Analysis of Speed Dependency for Feedforward Saliency Separation

Induction machine transient inductance often shows multiple saliencies that can be exploited for sensorless control. The resulting current slopes after an inverter-imposed voltage step can be arranged to form a saliency vector that contains the superposition of all machine saliencies. A crucial processing step is to separate motor saliencies during online operation. This is required in order to access a single saliency harmonic that is used as feedback in the control scheme. A robust saliency separation technique relies on an identification of all non-control machine saliency harmonics during a commissioning stage including their torque dependence. The stored saliencies are then feedforward compensated using the stored information. Yet, saliencies present a relevant speed dependency as well. This paper investigates the effects of the speed on the saliency amplitude and phase shift in the context of feedforward saliency separation, and provides a speed adaption method for accurate saliency compensation. To prove the saliency speed-dependency and performance of the proposed speed adaption method, experimental results taken on an induction machine are provided.