Multiresonant Frequency-Locked Loop for Grid Synchronization of Power Converters Under Distorted Grid Conditions

TLDR: A new multiresonant frequency-adaptive synchronization method for grid-connected power converters that allows estimating not only the positive- and negative-sequence components of the power signal at the fundamental frequency but also other sequence components at other harmonic frequencies is presented.

Abstract: This paper presents a new multiresonant frequency-adaptive synchronization method for grid-connected power converters that allows estimating not only the positive- and negative-sequence components of the power signal at the fundamental frequency but also other sequence components at other harmonic frequencies. The proposed system is called MSOGI-FLL since it is based on both a harmonic decoupling network consisting of multiple second-order generalized integrators (MSOGIs) and a frequency-locked loop (FLL), which makes the system frequency adaptive. In this paper, the MSOGI-FLL is analyzed for single- and three-phase applications, deducing some key expressions regarding its stability and tuning. Moreover, the performance of the MSOGI-FLL is evaluated by both simulations and experiments to show its capability for detecting different harmonic components in a highly polluted grid scenario.

Figures

Fig. 9. Frequency response of the single-phase MSOGI-FLL.

Fig. 1. Adaptive filter based on SOGI, i.e., SOGI-QSG.

Fig. 11. MSOGI-FLL for three-phase systems able to synchronize with “n” harmonic components of the input vector.

Fig. 10. Block diagram of the DSOGI-FLL divided into its building blocks: SOGI-QSG(β), SOGI-QSG(α), FLL, and PNSC.

Fig. 15. Experimental response of DSOGI-FLL under distorted voltage. (a) 50-Hz positive sequence (40 V/div–10 ms/div). (b) 50-Hz negative sequence (40 V/div–10 ms/div). (c) Frequency estimation (0.75 Hz/div–50 ms/div).

Fig. 4. Bode diagram of the FLL input variables.