Energy Synchronization of Grid-Connected Power Electronic Converters

This paper aims to revisit and challenge the well known synchronization method known as the Phase-Locked-Loop (PLL) commonly used when interfacing renewable energy sources via power converters to the grid. Unfortunately, this established synchronization method lacks global stability guaranties, particularly when the converter is synchronizing to a weak grid. Thus, this paper wants to reevaluate the way the power electronic converter synchronization mechanism is designed, working towards replacing the standard PLL with alternative controllers with promising large-signal stability features by relying on passivity arguments. Although our theoretical global stability proof associated to our synchronization alternative suggests that a nonlinear observer is needed-leading to an increased control complexity-we show via practical time-domain simulations that this requirement can potentially be relaxed. Both grid-following and grid-forming operating modes have been investigated.