The Adequacy of the Present Practice in Dynamic Aggregated Modeling of Wind Farm Systems

Large offshore wind farms are usually composed of several hundred individual wind turbines, each turbine having its own complex set of dynamics. The analysis of the dynamic interaction between wind turbine generators (WTG), interconnecting ac cables, and voltage-source converter (VSC)-based high voltage DC (HVDC) system is difficult because of the complexity and the scale of the entire system. The detailed modeling and modal analysis of a representative wind farm system reveal the presence of several critical resonant modes within the system. Several of these modes have frequencies close to harmonics of the power system frequency with poor damping. From a computational perspective, the aggregation of the physical model is necessary in order to reduce the degree of complexity to a practical level. This paper focuses on the present practices of the aggregation of the WTGs and the collection system, and their influence on the damping and frequency characteristics of the critical oscillatory modes. The effect of aggregation on the critical modes is discussed using modal analysis and dynamic simulation. The adequacy of aggregation method is discussed.