Design and control of an LCL-type single-phase grid-connected inverter with inverter current feedback using the phase-delay method

In this study, a novel single-phase grid-connected microinverter system and its control applications areintroduced for solar energy systems. The proposed system consists of two stages to transfer solar power to the grid. Inthe first stage, an isolated high-gain DC/DC converter is used to increase low solar panel output voltage. In the secondstage, an inverter is used to supply a sinusoidal current to the grid. Moreover, a proportional resonant controller isadopted to reduce grid current total harmonic distortions (THDs) and an LCL filter is used to provide better harmonicattenuation. However, the ratio between the sampling frequency fs and the resonance frequency fres should be greaterthan 6 in the LCL filter with the inverter current feedback for a stable system. In order to obtain higher phase margins,the sampling frequency should be increased, which increases the inverter switching frequency. The present study showsthat fs/fres can be lower than 6 by placing a phase delay on the inverter current feedback path to guarantee adequatestability margins. The effectiveness and feasibility of the proposed method are confirmed by the experimental test resultsbased on a 300-W laboratory prototype.

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