Inertia design methods for islanded microgrids having static and rotating energy sources

Dynamic frequency regulation and effect of penetration of static and inertial sources on system stability are important issues for islanded microgrid power quality and reliability. This work presents a novel strategy of utilizing an inverter based source as a voltage source inverter (VSI) or virtual synchronous generator (VSG). Electro-mechanical and power modes are critical for small signal stability of an isolated microgrid having static and inertial sources. Interaction of these modes is analyzed through eigen-value analysis of microgrid model and differential equations describing respective modes. Inertia is important for providing fault current, determining steady state and transient stability and better system frequency profile. A novel technique is proposed to include inertia virtually to the inverter based sources by adding swing equation. Further, inverter based sources with traditional and modified droop control and VSG are compared with respect to inertia, energy and stability. The proposed control and stability comparison are verified through experimental microgrid setup having three inverter based sources which can alternately be operated as virtual synchronous generators.