OPTIMIZATION OF INDUCTION MOTOR PERFORMANCE USING CIRCULAR FLUX TRAJECTORY IN DIRECT TORQUE CONTROL

Abstract

Induction machines have long held a pivotal role as robust and reliable workhorses within the industrial landscape, making them the prime choice for motor-driven applications. The prevalence of induction motor control drives in global markets underscores their dominance. This paper delves into the intricacies of controlling induction motor drives powered by voltage source inverters instead of the traditional three-phase main source. This approach offers enhanced control over both electromagnetic torque and stator flux linkage directly and seamlessly. The voltage source inverter facilitates the generation of precisely controlled PWM signals with amplitude governed by the DC link, which are then utilized to synthesize phase voltages. The focal point of this study is the analysis of the mathematical model of AC motors in the stator coordinate system. This framework serves as the basis for exerting control over the motor's flux linkage and torque. By adopting this methodology, the necessity for convoluted transformations and intricate calculations, such as vector rotation transformations, is obviated. Consequently, signal processing is simplified, and the control signals employed enable the observer to discern the physical processes of the AC motor with directness and clarity. Critical to this strategy is the utilization of the stator flux linkage for magnetic field orientation. Its observability hinges on knowledge of the stator resistance, thus mitigating control performance issues inherent in vector control technology and enhancing resistance against parameter fluctuations. The application of the space vector concept further streamlines the mathematical model analysis and physical quantity control of three-phase AC motors, simplifying the problem and enhancing its transparency. Within the realm of Direct Torque Control (DTC), two distinct schemes for magnetic flux trajectory are identified: the hexagonal scheme and the circular scheme. This paper predominantly focuses on the circular scheme, aligned with medium and low power applications where induction motors are energized by three-phase symmetrical sine waves. Consequently, motor loss, torque ripple, and noise are minimized, rendering the circular flux trajectory scheme preferable for such applications. The hexagonal scheme, more relevant to high-power scenarios due to associated switching frequency and switching loss constraints, is not explored herein.