The Impact of Non-synchronous Generation on Power Systems Dynamics

University dissertation from Stockholm : KTH Royal Institute of Technology

Abstract: Due to the increasing integration of Renewable Energy Sources (RES), and the installation of High Voltage Direct Current (HVDC) systems, more power is injected to the AC grid based on power electronic converters. This kind of power injection is called non-synchronous generation in this thesis.However, non-synchronous generation does not provide the inherent dynamical support to the system as a synchronous generator does. Thereby, the large inclusion of non-synchronous generation significantly affects the dynamics of the power system. This thesis analyses different aspects of the power system dynamics with the non-synchronous generation integration such as system frequency response, inertia and undamped oscillations.Initially, a theoretical frame is presented which deals with the basic concept of frequency response in power systems, the modal analysis, the Trajectory Sensitivity Analysis (TSA), Multi-Prony Analysis (MPA) and $Koopman$ Mode Analysis (KMA). The first dynamic aspect studied is the frequency response evaluating some indicators under the gradually increasing installation of non-synchronous generation. The second one, is the impact of non-synchronous generation on the Small Signal Stability (SSS). The analysis is emphasised in the dominant modes. Eigenvalues, mode shapes displacements and participation factors variations are analysed showing the changes during the gradually integration of non-synchronous generation.Furthermore, a second method for frequency mode estimation is applied which relies on on-line modified Prony method. The monitoring of the transient signals provides the observation of the frequency and damping modes from the simulation data measurements based on MPA. The impact on coherency is also shown through the application of KMA. To get the coherent groups it is used the so-called $Koopman$ operator, which is a based-measurements method. This method identifies and clusters the groups based on the spectral decomposition of Koopman modes. The groups obtained while the non-synchronous generation integration are shown. From the results it is shown that the non-synchronous generation inclusion effectively change the coherency in the test system. The test system, the Nordic32, is presented and the set-up scenarios are given. Finally, the TSA, which provides the sensitivity of power system trajectories with respect to the inertia is applied to another test system (IEEE 39) to show the impact of the inertia reduction on transient stability.

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