Static power converter synchronization and control under varying frequency conditions

Due to the increasing use of distributed and non-conventional power generation sources, grid synchronization and control of static power converters under variable grid frequency is of particular interest. This work develops a discrete-time phase locked loop (PLL) based on a rotating reference frame to be used in variable frequency systems. The PLL is used in combination with a time-varying transformation based on a rotating frame for control purposes. Finally, for a back-to-back static converter topology, linear and nonlinear control strategies are proposed and evaluated under frequency variations and different operating points. The results - including stability analysis - show their particular performance under frequency variations.