Saliency-based Encoderless Railway Traction Drives Considering Current Unbalance

Abstract:
Three-phase variable speed drive systems are typically designed to produce balanced motor currents. Taking advantage of this, some saliency-based encoderless control methods build upon the presupposition of balanced systems, such as transient voltage excitation methods that acquire a saliency vector without offset. While unbalanced systems are detrimental for drive performance, a very small amount of unbalance is still tolerable. Yet, encoderless methods can be very sensitive to such small unbalance. In this paper, the impact of slightly unbalanced current on saliency extraction under transient voltage excitation will be investigated for a 1.6MW locomotive motor used in railway applications.