Encoderless Sequential Predictive Torque Control with SMO of 3L-NPC Converter-fed Induction Motor Drives for Electrical Car Applications

Finite control set predictive torque control (FCSPTC) is well-known for its fast response and good flexibility. However, drawbacks such as speed dependence and tedious tuning efforts for weighting factors lead to system failure and implementation complexity. This work proposes a revised FCSPTC method for 3L-NPC converter-fed induction motor (IM) using a sliding mode observer (SMO) to estimate the speed errors caused by the rotor shaft encoder. The novelty lies in two aspects: I. The revised SMO frees the controller from the speed signal dependence, eliminating potential accumulated errors from the speed feedback channels. II. The cost function is realized with a sequential structure, avoiding tedious tuning efforts for weighting factors design. Theoretical analysis and simulation results reveal that: the proposed control scheme performs well without weighting factors and achieves encoderless torque control at both transient and steady-state operation phases.

I. Introduction

Finding an effective and reliable control strategy for induction motor drives has always been an interesting topic, in facing the new era of electrical vehicles. Various control schemes have been proposed in the field of electrical drives, with field oriented control (FOC) [1] and direct torque control (DTC) [2] being two of the classical and dominating methods in the industry. Compared with FOC, DTC dose not require the large tuning efforts for PI parameters. Besides, the good dynamic control performance and speed feedback independence of DTC attract much attention.