Optimal Dead Band Control of Load Tap Changers in Distribution Networks

On-load tap changers (OLTCs) and step-Type voltage regulators (SVRs) are widely used voltage regulation equipment in distribution networks. These devices regulate the feeder voltage by raising or lowering the tap position which adjusts the turns ratio of an autotransformer. Typically, a bang-bang control rule is used to automate the tap position change with respect to the sensed voltage. The bang-bang control rule is mainly characterized by the dead band, which defines a range around the set point, where the controller is in idle mode, i.e., neither lower nor raise action is initiated. Hence, the bandwidth is an important control parameter that affects the number of tap switching executed in a daily operation. In general, a constant dead band is set in controllers for the entire operation horizon. However, due to the intermittent nature of distributed energy resources (DERs) and varying loading characteristics, more frequent tap switching can be executed to regulate the feeder voltage, which results in equipment wear and tear. To extend the economical life and reliability of these equipment, proper control parameter selection and coordination with DERs are crucial for the utilities. Hence, this paper proposes a coordination approach to set the dead band parameter dynamically by considering the photovoltaic (PV)-based DER generation with different control modalities. The overall approach is formulated as a mixed-integer linear program (MILP), which is shown to achieve less tap switching than the constant dead band counterpart.