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. Table 1 Voltage ride-through requirement Voltage range, p.u. Clearing time, s

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A novel circuit topology is proposed for utility-owned photovoltaic (PV) inverters with integrated battery energy storage system (BESS) and compared to two state-of-the-art configurations. The proposed topology offers flexibility and can be applied to a range of distribution networks for tight voltage regulation. During BESS maintenance, the solar-storage system reconfigures itself for a self-run mode of operation, and actively compensates high penetration induced voltage fluctuation without activating overcurrent protection of the inverter, which is an added advantage of this strategy. This advantage is achieved by slightly increasing the inverter size to reserve a portion of inverter's current-carrying capability. A dynamic model of the new configuration is also developed to analyse its performance in providing fast response for high ramp up/down solar irradiance variation. As the proposed control strategy is implemented at the device level, the local voltage regulation is quite guaranteed to be in the permissible range. Results from the analysis performed on a modified IEEE 33 bus medium voltage distribution network with multiple inverters show evidence that the proposed strategy has the potential to mitigate voltage fluctuation in several extreme cases.

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