A Hybrid Method of Rounded Hexagon Flux Direct Torque Control for Traction Motor in Mid-speed Range

This paper proposes improved segment direct torque control (DTC) for full speed range in high-power urban rail vehicles engaged in frequent starting and braking. In the mid-speed range, based on a detailed harmonic analysis and comparison, a hybrid method of a rounded hexagon flux for DTC is proposed that can reduce the harmonic distortions in current and voltage. In addition, a circular flux is adopted to eliminate torque ripple in the low-speed range and a hexagon flux is adopted in the high-speed range to eliminate switching frequency. A transition control strategy for different speed segments is presented, and a smooth transition can be achieved. Hence, system stability and security are improved. The operation characteristics and design considerations for the proposed method are also introduced. Finally, a simulation model and a prototype of a full speed range system are built. The simulation and experimental results validate the effectiveness and the advantages of the proposed method.