Decoupled control strategy of grid interactive inverter system with optimal LCL filter design

Abstract

This thesis presents a control strategy for a three-phase grid interactive voltage source inverter (VSI) that links a renewable energy source to the utility grid through a LCL-type filter. An optimized LCL-type filter has been designed and implemented so as to reduce the current harmonics in the grid considering the conduction and switching losses at constant modulation index (Ma). The control strategy adopted here decouples the active and reactive power loops, thus achieving desirable performance with independent control of active and reactive power injected to the grid. The startup transients are also controlled by the implementation of this particular control method. Another control technique has also been studied so as to overcome the hitches faced by the conventional controllers. It counterbalances the distortions in grid voltage by injecting sinusoidal current into the grid. The filter has been designed considering the conduction and switching copper losses as well as core losses. A tradeoff has been made between the total losses due to the inductor and the THD% of the grid current, and the filter inductor has been designed accordingly. In order to study the dynamic performance of the system and to confirm the analytical results, the models are simulated in the MATLAB/Simulink environment and the results are analyzed.