Feedback Linearization Control of Converters with LCL Filter for Weak AC Grid Integration

This paper investigates the design and analysis of a robust nonlinear controller for voltage source converters (VSCs) connected to weak AC grids. Feedback linearization method is used to develop the control inputs that regulate the active power and output voltage of the grid-connected converter. The frequency-domain model of an LCL filter in dq-frame is used to develop the nonlinear control blocks for small-signal stability analysis. Impact of phase-locked loop (PLL) is added to the control block through feedforward loops. It is shown that unlike vector controlled converters, the proposed controller is not negatively affected by the PLL gains and a broader range of operation is achieved. In addition, the designed controller is robust against sudden active power commands from 0 to 1 p.u., and is capable of fault ride through when AC grid is very weak. The robustness of the proposed controller is evaluated using eigenvalue analysis of the linearized closed-loop model and time-domain simulations of a grid-connected VSC in various cases.