A novel neutral current control scheme for three-phase four-wire distribution transformers

Abstract

The neutral current can significantly harm the operation of a system, increase the losses of distribution transformers, and reduce the energy efficiency of a system. These negative effects of the neutral current highlight the importance and necessity of investigating neutral current control strategies. In this paper, we propose a novel scheme for controlling the neutral current caused by a linear unbalanced load in three-phase four-wire distribution transformers. The scheme, which is based on the static var compensator (SVC) technology, aims to: (i) control the neutral current, and (ii) reduce distribution transformer losses. It takes into account the effects of unbalanced fundamental currents and the SVC's compensating capability. Combining optimisation theory with a sequential quadratic programming method, we derive the optimal solution for the current control scenario we studied in this work. Simulation results show that our neutral current control scheme can significantly reduce the neutral current and distribution transformer losses. We also present some interesting observations on the SVC's capability and its significant impact on the neutral current and energy efficiency of a system. We hope that our work will encourage future research on SVC-based neutral current control approaches. © Institution of Engineers Australia, 2013.