Variable DC-link Voltage Strategy for Direct Torque Controlled IM
Drive train of City-Based Electric Vehicles
Thesis Brief: Numerous works have been carried out with perspectives to improve the energy
efficiency of electric vehicles (EVs) drivetrain; much of the attention has been on the design of
highly efficient electric motors, power converters and energy storage system. Besides the
mentioned, selection of the drivetrain configuration and control strategy also influence the
efficiency and performance of an EV drivetrain. The efficiency of a drivetrain for an electric
vehicle is an essential parameter, which determines the range of the vehicle on a single charge.
Hence, choosing an efficient drivetrain has always been significant attention in the electric
vehicle. This work aims at developing and analyzing drivetrain configurations for city commute
vehicles. Since city commute involves frequent start stops, it is necessary to focus on dynamic
performance as well as system efficiency. The efficiency of the drivetrain can be improved by
adopting a variable dc-link voltage scheme and changing the flux linkage values. Hence, to
improve the drivetrain efficiency using the mentioned parameters requires the determination of
the appropriate value of dc-link voltage and flux linkage value for desired operating conditions.
Therefore, this dissertation work aims at developing and analyzing drivetrain configurations for
city commute vehicles. Since city commute involves frequent start stops, it is necessary to focus
on dynamic performance as well as system efficiency. Hence, to enhance the motor efficiency,
an approach for the selection of the optimum value of reference flux linkage for the direct torque
control scheme of induction motor is developed. Moreover, a method is developed to determine
the required value of dc-link voltage based on desired torque, speed, reference flux linkage, and
motor parameters. Finally, the drivetrain efficiency is analyzed based on reference flux linkage
and dc-link voltage using a direct torque control strategy. A scaled-down drivetrain configuration
hardware setup comprising power converters, variable load, IM, and controller is developed to
check the effectiveness of the proposed algorithm.