Analysis of Voltage Support during Fault Ride Through of Converter-Interfaced Distributed Generation Considering the Grid Impedance

This paper analyzes different control strategies for voltage support during fault ride through of converter-interfaced distributed generation units using time-domain simulations of a distributed generation model. Symmetrical short circuits with varying distances to the point of common coupling are investigated. The study is carried out for varying grid impedance levels in order to investigate the influence of short-circuit ratio and X/R ratio at the point of common coupling on the effectiveness of the considered control strategies. Reactive current injection as required by German grid codes is compared with adjusted current injection. An enhanced control method based on existing approaches is proposed in order to ensure both optimal voltage support and continuous voltage control during faults. All considered control strategies are further analyzed with respect to the local angle instability phenomenon of voltage source converters.