Observer-Based Grid-Voltage Sensorless Synchronization and Control of a VSI-LCL Tied to an Unbalanced Grid

This paper proposes an observer-based grid-voltage sensorless strategy that allows to implement the synchronization and control of an LCL grid-tied voltage source inverter. By using exclusively the measurement of the current injected to the grid, an observer estimates both fundamental positive- and negative-sequence components of the grid voltage, with a quality (in terms of total harmonic distortion and convergence speed) comparable to that obtained with a classic double second-order generalized integrator-frequency-locked loop (DSOGI-FLL). The unmeasured LCL filter states are also estimated by the observer, and they are used to implement a full-state feedback control strategy suitable for low resonance frequency LCL filters. The effectiveness of the scheme proposed here is demonstrated by comparison with a DSOGI-FLL and with a controller recently proposed in the literature. Experimental and simulation results that demonstrate the validity and effectiveness of the proposal are presented.