Automatic Offline Measurement of Full-Cycle Unsaturated Inductance for Low-Speed Rotor Position Estimation in Switched Reluctance Machines

In this article, an automatic offline measurement of full-cycle unsaturated inductance is proposed for the low-speed sensorless control of a switched reluctance machine (SRM). First, a single-phase current chopping (SPCC) combined with a double-phase current chopping (DPCC) method is proposed to tune the rotor position without any rotor clamping device and position sensor. Second, high-frequency (HF) pulses are injected into three phases simultaneously and the well-known current slope difference (CSD) method is utilized to identify three-phase inductances. Then, the corresponding static rotor positions are calculated based on Clark transformation and arc tangent operation to obtain the unsaturated inductance versus rotor position characteristics, which are stored in the microprocessor. After that, the machine is connected to load and switches to normal sensorless control. The HF pulses are injected into one of the idle phases, and the instantaneous inductance is identified by the CSD method. Based on the prestored unsaturated inductance, the real-time rotor position can be calculated which is only a linear operation here. Afterward, a phase-locked loop (PLL) is adopted to obtain a more precise rotor position as well as the rotational speed. Finally, a series of experiments are conducted to demonstrate the feasibility and accuracy of the proposed method.