| Summary: In this thesis, a drive system used three level diode-clamped inverter is designed for induction motors, and sensorless Direct Torque Control (DTC) is realized with Extended Kalman Filter (EKF). In the proposed drive system, some limitations caused by the inverter topology make the use of conventional switching table and hysteresis controllers quite difficult. As a solution to this problem, a new switching approach based on simplified three-level Space Vector Modulation (SVM) method has been developed in this study. Compared to the classical SVM method, the computation load is reduced by using logical operations, and by accomplishing neutral-point voltage balance and soft commutations, all requirements for safe and stable operation of the inverter are fulfilled. The stator flux vector and speed estimations for the proposed drive structure have been another subject discussed. The performance of estimations, especially at low speeds, are highly depend on the variations in motor parameters and errors due to measurements. In this study, flux, moment and speed estimations are carried out by using an EKF structure which has the ability to take the noise and uncertainties from machine model and measurements into account. In addition to these estimations, to improve the response of speed estimation in both transient and steady states, the disruptive load torque is also estimated. The proposed algorithms are tested on the designed drive setup with the developed software using TMS320F28335 DSP (digital signal processor) and verified by the obtained results. |
