Grid-voltage sensorless control of a converter under unbalanced conditions: On the design of a state observer

Abstract

This paper deals with grid-voltage sensorless synchronization and control under unbalanced grid conditions. A three-phase grid-connected converter equipped with an LCL filter is considered, and no other signals than the converter currents and the DC-link voltage are measured for control. An augmented adaptive state observer is proposed for estimation of the positive- and negative-sequence components of the grid voltage. The proposed observer is tested as a part of a sensorless control system. Experimental results show that the proposed method works well even in highly unbalanced grid conditions.