Abstract：With the increased applications of the distributed power generation systems(DPGS), the output power quality of grid-connected inverters has drawn a lot of attention. The repetitive control technique is widely adopted in the inverter systems, due to its excellent steady-state tracking performance and low total harmonic distortion(THD). However in the DPGS, the grid frequency may slightly vary, and then the ratio of the system sampling frequency to the grid frequency could not maintain an integer, which will cause the resonant frequencies of the repetitive control deviate from the practical grid fundamental and harmonic frequencies. The performance of these systems will be significantly degraded using the conventional repetitive control. In this paper, an improved repetitive control scheme is proposed, which adopts a digital filter based on the linear interpolation; the proposed digital filter can approximate the delay function of the frequency ratio’s fractional part, and then the resonant frequencies of the repetitive control will match the practical grid fundamental and harmonic frequencies well. Through rapidly adjusting the parameters of the digital filter according to the practical grid frequency, the proposed scheme can make the system attain the due steady-state tracking performance and THD of the ideal repetitive control, and then the system adaptability to the grid frequency varying is achieved. Finally, the simulation and experimental results demonstrate the effectiveness of the proposed scheme.
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2014, Vol. 29 
