Real time voltage control of unbalanced distribution systems with photovoltaic generation

This paper presents a real time operation of tap changing transformers and converters interfaced with distributed generators (DGs) in unbalanced three-phase distribution systems. The unbalanced three-phase power flow equations are solved using Newton Raphson method, and the three phase elements models are considered. Since the renewable energies are attracting worldwide attention, the DGs considered here are supposed based on photovoltaic (PV) generators. However, the large amount of distributed generation causes voltage deviation beyond a statutory range in distribution systems. The method proposed in this paper control the voltage through the inverters interfaced with PV modules, using an optimized day-ahead schedule of reactive power resources, which include PV inverters and online transformers. The reactive power outputs of PV inverters are determined according to the locally measured voltage. The voltage droop characteristics are determined by fuzzy controllers. A 24-hour data are used to simulate real time and assess the effectiveness of the proposed voltage control strategy of unbalanced distribution systems. The simulation results show that the voltage fluctuations due to photovoltaic generation are minimized to be within the desired range.