An improved control scheme for grid connected voltage source inverter

In grid connected Distribution Generation systems, Voltage Source Inverters are used for interfacing the renewable energy source to the utility grid. DG has variety of problems during grid integration. The power quality problems may cause problems to the industries ranging from malfunctioning of equipment to complete plant shut down. Disturbances from the utility grid including voltage sags, harmonics and the grid impedance will affect the grid connected voltage source inverters connected to the grid. Hence the control of the grid connected inverter plays an important role in feeding a grid with high quality power. This report presents an analysis of the stability problem of a grid connected with Voltage Source Inverter and with a LC filter. The possible grid-impedance variations have a significant influence on the system stability. Whenever the grid inductive impedance increases, the low frequency gain and the bandwidth of the Proportional Integral (PI) controller have to be decreased to maintain the system stable, thereby degrading the tracking performance and disturbance rejection capability. To overcome this problem an H∞ controller is proposed with an explicit robustness in terms of grid impedance variations to incorporate the desired tracking performance and stability margin. The proposed method is simulated by using MATLAB/SIMULINK The results of the proposed H∞ controller and the conventional PI controller are compared, which validates the performance of the proposed control scheme.