Scalable Frequency Control in Electric Power Systems

Abstract: In an effort to curb climate change, the electric power system in many countries is transitioning from fossil fuels to more renewable power sources such as wind. At the same time, other countries are decommissioning their old nuclear power, and replacing it with wind power. When replacing synchronous machines with wind power the inertia in the system is decreased. If nothing is done about this the performance of electric power grids will deteriorate. For example, the frequency deviation at a disturbance in power balance will increase. In this thesis the effects of more wind power in the Swedish electric power system was investigated. This was carried out by building two models of the Swedish electric power system in Matlab Simulink®. The first model was a one node representation of the Swedish system, and the second was a two node representation. For the two models both today’s system, and a future scenario without nuclear power was tested. Simulations with different losses of generation were preformed and the results examined. The usage of wind turbines for frequency control was investigated. To do this, 10% of the power in the wind was curtailed to enable increased power output when needed. A controller was introduced for the wind turbine, with the grid frequency as the measurement signal. This was tested for different amounts of the wind turbines contributing to the frequency control. The stability of the two node model was also investigated with theory for distributed control. The effects of replacing nuclear power with wind power in Sweden was also investigated by simulations in the existing Nordic 32 model, implemented in the dynamic power system simulation software PSS®E. The different simulations, and the control theory, showed that if more wind power is being built without controlling the frequency of the grid, the performance at a disturbance will deteriorate as the inertia in the system is reduced. If wind turbines are used for frequency control the performance can be significantly improved, and actually preform better than today’s system (with nuclear power), with no frequency control from wind turbines.