Distributed dynamic grid support using smart PV inverters during unbalanced grid faults

A dynamic voltage support strategy using smart photovoltaic (PV) inverters during unbalanced grid faults events is proposed. It uses Karush-Kuhn-Tucker condition for finding optimal solutions to calculate the inverter's active and reactive current references. The proposed methodology also takes the X/R ratio into consideration which allows the inverter to differentiate weak or strong grid conditions and adjust its reference currents. Existing multiple-complex coefficient-filter based phase locked loop is used to extract the positive and negative sequence components. The proposed strategy deploys existing dual vector current control to ensure optimal current injection and low voltage ride through. A distributed ride-through coordination approach among multiple inverters is also proposed based on different optimisation goals - either fundamental positive or fundamental negative sequence voltage support. The strategy is simulated, and inverter's transient performance is experimentally verified on a modified IEEE-13 bus test feeder using controller hardware-in-the-loop approach. Results show substantial evidence that the proposed method can be successfully applied to support the grid during an unbalanced fault event.