Control of grid-connected voltage source inverter with LCL filter

This paper presents a control scheme for a grid-connected three-phase voltage source inverter with an LCL filter, which is suited for renewable energy applications. The proposed method has the following properties: fast tracking, optimized dynamics, grid disturbance rejection, and active resonance damping. The controller is based on an augmented linear quadratic regulation (LQR) scheme, which is optimized based on a weighted cost function. The LQR controller is augmented to include two complex conjugate poles at the grid frequency for sinusoidal voltage disturbance rejection upon connection to the grid. Furthermore, this control scheme actively damps the resonance introduced into the closed-loop system through the third-order LCL filter. Finally, the current reference is found by calculating the instantaneous power, which allows for faster power tracking compared to using the technique of measuring average power. Results verify the validity of the proposed control scheme.