Impacts of residential photovoltaic power fluctuation on on-load tap changer operation and a solution using DSTATCOM

Recently penetration of Photovoltaic (PV) systems in Low Voltage (LV) distribution networks has drastically increased. The stochastic nature of PV output coupled with the characteristic of high R/X ratio of LV distribution network results in a direct correlation between PV power and voltage fluctuations. Currently distribution networks rely heavily on existing On Load Tap Changing (OLTC) transformers to mitigate voltage fluctuations. However, during the regulation process OLTC transformers can experience excessive tap changing with high PV penetration, which in turn results in an increased maintenance requirement and shorter lifetime. Without the knowledge of how an increase in PV penetration impacts the operation of an OLTC, a Distribution Network Operator (DNO) cannot effectively coordinate compensation. This paper examines the effect of PV penetration levels on OLTC transformers and voltage regulation. The investigation of tap changing frequencies and voltage profiles is done through quasi-static time-series simulations using a residential street network and one year real world data obtained from local DNOs and research institutes. Then, a mitigation strategy is developed using a Distribution Static Compensator (DSTATCOM) and interaction between OLTC and DSTATCOM is also analyzed. This will enable DNOs to choose an appropriate size of DSTATCOM based on economic and technical requirements of voltage regulation.