Selection of Reference Flux Linkage for Direct Torque Control Based Induction Motor Drive in Electric Vehicle Applications

The surge in economic activities, in the developing nations, has resulted in rapid expansion of urban centres. This expansion of cities has caused a rapid increase in vehicular traffic, which in turn has caused deterioration of air quality. To overcome the problem of unprecedented air pollution, the governments worldwide have framed policies for faster adoption of electric vehicles. One of the major challenges faced is the development of low-cost drive for these vehicles and keeping the imports to a minimum. As a result of this, the trend is to move away from the permanent magnet-based motor technology and to use induction motor-based drivetrain. For the induction motors to be successful in electric vehicle drivetrain application, it is important to have a robust speed control algorithm. This work aims at adapting a direct torque control technique for induction motor's speed control. The work addresses the impact of reference flux linkage on the operation of an induction motor for direct torque control over a wide range of operation. A Finite Element Analysis based induction motor model is used to obtain values of reference flux linkage. The method uses offline calculations to determine the reference flux linkage, and a lookup table is generated using these flux linkage values. This lookup table is eventually implemented with the direct torque control algorithm. The proposed methodology for selecting reference flux linkage is compared with variable flux technique for various vehicle driving cycles. The comparison shows that the proposed approach gives satisfactory performance (in terms of speed response, torque and flux linkage) over a wide operating speed range. Furthermore, energy consumption analysis for considered driving cycles is also discussed.