Observer-based state-space current controller for a grid converter equipped with an LCL filter: Analytical method for direct discrete-time design in synchronous coordinates

State-space current control enables high dynamic performance of a three-phase grid-connected converter equipped with an LCL filter. In this paper, observer-based state-space control is designed using complex-valued modeling and direct pole placement in the discrete-time domain and in grid-voltage coordinates. The proposed observer reduces the number of measurements in control, and retained connection between the physical parameters and the control algorithms enables automatic tuning. Parameter sensitivity of the control method is analyzed, and experimental results show that the resonance of the LCL filter is well damped.