A novel communication-less control method to improve proportional power-sharing and SOCs balancing in a geographically dispersed hybrid AC/DC microgrid

Batteries' SOC balancing, proportional power-sharing, and keeping voltage and frequency in permissible operation areas along with ensuring system stability are of the most important challenges of the microgrids control algorithm. In this paper, a novel communication link-less control method for hybrid microgrids is proposed. In the AC subgrid, the droop gain of the energy storage units (ESUs) is defined as a function of their SOC. Next, a novel control method based on the AC signal injection for SOCs balancing in the DC side is suggested. After that, a new droop curve for the interlinking converter (IC) is defined. The IC droop coefficient is adjusted based on the DC subgrid SOC such that not only all SOCs in the AC and DC sides are converged, but also proportional powersharing is attained. The proposed method benefits of modularity and expandability, hence it can be implemented to a multi-subgrid microgrid with various DC buses voltage and different frequencies. The small-signal stability analysis proves that the proposed method is stable. Simulation results of the nonlinear model of the system confirm that the proposed method can balance batteries SOC, dispatch power properly, and maintain voltage and frequency deviations within the statutory range.