This paper presents the mathematical models and algorithms for calculating the forecast of three-phase active power demand change due to use of modern voltage regulation techniques in distribution networks. The aim of forecasting these values is to enable the flexible demand management – forecast results allow distribution networks to participate in primary and secondary frequency and active power controls, reduction of peak demand and elimination of two-way load flows. In this paper, a simulation forecasting method is used, which is based on simulating the application of a certain voltage regulation technique and calculating the regime for the next half-hour interval in the elements of interest within the distribution network. The parameters of these elements are used as input data, as well as the currently and averaged measured values of their certain variables.