An Improved Sensorless DTC Technique for Two/Three-Level Inverter Fed Asynchronous Motor

Abstract

The Direct Torque Control (DTC) technique was designed to provide high performance for a three-phase asynchronous motor’s behavior by accurately controlling the flux and torque of the latter. However, this conventional DTC generates strong ripples at the level of flux and torque and a variation of the switching frequency since it uses hysteresis comparators, for this reason, the sine-triangle pulse width modulation (SPWM) has been proposed to improve it. The use of Integral Proportional Regulators (PI) allows the generation of the voltage direct and quadrature components that serve as inputs for the SPWM. The technique thus presented provides a fixed switching frequency and lower undulations at the torque and the stator flux. The objective of this work is to apply the improved DTC technique for the control of a cage asynchronous motor that will be powered by two inverters of different topologies; the first is the two-level and the second is the three-level of Neutral point clamped NPC structure. In addition, the control strategy uses a speed estimator that allows the elimination of the mechanical sensor, which greatly increases the reliability of the system. To evaluate the performance and efficiency of the proposed method, a simulation using the MATLAB / SIMULINK software and a fair comparison between the results of the two inverters will be made.