Control Strategy To Suppress DC For Transformer-Less Grid-Connected PV Systems

Photovoltaic(PV) power systems are widely utilized, so that it can carry out the growing power demands. At present, Grid-connected PV systems are becoming more attractive. For increasing the overall efficiency of PV power systems, the tendency of using transformer-less grid-connected inverters are drawing more attention due to high efficiency, low cost and small size. This thesis presents an efficient control method, which mainly focuses on the suppression of Direct Current(DC) component injection to the utility grid for grid-connected single-phase PV inverter. The proposed control method is also able to reduce the total harmonic distortion(THD) in the grid current. A PI controller along with an integrator is used into the feedback closed-loop of grid-connected inverter system for achieving the zero steadystate error condition for the designed controller, which efficiently suppressed the DC injecting into the inverter output current and reduced the harmonics in the grid current. Proposed DC suppressing method is then compared with other methods based on the output waveforms of grid current and Fast Fourier Transform(FFT) analysis. In our proposed method, the DC component value and THD% is reduced to a very low level as compared to previously proposed techniques, which meets the international standards defined for grid-connected PV systems with a big margin. The simulation results testify the validity and significance of the proposed method.