Validation of impedance-based small-signal stability analysis for single-phase grid-feeding inverters with PLL

The interactions of more and more power electronics-interfaced power systems can worsen the power quality and the system stability in distribution networks. System stability can be addressed analyzing the source and load impedances at the interaction section and well-established approaches exist for DC and three-phase AC networks. Some papers focused also on single-phase AC systems, whose study is generally more difficult due to their nonlinear and time-varying characteristics. One viable solution to address this issue is the use of equivalent dq rotating reference frame even for single phase system so as to identify a steady-state operating condition. This paper uses this approach and proposes the small-signal analysis of a single-phase AC system that includes a current-controlled inverter synchronized to the grid via a Phase-Locked Loop (PLL). Experimental validations are provided herein to asses the feasibility of this approach and to verify the stability criteria based on the source and load impedances.