Optimal dispatch of ULTC and capacitors for volt/VAr control in distribution system with harmonic consideration by particle swarm approach

This paper describes an optimal dispatch for the under load tap changer (ULTC) of a substation transformer, substation capacitors, and feeder capacitors for volt/VAr control. The objective function of the problem is to minimize the system energy loss for a given daily load pattern. The problem is subjected to power flow equations, bus voltage limits, voltage distortion constraint and the maximum number of daily switching operations for the ULTC and the capacitors. A particle swarm optimization (PSO) is employed to determine the dispatch scheduling where power losses, bus voltages, and total harmonic distortion of voltages are derived from a power flow calculation based on backward-forward sweep technique and a harmonic power flow. The proposed PSO approach is tested with a 29-bus distribution system modified from a practical system of Provincial Electricity Authority (PEA), Thailand. The study results show that the obtained solution satisfies all the constraints while keeping the system energy loss at minimum.