Impedance estimation for transient stability enhancement of virtual synchronous machines

In this paper, a passive technique for estimating the impedance and voltage of a Thévenin grid is presented. The method can be applied when either the maximum active power or minimum reactive power operating point, with respect to the power angle, is crossed. This work addresses transient events, for which the former occurs. A key assumption is that the power response of the converter is sufficiently slow such that the steady-state equations for active and reactive power remain accurate as the power angle varies, which is valid for virtual synchronous machines. In conjunction with the equal-area criterion, the estimated parameters are used to appropriately adjust the reference active power to maintain synchronism with the grid. The methodology is validated in MATLAB/Simulink.