Abstract
This study proposes a method for optimally selecting the operating parameters of an energy storage system (ESS) for frequency regulation (FR) in an electric power system. First, the method allows the optimal objective function of the selected parameters to be set in a flexible manner according to the electric market environment. The objective functions are defined so that they could be used under a variety of electricity market conditions. Second, evaluation frequencies are created in order to simulate the overall lifespan of the FR-ESS. Third, calendar and cycle degradation models are applied to the battery degradation, and are incorporated into evaluations of the degradation progress during the entire FR-ESS lifespan to obtain more accurate results. A calendar life limit is set, and the limit is also considered in the objective function evaluations. Fourth, an optimal parameter calculation algorithm, which uses the branch-and-bound method, is proposed to calculate the optimal parameters. A case study analyzes the convergence of the proposed algorithm and the results of the algorithm under various conditions. The results confirmed that the proposed algorithm yields optimal parameters that are appropriate according to the objective function and lifespan conditions. We anticipate that the proposed FR-ESS algorithm will be beneficial in establishing optimal operating strategies.
Highlights
Installations of renewable energy generators are currently increasing, and electrical systems are undergoing significant changes
This study proposes an optimal parameter selection method of frequency regulation (FR)-energy storage system (ESS) control to smooth out the effects of these constraints
The three primary energy amounts can be calculated by analyzing the operation history of the FR-ESS: the energy (Efreq ) charged/discharged to maintain the frequency when it goes outside the range of 60 ± 0.03 Hz, the energy (Esoc ) charged/discharged to maintain the state of charge (SOC) at a fixed value to maintain a state in which the ESS can always charge/discharge, and the energy (Elimited ) for which actual charge/discharge actions could not be performed because of SOC constraints, even when the frequency was outside the range of 60 ± 0.03 Hz and charge/discharge activities were required
Summary
Installations of renewable energy generators are currently increasing, and electrical systems are undergoing significant changes. Energy storage systems, which use the lithium-ion battery family to connect multi-MW inverters in parallel to configure their capacity in a flexible manner, have been commercialized up to a scale of tens of MW [8] They require a smaller installation space than existing pumped-storage power generation, and can perform charge/discharge actions faster than output changes of existing generators. Because of this, they are an excellent means of frequency regulation [5,9,10].
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