Modeling on converter of direct-driven WECS and its characteristic during voltage sags

The output power of direct-driven wind energy conversion system (WECS) will be limited during grid voltage sag, but the operation of wind turbine will not be influenced by adding damp load in DC-side, then the capability of low voltage ride through (LVRT) may be enhanced. Full power back-to-back PWM converter is adopted in direct-driven variable-speed constant frequency WECS using permanent magnet synchronous generator (PMSG), which can effectively improve system efficiency; the principles of generator-side, grid-side converters and damp load are analyzed in detail, and the whole system modeling of converters is realized. Then the simulation model of converters is built based on Matlab7.3/simulink6.5, and the characteristic during grid voltage sag is simulated; the validity of the model and analysis is verified by simulation, and the results show that direct-driven WECS have good fault ride through capability.