State-feedback controller and observer design for grid-connected voltage source power converters with LCL-filter

We discuss observer and state-feedback controller design for grid-connected voltage source power converters with LCL-filter under symmetric grid voltage variations where only the converter-side currents are available for feedback. The LCL-filter is modeled as lossy network including resistances, capacitance and converter-side and grid-side inductance. Observability and controllability of the system are analyzed. Controller and observer design are based on linear quadratic regulator (LQR) design with stability margin. The designed proportional-integral (PI) state-feedback controllers are extended by filter current decoupling control (FCDC) and by grid voltage feedforward compensation (GVFC). Simulation results illustrate (i) the control performance of a proportional-integral and an integral state-feedback controller with and without FCDC and GVFC and (ii) the parameter sensitivity of the observer and the closed-loop system under parameter uncertainties of the inductances and the capacitance.