A new proposal to eliminate the DC current component at the point of common coupling for grid connected systems

Nonlinear loads as grid connected converters can cause, besides the generation of several current harmonics in the grid current, a DC current component injection. A DC current component can cause the magnetic core saturation of distribution power transformers. Transformers operating under saturation conditions present increased power losses, overheating and distorted current waveforms. Since a DC current component causes a small DC voltage component drop across the parasitic resistance of the distribution grid conductors, canceling the DC voltage component at the Point of Common Coupling (PCC) implies the compensation of the DC current injection by electric loads or grid connected converters connected at the same PCC. This paper proposes a low cost solution for an accurate detection, free from offset problems, of the DC voltage component present in the grid voltage. The DC voltage compensation strategy was embedded in a full bridge grid connected converter. Simulation and experimental results showed the effectiveness of the proposed strategy.