  As microgrids have advanced from early prototypes to relatively mature
technologies, converting data center integrated commercial buildings to
microgrids provides economic, reliability and resiliency enhancements for the
building owners. Thus, microgrid design and economically sizing distributed
energy resources (DER) are becoming more demanding to gain widespread
microgrids commercial viability. In this paper, an optimal DER sizing
formulation for a hybrid AC/DC microgrid configuration has been proposed to
leverage all benefits that AC or DC microgrid could solely contribute. Energy
storage (ES), photovoltaics (PV) and power electronics devices are coordinately
sized for economic grid-connected and reliable islanded operations. Time-of-use
(TOU) energy usages charges and peak demand charges are explicitly modeled to
achieve maximum level of cost savings. Numerical results obtained from a real
commercial building load demonstrate the benefits of the proposed approach and
the importance of jointly sizing DER for the grid-connected and islanded modes.
