Extended Kalman Filter–Linear Quadratic Regulator-Based Current Control for Dynamic Response Improvement and Robustness Enhancement of Grid-Forming Inverters

Abstract

This paper proposes an EKF–LQR-based current controller to improve the performance and robustness of the current control loop in grid-forming inverters (GFMIs). Since load variations, power-reference changes, and grid-condition variations affect the dynamic characteristics of the output current in GFMIs, fast and stable control performance of the current control loop is required. However, conventional fixed-gain current controllers may cause response delay, overcurrent, and oscillations under variations in grid impedance, short-circuit ratio (SCR), and operating conditions. Therefore, this paper combines EKF-based current-state estimation with LQR-based optimal state-feedback control to improve the dynamic performance and robustness of the current control loop. The effectiveness of the proposed EKF–LQR-based current controller is validated through MATLAB/Simulink simulations and hardware-in-the-loop simulation (HILS) experiments under various operating and grid conditions.