Voltage Control with D-STATCOM to Enable Increased Solar Power in Low Voltage Networks

Sammanfattning

This thesis investigated the potential of using reactive power compensation to solve overvoltage issues caused by high amounts of distributed generation, such as rooftop photovoltaic (PV) systems, in the low voltage grid. High voltages are caused by increasing distributed generation as the Swedish power grid shifts from centralised to decentralised power production. The aim was to manage overvoltages without traditional grid reinforcements. The proposed concept involved placing distributed static synchronous compensators (D-STATCOM) temporarily in areas experiencing overvoltages, allowing a fast and flexible form of support. To address this, different scenarios were set with different placements of D-STATCOM around a secondary substation with a significant amount of solar power installed, as well as different limitations. The four different placements were on the high voltage side of the transformer, the LV side of the transformer, at the distribution cabinet, and a combination of two D-STATCOMs placed on either side of the transformer. For each placement, three operational limits were tested: no limitations, minimum reactive power needed to maintain acceptable voltage levels, and maximum reactive power without component overloading in the system. The placements have been investigated with a grid model consisting of medium voltage and low voltage in DIgSILENT PowerFactory by performing load flow analysis and RMS-simulations. This aimed to assess both the steady state capacity of the system and the system’s dynamic voltage response to changing conditions, which is common with PV. The results show that using two D-STATCOMs placed on either side of the transformer, the voltages were within the acceptable range of ± 10% of nominal voltage and without causing overloading of other components. Even one D-STATCOM could bring the voltages within the range, but this was to a higher degree a trade-off with overloading nearby components such as transformers or lines. Overloading of components may reduce their lifespan, which can lead to increased maintenance and replacement costs. This approach could offer a fast and flexible alternative while postponing grid reinforcement, to enable increased penetration of PV in LV grids, increasing the production from renewable energy sources. However, cable loading limitations and the economic feasibility of the use of D-STATCOMs should be investigated further.