Robust Design of Control Structure for Three-Phase Grid-Tied Inverters

Grid-tied inverters are being widely used in distributed generation, as in photovoltaic generation. This paper presents the robust design and analysis of a control structure for three-phase grid-tied inverters based on stationary frame. The synchronization with the grid is carried out using a DMSOGI-FLL structure, which allows to estimate DC offset voltage and it increases the system robustness under grid voltage abnormalities. Furthermore, a current reference generator is detailed considering the dc-link voltage regulation and the control of active and reactive power. A proportional resonant (PR) approach with harmonic compensation (HC) is applied for the output inverter current control. Moreover, the proposed structure also includes an active damping technique with capacitor current estimation to improve the system robustness in weak or strong grids. Results under several operating conditions are presented from a numerical analysis and it demonstrates the performance of the proposed control structure.