Analysis of Speed Dependency for Feedforward Saliency Separation

Abstract

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.