A Utility Friendly High Power Induction Motor Drive with Direct Torque and Flux Control

In this paper, a three-level neutral point clamped (NPC) front-end ac-dc converter supplying a three-level inverter fed induction motor drive operating under direct torque and flux control (DTFC) is presented. The three-level ac-dc converter draws sinusoidal ac current from the supply and keeps the dc-link voltage constant. Hysteresis current controller is used for current control of the front-end converter because of its simplicity, easy implementation and good performance. A diode clamped multilevel inverter is used for driving induction motor operating under DTFC scheme. A new technique that ensures constant flux control for forward motoring and reverse motoring is proposed. This technique enables soft starting of the drive. In the proposed drive system, the DTFC principle can be applied in the entire speed range. Simulation results of three-level converter-inverter system demonstrate the validity of the proposed hysteresis current control method. The converter is found to be stable for a large range of hysteresis band. DC link voltage across each capacitor is maintained constant and balanced. The simulation results of the complete drive system are presented here for both forward and reverse motoring operations with regeneration.