Secondary voltage control: Nonlinear selection of pilot buses, design of an optimal control law, and simulation results

Secondary voltage control determines control device actions based on reference voltage values set at certain load buses, denominated pilot buses. A key factor for the appropriate functioning of secondary voltage control schemes is selection of the pilot buses. The paper addresses this problem using a nonlinear approach, i.e. using the full load flow equations. This constitutes a modelling improvement with respect to previous approximate linearised approaches. An optimal control law which keeps pilot bus voltage magnitude values at their respective reference values while achieving uniform relative reactive power generator loading is proposed. A simulation tool to analyse the behaviour of the proposed secondary voltage control scheme is also developed and reported. A comprehensive case study based on the New England 39-bus system is provided.