Modeling, Control and Stability Analysis for Low-inertia Power Grids
In recent years, significant inverter-based inertia-less renewable generation, e.g. photovoltaics and wind turbines has been integrated in both bulk power transmission and distribution power systems to improve the sustainability of electric power systems. The increasing penetration of these distributed energy resources (DERs) displacing conventional synchronous generators (SGs) is rapidly changing the dynamics of large-scale power systems due to their intermittent characteristics and lower inertial response. This reduced inertia has a considerable effect on transient response of the power system resulting in inter-area oscillations, less synchronization, and power oscillation damping. A novel power electronics converter named Z-Source virtual synchronous generator (ZVSG) is proposed to address low inertia issues in the power grid. This converter is also equipped with a low-voltage ride-through controller to revive the voltage of the system during reactive power related contingencies. The stability of ZVSG is also discussed by deriving its impedance and judged by general Nyquist criteria. The application of the VSG in wind generation power system is also studied and the impact of the VSG parameters on stability of the system is discussed by deriving the impedance of the system in sequence domain. Finally, using matrix inequality methods an appropriate pre-compensator is designed to decouple the VSG as a multi input multi output to a set of single input single output systems. The resulted controller shows a robust performance against voltage and load disturbances in the system.