Stability studies of a mixed islanded power network with varspeed units using simplified models of the converters

This paper presents the modeling, simulation and analysis of the dynamic behavior of a mixed islanded power network of 780 MVA comprising hydro, thermal and wind power plants. The modeling of each power plant is fully described. The model of the variable speed pump-turbine unit includes hydraulic system, electrical equipments, rotating inertias and control systems. The power plants are connected to five passive consumer loads via a 500 kV electrical line network. First, the capability of the pumped storage plant to stabilize the islanded power network is investigated through the time domain simulation of the dynamic behavior of the entire mixed power network by considering the complete models of the converters. Then a new approach related to simplified models of both converters feeding the rotor circuits is presented. Thanks to this approach, simulation time is significantly reduced. The scenarios considered consist of partial load rejection enabled by flywheel effect in generating mode and wind power fluctuations in pumping mode. The simulation results obtained by the complete and simplified models are presented and discussed.