While DC microgrids have many well-understood advantages (e.g., simpler, more efficient and compact power conversion system as well as less copper consumption in the cables), the unique DC electric characteristics, such as direct P-V coupling (i.e., even a small load/generation change can lead to voltage flickers and equipment malfunctions) and low system inertia (i.e., very little overload capacity), pose great challenges to grid stability. Small-signal stability can only ensure the stability of the system at the equilibrium point, but the true boundary of the stability domain cannot be determined; hence there are major limitations in securing stability when the system has large disturbances. Existing large-signal analysis tools in the literature have either limited applicable ranges or non-rigorous theoretical foundations. Therefore, there is an urgent need to develop a fundamental knowledge base of large-signal stability analysis in converter-dominated DC microgrids and a comprehensive design guideline for DC grid stability. The research findings of this project directly contribute to the overall goal in our country to maintain high reliability and resilience electricity with more and more microgrids and distributed energy sources. The proposed education and outreach research plan will (i) incorporate theoretical frameworks, curated data sets, and testbed from this project into the existing curriculum at both the University of Michigan-Dearborn and the University of Texas at Austin; (ii) promote K-12 students’ interest in STEM; (iii) disseminate all project materials, processes, designs and results in the public domain via public-access websites, top-ranking conference and journal publications and in diverse media; and (iv) provide rich research opportunities to under-represented undergraduates by creating societally meaningful projects on microgrids.
The goal of this project is to (a) take a rigorous step toward deriving the sufficient criteria for large-signal global stability in DC microgrids with multiple distributed energy sources and constant power loads, which is still an unsolved puzzle because traditional small-signal stability analysis does not apply to converter-dominated power systems when a large disturbance occurs, such as a fault, a pulse power load, or load switching; and (b) investigate a systematic methodology to improve the global asymptotic stability of a converter-dominated DC microgrid in a theoretically sound yet easy-to-implement manner, ultimately bridging the technology gap between three traditionally disjointed areas: control theory, power systems, and power electronics. The proposed project aims to fulfill this goal by leveraging the range and depth of the PIs’ expertise (e.g., power systems, power electronics, optimization, control theory, and machine learning). The proposed research will have intellectual merits in the following areas: (1) a fundamental knowledge base to understand the large-signal stability criteria of inertia-less DC microgrids with 100% penetration of constant power loads and converter-based distributed energy sources; (2) a stability-aware converter to collectively improve the global asymptotic stability of converter-dominated DC microgrids in a theoretically sound yet easy-to-implement manner; (3) rigorous mathematical methods and safe learning algorithms for estimating the region of attraction of a general dynamic system (i.e., a DC microgrid) with multiple equilibria; and (4) a power-hardware-in-the-loop testbed allowing for dynamic interactions of the proof-of-concept prototypes of innovative stability-aware converters.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
