Modeling of local controllers in distribution network applications

Local automatic controllers are an integral part of a modern distribution system. They control transformer load tap changer (LTC) positions and the status of switched capacitors to ensure voltage and loading constraints are satisfied under changing operating conditions. Distribution network applications, which traditionally have been used for planning, account for the presence of local controllers in a simplified manner. Distribution management systems (DMS) bring network applications to the operational practice which requires much more detailed modeling of local controllers, both for the purpose of real-time power flow monitoring, and for centralized control. In the latter case, the local controllers create both opportunities and restrictions for DMS optimization functions such as volt/VAr control and feeder reconfiguration. This paper describes how the LTC and capacitor local controllers are modeled as a part of the power flow solution, and how they interact and affect DMS optimization functions. The impact of the local controller modeling on power flow, volt/VAr control and feeder reconfiguration is illustrated by numerical examples.