Modell och analysverktyg för beräkningav frekvensförlopp
The power system modelled in this thesis work has been developed for simulationwhen e.g. the production in some part of the power system is changed. The powersystem has been modelled according to the swing mass of the system, the frequencydependency of the load and the turbine governor. The model determines the systemfrequency, the period of regulation and the power exchange between the differentsubsystems in the Nordic synchronized system.In this model the system frequency is assumed to be the same in all different parts ofthe power system and the voltage conditions in the power system are neglected. Forthat reason power swings does not occur between different subsystems in the powersystem, which usually occur as a result of the swinging connection between thetransmissions line. The loads in this power system are modelled to be voltageindependent.The power system has been implemented in Matlab Simulink. The model has beenimplemented according to different transfer block functions, such as transferfunctions, amplifiers and limiters. Two different power systems have been developedin this model, a 3-district model and a 10-district model. The 10-districts model is thesubdivision of the Nordic synchronized system in 10 districts. The number of districtsdefines the number of hydropower or steam power block functions with swing massesin the model, i.e. there are three hydropower block functions with swing masses in the3-district model. In both power systems the loads are modelled to be frequencydependent and controlled according to the turbine governor in the system. Thehydropower block functions in the power system can easily be changed to i.e.windpower block functions.The power system modelled in this thesis work was compared to a more accuratesimulation, (real time simulation) which is for ARISTO-simulation. Comparisonbetween the result of this model and simulations in the real time simulator are made tostudy i.g. the change of frequency when the system production is increased.Two different user interfaces have been implemented in this thesis work. The firstuser interface has been implemented to carry out the change of the control parametersand system parameters during the simulations. The second user interface has beenimplemented to analyze the result of the simulation at the end of the simulation. Forthe whole system or only for a part of the power system the user can analyze thefrequency of the system, the turbine power, the generated power from the machines,the power at the loads and the power imbalance.5