Assessment of GCCs' synchronization units under various grid voltage conditions

Operation of grid-connected converters strongly depends on the adopted synchronization strategy, as it estimates grid voltage components and angular frequency - variables extensively used by the rest of the control algorithm. The aim of this paper is to analyze and compare the performance of the phase-locked loop (PLL) techniques so that the optimal synchronization structure can be chosen and the identified shortcomings addressed. The assessment was done for transient voltage changes and under the distorted grid voltages. Specifically, the PLLs' responses were documented following the start-up and after the appearance of the voltage unbalances, phase jumps and harmonics. The study was done using hardware-in-the-loop (HIL) experimental setup.