Input impedance of grid-connected converters with programmable harmonic resistance

Power factor correction converters with a programmable harmonic input impedance can be used to reduce the harmonic distortion in the utility grid. Whereas previously proposed controllers tried to obtain a resistive behaviour of the converter with a constant input impedance for all frequencies, including the fundamental, another recently proposed control strategy allows the setting of a harmonic input resistance independent of the fundamental input impedance. Although previous papers showed the usefulness of this approach, the analysis and verification of the input impedance of the converter in a broad frequency spectrum is focussed here. The characteristics of the current controller will determine the input impedance of the converter in the frequency domain. The implementation of the control strategy with a programmable harmonic resistance on a digitally controlled full-bridge bidirectional converter is described. Experimental tests on a 1-kW prototype show that with the proposed implementation good concordance with the theoretical input impedance curves is obtained.