# Investigation of Nanogrids for Improved Navy Installation Energy Resilience
## 2 Background and Related Research
### Nanogrid System Design  
A variety of nanogrid system designs are proposed in the literature and have seen limited implementation in the real world. Different nanogrid designs can serve different purposes and will have different impacts on the energy resilience of an electrical system. From a systems engineering perspective, [PERSON] et al. advances six criteria for understanding electrical systems used to power military loads: (1) System Purpose (2) Stakeholders (3) System Boundaries (4) Functional Requirements (5) System Architecture (6) Operating Modes [2]. In this paper, the nanogrid system's purpose is to improve resilience, transmission efficiency, and ease of integration of renewable resource and energy storage. Though nanogrid resilience has not been validated, our analyses (detailed in subsequent sections) indicate that nanogrids do improve resilience over baseline microgrid infrastructure in many situations. Military nanogrid stakeholders include base commanders, tenant commands, local energy companies, microgrid providers and contractors, and maintenance and funding organizations. Higher authorities that base commands report to (e.g., The Pentagon) are also impacted by nanogrids. We view the physical and functional boundaries of a microgrid from a holistic perspective. The system includes physical equipment, processes, software, and people who sustaining operational effectiveness (e.g., maintenance, operations, supply chain, etc.). Nanogrid system boundaries differ from microgrid system boundaries in that nanogrids are much smaller than microgrids. However, individual nanogrids can be part of a larger microgrid from the perspective of a Systems of Systems (SoS). By considering several nanogrids as part of a SoS, individual nanogrids can be placed on various critical loads within a microgrid to work together to improve the microgrid's energy resilience. Nanogrids generally have external inputs from maintenance organizations, fuel providers, operator organization, a microgrid, and the external grid. The primary functional requirements from a systems engineering perspective of nanogrids are to generate, distribute, control distribution, and store energy. Where lower level functions under generate energy include generate electrical energy and adjust energy production. Distribute energy includes transmit energy, control energy flow, and convert energy. Controlling a nanogrid includes measure nanogrid state, process measurements for control decisions, and send control signals. Energy storage provides the benefit of stability of the nanogrid system when energy demand exceeds energy generation capacity. This includes store energy, release energy, and adjust energy flow. System Architecture for a nanogrid differs from a microgrid due to its complexity and potential configurations. We suggest specific system architecture details of any individual nanogrid be determined after an analysis of alternative existing nanogrid architectures is conducted in order to identify which type(s) of nanogrid architecture(s) best benefit the energy resilience of any specific military installation. Nanogrid operating modes include four primary modes of operation: microgrid-connected, transition-to-island, island, and re-connection. Microgrid-connected modeestablishes normal parallel operations with the microgrid and (assuming a microgrid-to-grid PCC) utility grid while all distributed resources in the grid operate within IEEE standards and information is exchanged with the nanogrid controller. Transition-to-island mode represents the nanogrid's transient state of transition between being connected to the microgrid and being fully islanded. The nanogrid must have sufficient energy storage available in addition to the ability to stabilize voltage and frequency (in the case of an AC or AC/DC nanogrid) for successful transition. A major concern of this mode is the dampening of transients in the nanogrid to avoid tripping protective devices [2].