Dynamic grid support in low voltage grids — fault ride-through and reactive power/voltage support during grid disturbances

Abstract

Faults in medium and high voltage grids lead to voltage sags in the low voltage level. Due to the voltage dip, distributed generators disconnect from the low voltage grid. Depending on the amount of disconnected generation, system stability could be compromised. With a dynamic grid support, distributed generators remain connected to the grid during faults, also called fault ride-through. Moreover, the feed in of reactive power supports the voltage during the fault. According to the present state of the art, no requirements exist for a dynamic grid support in low voltage grids. However, with a high penetration of distributed generation these requirements might change in the future. This paper investigates the dynamic grid support in low voltage grids. The impact of a dynamic grid support on a distribution grid is studied with IEEE/CIGRE benchmark models for low and medium voltage grids. Models of inverters, directly-coupled synchronous and induction generators are implemented. Furthermore, a present and a future protection system with fault ride-through capability are added to the grid models. The inverters are equipped with a reactive current controller to give a voltage support during faults. To determine the effect of a dynamic grid support, faults in high and medium voltage grids with and without dynamic grid support are simulated and evaluated. The results have shown that the effect of the voltage boost through dynamic grid support in order to recover the voltage is marginal. However, with a high penetration level of distributed generators the voltage boost increases and the impact of faults can be further limited. This investigation has demonstrated the potential of dynamic grid support in low voltage grids to avoid the loss of a large amount of power and to improve the voltage recovery.