat demand at minimum cost. In this work, two mixed integer programming models are proposed for solving the UCP with inclusion of CHP units: a nonlinear model that includes the real cost function of CHP units; and a model proposing a linearization of that function through a convex combination of a predefined number of extreme points. In both models, the non-convex feasible operating region of some CHP units is modelled by splitting it into two separate convex regions. Computational experiments performed with both models for multiple instances allowed to verify the effectiveness of the proposed linear model. This model allowed to obtain the optimal solutions achieved by the nonlinear model with significantly lower computational times. Moreover, both models were tested with and without the inclusion of ramp constraints, allowing to conclude tha such constraints increase the complexity of the problem in such a way that the time required solve the problem grows sharply when including these constraints.
Description
Keywords
Cogeração Combined Heat and Power (CHP) Unit Commitment Problem Programação linear Programação não-linear Programação inteira mista Região de operação admissível Cogeneration Linear programming Nonlinear programming Mixed integer programming feasible operating region Convex Non-convex