Implementation of variable structure DTC-SVM based VVVF for an induction motor drive using FPGA-SPARTEN III

This paper proposes a novel torque control scheme for induction motors. Compared with field orient control (FOC), direct torque control (DTC) is known to provide fast and robust response for induction motors. However, while offering high dynamic performance, classical DTC produces notable torque, flux, and current ripples, and operates with a variable inverter switching frequency. The proposed direct torque scheme is combined with simplified Space Vector Pulse Width Modulation (SVPWM) technique to control the inverter output voltage. The desired voltage vector for the inverter for controlling the torque is given by the proposed DTC SVM scheme. The direct torque control is based on the relation ship between instantaneous slip angular frequency and rotor angular frequency in adjustment of the reference stator flux angle. The amplitude of the reference stator flux is always kept constant at rated value. The proposed scheme therefore provides smooth, fast and robust regulations of the electrical torque and the stator flux. Simulation results are provided to evaluate the performance of the proposed scheme. The proposed scheme has been implemented in FPGA. Experimental results have been provided to evaluate the motor performance.