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.
NOMENCLATURE
A. Sets and IndicesS Set of representative days, indexed by s. T Set of time intervals, indexed by t. B. Decision variables c inv Total investments. c e/d s Energy/demand charges at day s. c lcl/lnl s Lost of critical/non-critical load costs at day s. c deg s Energy storage degradation costs at day s. x P V Installed PV capacities. x ES Installed batteries power ratings. x IC Installed interfacing converter capacities. x IN V Installed inverter capacities. x CON Installed converter capacities. p grid s,t Energy purchased from utility at day s time t. p peak s Net load peak demand at day s. lcl AC/DC s,t Critical AC/DC load shedding at day s time t. lnl AC/DC s,t Non-critical AC/DC load shedding at day s time t. v DC s,t PV DC output at day s time t. dch AC/DC s,t ES AC/DC discharge at day s time t. ch AC/DC s,t ES AC/DC charge at day s time t. soc s,t ES state-of-charge at day s time t. This work is funded by SGCC Science and Technology Program. f AC s,t AC bus flow at day s time t. f DCin s,t DC bus injection at day s time t. f DCout s,t DC bus extraction at day s time t. z DC s,t Binary indicator for DC bus flow direction at day s time t, 1 for injection, 0 otherwise. y ES s,t Binary indicator for ES discharging status at day s time t, 1 for discharging, 0 otherwise. vi DC s,t Islanded PV DC output at day s time t. dchi AC/DC s,t Islanded ES AC/DC discharge at day s time t. f i AC s,t Islanded AC bus flow at day s time t. f i DCin s,t Islanded DC bus injection at day s time t. f i DCout s,t Islanded DC bus extraction at day s time t. zi DC s,t Islanded DC bus flow direction indicator at day s time t, 1 for injection, 0 otherwise. u ES s,t /κ ES s,t Auxiliary variables for ES discharging state. C. Parameters π s Probability of representative day s. C P V Annualized investment for PV. C ES Annualized investment for ES. C IC Annualized investment for interfacing converters. C IN V Annualized investment for AC/DC inverters. C CON Annualized investment for D...