A novel current sensing DC offset compensation strategy in transformerless grid connected power converters

In grid connected power converters both from renewable or traditional energy sources a line frequency transformer is usually employed in order to suppress the DC component. Recently, solutions based on a high frequency transformer or without transformer, usually referred as transformerless, are being investigated in order to reduce size, weight and costs. As a consequence, unless a suitable remedy is adopted, a DC component, that might overcome limits forced by international standards, may appear. This paper proposes a simple and cheap solution to reduce the DC current component injected into the grid in case of a full-bridge, single phase, transformerless converter. The proposed strategy is intrinsically insensitive to offset measurement errors and can be utilized as a robust and dynamic offset compensator for the Hall effect sensor mostly used as current transducer. Experimental results, performed for different current values and for different current control architectures, show the effectiveness of the proposed solution.