Investigation of various solutions for improved voltage quality in weak distribution networks

Abstract

This thesis is investigating several solutions to improve voltage stability and the short circuit capacity of weak distribution networks. In order to do so electric machines are added to the grid and their impact is analysed. First a realistic grid is modeled using actual data provided by a utility and two induction machine models are implemented. In addition to the induction machine an electrically excited synchronous machine, a PMSM and an additional flywheel linked to the machines are examined as solutions as well. Typical parameters are chosen for all parts of the model. Finally a start-up of an induction machine and a short circuit simulation is conducted and the results are discussed. The conclusion drawn is the induction machine including a flywheel solution showing the best performance in an increased load scenario, as well as in a fault case. It provides voltage support both at the transformer bus and at a local load for a limited time and especially for the transient time frame. Only the big short circuit currents fed into the fault by the induction machine including the flywheel pose a disadvantage regarding protection schemes. All simulations and modelling is done in MATLAB© Simulink© Simscape©.