Advancing Steady-State and Dynamic Operation of Islanded Hybrid AC-DC Microgrids

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Last decade witnessed an unprecedented increase in the integration of DC-based distributed generation (DG) and loads in the grid via power electronic converters. This has created both a challenge, due to the additional losses introduced by the required DC/AC and AC/DC conversion stages, and an opportunity for efficiency enhancement through implementation of DC grids and elimination of unnecessary conversion stages. Coexistence of AC and DC grids forms a new paradigm called hybrid AC-DC grid. The most challenging configuration for realizing this concept is islanded AC-DC-coupled microgrid, where none of the two subgrids has a slack bus, power can flow between the subgrids bidirectionally, droop control of DGs makes system variables load-dependent, subgrids can get overloaded, and AC-side DGs can experience unbalanced loading. As an example, unbalances of up to 100% have been reported in AC microgrid of a remote community in Northern Ontario. The long term objective of the proposed research program is to develop improved, practical renewable-energy-based hybrid microgrid solutions for off-grid remote community, mining, and military applications, via analysis, planning, design, simulation and experimental verification. Within the 5-year Discovery Grant period, the applicant and his team will attempt to: (i) improve the accuracy and computational efficiency of steady-state analysis tools by taking an autonomous sequential approach to solving the AC and DC subgrids' power-flow problems, and using a symmetrical-component-based algorithm; (ii) avoid subgrid overloading and AC DGs' unbalanced operation by routing the power dynamically among the AC-side phases and DC-side through interlinking converters; (iii) improve performance of hierarchical controllers by coordination of hierarchical control of the interlinking converters with those of AC and DC subgrids; (iv) expedite provision of electricity access to unprivileged off-grid communities by developing innovative DC microgrid solutions; and (v) address high ramping rates of renewable-energy-based DGs and loads, and facilitate provision of ancillary regulation services, by incorporating hybrid energy storage systems and 4-quadrant EV chargers in hybrid microgrids. The plan is to expand the dimensions of research beyond Discovery Grant period by joining power industry and an off-grid remote community, and apply for a sizable grant to work towards design and implementation of an actual-size hybrid microgrid that, while serving the community, will act as a tool for collection of invaluable data. The proposed research program will contribute greatly to training of highly-qualified personnel for academia and industry and will advance global position of Canada as a country that invests responsibly to address global environmental issues and improve the lives of its indigenous people who form the remote communities of the north.