Adaptive resonant controller for grid-connected converters in distributed power generation systems

Due to its superior performance when regulating sinusoidal waveforms and the possibility to compensate for low order harmonics by means of harmonic compensator (HC), proportional resonant (PR) controller is a real alternative to the conventional proportional integral (PI) controller, when implemented in a grid connected system like distributed power generation systems (DPGS). Anyway, both PR and HC necessitate the resonant frequency value inside their internal model. Normally, the nominal value of the grid frequency and its multiples are used, but in the case when the grid frequency experiences fluctuations, the performance of both PR and HC is diminished. This paper discuss the possibility of improving the behavior of resonant controller and harmonic compensator in the case of grid frequency variations. The proposed solution makes use of the frequency information provided by the phase-locked loop (PLL) system already used in most of DPGS today. Experimental results are presented in order to validate the proposed solution and it shows to work very well.