Optimal Tuning of Local Voltage Control Rule of Load Tap Changers for Dynamic Operation of Unbalanced Distribution Networks

A bang-bang type control rule is typically adopted to automate the tap-changing process of on-load tap changers (OLTCs) and step voltage regulators (SVRs). The control rule is mainly characterized by a dead band parameter affecting voltage regulation performance. Due to the intermittent large-scale photovoltaic (PV) penetration, dynamic voltage fluctuations are induced along the distribution feeder, leading to frequent tap switching and equipment wear and tear. This article proposes an optimization-based dead band tuning method to reduce the number of tap switching and lengthen the economic use-life of the regulation equipment. Unlike existing works that often ignore the local controller mechanism of tap changers, this work extends the modeling efforts by formulating the dead band tuning as a distribution system optimal power flow (DOPF) problem by considering the unbalanced characteristics of multi-phase feeders. The overall DOPF is formulated as a mixed-integer linear program (MILP) to minimize the daily total number of tap switching and the amount of curtailed energy from the PV-based inverters while maintaining voltage regulation performance. Extensive numerical tests conducted on the IEEE 13-bus and IEEE 123-bus test networks suggest that the number of tap switching can further be minimized with the use of a dynamic dead band tuning strategy.