Stability boundary analysis in single-phase grid-connected inverters with PLL by LTP theory

Stability analysis of power converters in ac networks is complex due to the nonlinear nature of the conversion systems. Whereas interactions of converters in dc networks can be studied by linearizing about the operating point, the extension of the same approach to ac systems poses serious challenges, especially for single-phase or unbalanced three-phase systems. A general method for stability analysis of power converters suitable for single-phase or unbalanced ac networks is presented in this paper, based on linear time periodic theory. A single-phase grid-connected inverter with phase-locked loop (PLL) is considered as case study. It is demonstrated that the stability boundaries can be precisely evaluated by the proposed method, despite the nonlinearity introduced by the PLL. Simulation and experimental results from a 10-kW laboratory prototype are provided to confirm the effectiveness of the proposed analysis.