Sensorless control of IPMSM using a discrete-time super twisting observer by high-frequency current injection in low speed region

Control of interior permanent magnet synchronous motors (IPMSMs) has been extensively attempted without any position sensor. At extremely low speeds, sensorless operation would not rely on the fundamental model-based sensorless methods since the situation becomes more sophisticated. The existing high-frequency (HF) injection techniques predominantly concentrate on current or voltage excitations. Whereas, compromises are made between the signal strength and inevitably generated current fluctuations and torque ripples. Noise and disturbances could also deteriorate the performance. To accomplish the low speed sensorless operation successfully, this paper presents a position error observer and a current injection scheme for the extremely low speed sensorless operation. A discrete-time super twisting extended-state observer (STESO) extracts the estimated position and speed considering the disturbances. The design of the HF observer is carried out. The lowest speed is extended down to 2% rated value in the experimental tests.