The transient-state effect of the reactive power control of photovoltaic systems on a distribution network

Despite of their small capacity, distributed generation (DG) systems can cause an increase in feeder voltage when they produce power into a distribution system if not appropriately controlled. To prevent such an increase in voltage, the state-of-the-art inverter can adjust reactive power, referred to as Volt/Var control. Furthermore, such an inverter-based DG system has been continuously connected to a large distribution network. Thus, the objective of this study is to present an optimal reactive power control method for DG systems, particularly photovoltaic (PV) systems, in the steady state. The second objective of this study is to analyze the transient-state response of a sufficiently large distribution network integrated by high-capacity PV systems able to control reactive power. The large network can be more efficiently developed by a steady-state power-flow analysis program, or OpenDSS based on text editors, than a transient-state analysis program based on graphical editors. Therefore, this study proposes a method that imports the feeder models developed in OpenDSS into a transient-state power systems analysis program, or DIgSILENT. That is, the proposed method models a sufficiently large actual distribution network with thousands of nodes and high-capacity PV systems able to control reactive power. Then, this study examines transient-state dynamics of the feeders. From the steady- and transient-state analyses, this study found that high-capacity PV systems with the capability of Volt/Var control could mitigate an increase in voltage caused by their power injection to the feeder and they could regulate the voltage of a bus to which they are connected within a set voltage range if they are optimally controlled.