Comparison of the grid support capability of DFIG-based wind farms and conventional power plants with synchronous generators

Current grid codes stipulate the same or similar behaviour during grid faults for wind turbines as for conventional power plants based on synchronous generators. But the technology and control of both devices is completely different. Since modern wind turbines use IGBT-based frequency converters, they provide a very fast control with the disadvantage of tight thermal limits for the IGBTs. The excitation control of synchronous generators is rather slow and has nearly no effect on the transient process during faults. Only the synchronous generator itself provides good grid support during severe faults by virtue of its large overload capability. This paper compares both generation techniques through conceptual discussion and based on simulation results. The results show that there are significant differences in terms of their behaviour during grid faults. The results also point to the need for a revision of the current grid codes with respect to more dedicated requirements.