A NEW OPTIMAL-EFFICIENCY DIRECT-TORQUE-CONTROL INDUCTION MOTOR DRIVE FOR ELECTRIC VEHICLES

This paper presents a new optimal efficiency algorithm applied to a Direct Torque Control drive suited for electric vehicles. The proposed optimal efficiency algorithm is based on an analytical methodology derived from the state equations of the induction motor in the stator flux reference frame and it considers both the coil and the iron stator losses. This methodology has been proved to be less cumbersome from the computational point of view than others in scientific literature. Finally it has been applied in a Direct Torque Control scheme. Simulation results show that the optimal efficiency algorithm permits to highly improve the efficiency of the drive in all working conditions and fully maintain the dynamic performance both in the torque and speed loop. In particular, simulation results show that the highest efficiency improvement due to the optimal efficiency algorithm is obtained at high speeds and low torques and it is as much as 16%. Moreover, a comparison between the electromagnetic disturbances produced by the drive with both the proposed optimal efficiency algorithm and the classical DTC has been performed with regard to the conducted electromagnetic emissions. Simulation results in speed steady-state condition have shown that the harmonic content of the motor stator phase voltage in the low/medium frequency range - from 0 to 50 kHz - is lower with the optimal efficiency algorithm than with the classical DTC, with aTHD (Total Harmonic Distortion) as low as 12% in the first case. Also the common-mode voltage is reduced.