An Active Power Ripple Mitigation Strategy for Three-Phase Grid-Tied Inverters Under Unbalanced Grid Voltages

This letter proposes an active power ripplemitigation strategy for the three-phase three-wire grid-tied inverter. Under the unbalanced grid voltage scenarios, the double-line frequency oscillation will have occurred on the inverter output power and the dc-link voltage. Traditionally, the three-phase four-wire or the three-phase four-leg topology could be adopted to deal with this issue. Besides, the negative and the zero-sequence current component can be controlled to cancel out the power ripple. However, the circuit cost and control complexity might be increased. Therefore, a virtual phase-current regulation (VPCR) method is developed by adding compensation to the current feedback of the fault voltage. The compensation value is consistent with the voltage drop ratio, which can effectively offset the actual power ripple. The main feature of the VPCR is its simplicity, whereas it can be realized via the digital signal processor without adding extra circuit components. Theoretical analysis and mathematical derivations of the VPCR will also be revealed. Finally, a 3 kW prototype circuit with both simulation and experimental results verify the performance and feasibility of the proposed strategy. The experimental results show that the output power ripple can be eliminated with 64.3% via the proposed VPCR.