A direct phase-coordinates approach to fault ride through of unbalanced faults in large-scale photovoltaic power systems

Unbalanced faults pose significant risks to photovoltaic power systems, leading to unsteady conditions in DC-link voltage and photovoltaic output power. Such photovoltaic system instabilities will, in turn, cause detrimental impact on power grid security. Therefore, the fault ride through for unbalanced faults has been an emerging and challenging area of research and development. This article presents a phase-coordinates approach for computing grid-connected current references directly from phase quantities to achieve effective fault ride through to alleviate the impact from unbalanced grid faults. The novelty lies in the development and use of the vector relationship between three-phase currents and active power, which avoids the complication in adopting negative-sequence components. The method is simple to implement and shows the advantages of high reliability and computational efficiency. Tests on a distribution grid with a large-scale photovoltaic plant have verified the effectiveness of the proposed ride through strategy in dealing with unbalanced faults.