Dynamic Power Decoupling Strategy for Three-Phase PV Power Systems Under Unbalanced Grid Voltages

The objective of this paper is to propose a dynamic power decoupling (DPD) strategy for the three-phase PV power system under the unbalanced grid fault scenario. A two-stage structure consists of an interleaved dc-dc converter, and a three-phase dc-ac inverter is utilized for the PV power system. Under normal operation, the system will track the maximum PV power as well as transfer the energy to the grid. However, if an unbalanced grid fault occurs, there will be a double-line frequency oscillation on the output power. As a result, the double-line frequency ripple will occur on the dc-link voltage. The simplest way to deal with this problem is to increase the dc-link capacitance, but the cost and size of the circuit will be increased while the reliability of the system will be decreased. Therefore, the aim of this paper is to propose a DPD strategy for the three-phase PV power system to suppress the dc-link oscillation caused by the unbalanced grid fault without increasing the dc-link capacitance. Operational principles and thorough mathematical derivations will he presented in this paper. Finally, both simulation results and hardware verifications obtained from a prototype circuit demonstrate the performance and feasibility of the proposed strategy.