Observer-Based State-Space Current Controller for a Grid Converter Equipped With an LCL Filter: Analytical Method for Direct Discrete-Time Design

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 direct pole placement in the discrete-time domain and in grid-voltage coordinates. Analytical expressions for the controller and observer gains are derived as functions of the physical system parameters and design specifications. The connection between the physical parameters and the control algorithm enables automatic tuning. Parameter sensitivity of the control method is analyzed. The experimental results show that the resonance of the LCL filter is well damped, and the dynamic performance specified by direct pole placement is obtained for the reference tracking and grid-voltage disturbance rejection.