Kyo-Beum Lee, Joong-Ho Song, Ick Choy, and Joo-Yeop Choi, "An Observer-Based DTC of Induction Motors Driven by 3-Level Inverter for Improving Low Speed Operation," in Proc. PEVD Conf., Sep. 2000, pp. 170–175. > Paper

Direct torque control algorithm for 3-level inverter-fed induction motors is proposed. Conventional selection method of the stator

voltage vector shows problems of stator flux drooping phenomenon and undesirable torque control appeared especially at the low

speed operation. To overcome these problems, a proposed method uses intermediate voltage vectors, which are inherently generated

in 3-level inverters. An adaptive observer is also employed to estimate some state-variables and motor parameters, which takes a

deep effect on the performance of the low speed operation. Simulation and experiment results verify effectiveness of the proposed

algorithm.