Power Oscillation Suppression Control Strategy with Peak Current Limitation for Three-Phase Four-Leg Inverter Under Unbalanced Voltage Dips

Distributed generation inverters have been required to comply with low-voltage ride-through requirements in an era of increasing renewable energy sources. Unbalanced grid voltage dips cause power oscillation and overcurrent issues in three phase grid-tied inverter, which affect the reliability of the power supply system adversely. In order to solve the problem, a power oscillation suppression control strategy with peak current limitation for four-leg grid tied inverter is proposed in this paper. Compare to the three-wire inverter, extra degrees of freedom to cancel the power oscillation are introduced due to the path of neutral line current. So proposed control strategy eliminates both instantaneous active power oscillation (APO) and reactive power oscillation (RPO) at the same time by regulating negative- and zero-sequence currents. Furthermore, the maximum current amplitude within the three-phase current and neutral line current is calculated. And a scaling factor related to the maximum current amplitude and device specification is estimated to limit four wire current within a safe current operation range. Finally, experiment results verify the feasibility and effectiveness of the proposed control scheme.