This paper proposes a sensorless control approach for Wound Rotor Synchronous Machines (WRSMs) based on a high frequency voltage signal injection into the stator side U phase and VW line, respectively. Considering the machine itself as a rotor position sensor, the rotor position observer is established according to the principles of the rotary transformer. A demodulation method for the high frequency signal inducted in the rotor is proposed as well. Simulation and experimental results show that the proposed sensorless control approach has high performance and good practicability.