Grid-Following and Grid-Forming Converter Control Comparison Under Fault Conditions

Traditionally control of grid-connected converters is based on a grid-following structure, where a Phase Locked Loop is responsible for tracking the angle of the AC grid. However, such control structure leads to stability problems for weak and low inertia grids. Then, a grid-forming control structure is presented as a potential solution. This paper compares grid-following and grid-forming control structures under fault conditions, i.e. it is focused on the transient stability. In particular, grid-following controls consider several PLL implementations presented in the literature. Faults are analysed in an essential power system that includes the dynamics of converters and synchronous generators. Control structures are compared based on dynamic simulations in PSCAD/EMTDC.