Designing Inverters’ Current Controllers With Resonance Frequencies Cancellation
2016
This paper presents an innovative and effective linear current regulator for grid-connected converters interfaced by an LCL filter. The proposed scheme entails the use of voltages measured at the terminals of the output filter capacitors as feedforward signals to be included in a 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 the impact of the grid impedance’s variations on the converter’s performances is greatly reduced. The proposed solution simplifies the controller’s design, whose gains are obtained by a straightforward mathematical formula which prevents complex root locus analyses. Moreover, for a given phase margin, the proposed technique ensures the achievement of maximum possible bandwidth of closed-loop system, sidestepping the guesswork typical of the conventional methods used for selecting the crossover frequency. Conclusions are supported by a detailed mathematical analysis and validated by laboratory results obtained with a 7.5-kW three-phase inverter prototype connected to a power grid with time-variant impedance characteristics.
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