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Elimination of DC and harmonic current injection due to grid voltage measurement errors in three-phase grid-connected inverter

This study proposes an enhanced current control strategy to eliminate DC and harmonic current at the output current of three-phase grid-connected inverters caused by DC offset and scaling error in grid voltage measurement. The proposed current controller designed in the stationary (α-β) reference frame is developed with a proportional integral (PI) plus three resonant controllers where the resonant controller tuned at the fundamental grid frequency (ωs) is used to regulate the fundamental component; whereas the PI and resonant controllers tuned at 5ωs and 7ωs are employed to eliminate the DC and harmonic components in the grid current. The proposed control scheme is developed without the need of phase-locked loop, DC or harmonic detection scheme, and extra hardware circuit so that it can be integrated into the existing grid-connected inverter systems without extra cost. The effectiveness of the proposed solution is verified by experimental results.