A Hybrid AC/DC Microgrid with Bidirectional Virtual Inertia Support

In hybrid ac/dc microgrids, the dc grid bus voltage and ac grid frequency may easily go beyond the acceptable ranges under contingencies. As a result, undesirable load-shedding is required for system protection. In order to address this vulnerability in hybrid microgrids, this paper proposes a hybrid microgrid with bidirectional virtual inertia support, where virtual inertia is introduced to slow down dc voltage and ac frequency changes, and thus enhancing system stability. With a standard hardware configuration, inertia is delivered to both ac and dc subgrids via the change of bi-directional interlinking converter control. Specifically, the difference between the per-unit dc voltage and ac frequency goes through a proportional integral (PI) controller, forming the active power reference of the interlinking converter. In addition, other supportive functions, such as frequency and voltage droop and secondary control, can be further implemented. Finally, simulation results are provided, validating the superiority of the proposed hybrid microgrid. As a result, the frequency nadir, rate-of-change-of-frequency (RoCoF), and dc bus voltage deviation are improved by more than 40%, 50%, and 40%, respectively.