Development and Performance Evaluation of a Hybrid Fractional Order Proportional Integral Controller for Grid-Connected Inverters

Abstract

This article proposes the development of a Hybrid Fractional Order Proportional Integral (HFOPI) controller for decoupled active (P) and reactive (Q) power control to improve grid-connected inverter performances. The proposed controller gains are numerically tuned using the isodamping feature, which is a frequently used frequency method. The system under study is a grid-connected inverter system that contains a DC source, a three-phase inverter connected to the grid through an L filter. The proposed controller HFOPI combines a Variable Gain PI (VGPI) controller work in alternative with a Fractional Order PI (FOPI) controller and a selection algorithm that organize the two controller’s interventions. The performance and robustness of the proposed HFOPI controller is examined and assessed under various scenarios such as suddenly step change in active and reactive power references and compared with the simple structure based on FOPI or PI controller. The simulation is carried out using MATLAB/Simulink. Moreover, the grid-connected inverter test bench is set up in the laboratory. Where, the experimental results are consistent with the simulation and prove that the proposed HFOPI controller provides an important amelioration in term of maximum first overshoot/undershoot, tracking settling time and lower injected current Total Harmonic Distortion (THD) compared to the simple structure based on the PI/FOPI controllers.