A Novel Seamless Direct Torque Control for Electric Drive Vehicles

Abstract

Electric drive vehicles (EDV) have received much attention recently because of their environmental and energy benefits. In an EDV, the motor drive system directly influences the performance of the propulsion system. However, the available DC voltage is limited, which limits the maximum speed of the motors. At high speeds, the inverter voltage increases if the square wave (SW) voltage (six-step operation) is used. Although conventional direct torque control (DTC) has several advantages, it cannot work in the six-step mode required in high-speed applications. In this paper, a single-mode seamless DTC for AC motors is proposed. In this scheme, the trajectory of the reference flux changes continuously between circular and hexagonal paths. Therefore, the armature voltage changes smoothly from a high-frequency switching pattern to a square wave pattern without torque discontinuity. In addition, because multi-mode controllers are not used, implementation is more straightforward. Simulation results show the voltage pattern changes smoothly when the motor speed changes, and consequently, torque control without torque discontinuity is possible in the field weakening area even with a six-step voltage pattern.

Feed-Forward Approach in Stator-Flux-Oriented Direct Torque Control of Induction Motor with Space Vector Pulse-Width Modulation

“…Phase voltage and current measurement blocks are utilized for torque and flux linkage vector estimations with Equs. (3) to (12). The estimated torque and flux linkage are compared with the reference ones.…”

“…Induction motor (IM) and interior permanent magnet synchronous motor (IPMSM) have been utilized as the main traction system by commercial electric vehicle (EV) companies in the last decade [1]- [3]. IPMSM has high efficiency [4], [5], and IM is inexpensive and reliable.…”