This thesis presents a method for voltage profile control in active distribution networks with solar photovoltaic integration. It proposes a hierarchical control technique which utilizes minimal information techniques to monitor and control the voltage profile and the reactive power flow of a given unbalanced distribution network. The hierarchical control consists of three levels responsible for maintaining the distribution network's voltage profile and losses, thereby increasing its efficiency. Firstly, the thesis explores the influence of rising photovoltaic penetration in distribution networks to understand the voltage rise pattern and its impacts on the network's power losses and loading conditions. The exploration was followed by an analysis of local voltage control techniques which exploit the photovoltaic inverter capabilities by providing detailed comparison based on simulation results. The main concept, advantages, limitations, and weather scenarios in which these techniques are most suitable are discussed, and possible coordination of these techniques to realise lesser voltage violations is proposed. Secondly, due to the local control's inability to maintain all node voltages within predefined limits, pilot points are selected in the distribution network to represent the voltages of other load buses coupled with it in a manner that voltage variation at these points would represent the voltage variation within the network. Then an optimal coordinated voltage control algorithm based on only pilot point information to minimise the voltage deviations at all load buses in the distribution networks is proposed. The pilot points are obtained using a proposed multi-objective formulation considering multiple operating conditions for solar photovoltaic generation, loads, and electric vehicle uncertainties. Thirdly, a reactive optimal power flow is proposed to obtain optimal reference voltages for pilot points used in distribution networks. The algorithm employs a non-linear interior point method and differential evolution to minimise the overall distribution network's system losses, thereby improving the network's efficiency. Finally, the proposed methods are tested and validated on IEEE test systems and an actual large distribution feeder in New South Wales, Australia. Furthermore, the methods proposed are also compared further with other approaches to justify their superiority.