Enhanced Virtual Inertia Controller for Microgrid Applications

Unlike Synchronous Generators (SGs), Virtual Synchronous Generators (VSGs) inertia is not fixed once it is manufactured and only has an upper limit defined by its energy storage components. In this paper, a novel Enhanced Virtual Inertia Controller (EVIC) is proposed. The proposed controller alters the VSG inertia coefficient between two limiting levels in response to a grid transient. The key difference between the proposed controller and the variable inertia controller is that the proposed EVIC causes a smooth transition in the inertia coefficient while the variable inertia controller causes a discontinuous jump in it. The proposed EVIC guarantees an adaptive response to grid dynamics, such that a negligible change occurs at small disturbances and a linear and smooth increase occurs at moderate disturbances. For large disturbances, the proposed controller smoothly oscillates the inertia between two saturation levels, which then quickly returns the converter to its steady-state operating point with minimum oscillations. A qualitative study of the performance and stability margin of the proposed controller was conducted using a large signal model (nonlinear model) of VSG connected to a microgrid. The large signal model provided a complete description of the converter's behaviour under large disturbances, which is the area of interest of the proposed controller. It also contained the small-signal dynamics (linear dynamic) within the vicinity of the equilibrium (steady-state) point. Thus, a complete description of the proposed controller dynamics is conveyed to prove its validity and adaptability.