Optimal sizing of distributed generations in DC microgrids with comprehensive consideration of system operation modes and operation targets

With the continuous increasing requirement of dc power generations and dc electrical equipment, dc microgrids (MGs) show great natural advantages and development potential. In this paper, aiming at optimal sizing method of distributed generations (DGs) in the dc MGs, the output and capacity of photovoltaic units, wind turbine units, and an energy storage system (ESS) are presented based on the components structures and operation characteristics of the dc MGs. Due to the feature of the dc MGs that demands grid-connected converter (GCC) to exchange power with ac grid, the operating status of GCC and on-grid price are taken into account in the economic objective functions of the dc MGs. Meanwhile, with constraints including battery state of charge, loss of power supply probability (LPSP), renewable energy efficiency (REE), and so on, a particle swarm optimization algorithm is adopted to calculate the optimal sizing results targeting at the lowest annualized capital cost and operation maintenance (OM) cost. Furthermore, based on the analysis of the operation schemes of the dc MGs and the dynamic lifespan estimated results of ESS, an optimal sizing approach with comprehensive consideration of system operation modes and operation targets of the dc MGs is proposed. The variation trends of annualized capital cost and OM cost are investigated under different LPSP and REE. Meanwhile, the system operation schemes are validated by using the obtained results, and the comparison and analysis of the detailed results are conducted.