This paper discusses two techniques based on the feedback linearization (FBL) method to control the active and reactive output powers of three-phase grid-connected photovoltaic (PV) inverters. The first control scheme is an application of the direct FBL approach. The other is an appropriate combination of the FBL and fuzzy logic (FBL-FL), and is the main proposed method of this study. Wherein, a unique fuzzy logic controller (FLC) is designed to enhance effectiveness of the linear control method used in the direct FBL. In detail, its major objectives are to improve the transient response and reduce steady-state oscillations in the output powers. In this research, the illustrative PV inverter utilizes a three-level DC-AC converter, an R-L filter and a 250V/10kV wye-wye transformer to inject the energy, obtained from PV array with a nominal power of 100kW, into the 10kV/60Hz three-phase grid. Numerical simulations in MATLAB and PSIM illustrate that the two FBL-based structures perform very well in independently regulating the active and reactive output powers to the reference values, even within the parametric uncertainties and the unbalanced grid voltage condition. Moreover, comparisons of simulation results, obtained from the traditional proportional-integral (PI) control and the two FBL-based structures, show advantages of the proposed FBL-FL hybrid technique in terms of fast response, small overshoot, acceptable steady-state fluctuation and high robustness.
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