Interactions between power electronic converters are typically investigated by means of impedance-based model analysis. The effects of the PLL are usually neglected, but recent studies have shown the importance of including those effects for stability analysis purposes. This paper focuses on the investigation of interactions between synchronization units of converters operating in parallel. The impedance-based approach is used for the investigation in the frequency-domain. The converters are supposed to share the same point of common coupling (PCC) and the characteristic of the grid at the connection point is crucial for determining the effects of the interactions between the operating units. In order to isolate the effects of the synchronization, the converters is modeled as a current sources, whose reference currents are calculated using the angle detected by their PLLs. Time-domain simulations are performed as well as experimental laboratory tests in order to validate the presented analysis.