Stability Assessment and Optimization Methods for Microgrid With Multiple VSG Units

The virtual synchronous generator (VSG) is a control scheme for inverter-based generating units that uses a synchronous generator (SG) model to emulate the dynamic behavior of a SG in order to enhance the stability of the system. In this paper, the multi-VSG microgrid is introduced and the voltage angle deviations (VADs) of generators with respect to the angle of the center of inertia are defined as a tool for transient stability assessment of the multi-VSG microgrid. Afterward, particle swarm optimization is implemented to tune the parameters of the VSG units in order to achieve two objectives: first, to have a smooth transition after a change or disturbance and second, to maintain the VADs of generators within a specific limit. Moreover, another scheme termed alternating inertia is applied to the VSGs of the microgrid to suppress the oscillation quickly and improve transient stability after a large disturbance. This scheme switches the value of the moment of inertia of VSGs considering the angular frequency of the VSG with respect to the equilibrium point and its rate of change. The introduced multi-VSG microgrid is simulated by PSCAD/EMTDC and the performance of the proposed methods is evaluated.