Modelling a dynamic equivalent of active distribution networks for power system frequency and voltage disturbances

The complexity of distribution power system models is increasing due to the ever-increasing amount of distributed generators connected by power electronics in the distribution network. This leads to unreasonable simulation time for power system planners and operators. This thesis deals with the derivation of a reduced order dynamic equivalent model of a distribution grid with distributed generation. The equivalent model based on the grey-box modelling approach emulates the original unreduced distribution grid model in terms of active and reactive power flow at the point of interconnection with the medium-voltage grid for frequency and voltage stability studies. The model parameters are identified using the Mean-Variance Mapping Optimization algorithm. Particular attention is given to quantifying the accuracy of the model for all disturbances considered. It has been established that for the considered benchmark network, the equivalent model is able to simulate with reasonable accuracy the active and reactive power at the common coupling point about 78% faster than the detailed model. For larger benchmark networks with more distributed generators, the accuracy is still reasonable, and the simulation time gains are even higher.