Master’s Thesis at KTH School of Electrical Engineering
Abstract International agreements have set high demands on the share of renewable energy in the total energy mix. From the diﬀerent renewable sources, signiﬁcant investments are made in wind power. More and more wind turbines are being built and their number is due to rise dramatically. There are many diﬀerent generator technologies, but this paper focuses on the doubly-fed induction generator (DFIG). DFIGs are generators which are connected to the grid on both stator and rotor sides. The machine is controlled via converters connected between the rotor and the grid. The size of these converters determines the speed range of the DFIG. Wind farm connections to the grid must satisfy grid requirements set by transmission system operators. This means that the study of their dynamic responses to disturbances has become a critical issue, and is becoming increasingly important for induction generators, due to their growing size and number. Several computer programs exist to carry out dynamical simulations and this work will focus on one of them, namely Power Factory from DigSilent. It oﬀers a large choice of builtin components. These components can be controlled through input signals. It is therefore possible for the user to design control strategies. Power Factory has two models of DFIG. A new model has also been developed, based upon a controllable voltage source. These three models are compared, in terms of dynamical behavior and simulation time. One is then used to study the eﬀect of introducing a certain signal to the control strategy.
Many people have contributed to this work. First, I would like to thank Katherine and Mehrdad for their supervision and advice which have guided me all along the thesis. The whole department of Electric Power System should be...