A DQ-Frame Asymmetrical Virtual Impedance Control for Enhancing Transient Stability of Grid-Forming Inverters

This article proposes a
dq
-frame asymmetrical virtual impedance control scheme for preventing grid-forming (GFM) inverters from the loss of synchronization with the grid under large disturbances. The approach exploits the two degrees of freedom in the
dq
-frame virtual impedance synthesis of GFM inverters, and introduces a virtual transient impedance (VTI) scheme to improve the power transmission capability and, thus, restoring equilibrium points of GFM inverters during the large disturbances. The transient stability of GFM inverters with the different kinds of virtual impedance setting is analyzed to formulate the design guideline of VTI method. Simulations and experimental tests are presented to validate the effectiveness of the approach.