Localising oscillation source in power systems using Dissipating Energy Flow method

The increasing integration of renewable energy sources into power systems increases fluctuations which can lead to oscillations that can threaten the reliable and stable operation of the power system. Power system oscillations can be divided into two types of oscillations: natural and forced oscillations. In order to maintain reliable and stable power system operation, it is essential to understand the cause of these oscillations and locate where such oscillations have their origin so that the system operator can perform corrective operations. This thesis project analyses different case studies on both forced and natural oscillations. The aim of the project is to develop a test model for simulating both oscillation types and using PMU data from these simulations to verify the potential and limitations of the Dissipating Energy Flow (DEF) method of localising the oscillation source. DIgSILENT PowerFactory version of Nordic 32 test system was used as a benchmark for this project. Test models were constructed to simulate forced oscillation in the generator governor and excitation system. Moreover, simulations of forced oscillation in Battery Energy Storage System (BESS) were simulated in PQ control of the battery. A Matlab version of the DEF method was used to process the simulation data and to see the potentials and limitations of the DEF method of localising the oscillation source. A total of fourteen case studies were conducted in this project: twelve involving forced oscillations with constant and variable amplitudes in the generator governor, excitation system, and BESS, and two involving natural oscillations. In order to simulate the natural oscillation, gain in generator Power System Stabiliser (PSS) parameter was set to negative value along with short-circuit event that lasted for 110 ms. The different load models used in the project show no effect on the results of the DEF method. The method correctly localised the oscillation source in all cases with the different load models. 

The key observation of the analysis of the DEF method shows the capability and limitations of the method. DEF method gave accurate and reliable results for both forced and natural oscillations. The cases where the oscillation source is located inside the generator showed results that were accurate and consistent. For natural oscillation case studies, the DEF method could locate the oscillation source accurately. DEF method showed limitations in localising the oscillation source correctly when the oscillation was located inside BESS. The results of these cases showed that the DEF method identified some generators and transmission lines as oscillation sources which were wrong. The main conclusion of this analysis is that the DEF method has a good potential to localise different types of oscillation that originate from various parts of the generator. For oscillations that originate from the BESS, the DEF method shows limitations in identifying the oscillation source.