This paper presents a position sensorless operating method in WECS (Wind Energy Conversion System) based on PMSG (Permanent Magnet Synchronous Generator). A position sensorless operating method for direct-drive PMSG using sliding mode observer is proposed. With this method, position angles can be estimated only by measuring phase voltages and currents. By analyzing the cause of angle error, which increases when the PMSG is operating at high speed, a new dynamic angular compensation solution is developed. This method proves to be effective and necessary by experiments based on simulink.