A combined phase locked loop technique for grid synchronization of power converters under highly distorted grid conditions

In power distribution networks, the fundamental positive-sequence component detection of the utility voltage is required to synchronize the control reference signals of power converters with the fundamental components of this voltage. Accurate and fast positive-sequence information for grid synchronization under unbalanced and highly distorted conditions is essential to ensure the synchronization, the correct generation of the reference signals and to cope with different grid conditions such as line harmonics, voltage sags and frequency fluctuations. This paper presents a combined phase locked loop technique for grid- interfaced converters that is robust under two phases short-circuits, imbalances and high harmonic distortions, while being frequency-adaptive. The proposed system is called MVF-DSOGI-PLL since it is firstly based on a combination of multi-variable filter (MVF) and dual SOGI-based quadrature-signals generator (DSOGI-QSG) and secondly on a phase-locked loop (PLL), which makes the system frequency-adaptive. In this paper, a detailed study of the MVF-DSOGI-PLL is performed and various simulation results of the proposed technique are presented under highly distorted grid conditions to confirm its validity and robustness.