Position-Sensorless Control of  $\text{DC} + \text{AC}$ Stator Fed Doubly Salient Electromagnetic Motor Covered Full Speed Range
The position-sensorless control methods of dc+ac stator fed doubly salient electromagnetic motor (DSFDSEM) covered full speed range are presented in this paper. To implement these methods, the following procedures are done. First, the series self-inductance area difference method, in consideration of cogging torque produced by field current, is adopted for identifying the initial position. Second, the current pulse injection technique in the commutation point is proposed to detect the commutation moment at low speed. Finally, the terminal voltages are considered as vectors with a fixed phase difference, and the composed vector is rotated with varying rotor positions; the commutation point can be obtained by coordinate transformation of three terminal voltages at high speed. The filter with a low cutoff frequency is not required in this method. Moreover, the smooth-switch technology between startup and high-speed operations is researched to prevent the out-of-step fault. The sensorless control of a DSFDSEM from startup at standstill to high-speed operation can be easily implemented by the aforementioned methods. No additional hardware or complex computation is required. A 12/8 DSFDSEM prototype is built and tested to verify the feasibility of the proposed sensorless schemes.