PROJECT TITLE :

Designing Inverters’ Current Controllers With Resonance Frequencies Cancellation

ABSTRACT:

This paper presents an innovative and effective linear current regulator for grid-connected converters interfaced by an LCL filter. The proposed scheme entails the utilization of voltages measured at the terminals of the output filter capacitors as feedforward signals to be included in a very classical structure of proportional-resonant (PR) controller. Processing these signals by an opportune filter K(s), the resonance effects characterizing the LCL filter are neutralized and therefore the impact of the grid impedance's variations on the converter's performances is greatly reduced. The proposed resolution simplifies the controller's design, whose gains are obtained by a easy mathematical formula that prevents advanced root locus analyses. Moreover, for a given section margin, the proposed technique ensures the achievement of maximum attainable bandwidth of closed-loop system, sidestepping the guesswork typical of the conventional methods used for choosing the crossover frequency. Conclusions are supported by an in depth mathematical analysis and validated by laboratory results obtained with a seven.5-kW three-section inverter prototype connected to a power grid with time-variant impedance characteristics.