Active Filter for the Removal of the DC Current Component for Single-Phase Power Lines

Nonlinear loads and grid-connected converters can cause, in addition to 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 component injected/absorbed by electric loads or grid-connected converters connected at the same PCC. This paper proposes a low-cost nonlinear sensor for an accurate detection, free from offset problems, of the dc voltage component present in the grid voltage. The detection of the dc voltage component was used to realize an active filter of the dc current component. The proposed solution is outlined, and then the stability issue is addressed by means of a simplified model. Experimental results confirmed that the simplified model closely approximates the real system.