Robust Nonlinear Controller Design for Three Phase Grid Connected PV Systems with Improved Power Quality

The development of photovoltaic systems has increased due to the high demand for clean and green energy. Used worldwide for distributed power generation, the photovoltaic power must not only be maximized, but also adapted to the global standards on harmonic emissions limits. Therefore, tracking the Maximum Power Point and filtering harmonics became necessary. A three-phase grid-connected Photovoltaic system consisting of a photovoltaic (PV) array, a boost converter and a three-phase PWM inverter coupled through a low-pass filter to the electrical grid is studied in this paper. Two new control designs are developed to maximize power in the side of PV panels and to impose a unity power factor in the side of the grid, the first for the three-phase grid-connected systems with an L-filter and the second for the same systems with an LCL-filter. Both controls are analyzed and compared in details and their stability is demonstrated using Lyapunov analysis. The theoretical analysis and simulation results clearly illustrate that the proposed controllers have achieved the objectives. In order to demonstrate the good performance of the LCL-filter in minimizing the harmonics produced by the inverter, a comparison between the frequency responses of the injected currents using the LCL-filter and the L-filter is carried out.