Passivity-Based Optimal State-Feedback Control for LCL-Filtered Grid-Following Converter

As the grid incorporates more voltage-source converters (VSCs), the stability issues arising from VSC-grid interactions escalate. While passivity theory offers a promising solution, existing passivity-based controller designs primarily rely on heuristic methods, which do not advance stability beyond achieving passivity. To fully exploit the available degrees of freedom, this article proposes employing an optimal state-feedback control that refines control parameters using an optimization algorithm. The optimization objective aims at maximizing the external stability by minimizing the product of two-norms of the phase curve and magnitude curve of the VSC's output admittance. Compared with the conventional passivity-based design, the proposed control method improves the external stability with nondissipative grid impedance and can mostly achieve dissipativity. The optimization algorithm and the process for generating starting points for the optimization are detailed. Experimental validations confirm the effectiveness of this optimal state-feedback control in enhancing VSC-grid interaction stability.