Abstract

Optimizing the schedule of thermal generators is probably the most important task when the operation of power systems is managed. This issue is known as the unit commitment problem in operational research. It has been profoundly studied in the literature, where several techniques have been proposed to address a computationally tractable solution. In turn, the ongoing changes of paradigms in energy markets focus the attention on the unit commitment problem as a powerful tool to handle new trends, such as the high renewable energy sources penetration or widespread use of non-conventional energy-storage technologies. A review on the unit commitment problem is propo- sed in this paper. The easy understanding of the diverse techniques applied in the literature for new researchers is the main goal of this state-of-art as well as identifying the research gaps that could be susceptible to further developments. Moreover, an overview of the evolution of the Mixed Integer Linear Programming formulation regarding the improvements of commercial solvers is presented, according to its prevailing hegemony when the unit commitment problem is addressed. Finally, an accurate analysis of modeling detail, power system representation, and computational performance of the case studies is presented. This characterization entails a significant development against the conventional reviews, which only offer a broad vision of the modeling scope of their citations at most.

Highlights

  • The unit commitment problem (UC) is a traditional optimization problem where the best schedule for a group of thermal units is obtained

  • This paper presents a new review of the state-of-art of the unit commitment problem, where the distinctions between optimization techniques, problem formulations, and resolution algorithms are exposed in order to facilitate their understanding

  • Minimum time up (TU) and time down (TD): This inequality is used to guarantee that the unit is online for a minimum period of time since it is started-up or that it is offline for a minimum time since it is shut-down, in order to accomplish with technical limitations that reduce the risk of failure

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Summary

Introduction

The unit commitment problem (UC) is a traditional optimization problem where the best schedule for a group of thermal units is obtained. Maintenance cost: This cost represents the increase of the maintenance operations when the thermal unit is running for a longer time It is modeled as a linear function with respect to power generation, and it is often internalized in the production cost for the sake of simplicity. Capacity limits: This inequality is used to assure that the electricity generation of each thermal unit respects the minimum and maximum power output according to their technical limits This inequality is linear and uses integer variables. Minimum time up (TU) and time down (TD): This inequality is used to guarantee that the unit is online for a minimum period of time since it is started-up or that it is offline for a minimum time since it is shut-down, in order to accomplish with technical limitations that reduce the risk of failure It is linear and employs integer variables.

Optimization Techniques and Unit Commitment
Unit Commitment as an Optimization Problem
Formulating Options
Uncertainty Representation
Decomposition Techniques
Optimization Algorithms
Evolution of Unit Commitment Modeling Trends and Current Situation
Precise Description of the Modeling Detail Adopted in the Literature
Method
EIE is composed by
Conclusions
Methods
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