Two-Step Rotor Position Estimation Method for Doubly Salient Electromagnetic Starter-Generator Over Zero and Low Speeds Range

Doubly salient electromagnetic machine (DSEM) can constitute a novel aero starter-generator (SG) system, and position sensorless control of DSEM is a key technology to improve system reliability and power density. This article proposes a novel two-step rotor position estimation scheme for doubly salient electromagnetic starter-generator (DSESG) over zero and low speeds range. Based on the corresponding relation between the minimal phase self-inductance and rotor sector, the rotor position estimation is made by searching the minimal phase self-inductance, which is carried out through two comparing steps of two proper phase self-inductances, and each comparing step is implemented according to the magnitude relation of two parallel-connected phase currents. Then, the selection method of the diagnostic pulsewidth is studied by overall considering the rotor position estimation precision and the low speeds sensorless startup performance. Furthermore, the possible estimation error introduced by the limited resolution of the practical current sensor is analyzed, and a quasi-three-phase six-state conduction mode is put forward as the compensation strategy to guarantee the low speeds sensorless startup performance, in which three boundary sectors with different conduction states are added. Finally, the experiments on a 12/8-pole DSESG validate the correctness and feasibility of the proposed strategies.