An Optimized Frequency Scanning Tool for Sub-Synchronous Interaction Analysis of Non-Linear Devices

Frequency scan is a powerful and versatile approach for Sub-Synchronous Interaction (SSI) screening in power grids. Among different numerical and analytical frequency scan techniques, the harmonic injection method is well suited for the scan of black-box models with active elements, such as in wind farms and solar plants. The results can be used for SSI risk assessment, in which accuracy performs a decisive role. The ideal situation for this method, which leads to the most accurate results, is to perform one simulation per single-frequency harmonic injection. However, for SSI studies with a wide range of frequencies and simulations with very small time steps (scale of μs), this comes at the expense of increased simulation time and financial costs. This paper proposes a technique to improve the accuracy of the harmonic injection method through the optimization of crest factor while injecting all frequencies at one shot, therefore increasing the efficiency of the method by a considerable decrease in simulation time while maintaining good accuracy. The proposed technique was tested on a 100 MVA wind farm connected to the grid through a series-compensated line. The frequency scan results were benchmarked with both Electromagnetic Transient Simulation (EMT) and the ideal multiple single-frequency injection case and compared with other techniques. The results are indicative of the accuracy and robustness of the proposed method.