Feedforward Repetitive Control for Grid-Tied Inverters in Microgrids: Analysis, Design, and Verification

Conventional repetitive control (RC) with an internal model constant
$Q$
less than 1 has a limited resonant bandwidth and a limited open-loop gain and then has mediocre steady-state and dynamic performance when the frequencies of reference and disturbance signals fluctuate. To solve the problem, in this article, we present a feedforward repetitive control (FRC) scheme for grid-tied inverters in microgrids to track the fundamental reference signal and suppress the harmonic signals simultaneously. The proposed FRC scheme consists of a proportional controller in parallel with a modified RC controller with a feedforward channel. Compared with conventional RC, the proposed FRC has wider resonant bandwidths and much larger open-loop gains at the frequencies of interest. Taking the feedforward odd harmonic repetitive control (FORC) as an example, the stability analysis and the detailed parameter optimization design guideline of FORC are given. Experimental results verify that the proposed FORC scheme has a better immunity to grid frequency fluctuation and a faster dynamic response when the grid frequency fluctuates.