SOGI-FLL Based Optimal Current Control Scheme for Single-Phase Grid-Connected Photovoltaic VSIs with LCL Filter

Abstract

In grid-connected systems, a control that can ensure power flows with better performances and assure the injection of proper power quality into the utility grid is of prime interest. In this paper, an optimum design of a current controller based on Second-Order Generalized Integrator Frequency-Locked Loop scheme (SOGI-FLL) for single-phase LCL-filtered grid-connected photovoltaic VSI is presented. The main aim of this work is to ensure the grid current control with good transient response, injection of proper power quality, and optimization of the computation time. To this end, the SOGIFLL scheme which is characterized by its simplicity, good transient response, and better filtering performances is introduced into the system control. The SOGI-FLL is utilized to estimate proper filtered orthogonal components and frequency of the grid voltage and current to be used by the proposed controller which can enhance its performances. In addition, an improvement in the inner control loops, based on the manipulation of sinusoidal signals instead of dq components through PI controllers is also proposed. This improvement can optimize the computation time by eliminating some PI controllers and dq transformation blocks. Simulation results are provided for a single-phase grid-connected PV, showing the effectiveness of the proposed controller.