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Position-Sensorless Control Design for Safety-Relevant Steer-by-Wire Applications

Common self-sensing methods for permanent magnet machine drives are critically eyed in automotive applications, due to audible noise, high computational effort or insufficient performance from point-of-view of functional safety. This work presents a saliency-tracking technique for zero and low speed based on square wave signal injection that is used in combination with a slowly sampled current control and a modified pulse pattern to simplify the necessary signal processing and increase injection frequency. Improvements in reducing the computational load, shifting the injection frequency out of the audible range and providing high bandwidth advocate the proposed method for a position-sensorless control system. The proposed method is enhanced with a back electromotive force (BEMF) based position estimator for intermediate and high operating speeds for being applied to an electric power steering (EPS) drive application as a software-based redundancy concept. Experimental results verify robust and reliable sensor monitoring and sensor fault-compensation. Safe operation is shown to be ensured in case of a position sensor-fault, even during safety-relevant manoeuvres.