A Scheme of EDTC Control using a Three-Level Voltage Source Inverter for an Induction Motor

Abstract

The object of this paper is to study a new control structure for sensorless induction machine dedicated to electrical drives using a three-level voltage source inverter (VSI). The amplitude and the rotating speed of the flux vector can be controlled freely. Both fast torque response and optimal switching logic can be achieved; the selection is based on the value of the stator flux and the torque. A novel DTC scheme of induction motors is proposed in order to develop a suitable dynamic. We propose an approach; in wich we enhance the response of torque and flux with optimal switching strategies. However, the middle point voltage of the input DC voltages of the three-level NPC voltage source inverter presents serious problems caused by a fluctuation of the DC voltage sources U <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cU</inf> , U <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cL</inf> . As consequence to these problems, we obtain an output voltage of the inverter which is asymmetric and with an average value different from zero. In this paper, we will present one solution to minimise this fluctuation. This solution uses a clamping bridge to regulate the input voltages of a three-level inverter VSI NPC. A scheme of Enhanced direct torque control "EDTC" with complete cascade is simulated for an induction motor. The results obtained indicate superior performance over the FOC one without need to any mechanical sensor.