Improved Methodology for Microgrid Unit Sizing

Abstract

Understanding the limitations of microgrid design can aid in technically enabling a large penetration of inverter-based resources in the national power system. From the perspective of the microgrid end-user, their cost of energy, energy security and emissions can also be significantly improved if designed appropriately. There is concern that the sole use of quasi-steady state simulations during the unit sizing process of a microgrid may result in unit sizing that can lead to instability during operational states of the microgrid. A case study of a commercial scale microgrid in South Africa is used to demonstrate an improved design methodology. The methodology first employs the use of quasi-steady simulations to economically optimize the size of the solar and energy storage components. Following this, electromechanical dynamic simulations identify if instability could occur by analyzing worst case underload and overload events for various operational scenarios of the microgrid. Faults and conditions on start-up were excluded from this dynamic study. It was found that instability could occur for some operational states. The most vulnerable state was found to be during off-grid operation with the generator power as the primary reference voltage. The likelihood of these operational conditions and the dynamic events will need to be further assessed to determine appropriate risk mitigation. The design methodology provides a better understanding of microgrid unit sizing, contributing to improved end-user experience and the wider effort for increasing the integration of inverter-based resources in the national power system.