System Performance Comparison of Direct Torque Control Strategies Based on Flux Linkage and DC-Link Voltage for EV Drivetrains

Numerous works have been carried out with perspectives to improve the energy efficiency of electric vehicle (EV) drivetrains; much of the attention has been on the design of highly efficient electric motors, power converters, and energy storage system. Besides the abovementioned factors, selection of the drivetrain configuration and control strategy also influence the efficiency and performance of EV drivetrain. The drivetrain efficiency and performance indices, such as torque ripple and total harmonic distortion (THD) of voltage and current, are sensitive to the direct current (dc)-link voltage and flux linkage values for a drivetrain control strategy. Therefore, in this work, the efficiency and the performance of two popular direct torque controlled induction motor (IM) drives are compared on the basis of adjustable dc-link voltage and flux linkage values for desired operating condition. Both these techniques are implemented on a lab scale test bed. Extensive experiments are performed to determine and compare the drivetrain efficiency maps. Further, dynamic and steady-state (SS) control performance in terms of speed, torque, and flux linkage is examined. Other performance indices, such as root mean square error (RMSE) of torque and flux linkage, speed ripple, and THD of current and voltage, are also compared based on obtained experimental results for both control techniques. In addition, field weakening (FW) response and drive cycles input energy consumptions in both the control strategies are presented.