Current harmonic reduction for grid-connected photovoltaic system (PV) based on improved control of three-phase seven-level PUC inverter

Abstract

In this article, we have improved the control for three-phase of packed U-Cell seven-level inverter, the latter considered as a new multilevel converter topology and has the advantage of very high energy efficiency, and the number of components reduced but has disadvantages related to the harmonics injected into the grid causing switching states if the number of levels increased. In this paper, an improved control based on the sinusoidal control (SPWM), and space vector control (SVPWM) has been proposed for the seven-level packed PUC-Cell inverter. The Proportional resonant (PR) controllers are implemented to adjust the grid currents in the synchronous DQ frame and to maintain synchronism between the inverter and the grid, a Phase-locked loop technique (PLL) can be used. This control is composed of two regulation loops the first allows for regulation of the active and reactive currents delivered to the grid and the second regulates the DC voltage. The evaluation of our results obtained is based on the value of the total harmonic distortion obtained (THD ≪ 5 % of the international standard). This control strategy eliminates current harmonics, improves the quality of power delivered into the grid from the photovoltaic system. An analysis and comparison between this seven-level PUC-cell inverter structure, and the conventional seven-level cascade inverter structure is done, and the simulation results in Matlab/Simulink demonstrate the effectiveness and feasibility of the proposed control method.