Reliable operation of modern power transmission systems is increasingly dependent on power converters, which enable the integration of renewable energy sources and storage sys-tems. Despite the advantages brought by such integration, it also introduces new dynamic challenges, among which converter instability is one of the most serious. Therefore, this thesis focuses on the analysis of the system’s dynamic behaviour, with an emphasis on fast mutual interactions.
In the literature, converter stability is divided into two categories: those involving low-frequency and those involving high-frequency oscillations. Low-frequency oscillations arise from interactions between current control, delays, and the LCL filter, whereas high-frequency oscillations result from interactions between filter components and current con-trol or between the filter and the grid. As part of the thesis, a mathematical state-space mod-el of the converter-connected grid was developed, along with a model in the Simulink soft-ware environment. The analysis reveals that current control provides very low damping, which significantly affects system stability, indicating that even small parameter changes can lead to unstable behavior.
Delays further reduce stability, so minimizing delay times is crucial. High-frequency oscil-lations can be mitigated with passive damping in the form of appropriately sized series re-sistances within the LCL filter. Reducing these resistances leads to greater oscillations and poorer damping. The most unstable conditions with the highest frequencies occur due to interactions within the filter and current control, indicating that the system becomes very sensitive in the absence of proper damping.
The conclusion of the analysis highlights that stable operation of such a system critically depends on proper controller parameterization and appropriate filter damping configuration. Furthermore, minimizing delays significantly contributes to reducing the risk of converter instability.
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