Analysis of harmonic coupling and stability in back-to-back converter systems for wind turbines using Harmonic State Space (HSS)

Understanding about harmonic propagation in wind turbine converter is fundamental to research the influence of these on a large network harmonic distortion. Therefore, the analysis of wind turbine converter harmonic spectrum as well as the influence of converter operating point into the network is urgently important issues in harmonic studies on wind farm. However, the conventional modeling procedure and simplified model for controller design are not enough to analyze such complicated systems. Besides, they have many limitations in terms of including a non-linear component, different operating points and harmonic coupling analysis. Hence, it is critically needed to develop the advanced converter model, which can include almost all the possibilities. This paper develops the advanced Back to Back (BtB) converter model for wind farm application by means of Harmonic State Space (HSS) modeling method. The modeling and analysis results are remarkable that this model can include non-linear component and also show different operating points and harmonic coupling point, where this means each wind power converter can show the different impedance characteristics. The developed model can easily connected into the large wind farm model to analyze the overall steady-state harmonic as well as harmonic stability. All theoretical modeling and analysis is verified by means of simulation and experimental results.