A Robust H∞ State Feedback Controller Enabling a Medium Voltage Five-Level Grid-Connected Inverter for Grid Code Compliance

A novel robust
${H}_\infty $
state-feedback control system providing optimal stability as well as robust performance for a three-phase medium voltage five-level grid-connected inverter is proposed in this paper. The proposed one Degree of Freedom (DoF) control system provides high-quality sinusoidal grid current and guarantees optimal robust performance for the grid-connected five-level inverter in case of grid voltage disturbances, grid-side inductor parametric uncertainty, and ensures optimal reference tracking with optimal transient response in case of different grid fault scenarios following different grid standards such as the North American Electricity Reliability Corporation (NERC) and IEEE Std 2800-2022. To that end, the parametric uncertainty of the system is modeled as a polytopic-type uncertainty and a Linear Matrix Inequality (LMI)-based state-feedback controller based on convex optimization is implemented on the five-level grid-connected inverter. The system modelling as well as the design of the proposed controller will be discussed in this paper. The performance of the designed controller with the five-level grid-connected inverter is tested under different scenarios. Results are provided in PSCAD on a 5 MW, 34.5 kV system to validate the effectiveness of the proposed robust
${H}_\infty $
control system. Moreover, scaled-down hardware test results are provided to further validate the performance of the controller.