Abstract

Increased level of flexibility is essential in power systems with high penetration of renewable energy sources in order to maintain the balance between the demand and generation. Actually, the flexibility provided by energy storage systems and flexible conventional resources (i.e., generating units) can play a vital role in the compensation of the renewable energy sources variability. In this paper, the flexibility of the conventional generating units is quantified and incorporated in a unit commitment model in order to evaluate the impact of different system flexibility levels on the optimal generation dispatch and on the operational cost of the power system. An emerging flexible option such as the battery storage is included in the unit commitment formulation, evaluating the flexibility contribution of the storage and its effect on the system operational cost. In this paper, the flexibility of a real power system is assessed while the unit commitment problem is formulated as a mixed-integer linear program. The results show that the integration of a storage unit in the power generation portfolio provides a significant amount of flexibility and reduces the system operational cost due to the peak shaving and valley filling.

Highlights

  • The increasing integration of the renewable energy sources (RES) into the power system causes several operating and security problems due to the inherent stochastic nature of RES

  • The flexibility of the system is quantified according to [5], and the resulting flexibility indices are incorporated in a unit commitment (UC) model as a constraint, in order to assess the impact of different system flexibility levels on the optimal generation dispatch and on the operational cost of the system

  • The calculation of the system upward and downward flexibility indicates the impact of the battery storage and the incorporated flexibility indices on the ability of the system to respond to power changes

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Summary

Introduction

The increasing integration of the renewable energy sources (RES) into the power system causes several operating and security problems due to the inherent stochastic nature of RES. The flexibility of the system is quantified according to [5], and the resulting flexibility indices are incorporated in a UC model as a constraint, in order to assess the impact of different system flexibility levels on the optimal generation dispatch and on the operational cost of the system. The total upward and downward flexibility of the system is calculated through the generation dispatch and the storage operation of the UC solution for different levels of system flexibility provided by the conventional units. (b) In [12], the total upward and downward flexibility provided by the conventional units and the battery storage is determined without the incorporation of the units’ flexibility indices into the UC. The units’ flexibility indices are incorporated in the UC, and the total upward and downward flexibility is calculated for different minimum levels of system flexibility provided by the conventional units.

Flexibility Index Calculation
Unit Commitment Formulation
Objective Function
Constraints
Power Balance
Spinning Reserve
Primary Reserve
State of Charge
Battery Storage Restriction
Upward and Downward Flexibility
Simulation Results
Conclusions
Full Text
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