Design and Real-Time Implementation of Cascaded Model Reference Adaptive Controllers for a Three-Phase Grid-Connected PV System

This article proposes the development of a model reference adaptive controller (MRAC) for grid integration of a single-stage three-phase grid-connected photovoltaic system (GCPVS). The performance of a GCPVS is influenced by uncertainties such as measurement noise, solar irradiance, photovoltaic (PV) operating point, aging of the dc-link capacitor, and variation in the filter impedance. In order to achieve the desired tracking performance under both nominal and parametric uncertainties, MRACs are designed for both the outer PV voltage control loop and the inner grid current control loop. The proposed control scheme comprises a reference model and a Lyapunov-based parameter adaptation scheme, which provides the nominal tracking performance despite uncertainties in the GCPVS dynamics. As a result, improved performance of the GCPVS is achieved in terms of low dc-link voltage ripple, superior power extraction, and improved grid power quality. The performance of the proposed adaptive controller is verified by pursuing simulation in MATLAB/Simulink followed by experimentation on a 2.5-kW GCPVS. The control algorithm is implemented in real time on the SPARTAN-6 FPGA scheme. The efficiency of maximum power point tracking (MPPT) is obtained as 99.92%. The total harmonic distortion of grid currents and voltages at the point of common coupling is found to be less than 3%, which is well within the limit specified by the IEEE-1547 standard.