Speed and flux sensorless field oriented control of induction motors for electric vehicles

An electric bus system has been operating in the downtown area of Chattanooga, TN. The buses use traditional hard-switched IGBT inverters driving special induction motors with a speed sensor (tachometer) and two embedded flux-sensing windings to provide rotor speed and flux information to the motor controller for implementation of high performance field oriented control (vector control). The induction motor is oil-cooled and equipped with an internal planar gear reduction. The system has experienced failures in both speed sensors and flux sensors due to their unreliable and weak EMI-immunity feature and hostile (oil-leakage) environment. A speed- and flux- sensorless induction motor drive system with a new 100 kW soft-switching inverter has been implemented to replace the existing system, targeted at the use of commercially-off-the-shelf induction motors instead of the customer-designed special motors. The project was supported under the US Department of Energy funding and local industry partnership