Modification of electric drive vehicles performances using a direct torque control with over-modulation ability

In electric and hybrid-electric vehicles, the inverter output voltage is limited by available DC-link voltage, which restricts the vehicle speed and acceleration. Therefore the fundamental component of the motor voltage should be increased by operating inverter in the six-step mode at high speeds. Although hysteresis based direct torque control (DTC) is a straightforward approach and has several advantages, this method cannot work in the six-step mode. In this paper a new hysteresis based DTC with over modulation ability for interior permanent magnet synchronous machines (IPMSM) is suggested. In this method, unlike the previously proposed methods, the calculation of the voltage vector or flux reference in different phase angles is not necessary. In the proposed method, the flux trajectory is changed by adjusting the non-switching area and modifying switching table, and thus a seamless transformation between high-frequency switching and six-step square wave is possible. Also in this paper, the dynamic model for an electric vehicle is developed which its traction motor is controlled by proposed DTC. The simulation results prove that the proposed method modify the vehicle performances, notably. These results show that the vehicle with proposed method has a higher top speed and better acceleration. Also it is shown, that the proposed method can improve the vehicle efficiency for various driving cycles. In addition the results confirm the torque discontinuity does not appear in the whole range of vehicle speed.