Robust sensorless control of grid connected converters with LCL line filters using frequency adaptive observers as AC voltage estimators

This paper presents robust control of grid connected voltage source converters (VSC) with LCL line filter without grid voltage sensors, measuring only converter inductor currents and DC link voltage. As grid impedance and step-down transformer inductance values are usually not known, proposed control algorithm relies only on converter side inductor value for control parameter, making it robust against grid variations. Proposed method uses frequency adaptive observers as filter capacitor voltage estimators, which enables the use of well-known highly dynamic performing voltage oriented control (VOC). Two versions of the frequency adaptive observers are presented, one in synchronous frame and one in stationary frame. Theoretical results are verified in simulation environment and experimentally.