Sensorless control of IPM motors in the low-speed range and at stand-still by HF-injection and DFT processing

In this paper a sensorless controller for an IPM synchronous motor is presented, based on well-known high-frequency signal injection techniques. The issue of the demodulation process is the key-point of the paper. A novel approach based on Discrete Fourier Transform (DFT) and non conventional reference frame transformation is presented allowing a simple and robust non-coherent demodulation, i.e. in which no information about the carrier phase is needed. In the classically adopted coherent approaches, in fact, uncertainty about carrier phase reflects in uncertainty in the demodulated signal amplitude, affecting observer gains and signal-to-noise ratio, definitively providing a degradation of the performance of the estimator. Analytical development of the sensorless algorithm including the demodulation technique is provided. A complete investigation by simulation is carried out aiming at showing the performance of the proposed method. Finally, experimental results are presented based on a prototype motor drive for city-scooters.