An Enhanced Feedback Linearization with Fuzzy Logic to Control the Active and Reactive Powers of Bidirectional Three-Phase Grid-Connected Renewable Energy Inverters

Abstract

This paper proposes an enhanced feedback linearization method with fuzzy logic (enFBL-FL) to control the active and reactive powers of bidirectional three-phase grid-connected inverters used in renewable energy systems. The proposed control structure is a suitable combination of the direct Feedback Linearization (FBL) and Fuzzy Logic (FL) with newly-added helpful improvements and features. In detail, a unique fuzzy-based scheme is designed to adjust automatically the integral coefficients of the linear control method used in the direct FBL. Its key goals are to increase the response speed, eliminate the overshoot and diminish the steady-state fluctuations in the active and reactive powers. Also, two complementary proportional controllers for the powers are newly added at the outer loop to overcome unexpected errors of the Phase Lock Loop (PLL) and system modeling. In this study, the illustrative inverter utilizes a bidirectional three-level DC-AC converter, an R-L filter and a 250V/10kV 100kVA delta-wye transformer to deliver the total power, obtained from renewable sources and an Energy Storage System (ESS), to the 10kV/60Hz three-phase grid. As well, the inverter can absorb the active power from the grid to charge the ESS as needed. Numerical simulations in MATLAB demonstrate that the suggested enFBL-FL can regulate well the active and reactive powers of the inverter to the reference signals in both negative and positive values, even within large parametric uncertainties in the physical inverter and sudden changes in AC-system load of the grid. Furthermore, comparisons on simulation results, performed separately with the traditional PI control, the direct FBL approach and the newly proposed enFBL-FL, are provided to evaluate salient advantages of the proposed technique.