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 (ω
_s
) is used to regulate the fundamental component; whereas the PI and resonant controllers tuned at 5ω
_s
and 7ω
_s
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.