Fundamental Analysis of Grid-Forming Converters Enhanced with Feedforward Controls

Abstract

The grid-forming control for power converters can be enhanced by proper feedforward terms included in the active power control loop. Two basic structures are identified, the feedforward angle and the feedforward frequency. The formal analysis of the transfer functions reveals a structural similarity. The two schemes exhibit however a fundamental difference in their transient capabilities. The grid-forming controls are characterized with the introduction of two specific factors, for the direct assessment of the inertia and the damping which can be provided by the grid-forming converter. The sensitivity analysis of the two feedforward schemes indicates that the enhancement of the transient performances of the control results in a reduction of the inertia synthetically provided by the converter. The results show that the feedforward frequency is significantly more sensitive than the feedforward angle to the feedforward term, and that the feedforward frequency presents a suitable range of damping capabilities but limited possibility of improving the inertial capability. The considerations derived in the analytical investigations are finally verified with a simulation-based application case, implementing a detailed EMT model in the Simscape toolbox of Matlab/Simulink.