Designing Inverters’ Current Controllers with Resonance Frequencies Cancellation

This paper presents an innovative and effec-tive linear current regulator for grid-connected convertersinterfaced by an LCL filter. The proposed scheme entailsthe use of voltages measured at the terminals of the out-put filter capacitors as feedforward signals to be includedin a classical structure of proportional–resonant (PR) con-troller. Processing these signals by an opportune filterK(s), the resonance effects characterizing the LCL filter areneutralized and the impact of the grid impedance’s varia-tions on the converter’s performances is greatly reduced.The proposed solution simplifies the controller’s design,whose gains are obtained by a straightforward mathemat-ical formula which prevents complex root locus analyses.Moreover, for a given phase margin, the proposed tech-nique ensures the achievement of maximum possible band-width of closed-loop system, sidestepping the guessworktypical of the conventional methods used for selectingthe crossover frequency. Conclusions are supported by adetailed mathematical analysis and validated by laboratoryresults obtained with a 7.5-kW three-phase inverter proto-type connected to