This paper presents a novel flow invariants-based approach to microgrid management that is much more intuitive, less complex, and highly scalable in comparison with existing droop control, agent-based, and model predictive control-based approaches. These proclaimed advantages are exemplified by using a renewable energy-based microgrid (a microgrid-in-a-container) for a military forward operating base camp as the model system. The ability of the proposed approach to maintain the overall system stability and valid power flows while efficiently managing distributed energy resources through multiple operational modes is reflected by using a requirements matrix, and proven techniques in distributed systems and formal analysis. A Power System Computer Aided Design (PSCAD) simulation is used to validate and verify the real-world practicality of the proposed control approach.